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Metallic fuels, particularly U 10Zr, are promising candidates for next-generation sodium-cooled fast reactors. Irradiation of nuclear fuels in reactors can lead to the formation of solid and gas fission product which subsequently forms microstructural pores, deteriorating fuel performance. Due to the massive amount of pores and complex phases formed, a quantitative description of fission gas pores is not yet available, preventing the development of microstructure-informed fuel performance modeling for fuel qualification. This paper applied a pre-trained deep learning model to ∼10,260 high magnification scanning electron microscopy images. This method increased the accuracy of fission gas pore segmentation and allows statistical features to be extracted which cannot be achieved manually. A pre-trained decision tree model worked on the segemenation resutls and further classified the pores into different categories to produce a correlation between the pores, movement of lanthanides, and temperature gradient during irradiation. This paper emphasizes the potentials of machine learning models to accelerate fuel research, development, and qualification for advanced reactors. [Display omitted] • Deep learning model is used to detect pores in ∼10,260 scanning electron microscopy images. • About 230,000 pores are detected and classified based on their impact on nuclear fuel performance. • Pore statistics and orientations help to understand fuel performance from post-irradiation examination. [ABSTRACT FROM AUTHOR]

The surface faceting of metals has been studied for several decades, typically using experimental methods such as low-energy electron diffraction. In the current paper, surface faceting of tungsten pellets was studied during in situ heating inside an environmental scanning electron microscope (ESEM), which allowed for direct, high-fidelity observation of morphological changes in response to high-temperature annealing under a moderate vacuum (0.8 Torr). Additionally, a second set of tungsten samples was annealed in an ultrahigh vacuum chamber (10−8 Torr), albeit without direct observation via ESEM. This study revealed that oxygen plays a crucial role in tungsten surface faceting and in a morphological transition to vertex rounding. Furthermore, this paper discusses relevant techniques for identifying the crystallographic indices of surface facets. It is demonstrated that a combination of electron backscatter diffraction, tilted-sample imaging from multiple angles, and serial sectioning in a focused ion beam system can be effectively deployed to determine the geometry of faceting, which in turn can be verified with the aid of software for generating Wulff shapes. The influence of processing environment on tungsten surface faceting enables the possibility of designing and controlling the morphology and crystallographic facets of tungsten surfaces. • ESEM annealing of W at 0.8 Torr resulted in oxide sublimation and surface faceting. • The surfaces of samples annealed under UHV remained flat and smooth. • Temperature and grain orientation influence W surface facet size and sharpness. • SEM tilted-sample imaging and serial sectioning tomography aided facet indexing. • Wulffmaker software helped determine relative surface energies of low-index facets. [ABSTRACT FROM AUTHOR]

Mechanical vibration was utilized to enhance the mechanical properties of the WAAM 2319 aluminum alloy and address issues related to coarse grains and porosity in this paper. The research aims to investigate the impact of varying vibration accelerations on the microstructure and mechanical properties of the specimens. The mechanism of solutes transfer caused by vibration has been described in this paper, which significantly improved elongation. The dendrites during growth were broken by vibration, which led to microstructure refinement. The solutes located in the interstices of the dendrites were transferred to the liquid phase by vibration, reducing the concentration of solutes in the interstices of the dendrites. The continuous coarse precipitation phase becomes intermittent and fine; resulting in increased matrix plasticity. With the increase of vibration acceleration, the elongation was significantly enhanced. The longitudinal elongation was enhanced more significantly because of the alternating distribution of INZ and ITZ, with longitudinal elongation showing a 29.3% increase and transverse elongation a 52.5% increase, while the UTS and YS was not changed significantly in the presence of multiple factors. • Mechanical vibration increases the elongation without affecting the UTS and YS. • Mechanical vibration applies reciprocating force to the dendrite, causing the fracture of the dendrite and the refinement of the grain. • Mechanical vibration induces solutes located in the dendrite interstices toliquid phase, reducing the solute concentration in the INZ. • Intermittent precipitation phases and fewer intragranular precipitation phasesin the INZ lead to increased elongation. [ABSTRACT FROM AUTHOR]

To improve the performance of probeless friction stir spot welded (P-FSSW) joints, a fast electric pulse treatment (EPT) method was proposed firstly, and the microstructure evolution and mechanical properties of the joints after EPT was investigated in this study. Results show that the tensile and shear strength decreases slightly by about 10%, but the joint plasticity increases by about 23.7% after three electric pulse treatments. As the number of electric pulse treatments increases, the joint lap interface undergoes dynamic recrystallization and atomic diffusion, so microcracks are closed and interface bonding is improved. However, due to the different recrystallization degree in different characteristic zones of welded joints after electric pulse treatment, the plastic deformation gradient in the transition zone of welded joints increases. The incongruity of plastic deformation compatibility in the transition region would cause stress concentration. Therefore, the interface on both sides of the joint is favorable for crack propagation, which makes the shear fracture mode change into the plug fracture mode. • In this paper, AA2198-T8 probeless friction stir spot welded joints are used as a research object. • A fast EPT method is proposed firstly to improve the spot welded joint performance. • This paper elucidates the macroscopic interfacial morphological changes and microstructural evolution before and after the EPT. • This paper describes the microscopic mechanism of fracture morphology transformation of joints under the EPT. [ABSTRACT FROM AUTHOR]

A method was proposed to improve the fatigue crack growth (FCG) resistance of TC4 (Ti6Al4V) titanium alloy laminate by hydrogenation/low-temperature diffusion bonding/dehydrogenation (H-DB-DH) combined process. Effects of hydrogen contents and different dehydrogenation temperatures on FCG behaviors and tensile properties as well as microstructures were investigated. Residual hydrogen contents beneath fatigue fracture surfaces were measured to determine the safe dehydrogenation temperature. The hydrogen content of 0.3 wt% and dehydrogenation temperature of 780 °C are optimal to produce TC4 laminate with a 9.87 % improvement of FCG life compared with the diffusion bonded one without hydrogenation. FCG rate decrease results from the comprehensive effect of recrystallization volume fraction increase, grain refinement, mean geometrically necessary dislocations (GNDs) density decrease and texture intensity weakness as well as texture diversity improvement. This paper provides theoretical support for fatigue property improvement of titanium alloy by hydrogen diffusion bonding process. • FCG life increases by 9.87 % by using H-DB-DH combined process. • The optimal dehydrogenation temperature and the safe hydrogen content range are obtained. • FCG rate decrease results from comprehensive mechanisms. • Intragranular crack deflection in α p grains makes fatigue crack path tortuous. [ABSTRACT FROM AUTHOR]

In this paper, the microstructure and twinning behavior of tantalum (Ta) during dynamic plastic deformation (DPD) were jointly analyzed in combination with impact experiments and molecular dynamics simulations, with a focus on the mechanism of variant selection for twinning. The results indicated that twins nucleate at grain boundaries and gradually grows with increasing deformation until it penetrates the entire grain. Due to the difference of grain boundary dislocation density, strain rate and deformation temperature have significant impacts on the quantity and distribution of twins. In addition, at room temperature, nearly half of the twin variants in DPD samples do not conform to Schmid law, and almost all the twin variants in liquid nitrogen samples do not follow to Schmid law. The activation of these non-Schmid variants is mainly affected by the strain coordination. Through this study, we have deepened our understanding of the dynamic microstructural response of Ta under high-speed deformation conditions. • Twins nucleate at grain boundaries due to high dislocation density. • As the deformation increases, twins gradually grow and engulf the matrix grains. • Almost all activated variants do not follow Schmid law in the Ta deformed samples under liquid nitrogen. [ABSTRACT FROM AUTHOR]

Unlocking the full potential of advanced high-strength bainitic steels in spot-welding is a pivotal endeavor for harnessing their extraordinary mechanical properties in the automotive industry. This study suggests a shift in paradigm to address the inferior fusion weldability of this type of steel because of the formation of coarse martensite within the welded zone of weldments obtained by liquid-state welding, through the strategy of refining the martensite within the weld zone using the solid-state friction stir spot welding (FSSW) process. This paper delves into an in-depth investigation of the microstructural evolution and load-bearing capacity of a Fe-0.25C-3Cr-1.63Mn-1.5Si (wt%) ultrafine bainitic steel, having a remarkable tensile strength of 1.7 GPa, during the intriguing process of FSSW at rotational speeds of 600 to 2000 rpm. The research uncovers that the stir zone (SZ) undergoes dynamic recrystallization, resulting in a significantly refined microstructure. Regardless of the rotational speed employed, the high hardenability of the steel and rapid cooling during the process inevitably results in martensite formation within this region. However, a comprehensive microstructural characterization conducted by the electron backscatter diffraction (EBSD) analysis proves that the different thermal cycles induced by different rotational speeds lead into various prior austenite grain sizes, martensitic/bainitic packets and blocks attributes, and density of high-angle grain boundaries (HAGBs). Through the evaluation of strengthening mechanisms in different weld zones, the study sheds light on the key factors influencing strength. Block boundaries emerge as the primary contributor to SZ hardening, surpassing the role of geometrically necessary dislocations (GNDs) and solid solution strengthening. The load-bearing capacity observed during the tensile-shear test is governed by a delicate interplay between bonding width and crystallographic features (block size and HAGBs density) of the martensite formed within the SZ. The highest peak load was achieved under optimal welding conditions (rotational speed of 1000 rpm), which enabled the production of a sufficiently large bonding width, providing ample bonding area for load-bearing, along with an abundance of blocks and HAGBs to effectively impeding crack propagation. [Display omitted] • Advanced ultrafine bainitic steel is welded successfully by FSSW. • Block boundaries surpass GNDs as primary contributor to strength in weld zones. • Load-bearing capacity is influenced by bonding width and features of martensite in SZ. • Block size and HAGBs density are crucial for SZ toughness and joint performance. • Optimal load-bearing achieved at 1000 rpm with ample bonding width, blocks, and HAGBs. [ABSTRACT FROM AUTHOR]

Simultaneously improving formability and strength of commercial alloys in industrial production till a great challenge. In this paper, we have effectively fabricated a heterostructure with hard and soft microregions in automobile Al-Mg-Si-Cu-Zn alloy sheet by a short-flow route. Compared to the homogeneous alloy sheet prepared by conventional route, the alloy sheet with heterostructure displays an improved formability and strength (i.e., average r value: 0.686 → 0.739, Δr: −0.104 → -0.034, EI: 19.8% → 24%, TS: 379 MPa → 399 MPa) and almost constant corrosion resistance. The formation mechanism of the heterostructure, high formability and strength mechanisms, and corrosion resistance mechanism are systematically discussed and illustrated. Our work can provide a simple and practical method for the production of bulk automobile aluminum alloy sheets with simultaneously improved formability and strength. • Heterostructure with hard and soft micro-regions can be constructed by controlling solutes concentration distribution. • Appropriate hard/soft micro-regions can simultaneously improve formability and strength without changing IGC resistance. • The improved mechanical properties are ascribed to the enhanced coordinated deformation of hard and soft micro-regions. • There are significant differences of precipitation behavior between hard and soft micro-regions. [ABSTRACT FROM AUTHOR]

The main objective of this paper is to give a comprehensive discussion of the fracture toughness and oxidation resistance of Nb-16Si-20Ti-3Al-5Cr- x Sn- y Zr (x =0.5, 1.5; y =2, 4, 6) alloys, based on experimental evidence, phase formation and diffusion theory. Results demonstrate that the microstructure of Sn 0.5 Zr 2 and Sn 1.5 Zr 2 alloys consist of Nbss and α-Nb 5 Si 3 , and the other four alloys are composed of Nbss, α-Nb 5 Si 3 and γ-Nb 5 Si 3. At the same time, the area fraction of γ-Nb 5 Si 3 increases with the increase of Zr content. The coarsening of silicides increases with the addition of Sn. The K Q value of the Sn 0.5 Zr 4 alloy reaches the highest with the mean of 12.64 MPa·m1/2. After oxidation at 800 °C for 24 h, Sn 0.5 Zr 4 alloy alloy did not undergo pest oxidation. Sn 0.5 Zr 4 alloy forms a continuous and dense TiO 2 oxide layer oxidized at 1200 °C, which makes it have the best high temperature oxidation resistance. Sn 0.5 Zr 4 alloy has excellent fracture toughness, medium temperature and high temperature oxidation resistance. • The regulation of co-doping Sn and Zr affects the type and morphology of silicides. • The Sn 0.5 Zr 4 alloy shows the best fracture toughness and its K Q value is 12.64 MPa·m1/2. • A continuous and dense TiO 2 oxide layer in Sn 0.5 Zr 4 alloy improves oxidation resistance. [ABSTRACT FROM AUTHOR]

The electromigration (EM) failure of solder joints is closely related to the development of voids during EM. In this paper, an integrated approach combining experimentation and finite element simulation was employed to reveal the evolution of voids in solder joints under current stress. The results indicate that the quantity and volume of voids near the cathode consistently increase, while those close to the anode decrease. These asymmetric evolutions of voids are mainly due to the Sn flux, which is controlled by both current density and βSn grain orientation. The magnitude of Sn flux increases with higher current densities and larger angles γ between the c-axis of βSn and the current direction. The direction of Sn flux is more significantly influenced by the current direction rather than the βSn orientation, due to the weak anisotropic self-diffusion of Sn. Voids near the anode tend to shrink while those close to the cathode expand, parallel to the substrate, due to higher Sn flux distributions at the waists of voids, where current crowding is seen. Void splitting related to rapid Cu diffusion has been observed, leading to an abnormal increase in the number of voids near the cathode. This study enhances the understanding of the electromigration failure mechanisms involving void evolution in solder joints. • The quantity and volume of voids near the cathode/anode show different evolutions under electromigration. • Void evolutions are influenced by Sn flux that is governed by both current density and βSn grain orientation. • Current density has a greater impact on Sn flux direction due to the weak anisotropic self-diffusion of Sn. [ABSTRACT FROM AUTHOR]

The morphology and size of ceramic particles in cold spray additive manufacturing (CSAM) of metal matrix composites affects strongly particle acceleration behavior and deposition mechanisms. This study focuses Al 2 O 3 /2024 aluminum matrix composites and investigates the effect of the morphology of ceramic morphology and content in powder on the microstructure and mechanical properties with numerical simulation and experiments. The deposition mechanism of ceramic particles has been identified, as well as and the optimal properties of powder composition. It was shown that increasing ceramic content in the powder results in a significant deviation of ceramic content in the deposit from the design. At lower ceramic powder content (10 vol% and 20 vol%), the fracture surface of irregular ceramic deposits shows dimples, indicating an increased metallurgical bonding ratio compared to deposits produced with spherical ceramic powder. The tensile strength of deposits produced with spherical ceramic powders surpasses those of those produced with irregular ceramic powders. The study identified the optimal powder composition with particles size of 20 μm and spherical ceramic powder content of 30 vol%. There are performance differences between irregular and spherical ceramic powder deposits because the antagonism between positive tamping effect and the negative effect of the weak metal/ceramic powder interface. The deposit hardness and wear resistance are strongly affected by ceramic content, where larger ceramic powder content is associated with increased hardness and improved wear resistance. The latter improves significantly when it exceeds 7.4 vol%. • The impacting behavior of ceramic particles is revealed in this paper. • It is found that metallurgical bonding is more likely to be formed in irregular ceramic deposits. • It is found that the particle content of spherical ceramic deposits is more than 7.4 vol%, and the wear resistance of spherical ceramic deposits is similar to that of irregualr ceramic deposits. • The optimal ceramic particle content is obtained. When the spherical ceramic content in the powder is 30 vol%, the mechanical properties of the deposit are the best, which is 282 MPa. [ABSTRACT FROM AUTHOR]

The brittle intermetallic phases in the interface of Ti6Al4V-Inconel 718 graded material limits its application. It is of great significance to reveal the formation and transformation mechanism of intermetallic phases for the regulation of interface. In this paper, Ti6Al4V-Inconel 718 graded material was manufactured by laser additive manufacturing technology. In the gradient interface region, Ti 2 Ni, TiNi and Ni 3 Ti were successively formed with the decrease of Ti element and the increase of Ni element. At the same time, intermetallic phases such as Fe 2 Ti and FeTi are formed in the interface near Inconel 718. The gradient interface was divided into three regions according to the types of intermetallic phases. The main phase is mostly precipitated directly from the liquid phase, and there are two types of eutectic reactions (L → β-Ti + Ti 2 Ni, L → Ni 3 Ti + γ) and two types of peritectic reactions (L + TiNi → Ti 2 Ni, L + Fe 2 Ti → FeTi). The Ti6Al4V region has a stronger texture strength than the gradient interface. Due to toughness difference and thermal stress, the Ti 2 Ni phase in gradient interface have higher KAM values. At the same time, the variation trend of each phase content was predicted by thermodynamic calculation, which reflects the phase transition process of the interface. The research on the formation mechanism of intermetallic phase and the prediction of the content of phases by thermodynamic calculation has guiding significance for the regulation of interface phase and the manufacture of graded materials. • Ti6Al4V-Inconel 718 graded material was successfully manufactured. • Three typical regions were generated at the gradient interface. • The intermetallic phase features and generation paths in three regions were revealed. • The change trend of intermetallic phases was predicted by thermodynamic calculation. [ABSTRACT FROM AUTHOR]

Electromagnetic pulse welding technology can achieve effective bonding of different metals without intermetallic compounds and heat-affected zones. Current research primarily focuses on bonding interface and strength, neglecting the fact that the strength of the joint is also related to the performance of the plate itself. This study investigates the macro-microscopic responses, and relevant mechanisms of plates under electromagnetic-mechanical coupling effects are revealed by the integration of microscopic characterization, a finite element model, and mechanical tests. The results show that diverse crystal structures have different mechanical response behavior. The elongation of aluminum after pure pulsed electromagnetic field (EMF) treatment is 27% higher than the untreated specimen while the tensile strength remains the same. But magnesium alloys show an increase of 16%, and 23% for tensile strength, and elongation, respectively. Under a pure EMF, the movement and recombination of dislocations are promoted in aluminum alloy, which is beneficial to reducing the dislocation density of aluminum alloy. As for magnesium alloy, twinning and recrystallization are induced to realize grain refinement. Under the coupling of electromagnetic-mechanical, there is an interaction between the electromagnetic effect and strain rate hardening on dislocations. The tensile strength of the Al specimen increases first and then decreases with the discharge voltage rising. This is determined by the dislocation entanglement behavior. This paper can provide a reference for an in-depth understanding of the mechanism and welding process of electromagnetic pulse welding. • Microstructure evelution of HCP crystal induced by electromagnetic pulse field (EMF) is different from that of FCC crystal. • EMF and strain rates have interaction influences on dislocation movement. • Under coupled effects of EMF and high strain rates, the dislocation density reveals pamameters sensitivity at different ranges. • Mechanisms of the parameters sensitivity during the competing influences is demonstrated. [ABSTRACT FROM AUTHOR]

The effect of friction stir welding (FSW) with different heat input on microstructure evolution, mechanical properties and deformation behavior of twin-induced plasticity steel was investigated in this paper. The results show that compared to the basal material (BM), the grain size in the stir zone (SZ) of FSW joint with low heat input was refined, and a large amount of deformation twins was formed. The grain was refined and numerous dislocations were formed in the stir zone-heat affected zone (SZ-HAZ) interface. In the FSW joint with high heat input, the grain size in SZ increased, while no deformation twins were observed. A large number of fine equiaxed grains were formed in the SZ-HAZ interface, while the grains in HAZ coarsened. Compared to the BM, the tensile strength and yield strength of low heat input joint increased to 1108 MPa and 597 MPa, respectively, while the elongation decreased to 50.4%, resulting in a strength-elongation product of 92% of BM. The joint with high heat input experienced a decrease in tensile strength, yield strength, and elongation to 806 MPa, 465 MPa, and 22.8%, respectively, with a strength-elongation product of only 30% of BM. During the tensile deformation process, the plastic deformation in the low heat input joint was mainly concentrated in BM, followed by HAZ, while SZ exhibited minimum plastic deformation, and the tensile fracture occurred at zone between SZ and HAZ. In the high heat input joint, the maximum plastic deformation occurred in the SZ, with lower plastic deformation in BM and HAZ, and finally fractured at the SZ. The constrain effect of different micro-zones and hindrance effect of dislocations and fine grains were main responsible for the deformation behavior of low and high heat input joints. • An ultra-high strength FSW joint was obtained, and its strength-elongation product reached 92% of the basal material. • The microstructure evolution and mechanical properties of different micro-zones of FSW joints were revealed. • The constrain and hindrance effects were mainly responsible for different deformation behavior of FSW joints of TWIP steel. [ABSTRACT FROM AUTHOR]

In order to reveal the evolution mechanism of the deformation microstructure of 2219 aluminum alloy tube under compression-shear stress, in this paper, flow forming tests and their numerical simulations were carried out, respectively, at temperatures from 250 °C to 400 °C. Meanwhile, a midrange layer index was proposed to analyze the gradient of deformation microstructure. The results show that multiple recrystallization mechanisms of the 2219 aluminum alloy are presented simultaneously during hot flow forming. The shear stress during forming is the main factor that generated the microstructure gradient along the thickness direction, and the recrystallization level is higher with higher shear strain. In addition, it is beneficial to improve microstructure homogeneity and mechanical properties by increasing thickness reduction or decreasing the temperature. This study provides guidance for microstructure control of the 2219 aluminum alloy tube flow forming process. • AA2219 presents multiple recrystallization mechanisms in hot flow forming. • A midrange layer index is proposed to represent the microstructure gradient. • The shear stress in flow forming induces the strain and microstructure gradient. • The recrystallization level of spun components is directly related to shear strain. [ABSTRACT FROM AUTHOR]

The aim of this paper is to understand microstructural evolution and their key effects on mechanical properties of rolled molybdenum (Mo) from as-received sintered sheet. A batch of pure Mo sheets with various thickness reductions have been characterized in detail. The results reveal that the microstructure evolves by three stages including grain refinement, dynamic recrystallization (DRX) and grain elongation. For the rolled Mo, the fractions of low angle grain boundaries (LAGBs) are much higher than that of as-sintered Mo but do not increase monotonically with increasing thickness reductions. The occurrence of DRX results in the decrease of LAGBs at the intermediate stage while a larger rolling reduction results in grain boundaries bursting with high angle characters at the later stage. All rolled sheets are textured with dominant orientation locating at γ-fiber and θ-fiber line. Room-temperature tensile tests demonstrate that all rolled Mo sheets are much stronger and more ductile (ultimate tensile strength, UTS = ∼650–1000 MPa and total elongation, TE = ∼10–35%) than as-sintered Mo (UTS = ∼400 MPa and TE = 0), but a larger thickness reduction unexpectedly results in the deteriorated ductility which can be attributed to the increased number of HAGBs. The elongated microstructure with refined grains and the high fraction of LAGBs induced by rolling are considered to be the dominant parameters responsible to the improved mechanical properties of Mo. We suggest that rolling parameters should be optimized carefully to avoid the detrimental effect of crack initiation from the increase in high angle grain boundaries (HAGBs). • Microstructural evolution of Mo during whole rolling process is elucidated. • Key microstructural effects on mechanical properties in rolled Mo are discussed. • Grain refinement and LAGBs are dominant parameters for improved mechanical properties. • Severely accumulated strain results in more HAGBs that deteriorate the ductility. [ABSTRACT FROM AUTHOR]

Nanoindentation has now become the key technique for measuring the mechanical properties of materials at small scales. However, the quantitative and accurate processing of nanoindentation data relies on a physical quantity that is not directly available: the contact area (Ac) between the indenter tip and the sample under test. In complex systems, determining Ac is challenging due to the limitations of standard methods: analytical models have restricted validity domains (sample homogeneity and rheology), and post-mortem observations of residual imprints are time-consuming, do not appraise property gradients and cannot be applied to materials with significant elastic recovery. In this paper, a comprehensive methodology is proposed to continuously measure contact area during indentation. The proposed methodology, referred to as electrical-nanoindentation (ENI), is based on real-time monitoring of the electrical contact resistance (ECR). The protocol only requires mechanical and electrical calibrations of the indenter tip on reference materials, leading to one-to-one relationship between ECR and contact area. An original approach is also proposed to deal with the presence of surface passivating layers that generally disturb ECR measurements. As an illustration, the methodology is applied to the characterization of a multi-phase alloy (MPA) composed of silver, copper and palladium. This alloy raises the same challenges as those usually faced by nanoindentation in advanced metallurgy: heterogenous distribution of individual phases at the micro-scale, composite response of a complex mixture of hard/stiff and ductile/soft phases, ... In addition, the ohmicity of contact is disturbed by surface passivating layers. Despite these numerous hindrances, the proposed methodology is successfully applied to this material. The evolution of contact area is compared with standard methods: an impressive accuracy of <2% standard-deviation is achieved when compared to post-mortem observations. The elastic moduli and hardnesses of individual phases are then accurately extracted. In addition, in order to gain in spatial definition, the ENI set-up is integrated into a scanning electron microscope (SEM), enabling indent positioning with a precision close to 100 nm. Two challenges are successfully met with the ENI methodology. On a mechanical point of view, the response of individual phases can be identified despite the complex rheology of heterogeneous materials, proving the approach applies to all mechanical behaviors (sink-in or pile-up rheologies, homogeneous or heterogeneous materials, with or without elastic recovery, ...). On an electrical point of view, even if contact ohmicity is the only requirement of the methodology, it is possible to identify and overcome deviations from contact ohmicity induced by surface passivation. In particular, the non-linear resistive contribution of insulating layers fades during indentation thanks to its dependence as the reciprocal of the square of contact radius. The present work provides the keys to monitoring the contact area on any metallic sample, whether oxide-free or oxidized, making this methodology a promising alternative to standard methods. [Display omitted] • A methodology is proposed to continuously measure contact area during indentation. • The methodology processes ECR after simple electrical and mechanical calibrations. • The effect of surface passivating layer on electrical contact ohmicity is discussed. • Applied to a multi-phase alloy, an impressive accuracy is obtained (2% std-dev.). • Hardness and modulus can then be extracted accurately at a micrometer-scale. [ABSTRACT FROM AUTHOR]

Austenitic stainless steel is a promising candidate structural material for direct contact components with lead‑bismuth eutectic (LBE) in lead-cooled fast reactor (LFR). However, the preferential dissolution of Ni from austenitic steels at low oxygen concentrations will lead to the precipitation of Ni-containing phases in the low-temperature parts of reactors, which has a risk of pipe clogging. In this paper, three samples, comprising one extracted from a corrosion tank after prolonged operation and two prepared, respectively, by quenching in liquid nitrogen and cooling in the furnace, were obtained to investigate the effect of cooling rate on the precipitation characteristics and growth mechanism of Bi 3 Ni that forms by the reaction of dissolved Ni and Bi in LBE. The results showed that rod-like Bi 3 Ni was found in all three Ni-containing LBE samples. As the cooling rate increased, the width of Bi 3 Ni decreased. The Bi 3 Ni in all three samples displayed a pseudo-hexagonal prismatic shape and had a typical faceted growth character; the cooling rate had no effect on the morphology of them. The crystallographic analysis showed that the growth axis of Bi 3 Ni was in the 〈010〉 direction, and the prism planes were composed of {001} and {101}. In addition, the precipitation of Bi 3 Ni inevitably increased the content of Pb 7 Bi 3 , which would in turn enhance the volumetric expansion of solid LBE samples. For the growth mechanism, Bi 3 Ni phases were controlled by the screw dislocation mechanism, with the step growth rate of the dislocation core being greater than that of the outer edges. Given the low cooling rate and low Ni content in the LBE coolant of reactors, the precipitation of Bi 3 Ni with a rod-like morphology seems to be inevitable. • Three Ni-containing LBE samples were prepared with different cooling rates. • Regardless of the cooling rate, Bi 3 Ni in all three samples displayed a pseudo-hexagonal prismatic shape. • The Bi 3 Ni grew along the <010> direction, and the prism planes were composed of {001} and {101}. • Considering the low cooling rate and low Ni content, the precipitation of rod-like Bi 3 Ni seems to be inevitable. [ABSTRACT FROM AUTHOR]

In this paper, continuous SiC fiber-reinforced Ti60 (SiC f /Ti60) composites were fabricated by preparing SiC f /Ti60 precursor wires from matrix-coated fibers and hot isostatic pressing (HIP) consolidation. The microstructures of the precursor wires and composites were investigated using XRD, SEM, EPMA, EBSD, and TEM, which led to the microstructure evolution of the composites. The conclusions of this study are as follows. 1. A reaction layer (RL) with a thickness of approximately 0.1 μm already exists at the interface of the precursor wires during the preparation. The HIP process accelerates the diffusion of the carbon coating with the Ti60 matrix, resulting in an increase in the thickness of the RL to approximately 0.5 μm. This layer is primarily composed of fine-grained TiC layer || discontinuous silicides || coarse-grained TiC layer. 2. The matrix of SiC f /Ti60 precursor wires contains α-Ti (∼ 1.9 μm), S2 (∼ 50 nm), and β-Ti (∼ 50 nm), in the matrix, β-Ti is precipitated from α-Ti, and HIP makes α-Ti, S2, and β-Ti grow to ∼ 2.4 μm, ∼ 200 nm, and ∼ 300 nm, respectively. 3. There are 〈0001〉//axial direction (AD) and 〈10−10〉//AD fiber textures in the matrix of the precursor wires, and HIP makes the matrix undergo a plastic deformation dominated by dislocation slip, and the pole density of the two kinds of textures are both increased. • Detailed study of precursor wires to SiC f /Ti60 composites interface and matrix microstructure evolution during hot isostatic pressing. • Sample preparation and characterization using advanced techniques such as FIB, EBSD, TKD, and TEM, etc. • During hot isostatic pressing, the reaction layer is transformed from fine-grained TiC to fine-grained TiC layer || discontinuous silicides||coarse-grained TiC layer. • During hot isostatic pressing, β-Ti and S2 silicides are precipitated from the Ti60 matrix, and the pole density of α-Ti changes. [ABSTRACT FROM AUTHOR]

In this paper, the intermetallic compound ZrTe 2 phase is formed within a copper matrix by data-driven elemental screening. This low melting point ZrTe 2 phase is uniformly and diffusely distributed within the copper matrix, which avoids the need for an energy-intensive process while providing superior resistance to arc ablation. On this basis, a novel Cu-0.6Te-0.3Cr-0.15Zr-0.008P alloy is designed and prepared, and the alloy achieves an electrical conductivity of 95.7 %IACS, a tensile strength of 302 MPa, and an elongation of 39.53% after the thermomechanical treatment. The ablation current of the novel alloy under large voltage is 31.2% lower than that of the Cu-0.6Te alloy, and the cross-sectional area of the ablation traces is reduced by 85%, which effectively illustrates the substantial improvement of the novel alloy's ability to resist arc ablation. There are ZrTe 2 phases of 0.5–2 μm as well as pure Cr phases of about 5–20 nm in the alloy. The ZrTe 2 phases absorbs heat through melting decomposition to achieve arc extinction, and the Cr phases pinning dislocations to promote strength enhancement. In addition, the synergistic addition of Cr and Zr plays a role in the grain refinement of the alloy, and the average size of the grains decreases from 4.2 μm to 3.1 μm, a decrease of 26%, under the same process. This novel CuTe alloy with high strength, high conductivity and high resistance to arc abrasion is easy to produce and low energy consumption, and is expected to be widely used in the new generation of high-voltage fast-charging electrical connector materials for new energy vehicles. • A novel high-strength, high-conductivity and high-resistance arc-ablation Cu-0.6Te-0.3Cr-0.15Zr-0.008P alloy is designed. • Data-driven screening of Cr and Zr elements for synergistic addition to CuTe alloys. • The alteration of the new phase is characterised by SEM and TEM. • Compared to Cu-0.6Te alloy the novel alloy's tensile strength and electrical conductivity increase by 44 MPa and 3.2% IACS. • Compared to the Cu-0.6Te alloy the novel alloy's elongation increase by 3.55%. • At high voltages, the resistance to arc ablation of the novel alloy is significantly improved over that of Cu-0.6Te alloy. [ABSTRACT FROM AUTHOR]

In this paper, CuCrZr alloys were prepared by laser powder bed fusion technique. Under optimum forming process conditions, a relative density of 99.7% was obtained and the specimens were analyzed for microstructure and properties. To enhance the mechanical properties of the copper alloy, the specimens are post-treated using both solution aging and direct aging heat treatments. The variation and influence mechanism of microstructure and mechanical properties, thermal conductivity and electrical conductivity were studied and analyzed. With direct aging heat treatment a large number of Cr nanoprecipitates can be obtained, significantly improving the properties of the alloy. The best synthesis properties obtained at an aging temperature of 450 °C were: microhardness 168.7 ± 3.1 HV, ultimate tensile strength 481.7 ± 7.6 MPa, electrical conductivity 73.9 ± 0.9 %IACS, thermal conductivity 314.3 ± 5.3 W/(m·K). • CuCrZr alloy with relative density up to 99.7% can be prepared by laser powder bed melting (infrared laser). • The hardness and ultimate tensile strength of CuCrZr alloy samples were 168.7 ± 3.1 HV and 481.7 MPa respectively under the optimum heat treatment conditions: 450 °C for 4 h. • The CuCrZr alloy has an electrical conductivity of 73.9 ± 0.9% IACS and a thermal conductivity of 314.3 ± 5.3 W/(m·K) after heat treatment. [ABSTRACT FROM AUTHOR]

In this paper, high-temperature impact fatigue (HTIF) was carried out on a Co-based surface layer cladded by TIG welding, and cracks emerged at 400-cycle condition. The reasons for cracking were investigated from three aspects: microstructure, stress distribution, and crystal orientation. Crack generation was induced by high stress distribution in eutectic carbides at grain boundaries and the great disparity in orientations between grains on two sides of the crack path. The microstructural advantage for cracking behavior played a key role in emergence of cracks, which was verified by the investigation and comparison of three distances from the weld interface. Moreover, the interface microstructure of Co-based layer and FB2 substrate was characterized by transmission electron microscopy, and the phase composition of the weld interface comprised Fe Co and M 23 C 6. The results presented that the addition of Ni-based transition layer caused the acquisition of the crack-free surface layer after HTIF. Finally, microhardness test was conducted on samples with and without a transition layer. The hardness of Co-based surface layer without the transition layer was mainly affected by the transformation of carbides, dilution of Fe, and work hardening during HTIF. The hardness of Co-based surface layer with the transition layer showed minimal change during HTIF, and this finding was attributed to the slight variation in the microstructure. • The microstructural evolution of Stellite 6 layer was revealed. • Mechanisms of cracks generation during HTIF were illustrated. • Crack problem was solved by the addition of Inconel 625 transition layer. • The phase composition of interfacial layer was determined. • Reasons for hardness variation during HTIF was explained. [ABSTRACT FROM AUTHOR]

This paper introduced spherical and non-spherical TiC ceramic particles into 4Cr5MoSiV1 steel through laser cladding technology, employing various TiC volume fractions to produce ceramic matrix composites. Scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) were used to examine TiC-reinforced composites' microstructure. The results reveal that the two ceramic matrix composites with different TiC geometries have the same phases: martensite and TiC. Because of the superior fluidity of the spherical TiC particles in the molten pool, which is distributed more evenly in the composite layer than the non-spherical TiC particles. Additionally, spherical TiC exhibits a lower dissolution rate in the laser-molten pool and has a noticeable grain refinement for the microstructure of 4Cr5MoSiV1 steel, attributed to the increase in the proportion of high-angle grain boundaries. Therefore, under the action of grain refinement, the hardness of the composite material increases. • The microstructure of the composite coatings reinforced with TiC particles of different geometry were studied in detail. • The spherical TiC-reinforced composite layer displays a more even surface and sufficient compactness and ductility. • Spherical TiC particles have a more significant grain refinement effect on the matrix, contributing the higher strength and hardness of composites. [ABSTRACT FROM AUTHOR]

The ultrasonic welding technology is widely promoted as a new connection approach in the field of current energy vehicle wiring harness connection. In this paper, three kinds of 25mm2 copper wire harnesses with different wire diameters and T2 copper terminals with different surface roughness were welded by ultrasonic welding. The mechanical properties of the joints were investigated by tensile experiments and the microstructure of joints was characterised using SEM and EBSD techniques. Excessive roughness increases plastic deformation at the weld interface during ultrasonic welding. This increases the dislocation density at the weld interface and refines the grain size. However, at the same time it inhibits recrystallisation to a certain extent. The lower roughness facilitates recrystallisation, but the low density of HAGBs makes the interface susceptible to slip in extended crystallographic plane and direction. Appropriate roughness allows the weld interface to generate fine equiaxed grains and a high density of HAGBs. This facilitates the obstruction of dislocation movement and improves the strength of joint. In addition, the high porosity of a longitudinal cross-section of the conductor with its small diameter was investigated. This results in a large number of wires remaining on the terminals when force is applied. It was determined that the larger a diameter of wire, the higher a cross-sectional porosity. The copper wire breaks at a weak point in cross-section when the force is applied, resulting in the entire wire being left on terminal. At a wire diameter of 0.2 mm, the porosity of a cross-section reaches an equilibrium and the strength of joint is even higher than the strength of material itself, resulting in the joint pulling off. The maximum strength reaches 4703.77 N. • Copper wires were soldered to terminals with right roughness and improved mechanical properties and stability of joints. • Observation of the transverse and longitudinal interfaces of the joints revealed opposite moulding effects. • Joint strength has achieved peak with balanced transverse and longitudinal porosity for 0.2 mm wire diameter. • EBSD analysis explored, how terminal surface roughness affects recrystallization and mechanical properties. • Three connector failure modes are outlined and the cause of the failure is investigated and explained. [ABSTRACT FROM AUTHOR]

In this paper, the effects of cooling rate after casting and stirring process on γ' phase, γ / γ' eutectic phase, MC type carbide morphology and grain structure of K447A alloy turbine blisk were studied systematically. The quantitative relationships between cooling rate, stirring process and γ' phase, γ / γ' eutectic phase, MC type carbide and grain size were described in detail. The results show that with the increase of cooling rate, the distribution region of γ / γ 'eutectic phase from the center of blisk to blade decreases gradually and MC type carbide changes from skeleton to block due to the shorter formation time of eutectic and carbide in the later stage of solidification. Besides, with the decrease of cooling rate, the size of γ' phase increases under the influence of interfacial strain energy and elastic strain energy, and the morphology of γ' phase gradually evolves from cuboid to concave cuboid, octet and dendritic. At the same time, due to the synergistic effect of cooling rate and stirring process, the blade part is columnar grain and the central part of the blisk is equiaxed grains. In this paper, the evolution mechanism of γ 'phase, γ / γ' eutectic phase, MC type carbide and grain size with cooling rate and stirring process was proposed. The research results would play a key supporting role in precise control during solidification for microstructures and properties of dual-performance superalloy blisk. [Display omitted] • The precipitation phase and grain are affected by the cooling rate and stirring process. • The effects of cooling rate after casting and stirring process on γ' phase, γ / γ' eutectic phase, MC type carbide morphology and grain structure of K447A alloy turbine blisk were studied systematically. • The blade part is columnar grain and the central part of the blisk is equiaxed grains. • The evolution mechanism of γ 'phase, γ / γ' eutectic phase, MC type carbide and grain size with cooling rate and stirring process was proposed. [ABSTRACT FROM AUTHOR]

One effective method for fabricating liquid rocket engine thrust chambers involves using laser directed energy deposition (LDED) to produce Cu/Ni bimetals by depositing Ni-based superalloys onto a High Strength and High Conductivity (HSHC) copper alloy. However, it is difficult to fabricate strengthening layer to the surface of HSHC Cu alloy due to its extremely high thermal conductivity. This paper investigates the influence of states of the HSHC CuCuCr0.8 substrate e.g., as-built of LPBF, rolled and annealed, and direct age after LPBF at 480 °C for 4 h, on the formability of In718 single track by LDED. The results indicate that the thermal conductivity is significantly influenced by the state of the HSHC CuCuCr0.8 substrate. At room temperature and 300 °C, the order of the thermal conductivity from low to high is as-built of LPBF, rolled and annealed, and direct age after LPBF at 480 °C for 4 h, while at 500 °C, the as-built of LPBF substrate has the lowest thermal conductivity, while the rolled and annealed substrate has the largest thermal conductivity. Thermal conductivity has a significant effect on the formability of LDED. The LPBF-ed substrate has the best formability, with a minimum Ra value of 9.72 ± 0.12 μm, a maximum deposition depth of 193.00 ± 4.32 μm, and a minimum grain size of 5.2 ± 2.6 μm because of its smallest thermal conductivity. These findings demonstrate that using an as-built LPBF-ed substrate can improve the LDED formability of the In718 single track compared with the other two substrates. This paper presents a new approach for LDED on alloy surfaces with high thermal conductivity. [Display omitted] • In718 single tracks were fabricated on CuCr0.8 substrates in three different states of LPBF-ed, RA, and LPBF-DA by LDED. • The morphology, geometric characteristics, microstructure, and the element distribution of LDED In718 single track on different CuCr0.8 substrate states were mainly investigated. Meanwhile, the influence mechanism of the substrate state on the molten pool was discussed. • The LPBF-ed substrate reduces the influence of CuCr0.8 thermal conductivity on LDED and improves the LDED formability of the In718 single track. • This paper presents a novel approach to mitigate the challenges for LDED on surfaces associated with high thermal conductivity substrate. [ABSTRACT FROM AUTHOR]

Abstract This editorial introduces a special issue on metal additive manufacturing (AM) discussing the main highlights and contributions to the field of each paper of the special issue classified by alloy type. These papers treat a range of additive manufacturing technologies. [ABSTRACT FROM AUTHOR]

Recent studies demonstrated that the added glass powder with high-alumina content could significantly reduce Alkali-Silica Reaction (ASR) damage in cement concrete. This paper aims to investigate the gel water content, chemical composition and expansion behavior of the alkali-glass powder reacted gel by using neutron scattering and other characterization techniques. Three types of samples were prepared with glass powder, sodium oxide and deuteroxide/hydrogen water with different molar ratios. The swelling potential of this alkali-glass powder reacted gel was much lower than that of the reported alkali-silica reacted gel. The gel water content and chemical compositions were characterized with small-angle neutron scattering (SANS) technique, supported by small-angle X-ray scattering (SAXS), prompt-gamma ray neutron activation analysis (PGAA) measurement. The SAXS test results showed the close scattering intensities, and thus similar internal microstructures among these samples. The elemental molar ratios of gels were obtained from the PGAA test results. Then the gel water molar ratio and mass density were determined by neutron scattering contrast calculation. The determined gel water content from neutron scattering analysis was validated with zero contrast analysis and TGA experimental measurement. Overall, this paper demonstrated the feasibility of using SANS technique to determine the water content of alkali-glass powder reacted gel. [ABSTRACT FROM AUTHOR]

laser shock forming (LSF) is a high strain rate forming process, which can significantly improve the formability of materials. Nevertheless, there is a lack of research on the microstructure evolution and improving mechanical properties of parts deformed by LSF. In this paper, pure copper sheet are formed into flat bottom parts under one- and two-shot LSF. The deformation topography, surface morphology and thickness distribution of the deformed parts are tested. The surface micro morphology of the mould can be additionally printed in the formed parts, and the sheet forming accuracy improved continuously and lower thickness thinning with the increase of the shock number. Transmission electron microscopy (TEM) showed that the microstructure on the surface of the formed specimens was composed of nanocrystalline arrays elongated in the direction of the transverse flow of the workpiece material. The dislocation density decreased and the twinned structures gradually disappeared with an increasing depth from the treated surface. More laser shocking can refine the metal material grain and improve material mechanical property of the formed part further. Eventually, the underlying improvement mechanism of mechanical properties induced by LSF-induced microstructure evolution on pure copper was systematically revealed. • The effect of laser shock number on the morphology, thickness and microhardness of the copper was investigated. • The microstructure evolution of sheet shocked by laser with shots was characterized and the evolution model was proposed. • The strengthening mechanism of the copper part formed by two-shot laser shock was analyzed. [ABSTRACT FROM AUTHOR]

High-throughput image segmentation of atomic resolution electron microscopy data poses an ongoing challenge for materials characterization. In this paper, we investigate the application of the polyhedral template matching (PTM) method, a technique widely employed for visualizing three-dimensional (3D) atomistic simulations, to the analysis of two-dimensional (2D) atomic resolution electron microscopy images. This technique is complementary with other atomic resolution data reduction techniques, such as the centrosymmetry parameter, that use the measured atomic peak positions as the starting input. Furthermore, since the template matching process also gives a measure of the local rotation, the method can be used to segment images based on local orientation. We begin by presenting a 2D implementation of the PTM method, suitable for atomic resolution images. We then demonstrate the technique's application to atomic resolution scanning transmission electron microscopy images from close-packed metals, providing examples of the analysis of twins and other grain boundaries in FCC gold and martensite phases in 304 L austenitic stainless steel. Finally, we discuss factors, such as positional errors in the image peak locations, that can affect the accuracy and sensitivity of the structural determinations. [Display omitted] • We develop the 2D-PTM technique to analyze atomic resolution electron microscopy images. • 2D-PTM matches local atomic peak positions to predefined templates. • The technique segments images into local structural regions and maps local rotations. • We demonstrate the 2D-PTM for polycrystalline Au and martensite phases in stainless steel. • Our analysis addresses sensitivity of the 2D-PTM to positional errors in peak location. [ABSTRACT FROM AUTHOR]

Cu/Al composites have the excellent properties of both Cu and Al, and have the properties of light weight and high conductivity, so they have been widely concerned. In this paper, 5-mm-thick Cu/Al composites prepared by the cast-rolling process are used as experimental materials. To reveal the strengthening and toughening mechanisms of the Cu/Al composites, the interfacial structure, micro-morphology, stress-strain condition, and GND distribution of Cu/Al composites before and after deformation were characterized utilizing TEM, TKD, and EBSD. The results show that the submicron intermetallic compounds Al 2 Cu and Al 4 Cu 9 are formed from the casting-rolling Cu/Al composites. After 15% tensile deformation, many gaps occurred in the interface layer, but at the gaps, there was no crack spreading to the Cu and Al layers. Meanwhile, the deformation in different directions occurs in the Cu grains near the interface, forming a dislocation wall, and the entanglement of the dislocation occurs in the Cu layer near the interface, which contributes to the improvement of tensile strength. The Al layer near the interface layer produces kink bands, which helps to improve the ductility of the composites. Besides, due to the action of the hard intermetallic compound layer, with the increase in tensile deformation, a large number of GND are gradually accumulated in the Cu and Al layers near the interface, resulting in remote back stress, which makes the softer Cu and Al layers obtain higher strength. At the same time, the back stress caused by GND will induce strain hardening, which helps to maintain ductility, so that Cu/Al composites have higher plastic deformation ability while improving mechanical properties. • The effect of the interfacial layer on the strengthening and toughening of Cu/Al composites during deformation was studied. • The Cu/Al composites could induce dislocation pile-up in the Cu side, after tensile deformation. • The deformation in different directions is generated in the Cu layer grain and the dislocation wall is formed. • GND accumulates gradually at the interface, with the progress of tensile deformation. [ABSTRACT FROM AUTHOR]

TiAl-based alloys are known for their exceptional high-temperature properties but suffer from low hot workability. The emergence of additive manufacturing (AM) technology significantly decreases the workability requirement, while the microstructure heterogeneities in AMed TiAl are troublesome. This paper explores the hot deformation behavior and microstructure evolution of a layered heterogeneous microstructure TiAl alloy prepared by selective electron beam melting. The Arrhenius constitutive model with strain compensation was established, and hot processing maps were constructed. The microstructure showed that at the initial stage of deformation, a large number of dislocation slips occur preferentially in the soft coarse-grained layers. With the increase of strain, dislocation accumulation in heterogeneous interfaces, and dynamic recrystallization (DRX) occurs. Eventually, the coarse-grained region is constantly occupied by fine DRX grains. A high density of deformation twins at high strain rates further promotes the formation of tiny DRX grains. When the hot compression temperature reaches 1200 °C, the initial alternative fine-grained and coarse-grained hetero-structure transforms into duplex (DP) and near-lamellar (NL) microstructure, and microstructure heterogeneity is eliminated. The results enhance understanding of the hot deformation behavior of heterogeneous microstructure TiAl alloys. • Constitutive equation and processing map of heterogeneous TiAl alloy are established. • Thermal plastic deformation promoted the elimination of microstructure heterogeneity. • Coarse-grained and fine-grained layer exhibit different deformation mechanisms. [ABSTRACT FROM AUTHOR]

WAAM-LDM hybrid additive manufacturing can achieve high efficiency and high precision preparation of Ti-6Al-4V alloy. However, the inhomogeneous microstructure of WAAM-LDMed Ti-6Al-4V samples results in overall poor tensile properties. Therefore, this paper attempts to ameliorate the inhomogeneous microstructure of the hybrid sample by STA, and simultaneously improve the strength and plasticity. The results showed that the WAAM zone and HAZ were composed of α colonies, the RZ and LDM zone were distributed with fine basketweave structure of the AD samples. With the introduction of STA, the microstructure of each zone of the hybrid sample changes and transformed into a 'dual-phase' structure with bi-modal α p and β t. With the increase of aging temperature, the volume fraction of β t increased and the volume fraction of α p phase decreased, accompanied by the formation of bulk α phase and the coarsening of α s phase. It is worth noting that the strength of WAAM zone was obviously improved by STA, and the fracture positions of the STA samples were randomly distributed in the WAAM and LDM zones. Additionally, with the aging temperature increased, the strength of WAAM-LDMed samples was weakened, and the ductility was improved because the coarsened bulk α played a role of coordinating deformation in the tensile process. The excellent strength and ductility (UTS = 976 MPa, YS = 876 MPa, EL = 13.57%) of WAAM-LDMed samples was achieved at aging temperature 750 °C, compared with the AD samples (UTS = 860 MPa, YS = 767 MPa, EL = 12.5%). Finally, by optimizing the STA (940 °C/1 h/WQ + 750 °C/4 h/AC), the amelioration of the microstructure and the improvement of the strength-ductility of the hybrid samples were achieved. • The microstructure of WAAM-LDM sample is homogenized into α p + β t by STA. • STA treatment makes the strength of WAAM zone comparable to that of LDM zone. • The WAAM-LDM sample prepared by STA obtain excellent strength and ductility. [ABSTRACT FROM AUTHOR]

In this paper, three nickel-based superalloys with different Al/Ti atomic ratios (1, 1.8 and 16), designated as ODS-1, ODS-1.8 and ODS-16, respectively, were prepared by mechanical alloying (MA) followed by hot isostatic pressing (HIP). The evolution of microstructure and tensile properties of the alloys under varying Al/Ti ratio was analyzed and discussed. The result showed that the size, type and constitution of oxides change with variation of Al/Ti ratio. The average size of the oxides decreases with increasing Al/Ti ratio, which is 15.8 nm for ODS-1, 13.8 nm for ODS-1.8 and 11.8 nm for ODS-16, respectively. The oxides in ODS-1 contain 21.4% Y 4 Zr 3 O 12 , 42.9% Y 2 TiO 5 , 21.4% YAM and 14.3% YAP. The oxides in ODS-1.8 consist of 23.5% Y 4 Zr 3 O 12 , 35.3% Y 2 TiO 5 , 17.6% YAM and 23.5% YAP. In contrast, only two types of oxides are formed in ODS-16, including 50% Y 4 Zr 3 O 12 and 50% YAP. As the Al/Ti ratio is increased from 1 to 16, the percentage of Y-Al-O phase increases from 35.7% to 50%, while the proportion of Y-Ti-O phase decreases from 42.9% to 0%. Increasing Al/Ti ratio inhibits the formation of Y-Ti-O phase while promoting the generation of Y-Al-O particles. The finer oxide distribution in ODS-16 is considered to be the main reason for its finer grain size distribution. The bimodal distribution of the γ' phase can be found in all three alloys, but the bimodal distribution feature of the γ' phase in ODS-1 and ODS-1.8 is more significant than that in ODS-16. The average grain size decreases with increasing Al/Ti ratio. The tensile strength at 700 °C is reduced, but the ductility is improved with the increase of Al/Ti ratio. The influence of Al/Ti ratio on the formation of nanoscale oxides and γ' phases are revealed. • ODS Ni-based superalloys with different Al/Ti ratios were prepared by MA and HIP. • The average grain size decreases as the Al/Ti ratio increases. • The bimodal distribution of γ' is observed and the average size decreases with the increase of Al/Ti ratio. • The size, type and composition of oxides depend on the Al/Ti ratio. • The tensile strength at 700 °C decreases while the ductility increases with the increase of Al/Ti ratio. [ABSTRACT FROM AUTHOR]

Damping and mechanical properties are often incompatible in metallic materials. In this paper, bio-inspired laminated graphene nanoplatelets (GNPs) reinforced Al-30Zn alloy matrix composites with an outstanding combination of damping-mechanical properties are prepared using a flake powder metallurgy (FPM) process. The increased grain/phase boundary owing to grain refinement improves the intrinsic damping properties of the composites, while the lamellar grains promote the oriented alignment and crack deflection of GNPs. The multilayered GNPs with large specific surface area experienced repeated stretching and compression during cyclic bending deformation, leading to intense interfacial frictional slip, and GNPs' high intrinsic thermal conductivity also helped to dissipate heat quickly, which promoted mechanical energy dissipation. The improvement in mechanical properties is mainly attributed to grain refinement, the load transfer effect of GNPs and their interaction with dislocations. The Al-30Zn-0.5GNPs composites showed the best combination of damping properties and mechanical properties. • Two steps flake powder metallurgy was utilized for the preparation of Al-30Zn-GNPs composites. • Laminated structure of Al-30Zn alloys facilitates interfacial damping. • Incorporation of GNPs improves damping properties and mechanical properties. • Interfacial and dislocation damping are the main damping mechanisms in composites. [ABSTRACT FROM AUTHOR]

Ti/Ni/Ti layered composites, which combine the advantages of Ti and Ni, are widely used in sensor and biomedical applications due to their light weight, high strength, high conductivity, good stability and excellent corrosion resistance. However, it is difficult to control the structural parameters, microstructure, and mechanical properties of layered composites during co-deformation processing due to the distinct differences in the crystal structure, mechanical properties, and deformation behavior of Ti and Ni layers. In this paper, the hot deformation, processing maps, and microstructural evolution of Ti/Ni/Ti layered composites during hot deformation processing are investigated through hot compression tests at 550–850 °C/0.001–1.0 s−1, with a reduction of 65%. It is shown that the composites exhibit mainly dynamic recovery or similar dynamic recrystallization characteristics. Combined with the interface structure, processing maps and microstructure, the optimal parameters for Ti/Ni/Ti layered composites are 680–730 °C/0.007–0.015 s−1. During co-deformation, the microstructural evolution of the constituent layers is very complex. The deformation mechanism is mainly dynamic recovery (DRV), or DRV and dynamic recrystallization (DRX) in Ti layer, and work hardening (WH) or DRV in Ni layer. • Hot deformation, processing maps, and microstructural evolution of Ti/Ni/Ti layered composite were studied. • The rheological properties of Ti/Ni/Ti layered composites were investigated by the Deform software. • The deformation mechanism of Ni and Ti layers during co-deformation was analyzed by EBSD. • The parameters are determined based on processing maps, interface structure and microstructure of Ti/Ni/Ti composite. [ABSTRACT FROM AUTHOR]

This paper proposes a new stretch bending approach for aluminum alloy extrusion profiles based on a novel pre-hardening forming (PHF) process. Tensile tests were carried out to examine the flow behavior and mechanical responses of a 7A09 extrusion profile in PHF process. Microstructure evolution was investigated through X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscope (SEM), electron backscatter diffraction (EBSD), and small angle X-ray scattering (SAXS). It is interesting to find that the yield stress at 200 °C was higher than that at 185 °C. The quantitative analysis revealed that the higher volume fraction of precipitates (200 °C) played a greater role than the refinement of precipitate sizes (185 °C) in precipitation strengthening mechanism, thereby causing an enhanced hardening effect. This phenomenon indicated that there was a preferred temperature zone for the precipitation behavior in PHF process, and it also explained the lower yield stress at 185 °C than that at 200 °C. Additionally, similar results were also observed in strength of the warm-deformed alloys. The optimal strength (σ / σ 0.2 =589/517 MPa) can be achieved at 200 °C without subsequent heat treatment, which exceeded the typical strength of 7A09-T6 extrusion. The primary strengthening mechanisms in PHF process were strain hardening and precipitation strengthening, and the warm forming procedure caused a hardening effect, rather than a softening impact as in traditional warm/hot forming procedures. [Display omitted] • The yield stress and warm-deformed strength initially increased and then dropped with the increasing forming temperature. • An optimal warm-deformed strength superior to typical 7A09-T6 was obtained at 200 °C without subsequent heat treatment. • The higher volume fraction played a greater role than refinement of precipitate sizes in precipitation strengthening. • The warm forming procedure caused a hardening effect, rather than a softening effect during traditional warm/hot forming. [ABSTRACT FROM AUTHOR]

Precipitation hardening provides a great potential to achieve superior strength-ductility trade-off in high-entropy alloys (HEAs). However, the formation of some precipitates such as brittle sigma phases may significantly deteriorate the ductility. Empirical criteria such as PSFE, VEC, and M d were proposed to predict the formation of undesirable phases during aging, nevertheless, they are insufficient to describe their stability and are not dependable for the noted purpose. Accordingly, for the first time, machine-learning models were conducted for this prediction. A feature selection based on Pearson correlation and mutual information has been used to improve the performance of models. Linear regression, second-order polynomial regression, decision tree, and neural network are conducted by machine learning methods in this paper. Among the implemented methods, the neural network had the best performance which improved the accuracy of the prediction by ∼20% compared to the conventional methods. Additionally, a new parameter based on linear regression, which is more reliable and user-friendly than thermodynamic parameters was developed in this investigation. The results showed that some elements such as Cr, Mo, and V may promote sigma precipitation. A HEA with a sigma-free microstructure was developed for validation of the model. We strongly believe that this HEA has a great potential for overcoming the strength-ductility trade-off because of not only the lack of sigma precipitate but also the presence of NiAl precipitate. The results are a step forward in designing alloys with the potential of microstructure engineering to achieve superior properties. • Sigma phase formation was predicted by machine learning (ML) models in high-entropy alloys. • The ML models provide higher average accuracy compared to empirical criteria for predicting sigma phase formation. • Cr, Mo, and V play key role on stabilization of the sigma phase in the microstructure based on model. • A novel Co 30 Ni 25 Mn 30 Cr 10 Al 5 (at. %) HEA was developed to assess the applicability and validity of the ML model. [ABSTRACT FROM AUTHOR]

In this paper, uniaxial hot compression tests of β-quenched Zr-1Nb-1Sn-0.1Fe alloy under a strain of 0.91 were conducted at various temperatures ranging from 600 °C to 750 °C. The microstructure, texture evolution, deformation mode and dynamic recrystallization (DRX) mechanism were investigated using electron backscatter diffraction (EBSD). The results of the In-Grain Misorientation Axis (IGMA) method showed that the prismatic was the dominant deformation mode when the temperature was 600 °C. The prismatic and pyramidal were the dominant deformation modes during hot compression between 650 and 750 °C. To study the mechanism of DRX, the geometrically necessary dislocation (GND) density, grain orientation spread (GOS) and grain reference orientation deviation (GROD) maps were calculated. The results showed that both discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX) coexisted during hot compression. When deformed at 600 °C, the recrystallization mechanism was mainly DDRX, while it was mainly CDRX above 600 °C. The change in the DRX mechanism can be attributed to the activation fraction of different slip systems and the resulting development of misorientation. • The effects of the temperatures on microstructure evolution and deformation mode were analyzed. • Different DRX mechanisms and their effects on texture are discussed in detail. • The DRX mechanism changed due to the activation of different slip systems and the resulting development of misorientation. [ABSTRACT FROM AUTHOR]

The MoSi 2 coating is an ideal coating system for stainless steel due to its good wear resistance and oxidation resistance in the sea service environment. However, there are always some cracks in the MoSi 2 coating due to different thermal expansion coefficients compared with stainless steel, which has an important effect on the corrosion behaviors. In this paper, MoSi 2 coatings on laser powder bed fusion (LPBF) high-strength stainless steel prepared by laser cladding technology were optimized by the addition of a TiVAlZrNb high-entropy alloy. The results showed that the addition of a TiVAlZrNb high-entropy alloy could optimize the cracks in the MoSi 2 coating by refining the grain size and optimizing the expansion coefficient. The open circuit potential and corrosion potential of the MoSi 2 coating were − 158 mV and − 262 mV, respectively, which were lower than those of the composite coating (148 mV and − 225 mV, respectively). The electrochemical impedance value of the MoSi 2 coating was higher than that of the MoSi 2 + TiVAlZrNb composite coating. The obvious local corrosion originated from the cracks in the MoSi 2 coating. Therefore, the addition of TiVAlZrNb high-entropy alloy could optimize the cracking and corrosion resistance of MoSi 2 coating on LPBF high-strength stainless steel. • The crack and density of MoSi 2 coating was optimized by doping of TiVAlZrNb high-entropy alloy. • The obvious local corrosion originated from the cracks of MoSi 2 coating. • The corrosion resistance of MoSi 2 + TiVAlZrNb composite coating was higher than that of MoSi 2 coating. [ABSTRACT FROM AUTHOR]

To achieve superior damage tolerance and fatigue properties, it is desirable for the microstructure of Ti-6Al-4V ELI (Extra Low Interstitial) titanium alloy to consist of equiaxed grains with a homogeneous lamellar structure. However, traditional forging and single additive manufacturing techniques require extreme processes such as quasi β heat treatment and hot isostatic pressing. In this paper, a hybrid directed energy deposition method that integrates in-situ rolling with simple annealing is proposed to simultaneously achieve these microstructures. The results indicate that the initial microstructures produced by hybrid directed energy deposition consist of fine equiaxed prior-β grains, inconspicuous interpass bright bands, randomly oriented lamellar structure and numerous small substructures at the TEM scale. Due to the plastic deformation caused by in-situ rolling, the primary β grains underwent significant refinement with a reduction in grain diameter from over 2000 μm to 113.8 μm. Besides, the unique microstructures and thickness of α laths are influenced by coarsening and dissolution mechanisms that are controlled by diffusion during phase transformation. Furthermore, a uniform microstructure without bright bands and excellent comprehensive properties can be achieved through heating at 880 °C for 2 h and natural cooling. These findings validate that hybrid directed energy deposition coupled with simple annealing present a novel and cost-effective approach for the direct manufacturing of uniform titanium alloy forgings. • Microstructure evolution in DED with in-situ rolling and annealing was studied in detail. • Uniform microstructure realized with fine equiaxed grains. • Driving forces and mechanisms of α lamellae evolution were summarized. • Optimal comprehensive properties were analyzed. [ABSTRACT FROM AUTHOR]

In this paper, the influence of electrical pulse treatment (EPT) on the evolution of microstructure and texture and the resultant magnetic and mechanical properties of a cold rolled Nb-alloyed non-oriented silicon steel (NOSS) was investigated carefully. When the temperature rise caused by Joule heat is higher than the starting temperature of dissolution, more precipitates are dissolved in the EPT specimens than those subjected to the conventional heat treatment (CHT) at the same temperature, and higher current density resulted in Laves precipitates dissolved at lower temperature. The permeability of all the EPT and CHT specimens increase first and then decrease with the increasing temperature, and it reaches the maximum at the temperature for nearly the complete recrystallization. B 50 is higher for the EPT specimen than CHT before the completion of recrystallization due to enhanced recrystallization, but lower than CHT after the completion because the athermal effect of pulsed current promotes the growth of γ-fiber grains, disfavoring the permeability. Moreover, the EPT specimen has the lower iron loss and lower yield strength than the CHT one at the same annealing temperature, because the dissolution of precipitates, recrystallization and grain growth in cold rolled matrix are all enhanced due to the athermal effect of pulsed current. [Display omitted] • Higher current density leads to Laves precipitates in NOSS dissolved at lower temperature. • The maximum B 50 in EPT samples appeared at lower temperature than that of CHT ones. • Athermal effect of pulsed current resulted in the lower iron loss and lower yield strength. [ABSTRACT FROM AUTHOR]

This paper proposes a method involving low-temperature SPS for preparing ZrTi/GH4169 alloy blanks. The addition of GH4169 alloy significantly reduces the sintering temperature of ZrTi alloy. The Zr30-Ti62-Ni8 ratio was used to obtain equiaxed grains of ZrTi alloy through sintering at 1000 °C, and billets with excellent strength and plasticity under high-temperature deformation were obtained by sintering at 1100 °C. In the sintering temperature range from 1000 °C to 1200 °C, while both α-phase and Zr 2 (Fe,Ni) phase size increased with the sintering temperature, the amount of increase was different. Specifically, the α-phase in the alloy blanks sintered at 1100 °C was fine and reticulated, whereas that sintered at 1200 °C developed into a slatted structure. Strengthening mechanism analysis showed that the strength and plasticity of the 1100 °C sintered blanks were excellent, especially because of the effect of the reticulated α-phase and Zr 2 (Fe,Ni) phase. Furthermore, the high density of the phase interface hindered dislocation movement and inhibited stress concentration. In particular, the Zr 2 (Fe,Ni) phase distributed along the β-phase grain boundaries and around the α-phase in the grain acted as a nail, and it could inhibit grain growth and increase resistance to dislocation motion. The weaker β-phase weave and lower defect density also contributed to the superior material properties of the 1100 °C sintered blanks. • This paper proposes a method involving low-temperature SPS for preparing ZrTi/GH4169 alloy blanks. • Zr30-Ti62-Ni8 blanks with excellent strength and plasticity under high temperature deformation were obtained by sintering at 1000°C–1200 °C. • 4) The weaker β-phase weave and lower defect density were also responsible for the superior material properties in the case of sintering at 1100 °C. [ABSTRACT FROM AUTHOR]

The paper describes a high-throughput method for alloy design in in Co-based superalloy. The approach is an extension of the diffusion couple method used for the determination of diffusion coefficients. We present the use of such a method in low-density cobalt-based superalloys Co-30Ni-10Al-5Mo-2Ta-2Ti-xCr (x = 0–14 at. %) exploring the effect of Cr content on the microstructural evolution, mechanical, and oxidation properties. The composition profile is developed at relatively high temperature with Co-30Ni-10Al-5Mo-2Ta-2Ti and Co-30Ni-10Al-5Mo-2Ta-2Ti-14Cr as end members in which only the solid solution γ phase grows in the interdiffusion zone. This is subsequently subjected to heat treatment for the evolution of g and γ՛ phases. The composition-dependent microstructure and respective mechanical properties were probed using FE-SEM and nano-indentation respectively. The following composition-dependent properties were successfully probed from the high-throughput diffusion couple: 1) The morphological transition of γ՛ precipitates, 2) The solubility limit of Cr in the alloy for TCP formation, 3) Hardness and average elastic modulus, and 4) The nature and topology of oxidized layers as a function of chromium concentration. Therefore, this method facilitates the optimization of multiple properties in a single experiment, identifying the optimal composition range typically between 5 and 8 at. % of Cr in the present alloy. • The P-B diffusion couple method was demonstrated as a high-throughput experiment for alloy design in cobalt-based superalloys. • Microstructural evolution in the IDZ reveals the morphological transition of γ՛ precipitates from cuboidal to spherical with increasing Cr. • The solubility limit of Cr was determined, beyond which the TCP phase precipitates. • Hardness and elastic modulus values, probed by nano-indentation, were correlated with the microstructure. • Enhanced oxidation resistance with Cr was analyzed by examining oxide morphology and thickness. [ABSTRACT FROM AUTHOR]

The external atmosphere can significantly affect the microstructure within the oxide scale of alloys during high temperature oxidation. In this paper, we investigate the isothermal oxidation of CoNiCrAlHf alloys in dry air and water vapor (Ar-25%H 2 O and air-25%H 2 O). The different test atmospheres led to very different results. HfO 2 peg formed at the Al 2 O 3 /alloy interface duo to in-situ oxidation. The presence of water vapor significantly increases the oxygen potential gradient and the diffusive flux of Hf, causing the linear distribution of HfO 2. In addition, water vapor has effectively retard the phase transformation of metastable-Al 2 O 3 to α-Al 2 O 3. In high temperature water vapor, the CoNiCrAlHf alloys form a duplex-layer, consisting of external δ-Al 2 O 3 and internal γ-Al 2 O 3. The distinction can be attributed to the promotion of defect concentration due to the adsorbed water molecules. The formation of Al vacancies would promote the outward diffusion of Al and the inward diffusion of O, which greatly facilitates the formation of γ -Al 2 O 3. • The external atmosphere can significantly affect the microstructure within the oxide scale of alloys during high temperature oxidation. • Different distributions of HfO 2 were formed within the oxide scale in dry air and water vapor. • High water vapor has effectively retard the phase transformation of metastable-Al 2 O 3 to α-Al 2 O 3. • The distinction of microstructure can be attributed to the promotion of defect concentration due to the adsorbed water molecules. [ABSTRACT FROM AUTHOR]

In the process of material removal, the metallurgical and mechanical properties of the surface layer of GH4169 superalloy have changed significantly, which has an adverse effect on the fatigue life. Therefore, surface strengthening process is indispensable as the last process of part manufacturing. In the paper, once and four times of ultrasonic surface rolling process (USRP) are carried out on GH4169 superalloy. The results show that USRP treatment improves the degree of grain refinement, the proportion of low angle grain boundaries (LAGBs) and dislocation density of the surface layer. The USRP treatment with four times forms a preferred orientation (〈101〉//TD) on the surface layer, and, the grain refinement mechanism is revealed. Moreover, USRP treatment changes the crack propagation mode from transgranular to intergranular. The fatigue tests indicate that the fatigue life of samples treated with USRP with once and USRP with four times increase by 55.6% and 138.6%, respectively. It can be inferred that the surface topography, residual stress, microstructure and degree of working hardening are the main factors affecting the low cycle fatigue properties of USRP treated samples. • The grain refinement mechanism of USRP treated samples was revealed. • The effect of USRP treatment on grain texture orientation was researched. • The effect of USRP treatment on crack propagation mode was analyzed. [ABSTRACT FROM AUTHOR]

The preparation of superior performance supercapacitors to achieve high energy density, fast charge-discharge speed and long cycle stability characteristics has become the focus of attention to realize their potential as practical energy storage devices. In this paper, a cross-linking CNTs@MXene (CMX) architecture is selected as the negative electrode to increase the contact area with electrolyte, and corrugation-like morphologies MoS 2 and WS 2 nanoparticles modified CMX (Mo/W-CMX) two-dimensional nanostructure as the positive electrode to provide multiple ion diffusion through its channels structure, which presents good electrochemical performance with high specific capacitance and high energy density in 1 M KOH alkaline electrolyte. CNTs introduced into MXene interface by bridges can effectively impede the re-stacking of MXene, meanwhile, CMX as a matrix can also alleviate the properties degradation caused by the agglomeration and volume strain for sulfides. Benefiting from the facilitate accessibility of ions and high ability of electron transfer, the prepared Mo/W-CMX electrode exhibits a dramatic specific capacitance of 1160 F g−1 at 1 A g−1 and excellent capacitance retention of 88.67% at 25 A g−1 after 10,000 cycles. Meanwhile, the assembled asymmetric supercapacitor (Mo/W-CMX // CMX) presents an ultrahigh energy density of 28.1 Wh kg−1 at the power density of 697.3 W kg−1 and maintains 81.25% cycle stability at 15 A g−1 for 10,000 charge-discharge cycles. It is essential to highlight that the superior performance fabricated asymmetric supercapacitor holds a wide application prospect and very competitive energy-storage values in the upgrading of new high-performance devices. [Display omitted] • • The CNTs interfaced by bridges generate pores and nanosized contact layers. • • Corrugation-like MoS 2 and WS 2 nanoparticles modified CMX were fabricated. • • The Mo/W-CMX exhibits a dramatic specific capacitance of 1160 F g−1 at 1 A g−1. • • The supercapacitor (Mo/W-CMX // CMX) presents an ultrahigh energy density. [ABSTRACT FROM AUTHOR]