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• Evolution of molecular structure of handmade papers in aging process is traced by two-dimensional correlation spectroscopy. • Quantitative changes of molecular and supramolecular structures of Kaihua handmade papers in aging process are presented. • The degradation mechanism of Kaihua handmade paper in dry-heat and wet-heat aging process is revealed. • Correlations between the microstructural evolution and macroscopic deterioration are explained. Valued for its toughness and durability, Kaihua paper has been famous in China since the Qing Dynasty. It attracts great attention on the extension of paper life. Understanding of the complex degradation behavior of handmade paper under various aging conditions is an essential precondition for preparing long-life handmade paper. However, it is still difficult to explain the reactions sequence of cellulose microstructure and its relationship with the macroscopic deterioration of handmade paper. Herein, different types of Kaihua handmade papers, produced by various raw materials and crafts, were artificially aged. The evolution of their multi-scale structures in dry-heat (DH) and wet-heat (WH) conditions was explored systematically. Two-dimensional correlation spectroscopy (2D-COS) distinguished possible carbonyl vibrations involving hydrolysis and oxidation of cellulose and gave sequential changes of various carbonyl groups, illustrating different evolutionary behaviors of molecular structure of papers in DH and WH aging process. The energy and distance of hydrogen bond, crystal size and microfiber accessibility were quantitatively calculated during the degradation of cellulose. In addition, correlations between microstructural evolution and macroscopic deterioration of handmade papers involving reduced mechanical properties and yellowing were revealed. The current results will help to establish a platform for the multi-scale detection of handmade paper and improve the understanding of the degradation mechanism of handmade paper under different reaction paths. It also provides useful foundation on the preparation of long-life paper and the conservation of paper-based culture relics. [ABSTRACT FROM AUTHOR]

The exploration of the relationship between process parameters and grain evolution during the thermal deformation of rare-earth magnesium alloys using simulation software has significant implications for enhancing research and development efficiency and advancing the large-scale engineering application of high-performance rare-earth magnesium alloys. Through single-pass hot compression experiments, this study obtained high-temperature flow stress curves for rare-earth magnesium alloys, analyzing the variation patterns of these curves and the softening mechanism of the materials. Drawing on physical metallurgical theories, such as the evolution of dislocation density during dynamic recrystallization, recrystallization nucleation, and grain growth, the authors of this paper establish a cellular automaton model to simulate the dynamic recrystallization process by tracking the sole internal variable—the evolution of dislocation density within cells. This model was developed through the secondary development of the DEFORM-3D finite element software. The results indicate that the model established in this study accurately simulates the evolution process of grain growth during heat treatment and the dynamic recrystallization microstructure during the thermal deformation of rare-earth magnesium alloys. The simulated results align well with relevant theories and metallographic experimental results, enabling the simulation of the dynamic recrystallization microstructure and grain size prediction during the deformation process of rare-earth magnesium alloys. [ABSTRACT FROM AUTHOR]

The utilization of Al2O3 nanopowder to reinforce AA5754 aluminum alloy through blind holes employing the friction stir processing (FSP) technique to produce an aluminum matrix nanocomposite is explored in this paper. Motivated by the necessity to enhance the strength and ductility of welded joints, the impacts of varying the tool rotational speed (rpm) and blind hole diameter on the microstructure and mechanical properties of the joints are investigated. Experimental characterization techniques including SEM, optical microscopy, microhardness, and tensile tests were employed to analyze the welded joints produced under different processing parameters (tool rotational speeds of 910, 1280, and 1700 rpm, and blind hole diameters of 0, 1, 1.5, and 2 mm). Comparative analyses were conducted against base metal properties and joints without reinforcement powder. It was found that the addition of nanopowder resulted in a decrease in the maximum generated heat during FSP, while also reducing the stir zone size compared to samples without nanopowder. Moreover, enhancements in both the strength and ductility of the joints were observed with the incorporation of Al2O3 nanoparticles. The optimal combination of welding conditions, observed at 1280 rpm rotational speed and 1.5 mm hole diameter, yielded a remarkable ultimate tensile strength of 567 MPa, accompanied by a hardness of 45 HV. These results underscore the potential of nano-Al2O3 reinforcement in significantly improving the mechanical properties of the produced nanocomposite, with implications for advancing the performance of welded structures in various engineering applications. [ABSTRACT FROM AUTHOR]

The aim of this paper is to characterize the evolution of fine and spheroidal microstructure of Al–Zn–Mg–Cu alloy by strain-induced melting activation (SIMA) and recrystallization and partial remelting (RAP) routes. The phase transformation and microstructural evolution were investigated during the isothermal treatment in a wide semisolid temperature range from 550 to 610 °C. Effects of isothermal temperatures and processing routes on coarsening rate constant were also analyzed. The results show that during the semisolid isothermal treatment, recrystallization process occurred and intermetallic particles were gradually dissolved into the liquid matrix once the heating temperature was above the solidus. Further extension of soaking time led to the coarsening and spheroidization of the solid grains. The increase in the soaking temperatures raised the liquid fraction and accelerated the spheroidization process. Smaller spheroidal grains and better spheroidization effect were obtained in SIMA microstructure in comparison to RAP microstructure. The coarsening rate constants were, respectively, 319 and 454 μm3·s−1 in SIMA samples after soaked at 600 and 610 °C. The coarsening rate constants of 349 and 522 μm3·s−1 were achieved in RAP microstructure. [ABSTRACT FROM AUTHOR]

Soil thixotropy plays an important role in many engineering practices, which recently has been drawn an increasing attention by many researchers. In this paper, an experimental investigation on the thixotropy of deepwater marine clays in the South China Sea was carried out. The thixotropy-induced changes of undrained shear strength were measured by fall cone method, and the microscale evolution of soil structure, particularly the change of various types of water, was observed and quantified via employing scanning electron microscopy and thermogravimetric analysis, respectively. The test results show that the thixotropy strength ratios of all deep-sea clays increase quickly at the early stage (before about 10 days), then followed by a gradually lower increasing rate with prolonged time. The microstructural evolution of clay during thixotropic hardening is characterized by the transformation from a dispersed structure with parallel-arranged particles to a well flocculated one. The different types of water and their changes of mass fraction with thixotropic time could be well classified and quantitatively measured by thermogravimetric analysis, in which both the weakly and strongly bound water contents decrease, with the corresponding increase in the free water fraction. The thixotropic mechanism was then revealed from the perspective of the microstructural evolution and the adjustment of the thickness of bound water. The recovery of strength is majorly attributed to the forming and strengthening of inter-particle bonds or contacts and the adjustment of bound water layer. This research could help to provide a deeper insight into the inner reason of soil thixotropy. [ABSTRACT FROM AUTHOR]

In this paper, a 3D molecular dynamics (MD) simulation is performed to investigate the nanoindentation process, the most frequently used technique to measure mechanical properties such as hardness, of three Al/Mg intermetallic compounds, where Mg is the main element added to pure Al. To further improve the understanding of the mechanical response, in this study, we examine the hardness-strength data for three kinds of typical materials, including β -Al3Mg2 and γ - Al 1 2 Mg 1 7 and - Al 3 0 Mg 2 3 phases with different microstructures. In terms of the observed morphologies around the indentations, the influencing variables of the general link between strength and hardness are described. Accordingly, atomic simulations in this paper are performed under the same loading (2 1 × 1 0 1 0 s − 1 ) using a spherical diamond indenter. At both the - Al 3 0 Mg 2 3 and γ - Al 1 2 Mg 1 7 phases, we can see that the indenter generates a bigger deformation zone and a greater number of dislocations in the z direction. The simulation findings show that the microstructure has an impact on the shape of the deformation in each phase. After the deformation process, we get the depth-displacement (P – h) curves to describe the mechanical behavior of β -Al3Mg2, - Al 3 0 Mg 2 3 and γ - Al 1 2 Mg 1 7 phases. From the P – h curves, we got the radial distribution function, mechanical properties, such as micro hardness, Yield point and maximum load are determined and presented. According to the findings, the chemical composition of these phases has a considerable impact on their characteristics. These P – h curves obtained show a rapid increase in loading up to a maximum. The deformation behavior of −Al3Mg2 and − Al 1 2 Mg 1 7 phases under nanoindentation is slightly identical, and they have also a high elasticity limit, the ability to endure deformation and the characteristic of being very ductile and malleable. While - Al 3 0 Mg 2 3 phase was shown to be brittle and weak under the same uniaxial nanoindentation loading compared to other phases, it was found that there is a good correlation between the previous simulated studies. [ABSTRACT FROM AUTHOR]

The 2195 Al–Li alloy, as one of the representative third-generation Al–Li alloys, has extensive applications in lightweight aerospace structures. In this paper, the anisotropy in mechanical properties and microstructure evolution of 2195 Al–Li alloy sheets were investigated under a strain rate of 0.01, 0.1, 1 s−1 and a temperature of 440 and 500 °C. Experimental results showed that the hot tensile properties of the 2195 Al–Li alloy sheet exhibited a strong dependence on loading directions. The peak stress (PS) and elongation (EL) along the rolling direction (RD) were larger than the transverse direction (TD). For the tests carried out at 440 °C-1 s−1, the PS values of the sheets stretched along the RD and TD are 142.9 MPa and 110.2 MPa, respectively. And, most of the PS anisotropy values are larger than 15%. The anisotropy in EL is less significant than in PS. All the differences are about 10%. Moreover, dimples in the samples stretched along RD were more and deeper than those along TD at 440 °C. The fracture morphology along RD and TD were similar, and both were cleavage fractures at 500 °C. Particularly, the fractions of high angle grain boundaries (HAGBs) along TD were all about 5% larger than those of RD. And, there were more small-sized continuous dynamic recrystallization (CDRX) grains inside the initial grains and discontinuous dynamic recrystallization (DDRX) grains featured with the local bulge of grain boundaries along TD. This was due to the smaller average Schmid factor and the vertical EL trend of the initial grains when the samples were stretched along TD. A model of grain evolution during the dynamic recrystallization (DRX) along RD and TD was proposed based on EBSD results. The Schmid factor and banded structure had a more prominent effect on the hot ductility of the 2195 Al–Li alloy compared with the degree of DRX, thus presenting a higher EL and better hot ductility along RD. [ABSTRACT FROM AUTHOR]

In this paper, citric acid-modified chitosan (CAMC) was added to cement slurry and its adsorption and hydration regulation mechanism on cement particles was studied. The rheological properties, agglomeration properties, and adsorption properties were characterized by different testing techniques. The effect of CAMC on the evolution of C-S-H gel and aluminum hydrate was further studied by the NMR technique. The results show that the negatively charged CAMC will adsorb on the surface of cement and agglomerate cement particles. In addition to being adsorbed on the positively charged aluminate phase surface under the electrostatic effect, CAMC was also adsorbed on the negatively charged silicate phase through complexation between carboxyl groups and calcium ions. The formation of complexes on the surface of the silicate phase hinders the hydration of calcium silicate (C3S).CAMC significantly reduced the hydration rate of early cement, hindering the nucleation of C-S-H and ettringite (AFt). [ABSTRACT FROM AUTHOR]

Reactor pressure vessel (RPV) studs act as sealing fasteners connecting the top cover and cylinder of RPVs. The failure of the external threads of RPV studs negatively affects the operation and maintenance of nuclear islands. In this paper, triaxial rolling technology was applied to the production of RPV studs for the first time, and the process parameters were optimized based on finite element simulations and rolling tests. The effects of triaxial rolling on the surface morphology and microstructure of the external threads of an RPV stud were examined. Scanning electron microscope (SEM), transmission electron microscope (TEM), and electron back-scattered diffraction (EBSD) were employed to explore the grain refinement mechanism of the external threads of the RPV stud induced by severe plastic deformation during the triaxial rolling process. An RPV stud assembly test platform was used to conduct a 1:1 installation and tensile pre-tightening test on the external threads of the RPV stud processed by turning and rolling. It was found that the surface roughness of the RPV stud processed by triaxial rolling was less than 0.2 μm, which was 88% lower than that of the RPV stud processed by turning. A large number of ultra-fine grains appeared at the grain boundary of lamellar ferrite, forming a chain structure, and the proportion of ultra-fine grains on the thread root surface reached 63.5%. The microhardness at the thread root was 385 HV, which was 16% higher than that of the matrix. Under the same load, the RPV stud processed by triaxial rolling had more stable mounting torque and less tensile elongation than the RPV stud processed by turning, manifesting better assembly performance. [ABSTRACT FROM AUTHOR]

Microstructural stability at elevated temperatures is one of the main concerns for the service reliability of aero-engine turbine blades. Thermal exposure, as an important approach to examine the microstructural degradation, has been widely studied in Ni-based single crystal (SX) superalloys for decades. This paper presents a review on the microstructural degradation induced by high-temperature thermal exposure and the associated damage in mechanical properties in some typical Ni-based SX superalloys. The main factors affecting the microstructural evolution during thermal exposure and the influencing factors in the degradation of mechanical properties are also summarized. Insights into the quantitative estimation of the thermal exposure-affected microstructural evolution and the mechanical properties will be beneficial for the understanding and improvement of reliable service in Ni-based SX superalloys. [ABSTRACT FROM AUTHOR]

Interstitial oxygen (O) on the formation mechanism and enrichment distribution of body-centered cubic (BCC) molybdenum (Mo) has rarely been reported, and the O usually can cause serious brittle fracture in Mo. In this paper, we studied the formation mechanism and evolution of oxygen (O) when it was precisely controlled in the range of 3700–8600 parts per million (wppm). It was found that, with an increase in O concentration, O element not only existed in the form of solid solution but generated O element with different valence states in Mo metal. Large amounts of MoO2, MoO3, and Mo4O11 intermediate oxides were identified by electron probe micro-analyzer (EPMA) and X-ray photoelectron spectroscopy (XPS). Thermodynamic calculations revealed the formation process of oxides, and authenticity of the presence of O was verified by XPS. Enrichment and distribution of O element were analyzed by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and EPMA. Moreover, the compressive yield strength and hardness of Mo were greatly affected by O content range of 4500–8600 wppm. Our study is helpful to understand the behavior of interstitial impurity O in refractory Mo metals and provides important guidance for development of high-purity rare Mo metals. [ABSTRACT FROM AUTHOR]

The electromagnetic arc constriction technique was implemented to mitigate the heat input related weldability issues in Tungsten Inert Gas (TIG) welding of Alloy 718 particularly solute segregation and substantial laves phase evolution in fusion zone which significantly deteriorates the strength and elongation of welded joints. This paper reports the direct effect of arc constriction current (ACC) on microstructural evolution and tensile properties of Constricted Arc TIG (CA-TIG) welded Alloy 718 joints. ACC is the important parameter which induces the electromagnetic filed and controls the arc constriction characteristics. The basic mechanism responsible for microstructural modification and corresponding influence on the tensile properties of joints is studied both in quantitative and qualitative manner related to the mechanics of electromagnetic arc constriction and correlated to the cooling rate. The joints made by applying ACC of 50 A yielded superior tensile properties. It is correlated to the grain refinement of fusion zone resulting in the evolution of laves phase with finer discrete morphology in interdendritic spacings. Increase in ACC above 50 A causes severe growth of grains in fusion zone and substantial decrement in tensile properties of joints. Beneficial effects of ACC were not perceived at maximum level owing to the high heat input. [ABSTRACT FROM AUTHOR]

Semi-solid metal (SSM) processing has been an attractive method for manufacturing near-net-shape components with high integrity due to its distinct advantages over conventional forming technologies. SSM processing employs a mixture of solid phase and liquid metal slurries and/or non-dendritic feedstocks as starting materials for shaping. Since the original development from 1970s, a number of SSM processes have been developed for shaping components using the unique rheological and/or thixotropic properties of metal alloys in the semi-solid state, in which the globular solid particles of primary phase are dispersed into a liquid matrix. In this paper, the progress of the development of shaping technologies and the formation of non-dendritic microstructure in association with the scientific understanding of microstructural evolution of non-dendritic phase are reviewed, in which the emphasis includes the new development in rheomoulding, rheo-mixing, rheo/thixo-extrusion and semi-solid twin roll casting, on the top of traditional rheocasting, thixoforming and thixomoulding. The advanced microstructural control technologies and processing methods for different alloys are also compared. The mechanisms to form non-dendritic microstructures are summarised from the traditional understanding of mechanical shear/bending and dendrite multiplication to the spheroidal growth of primary phase under intensively forced convection. In particular, the formation of spheroidal multiple phases in eutectic alloys is summarised and discussed. The concluding remarks focus on the current challenges and developing trends of semi-solid processing. [ABSTRACT FROM AUTHOR]

The paper studies the influence of 0.5–1.8 wt.% Ni alloying on the superplasticity, microstructural evolution, and dynamic grain growth effect in a temperature range of 625–775 °C and room temperature mechanical properties of two-phase Ti-Al-Mo-V alloys. Due to a decrease in β transus and an enhancement in the alloy diffusivity, an increase in Ni content significantly improved superplasticity. The Ni-modified alloys exhibited 1.5–3-fold lower flow stress, a 2.5–3-fold greater elongation to failure, and 1.4–1.7-fold higher strain rate sensitivity m coefficient compared to the Ni-free alloy. An intermetallic Ti2Ni compound precipitated in the 1.8 wt.% Ni-modified alloy during low-temperature deformation at 700 °C and decreased superplastic properties. The Ti-4Al-3Mo-1V-0.1B alloy with 0.9 wt.% Ni exhibited a good combination of the superplastic behavior and room-temperature mechanical properties: an elongation to failure of 500–900% at a low-temperature range of 625–775 °C and constant strain rate of 1 × 10−3 s−1 and a yield strength of 885 MPa and ultimate tensile strength of 1020 MPa after pre-straining for 100% in a superplastic regime and strengthening heat treatment. [ABSTRACT FROM AUTHOR]

High-speed steels (HSSs) are frequently utilized as cutting tools and wear-resistant components for a variety of applications because of their exceptional hot hardness and desirable wear resistance. Over the last few decades, numerous strategies for the manufacture of HSS components have been developed. Among these methods, advanced manufacturing (AM) techniques, including powder bed fusion (PBF), direct energy deposition (DED), and material jetting (MJ), have gained great scientific attention because they allow the fabrication of complicated mechanical components with high customization and specialized qualities. However, a comprehensive review of the recent progress of AM of HSSs is still lacking and this paper aims to address this need. This present paper reviews all the significant attributes of the state-of-the-art AM techniques for the fabrication of HSSs. The process designs of AM by means of PBF, DED, and MJ are discussed and compared. Process modeling work, including the microstructure prediction and solidification behavior of AM-fabricated HSS is reviewed. The microstructural evolutions during AM processes in terms of carbide precipitation dynamics, grain growth behavior and defect formation mechanism of HSSs are discussed. Moreover, the engineering properties of the AMed HSS are summarized, including residual stress, hardness, strength, impact toughness and enhanced wear resistance. Furthermore, the existing difficulties of AM technology and the future research objectives for producing HSS components are offered and explored.

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]

Reflood plays an important role in preventing the serious accident process. In this paper, the reflood oxidation performances of Cr-coated Zr-Sn-Nb alloy cladding tubes at 1000 °C, 1100 °C and 1200 °C were studied by high-temperature steam oxidation followed by in-situ water quenching. The oxidation kinetics, macroscopic morphology, phase transformation and microstructural evolution were investigated. Cr coating can provide excellent anti-reflood oxidation protection for Zr-Sn-Nb alloy, resulting in an oxidation rate constant of only 1/4–1/7 of that of uncoated Zr-Sn-Nb alloys. However, the cladding tube degraded into fragments due to excessive thermal stress during the in-situ water quenching after reflood oxidation at 1200 °C for 4000 s. After reflood oxidation at 1000 °C and 1100 °C, the most prominent feature of the surface is a porous flocculation structure main due to the formation of volatile products, while after 1200 °C, it is a fine mackerel scale-like structure accompanied by protruding whiskers main owing to Cr3+ rapidly migrates outward to the outer surface via short circuit paths. After oxidation, the cross-section of Cr-coated Zr-Sn-Nb alloys exhibits a multi-layer structure. The thickness of each layer changes approximately linearly with oxidation time. However, due to the redox reaction, compared to that after oxidation for 2000s, the Cr 2 O 3 layer becomes thinner and the residual Cr coating becomes thicker after oxidation at 1200 °C for 4000 s. [ABSTRACT FROM AUTHOR]

Although FeCoNiAlTaB alloys with better properties and formability can be prepared by LPBF, higher strength is still necessary through post-treatment to expand applications. This paper examines post-printing aging to enhance their strength, showing that aging increases the yield strength from 704 to 1025 MPa due to precipitation strengthening. [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]

• Cyclic hardening and cyclic saturation appear in the plastic shakedown state. • Investigating deformation mechanisms during plastic shakedown and ratcheting. • AE signals monitor the fatigue process in plastic shakedown and ratcheting. Fatigue performance and durability application have always been the key issues impeding the understanding of aero-engine pressure pipe due to its non-standardized shape, making tests more challenging. This paper constructs an optimized testing system to elucidate the plastic shakedown and ratcheting behavior of 1Cr18Ni10Ti pressure pipe subjected to in-service loadings. Moreover, microstructural evolution's role in regulating the cyclic plasticity behavior is qualitatively established. Experimental results indicate that the pipe deformation exhibits compressive ratcheting behavior in plastic shakedown state, and the initial cyclic hardening followed by cyclic saturation occurs during the whole cyclic response. This corresponds to a decreasing ratcheting displacement rate followed by a steady state appears. Except for the first two similar deformation stages mentioned above, the abrupt cyclic softening and the resultant increasing ratcheting displacement rate are obtained at the final fracture stage of the pipe deformation in ratcheting state. A series of detailed microstructural characterizations, including optical microscopy (OM), scanning electron microscopy (SEM), electron backscattered diffraction (EBSD), transmission electron microscopy (TEM), and acoustic emission (AE) are combined to reveal the underlying microstructural mechanisms during cyclic deformation. The volume fraction of austenite and ferrite and the average grain size change during different stages of plastic shakedown and ratcheting deformation. The synergistic effects of dislocation structure multiplication, destruction, and dissolution at different stages of plastic shakedown and ratcheting deformation dominate the cyclic plasticity behavior. [ABSTRACT FROM AUTHOR]

This paper investigates the thermal stability of lithium slag geopolymer (LSG) containing fly ash (FA) and silica fume (SF) exposed up to 900˚C. The effects of elevated temperatures on the microstructural evolution were investigated by thermogravimetric analysis (TGA), X-ray Diffraction (XRD), mineral analysis, surface porosity, and compressive strength of LSG modified by optimum incorporation of fly ash and silica fume. The results indicated that elevated temperature exposure significantly affects compressive strength, surface porosity, void size, weight loss, and phase transformation of fly ash incorporated lithium slag geopolymer (LSG FA) and silica fume incorporated geopolymer (LSG SF). The maximum loss in compressive strength of 44.07% was observed in LSG FA compared to 31.50% loss in LSG SF after exposure at 900˚C. The weight loss of LSG SF was higher than that of LSG FA between 500 and 800˚C and 800–1000˚C indicating a higher degree of dehydroxylation, crystal phase transformation, and viscous sintering observed in the former mix. A larger shrinkage cracking was observed in LSG SF by self-desiccation of the aluminosilicate paste matrix by dehydroxylation of mordenite molecules. Therefore, the degradation of compressive strength is governed by the combination of the crystallization of aluminosilicate gel and the formation of voids. • Sintering of LSG attributed the phase transformation, pore formation, and strength variation. • LSG FA has higher thermal stability and resistance to dehydroxylation than LSG SF. • LSG containing silica fume shows less shrinkage and more residual strength post fire exposure at 900°C by silica sintering. • High temperature LSG sintering forms aegirine-augite and plagioclase from mordenite and anorthite. [ABSTRACT FROM AUTHOR]

• Cu coating is melted, desquamated, and solidified into near-spherical particles. • Cu coating can protect MWCNTs from structural damage at a laser power of 600 W. • MWCNTs are cut into segments and transformed into near-spherical amorphous particles. • Spheroidization of amorphous carbon is driven by the reduction in surface energy. The Cu coating on carbon nanotubes (CNTs) with low infrared laser absorptivity was applied to provide a protective layer against the structural damage caused by laser irradiation in this paper. The effect of Cu coating on the structural evolution of multi-walled carbon nanotubes (MWCNTs) under a ring-shaped high-energy laser beam was studied. As the laser power increases, the morphology of 35 wt.% Cu-coated MWCNTs (35Cu-CNTs) samples transforms from discrete fine powder particles to caking structure with a roughened surface. A 45 wt.% Cu coating effectively provides structural protection for MWCNTs against laser-induced damage at a laser power of 600 W. During laser irradiation, the Cu coating melts, detaches from the surface of MWCNTs, and subsequently solidifies into a mixture of nearly spherical particles. Without the protection of Cu coating, the MWCNTs bundles are fragmented into nanoscale segments in varying sizes. These segments undergo a transformation into amorphous carbon particles as a result of the rapid heating and cooling process induced by the high-energy laser irradiation. The thermal impact of the high-energy laser beam plays a crucial role in determining the structural transformation of MWCNTs. The coalescence and spheroidization of amorphous carbon particles can be induced by the reduction of surface energy. [ABSTRACT FROM AUTHOR]

The Laasraoui segmented and Arrhenius flow stress model, dynamic recrystallization (DRX) model, grain size prediction model, and hot processing map (HPM) of Fe-Cr-Mo-Mn steels were established through isothermal compression tests. The models and HPM were proven by experiment to be highly accurate. As the deformation temperature decreased or the strain rate increased, the flow stress increased and the grain size of the Fe-Cr-Mo-Mn steel decreased, while the volume fraction of DRX (Xdrx) decreased. The optimal range of the hot processing was determined to be 1050–1200 °C/0.369–1 s−1. Zigzag-like grain boundaries (GBs) and intergranular cracks were found in the unstable region, in which the disordered martensitic structure was observed. The orderly packet martensite was formed in the general processing region, and the mixed structure with incomplete DRX grains was composed of coarse and fine grains. The microstructure in the optimum processing region was composed of DRX grains and the multistage martensite. The validity of the Laasraoui segmented flow stress model, DRX model, grain size prediction model, and HPM was verified by upsetting tests. [ABSTRACT FROM AUTHOR]

The microstructural evolution and crystallographic texture formation of β-solidifying Ti-44Al-6Nb-1.2Cr alloy were identified under single- and multi-track exposures via laser powder bed fusion (L-PBF) for various process parameters. Under single-track exposure, the microstructure of the melt pool was divided into the band-like α2 phase in the melt pool boundary and β phase in the melt pool center. Numerical and thermodynamic simulations revealed that the underlying mechanism of phase separation was related to the variation in the cooling rate in the melt pool, whereas microsegregation induced a shift in the solidification path. Meanwhile, the crystallographic texture of the α2 phase region was identical to that of the substrate owing to the epitaxial growth of the β phase and subsequent α phase nucleation. In contrast, the β phase exhibited a ± 45° inclined <100> alignment in the melt pool, which was tilted to align along the build direction toward the center of the melt pool corresponding to the simulated thermal gradient direction. Furthermore, the narrow hatch space condition maintained the crystallographic texture to the subsequent scan, forming a continuous band-like α2 phase with a strong selection. However, the crystallographic texture in a wide hatch space condition manifested a random distribution and constituted a fine mixture of the β and α2 phases. For the first time, these results will offer an understanding of an anisotropic microstructure control via the L-PBF process and ensure the tailoring of the mechanical properties in the β-solidifying γ-TiAl-based alloys by approaching hatch spacing control. [ABSTRACT FROM AUTHOR]

A new approach is proposed that identifies three different zones of the Si-rich network structure (the cellular structure) in laser powder bed fused (LPBF) AlSi10Mg alloy, based on the variation in morphology, grain growth transition, and melt pool solidification conditions. The three identified zones are denoted in the present work as the liquid solidification zone (LSZ), the mushy solidification zone (MSZ), and the heat affected zone (HAZ). The LSZ is the result of liquid–solid transformation, showing small planar growth at the boundary and large cellular growth in the center, while the MSZ is related to a semisolid reaction, and the HAZ arises from a short-time aging process. The boundary between the LSZ and MSZ is identified by the change of grain growth direction and the Si-rich network advancing direction. The boundary between MSZ and HAZ is identified by the start of the breakdown of the Si-rich network. In addition, it is found that the fracture is generated in and propagates along the HAZ during tensile tests. [ABSTRACT FROM AUTHOR]

Thermal deformation behavior of Cu–Cr–Sn alloy ingots under deformation temperatures ranging from 600 °C to 950 °C and strain rates from 0.01 s−1 to 10 s−1 was investigated in detail. The thermal deformation constitutive equation and thermal processing map of the alloy were established, respectively. The activation energy Q was determined as 430.61 KJ/mol. The optimal deformation system corresponding to the hot working diagram was a deformation temperature of 900 °C and strain rate of 0.1 s−1. Under these deformation conditions, twin dynamic recrystallization (TDRX), continuous dynamic recrystallization (CDRX), and discontinuous dynamic recrystallization (DDRX) occurred simultaneously, with the twinning process causing the stress–strain curve to exhibit a wavy change. The thermal deformation microstructure of the alloy is co-regulated by different recrystallization mechanisms, with DDRX occurring mainly at low deformation temperatures, and both CDRX and DDRX occurring at high deformation temperatures. [ABSTRACT FROM AUTHOR]