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Lightweight strategy is essential for the development of transportation vehicles and aerospace industries. As a type of lightweight material, high-strength aluminum alloys are limited to service temperatures below 200 °C due to the rapid coarsening of strengthening nano-precipitates, which cannot satisfy the increasing demands of practical applications. High-temperature applications beyond 250 °C become the bottle-neck problem of Al alloys. In this paper, we review existing literature on the improvement of high-temperature performance of aluminum alloys by stabilizing nano-precipitates. On the basis of atomic-scale microstructure regulation, several design strategies, such as interface segregation, co-precipitation, core/shell structure, and interstitial ordering, have been proposed, resulting in the development of a number of heat-resistant Al alloys for use at 300–400 °C. Moreover, the fundamental theories of solid-state phase transformation, especially precipitation aging and coarsening, are correspondingly advanced on the frontiers of science. [ABSTRACT FROM AUTHOR]

With development of present energy-saving society, lightweight and green development in the automotive and aerospace industries have put forward urgent demands for heat-resistant cast aluminum alloys. Present cast aluminum alloys are of lightweight and have excellent mechanical properties when serving in ambient environment. However, when serving at temperatures of 200–300 ℃ or even higher, the alloys inevitably soften and the high-temperature mechanical properties decline rapidly, hardly meeting the requirements for high-performance equipments. This paper summarizes the development process of classic heat-resistant aluminum alloys, especially the microstructural characteristics of heat-resistant cast aluminum alloys in the past decade, and reviews the current microstructure tuning strategies of heat-resistant aluminum alloys from the aspects of intrinsic heat resistance of the second phases, phase interface modification, diffusion-controlled phase transition, grain boundary stabilization and composite material design. Finally, we propose the prospects for the future development of heat-resistant aluminum alloys. [ABSTRACT FROM AUTHOR]

The mechanisms of microstructure transformation and mechanical anisotropy of laser-MIG hybrid additive manufacturing TC11 titanium alloy after solution aging treatment are investigated. In this paper, different solution temperatures and cooling modes are applied to tailor the microstructure and improve high-temperature properties and anisotropy. The result shows the microstructure of the samples in the as-deposited state is dominated by a widmanstatten structure composed of lamellar α clusters. Following solution aging treatment, a large area of basket-weave structure is obtained in the samples. A major influence of spheroidization of lamellar α clusters and dynamic recrystallization on mechanical anisotropy is revealed. The heat-treated samples exhibit more superior combined strength, elongation, impact toughness. The hardness difference between the layers and mechanical anisotropy decreases. During high-temperature tensile tests, the tensile strength increases with rising solution temperature; while, the elongation shows the opposite trend. The tensile fracture exhibits abundant uniform equiaxed dimples, and the fracture mode changes from intergranular fracture to transgranular fracture. Solution treatment at 990 °C for 2 h followed by air cooling is considered to be the optimal heat treatment process. Consequently, it results in a high tensile strength of 811 MPa and an excellent impact toughness of 50 J, representing improvements of 16.08% and 71.08%. [ABSTRACT FROM AUTHOR]

In this paper, high-density (60−x)Fe−Cr−Co−xCu (x: 0–6 wt.%) permanent magnet alloys were fabricated by laser powder bed fusion (LPBF) in-situ alloying technique, and the effects of Cu content on the microstructure, magnetic, and mechanical properties of the alloy were systematically investigated. The addition of 2 wt.% Cu enhanced the coercivity H c and the energy product (B H) max of the alloy in the isotropic state by 19.4 and 27.9%, respectively, compared to the alloy without Cu. The impacts of Cu content on the magnetic properties were investigated by combining experimental results and first-principles calculations. Furthermore, the addition of Cu improved the yield strength of the alloy, and the strengthening mechanism was analyzed in detail. The yield strength of the alloy with 2 wt.% Cu reached 908 MPa, representing a notable 7% increase relative to the Cu-free alloy. [ABSTRACT FROM AUTHOR]

Tribaloy™ T800, a Co-based alloy, exhibits remarkable tribological properties by virtue of its high-volume fraction of intermetallic Laves phase making it an attractive hard-facing material. Hard-facing by laser deposition results in dilution from the substrate, and thereby, the properties of the clad are altered. This paper reports the influence of processing parameters on the dilution, microstructure, and wear behaviour of Tribaloy™ T800 on AISI 316 stainless steel. A systematic set of 20 clads was deposited by varying laser power and cladding speed, keeping powder flow and spot diameter constant. While dilution decreased at lower laser powers (800 and 1000 W) with increasing cladding speed (5–20 mm s−1), at higher laser powers (1200 and 1400 W), the opposite trend was observed. The Fe intermixing from the substrate along with the cooling rate governs the volume fraction and size of the Laves phases which controls the properties of T800 clads. The clad with the least geometric dilution (5.7%) exhibits the lowest wear rate of 0.54 × 10−5 mm3 N−1 m−1, increasing to 2.88 × 10−5 mm3 N−1 m−1 as the dilution increased to 60%. [ABSTRACT FROM AUTHOR]

The effect of Ru on microstructures, coating texture changes, mechanical properties improvement, and cutting performance enhancement in CVD TiN-TiCN-Al2O3 coated cemented carbide was investigated in this paper. The results show that with the increasing amount of Ru, the mean grain size of the matrix decreases from 1.28 to 0.95 μm. The microstructural refinement of the matrix creates more nucleation sites for coating growth, which further reduces the grain size of the coating. Moreover, the Ru, diffusing from the matrix into the coating, changes the growth direction of partial grains. The coated cemented carbide with 1.5wt% Ru shows the largest hardness of 17.8GPa, which results from the combined influence of the reduction in coating grain size and the decrease in the concentration of TiCN coating {111} texture. In the process of turning 17-4PH stainless steel, due to the improved hardness and plastic deformation resistance of the composite coating, as well as enhanced (104) texture of Al2O3 coating, the flank wear of the coated tool with 0.5wt% Ru is 31.25% lower than that without Ru, which exhibits the best cutting performance. [ABSTRACT FROM AUTHOR]

Selective electron beam melting (SEBM) has been recently employed for additive manufacturing (AM) Al alloys but showing comparatively low hardness and strength. In this work, SEBM technique was employed to additive manufacture an in-situ TiB2 particle reinforced AlSi10Mg composite. With optimized processing parameters, the SEBM TiB2/AlSi10Mg composite showed good surface quality and a high relative density. The as-printed composite exhibited a refined equiaxed grain structure with an average size of 27.7 µm. The eutectic Si phase was mostly spherical and uniformly distributed in the Al matrix, while the nano-sized TiB2 particles were partly agglomerated. The resultant microstructure was associated with the combined effect of the rapid solidification and annealing-like process during SEBM. Additionally, TiB2 particles facilitated grain refinement by enhancing the heterogeneous nucleation and retarding grain growth. The SEBM TiB2/AlSi10Mg composite presented a yield strength (YS) and ultimate tensile strength (UTS) of 103.6 MPa and 165.4 MPa, respectively, with an appreciable elongation of 15% at as-printed state. After a T6-like treatment, the YS and UTS of the composite were further improved to 225 MPa and 316 MPa, respectively, and an elongation of 12% was maintained. This paper shows the potency of SEBM in AM metal matrix composites (MMCs) with both agreeable strength and ductility. [ABSTRACT FROM AUTHOR]

The mechanism of microstructure evolution during rapid solidification and the proactive regulation of phase constitution to optimize the micromechanical properties of multicomponent alloys have been the focus of research in recent years. In this paper, the evolution of microstructural growth kinetics and the formation of amorphous phase in CoCrFeNiZr0.5 alloy were achieved by melt spinning technique and electrostatic levitation coupled melt quenching. According to the theory of transient nucleation, the nucleation incubation time of Laves, FCC, Fe23Zr6 and BCC phases with undercooling during rapid solidification of the alloy was calculated. And based on this, the mechanism of phase transition in the process of regular eutectic → anomalous eutectic → nanocrystalline → amorphous composite → complete amorphous structure was discussed and explained. The growth behavior of primary and eutectic phases solidified at different undercoolings was investigated. Combined with melt quenching, the alloy melts were quenched in the superheated state, liquidus, undercooled state and recalescence process. Multiple microstructures, including amorphous structure, amorphous plus nano-eutectic, gradient nano-eutectic and composite structure of primary Laves phase, along with primary eutectic plus secondary quenched eutectic structures were obtained, respectively. Moreover, the shear band and free volume theory were applied to explain the deformation behavior and the discrepant mechanical performance between amorphous composites and amorphous structures. The formation of quenched nano-eutectic and amorphous structure not only improves the hardness of the alloy, but also enhances the fracture toughness. [ABSTRACT FROM AUTHOR]

The effects of supersonic particle bombardment (SFPB) on the microstructure, microhardness and wear property of Ti6Al4V alloy prepared by laser metal deposition (LMD) were investigated in this paper. The electrochemical corrosion behaviors of the LMDed Ti6Al4V alloy samples before and after SFPB treatment in 3.5% NaCl solution were measured. The results showed that a gradient severe deformation layer of ~ 350 μm thickness was formed with refined equiaxed grains oriented in various directions on the surface of LMDed Ti6Al4V alloy after SFPB treatment. The microhardness of the deformation layer was significantly increased due to the plastic deformation, grain refinement, dislocations and deformation twins increment. After SFPB treatment, the LMDed Ti6Al4V exhibited higher wear resistance which is about 55.6% decrease in wear loss than that of the untreated sample. Moreover, the corrosion resistance and corrosion rate of the SFPB-treated samples in 3.5% NaCl solution improved due to the finer hexagonal grains and high density of grain boundary in the severe deformation layer. [ABSTRACT FROM AUTHOR]

Due to its excellent performance of lightweight and high strength, Al/Mg bimetal has high application value in the aerospace field. However, the poor bonding quality of the Al/Mg bimetallic interface is still an urgent problem to be solved. Therefore, this paper proposes to use Ni foil as the interlayer to control the interface structure and improve bonding strength. The results show that the Ni interlayer has a positive influence on Al/Mg interface structure regulation. The interface is composed of Al3Ni, Al3Ni2 and Mg2Ni phases, and no Al–Mg brittle intermetallic compounds (IMCs) are formed. Meanwhile, the Mg2Ni phase is distributed as islands on the interface at 490 °C, effectively preventing crack propagation. The average shear strength of the interface reaches a maximum of 69.5 MPa. Besides, the interface fracture mechanism was deeply analyzed. The Al/Ni interface has excellent bonding performance, and the fractures occur at the Mg/Ni interface. The fracture mode from intergranular and cleavage mixed fracture at 490 °C to brittle cleavage fracture at 505 °C. [ABSTRACT FROM AUTHOR]

A new type of inorganic fiber-fly ash continuous fiber was innovatively developed in this study to alleviate the problems of low comprehensive utilization rate and lacking of high-value utilization means of industrial solid waste fly ash. The melt flow temperature and macro-mechanical properties of different samples were studied. The results showed that with the increase in acidity coefficient index (MK), the melt flow temperature decreased first and then increased, and the lowest value was 1340 °C when MK was 3.1. Meanwhile, with the gradual increase in MK, the tensile strength and elastic modulus of monofilament increased first and then decreased. When the MK was 3.8, the tensile strength and elastic modulus of fiber monofilament reached 2064 MPa and 16.7 GPa, respectively. According to the results of XRD, TG-DSC, FTIR and SEM microstructure analysis methods, it is found that the macro-mechanical properties of fibers are closely related to the chemical composition and phase structure evolution of raw materials. After melting at high temperature, the samples with high MK form a dense three-dimensional glassy network structure, which leads to the higher mechanical strength of the fibers. However, in the samples with lower MK, the vitreous network structure is loose, which reduces the mechanical properties of the fiber. Finally, the MK range (2.5–3.8) for preparing high-performance fly ash fiber was proposed in this paper. In this range, the synthesized fly ash continuous fiber has low melting temperature and excellent mechanical properties, which has a potential of industrial application. [ABSTRACT FROM AUTHOR]

In this paper, perfect interface model of Al/AlCu alloy and defect interface model of Al/AlCu alloy after cracks were introduced at different positions of the interface were established by using cohesive zone modeling method. Classical molecular dynamics simulation was used to study the deformation behavior and microstructure evolution of Al/AlCu alloy interface model at a strain rate of 0.05 Å/ps and the temperature of 300 K. The simulation results show that perfect interface exhibits a uniform plastic deformation stage due to structural relaxation after yielding, while there is no structural relaxation during the deformation of defect interface and the tensile strength is much lower than that of perfect interface as well. In the process of deformation, stacking faults formed in perfect interface and cracks are generated and expanded in Al matrix, while there was no stacking faults forming along with the expansion and cracking at the position of introduced cracks in defect interface. Massive dislocation nucleation leads to the reduction in stress at the perfect and defect interfaces after yielding. The extension of Shockley partial dislocation and the nucleation of Stair-rod dislocation are the main mechanisms of interface deformation. Densities of Shockley partial dislocation and Stair-rod dislocation decrease with increasing strain before crack propagation. This study enriches the analysis of microstructure evolution of Al/AlCu alloy interface and similar interfaces during deformation. [ABSTRACT FROM AUTHOR]

In this paper, the effect of deep cryogenic treatment (DCT) on the microstructure and properties of automotive 6063 aluminum alloy at different times was investigated with automotive 6063 aluminum alloy as the research object. The results show that under the conditions of deep cryogenic treatment, the lattice distortion occurs in the alloy matrix microstructure, and the resulting internal stress promotes the large proliferation of dislocations within the alloy and the increase of dislocation density; meanwhile, after the deep cryogenic treatment, the deformed grains are transformed into recrystallized and sub-crystals structural grains, the grains are refined, and the size of the grains is refined from the original 25.2 μm to 20.3 μm, with fine equiaxed crystals. Among them, the mechanical properties of the DCT36h specimen were the best, and its hardness, tensile strength, yield strength and elongation reached 142.44 HV, 328.32 MPa, 177.42 MPa, and 29.29%, which were 34.17%, 5.62%, 11.10%, and 32.77% higher than the original sample, respectively. We believe that the main mechanism for the increase in toughness is multiple reinforcement such as dislocation strengthening, grain refinement strengthening, precipitated phase strengthening and texture strengthening. [ABSTRACT FROM AUTHOR]

Ni-based wrought superalloys are a type of superalloy produced through casting-forging processes, and usually their high-temperature performance is strongly influenced by microstructure and deformation mechanism. The typical microstructure of Ni-based wrought superalloys after heat treatments comprises equiaxed grains, numerous annealed twins, carbides within the grain interior and/or at grain boundaries, and spherical γ′ precipitates (typically comprises around 20% of their volume). The common deformation mechanisms in Ni-based wrought superalloys mainly include anti-phase boundary formed by paired dislocations shearing γ′ phase, stacking fault formed by single dislocation shearing γ′ phase, dislocation bypassing γ′ phase (precipitation-strengthened) and dislocation entanglement, dislocation networks (solid solution strengthened). In this paper, the microstructure and deformation mechanism of tensile and creep in Ni-based wrought superalloys for Advanced ultra-supercritical (A-USC) power plants are reviewed, for the two prominent areas of current research, Ni–Fe-based wrought superalloys exhibit superior processability and cost-effectiveness compared to Ni–Co-based wrought superalloys, thereby offering a more advantageous solution. [ABSTRACT FROM AUTHOR]

This paper presents the experimental investigation of the effect of Nb2O5 content on the phase composition, microstructure, and physical and mechanical performance of the zirconia-toughened alumina (ZTA) ceramics, aimed to optimize the additional amount of Nb2O5, refine the ceramic grains, and improve the densification, hardness and fracture toughness. ZTA ceramics with various Nb2O5 contents were prepared using the spark plasma sintering method. The addition of trace amounts of Nb2O5 did not produce a new Nb-rich phase; the Nb atoms were dissolved in the ZrO2 grains. The addition of trace amounts of Nb2O5 led to grain refinement and an increase in density, but the addition of excessive Nb2O5 resulted in grain growth and a decrease in relative density. Furthermore, the addition of Nb2O5 promoted uniformity of the microstructure. The sample with 0.25 wt.% Nb2O5 had the maximum Vickers hardness and indentation fracture toughness, which were 1228.40 HV and 9.17 MPa √m, respectively. Mechanical properties of the composite mainly depended on the grain size, which was influenced to some extent by the relative density. [ABSTRACT FROM AUTHOR]

In this paper, semi-solid compression of 2A14 aluminum alloy was conducted on the Gleeble1500D thermophysical simulation experimental compressor to investigate the rheological behavior of 2A14 alloy at high solid fraction in the semi-solid state. The main objective of the study was to establish the constitutive equation suitable for serving the simulation and practical thixoforging forming process of the 2A14 alloy. Another purpose is to investigate the effect of heat deformation parameters on the microstructure of 2A14 alloy. The apparent viscosity of semi-solid 2A14 alloy with high solid fraction as a function of equivalent shear rate was obtained. The constitutive equation for 2A14 aluminum alloy at true strain below 0.2 was established. Increasing the compression temperature or strain rate is beneficial to the deformation and grain refinement in the hard deformation zone, but at the same time, it will also intensify the aggregation of micro-voids in the transition zone into micro-cracks and the formation of macro-cracks. The macroscopic compression instability at true strains above 0.2 was discussed, mainly attributed to the dilatant shear bands generated in the strain localization region inherent in the compression deformation and the higher thermal crack sensitivity of the 2A14 alloy. [ABSTRACT FROM AUTHOR]

The conventional approach to achieve desired effective thermal conductivity (ETC) of porous thermal interface materials (TIM) is processing-microstructure-properties forward analysis, which contains various trial-and-error cycles and is hence inefficient for materials development. Establishing the linkage from ETC to microstructure is essential; however, the recently developed methods including microstructure characterization and reconstruction are suffering from limited accuracy and computational efficiency. To address these problem, in this paper, generative artificial intelligence (AI) model was first implemented to design microstructure of porous TIM with desired ETC. Here, we introduced a representative porous TIM, sintered silver, and a typical kind of generative AI model, conditional generative adversarial network (CGAN), as an example for illustration. The CGAN model can efficiently generate sharp and crisp microstructures of sintered Ag with excellent morphology realism. Besides visual inspection, the ETC values of generated microstructures were evaluated by convolution neural network (CNN) model. It was found that the CGAN model also exhibits satisfactory performance in physical meaning, since the determination coefficient R2 between target ETC and CNN predicted ETC values is 0.985. These results confirm the effectiveness of generative AI model capable of synthesizing microstructure of porous TIM with desired ETC, and not limited to porous TIM, the approaches present here can also be generalized and applicable to design microstructure of other porous media and composites. [ABSTRACT FROM AUTHOR]

Dynamic recrystallization mechanism and microstructure evolution of a novel quasi-continuous network reinforced TiAl matrix composites, TiAl/B4C composites were studied in this paper. The isothermal compression experiments, the scanning electron microscopy, and the electron back-scattered diffraction were carried out. Besides the discontinuous dynamic recrystallization (DDRX), the continuous dynamic recrystallization occurred in γ-phase grains during the loading, characterized by crystal orientation accumulation. Additionally, a large number of 89 ± 3° grain boundaries associated with DDRX also appeared during the loading. With the temperature increasing or/and the strain rate decreasing, the volume fraction of recrystallized grains increased significantly, the < 010 > crystal direction of γ-phase grains within the matrix unit of present composites was gradually parallel to compression direction, and the texture changed from scatter to concentration. The variety of texture was mainly related to different dynamic recrystallization mechanisms in various conditions. [ABSTRACT FROM AUTHOR]

TiAl alloy becomes a promising high-temperature structural material due to excellent mechanical properties at elevated temperature. However, the inherent brittleness makes it difficult to be processed by traditional technologies. Therefore, an innovative twin-wire plasma arc additive manufacturing (TW-PAAM) process is developed to fabricate TiAl alloy. Substrate heating is indispensable during additively manufactured TiAl alloy, which can alleviate its crack tendency. In this paper, crack-free TiAl alloy samples are fabricated using TW-PAAM, and the effect of substrate temperature (560, 620 and 680 °C) on as-deposited TiAl alloy is investigated in detail. With the increase in substrate temperature, microstructural lamellar spacing and colony size exhibit the tendency of increase. Also, α2 phase content, recrystallization degree and high Schmid factor frequency present the decrease tendency. These variations of microstructure characteristics further lead to the decrease in both microhardness and tensile properties of the deposit. These findings provide a valuable reference for optimizing microstructures and mechanical properties of additively manufactured TiAl alloys. [ABSTRACT FROM AUTHOR]

In this paper, we present the analysis of an interpenetrating metal ceramic composite structure. We introduce a new generation algorithm for the modeling of interpenetrating composite microstructures with connected, spherical cavities embedded into an open-porous foam structure. The method uses a geometric ansatz and is designed to create structures of special topology, as the investigated metal ceramic composite structures consisting of a connected AlSi10Mg phase showing spherical shapes embedded into an Al2O3 preform. Based on the introduced enhanced random sequential absorption approach, the generated microstructures yield numerical insights into the material that are not accessible by experimental techniques. The generated microstructures are compared to structures reconstructed from experimental CT scan data considering microstructural features and mechanical behavior. We show that the proposed method is able to generate statistically equivalent microstructures by using only a small number of statistical descriptors. The numerical formulation is validated using compression tests including plastic yielding in the aluminum and damage progression in the ceramic phase. Both the composite material and the pure ceramic preform are considered in this analysis, and good agreement is found between reconstructed and generated microstructures. Furthermore, the observations reveal the importance of the local geometrical sphere arrangement with respect to the mechanical behavior. A validation with experimental results is presented and it is shown that the model predicts microstructural properties and gives meaningful insights into the structural and material interplay. Finally, we discuss the potential of the method for the investigation of failure mechanisms. [ABSTRACT FROM AUTHOR]

The effects of rare-earth (RE) inoculants are excellent, but RE is rare and expensive. Consequently, it is necessary to choose other elements to reduce the use of RE. In this paper, research was done to investigate the effects of different content La–O–S complex inoculant on the microstructure and mechanical characteristics of ductile iron (DI) through SEM, EDS, XRD, etc. Studies have shown that the as-cast structures of the samples are graphite nodules, ferrites, and a few pearlites. The graphite core consists of oxides (Al2O3, SiO2, Fe2O3), sulfides (La2S3, LaS), and XO·SiO2·Al2O3 silicate (X: Ca, Ba, Sr). The amount of graphite nodules increases firstly and then slightly decreases, ferrite increases gradually, and pearlite decreases by degrees with the increase in S or O content, which makes the Brinell hardness and tensile strength of the sample decrease, and the elongation of the sample slightly decreases after increasing. When both O and S are 0.3%, mechanical characteristics of the samples are best, Brinell hardness is 163.3 BHW, tensile strength is 513 MPa, and elongation is 16.1%. [ABSTRACT FROM AUTHOR]

The ability to measure elongated structures such as platelets and colonies, is an important step in the microstructural analysis of many materials. Widely used techniques and standards require extensive manual interaction making them slow, laborious, difficult to repeat and prone to human error. Automated approaches have been proposed but often fail when analysing complex microstructures. This paper addresses these challenges by proposing a new, automated image analysis technique, to reliably assess platelet microstructure. Tools from Mathematical Morphology are designed to probe the image and map the response onto a new feature-length orientation space (FLOS). This enables automated measurement of key microstructural features such as platelet width, orientation, globular volume fraction, and colony size. The method has a wide field of view, low dependency on input parameters, and does not require prior thresholding, common in other automated analysis techniques. Multiple datasets of complex Titanium alloys were used to evaluate the new techniques which are shown to match measurements from expert materials scientists using recognized standards, while drastically reducing measurement time and ensuring repeatability. The per-pixel measurement style of the technique also allows for the generation of useful colourmaps, that aid further analysis and provide evidence to increase user confidence in the quantitative measurements. [ABSTRACT FROM AUTHOR]

In this paper, the effects of Nb contents (0.05 ~ 0.50wt%) and hot rolling temperatures (1000 ~ 1200 °C) on microstructure and mechanical properties of high-silicon electrical steel were studied. The results show that adding a small amount of Nb can significantly improve the plasticity of high-silicon electrical steel. Compared with the specimens without Nb, the three-point bending load–deflection curves of the alloys with Nb contents of 0.05 ~ 0.50wt% after warm rolling showed obvious plastic stage. The average fracture deflection increases from 4.5 to 9.9 mm with the Nb content increasing from 0.05 to 0.50wt%. When the hot rolling temperature is 1000 °C, the Nb-containing high-silicon electrical steel has a layered microstructure along the thickness direction. The surface layer is equiaxed grains with dynamic recrystallization, while the center of the thickness is a long strip structure with dynamic recovery. The mechanism of Nb microalloying to improve plasticity includes three aspects: Firstly, the layered structure hinders the propagation of cracks and delays the progress of fracture; secondly, a large number of fine Nb precipitates will hinder the grain growth and refine the grains; thirdly, the formation of the Nb-precipitated phase destroys the ordered rearrangement between adjacent Fe and Si atoms in the matrix, inhibits the ordered transformation and reduces the ordered degree of high-silicon electrical steel. When the hot rolling temperature is increased to 1100 °C or above, the layered structure disappears, the grain coarsens obviously, and the plasticity of the warm-rolled specimens is significantly reduced. [ABSTRACT FROM AUTHOR]

The development of discontinuous reinforced titanium matrix composites (DRTMCs) provides a new idea to further improving the comprehensive mechanical properties of titanium alloys, which is expected to further expand their application fields to meet the new requirements of modern industry for metallic materials. In this study, the effects of Fe content on the microstructure and mechanical properties of Ti-TiBw-xFe composites were studied by adding alloying element Fe to Ti-TiBw composite powders. It was found that the grain size of α-Ti matrix was significantly refined with increasing Fe content. When Fe content was increased from 3.0 to 6.0 wt.%, the grain size of α-Ti decreased from 3.50 to 2.58 μm, representing a 26% decrease. Furthermore, the tensile strength of Ti-TiBw-6.0Fe reached 1065 MPa, which is 105.2% remarkable higher than that of Ti-TiBw with the same conditions, with an elongation at 5.3%. It was shown that the addition of Fe significantly improves the mechanical properties of Ti-TiBw-xFe composites. Solution strengthening, fine grain strengthening and load-bearing strengthening play a major role in improving the mechanical properties of Ti-TiBw-xFe composites. [ABSTRACT FROM AUTHOR]

A low-alloyed Mg-1.2Zn-0.1Ca (wt%) alloy was extruded at different temperatures (150 °C, 200 °C, 250 °C, 300 °C), and the effect of extrusion temperature on the microstructure and tensile properties was investigated systematically. While the as-cast alloy presented many cracks on the surface when extruded at 150 °C, it demonstrated good extrudability at temperatures above 200 °C. With increasing extrusion temperature from 200 to 300 °C, the average dynamic recrystallization (DRX) grain size increased from ~ 2.6 to ~ 6.4 μm, and < 10–10 > texture gradually transformed to < 11–21 > rare-earth texture component. Solute segregation was observed along grain boundaries and dislocations. The sample extruded at 200 °C exhibited a superior combination of both strength and ductility, with a yield strength of 179 MPa, an ultimate tensile strength of 228 MPa and an elongation of 35%. The improved tensile properties were mainly attributed to the fine grain size together with a high density of dislocations. The basal slip Schmid factor increased with increasing extrusion temperature due to the attainment of full DRX microstructure and the presence of non-basal texture component, which resulted in a lower yield strength at higher extrusion temperatures. The findings pave the way for the development of low-cost and low-alloyed high-performance magnesium alloys via the strategy of tailoring extrusion temperatures. [ABSTRACT FROM AUTHOR]

The microstructure, compressive properties and in vitro degradation behavior of as-cast Mg alloys with high Zn or Ca content were investigated. The results showed that the addition of Ca (1 wt%) to Mg–5Zn or Zn (1 wt%) to Mg–5Ca changed the shape, distribution, volume fraction and the type of second phase. When 1 wt% Ca was added to Mg–5Zn alloy, the second phase changed from Mg7Zn3 to Ca2Mg6Zn3 phase and it was distributed from granular formation to a continuous network structure. While the second phase was changed from Mg2Ca in Mg–5Ca alloy to the coexistence of Mg2Ca(Zn) and slight Ca2Mg6Zn3 phase in Mg–5Ca–1Zn alloy. The second phase exhibited a continuous network distribution in both of Mg–5Ca and Mg–5Ca–1Zn alloys, but the width of Mg2Ca(Zn) phase was reduced obviously after adding 1 wt% Zn to Mg–5Ca alloy. The compressive test revealed that Zn element was contributed to the promotion of ultimate compressive strength and fracture elongation, while Ca element was beneficial for improving the yield strength of Mg alloys. The immersion test proved that the weight loss of Mg–5Zn–1Ca was the highest, followed by Mg–5Zn, Mg–5Ca and Mg–5Ca–1Zn alloy. The Mg–5Zn-based alloys suffered severe pitting, while Mg–5Ca-based alloy exhibited a relatively uniform corrosion. The Ca addition accelerated the corrosion of Mg–5Zn alloy due to the expansion of potential difference between second phase and Mg matrix, while Zn addition reduced the micro-galvanic corrosion of Mg–5Ca alloy due to the lowest potential difference between Mg2Ca(Zn) phase and Mg matrix. [ABSTRACT FROM AUTHOR]

Introducing of thermodynamically stable strengthening phases is an important means enhancing the properties of magnesium alloys. To introduce a stable Al2Nd strengthening phase, the Mg-Al-Nd alloys were prepared with a fixed atomic ratio of 2:1 for Al and Nd. The total content of Al and Nd was varied at 1%, 3%, 5%, and 7%, respectively. The effects of Al2Nd phase on the microstructure and mechanical properties of the Mg-Al-Nd alloys were systematically studied in this work. The experimental results indicated that the as-cast alloy primarily consisted of the acicular Al11Nd3 phase as a secondary phase. After undergoing a homogenization treatment at 500 °C for 12 h, the secondary phase underwent a transformation, resulting in the formation of short rod shape Al2Nd structures. Simultaneously, layered Al2Nd precipitated within the α-Mg matrix. The formation of twinning was inhibited, while the Al2Nd phase promoted recrystallization and refined the microstructure through the mechanism of particles stimulated nucleation (PSN), as the Al and Nd contents increased during thermal deformation. At the same time, the increases of Al2Nd phase can enhance the strength and the plasticity of the alloy. The mechanical properties of extruded Mg-1.36Al-3.64Nd (AE5) alloy were excellent with yield strength of 175 MPa, ultimate tensile strength of 249 MPa, and the elongation of 15.4%. The enhanced performance can be primarily attributed to the refined microstructure and the presence of Al2Nd precipitates with small size, which contributed to effective fine grain strengthening and secondary phase strengthening. [ABSTRACT FROM AUTHOR]

Multi-material components, also known as functionally graded materials (FGMs), are innovative materials that possess unique properties due to their composition and have many potential applications in engineering and science. The effect of the heat treatment (HT) of functionally graded materials 15–5 precipitation-hardened (PH) martensitic steel and SAF 2507 duplex stainless steel (and the opposite order of deposition, i.e. SAF 2507 first followed by 15–5 PH stainless steel) on the interface microstructures was systematically investigated in the presented research. The choice of HT followed the trend of optimum post-processing for the individual alloys. A significant modification in the interface microstructure, characterized in the microstructural transition zone (MTZ) formed above the fusion line. Mechanical properties by miniaturized testing method including hardness measurement characterized both types of interfaces. The sequence of the materials' application did not have a significant effect on their final mechanical tensile properties in the heat-treated states. Nevertheless, the microstructural change at the MTZ led to drop in the hardness at the interface. The research presents heat-treated FGMs in a horizontal configuration to form a high-quality metallurgical joint between heterogeneous materials manufactured by powder-based directed energy deposition method. [ABSTRACT FROM AUTHOR]

The eutectic Nb30Ti35Co35 and hypoeutectic Nb15Ti42.5Co42.5 filler alloys are used to join bcc Nb–Ti solid solution alloy. It is found that the composition of filler alloy affects the dissolution of the Nb–Ti matrix into the filler alloy, and consequently influences the interfacial morphology of the brazing seam. The Nb30Ti35Co35/Nb–Ti joint at elevated temperature is mainly composed of the Ti2Co phase and the Ti–rich phase, while the Nb15Ti42.5Co42.5/Nb–Ti joint mainly consists of the TiCo phase. With the increase in brazing temperature, the TiCo or Ti2Co phases in the Nb–Ti–Co/Nb–Ti joints increase. The shear strength of the joints is closely related to the number of TiCo and Ti2Co phases because of their high shear modulus. As the brazing temperature further increases, however, the Ti–rich phase precipitates in the Ti2Co phase, leading to the increases of interal stress and the decrease in shear strength. The maximum shear strength of Nb30Ti35Co35/Nb–Ti and Nb15Ti42.5Co42.5/Nb–Ti joints is 598.9 MPa and 573.1 MPa, respectively. [ABSTRACT FROM AUTHOR]

Polymer–clay nanocomposites are the most remarkable nanomaterials of the current decade with broad range of applications, because they attempt a great competence to impart outstanding properties when compared to pure polymers even at a very less percentage of nanofiller inclusion. Montmorillonite, vermiculite, halloysite, sepiolite, laponite, bentonite, and attapulgite are the dominant classes of clay used as reinforcement in polymer–clay nanocomposites. Clay is easily accessible, easily processed, inexpensive, and non-toxic, and clay nanocomposites have seen significant commercial interest due to improvements in processing. Clay nanocomposites show distinctive properties of outstanding thermal stability, enhanced flame retardancy, high dimensional stability, decreased gas permeability, and enhanced anticorrosive and improved mechanical properties. This review reveals the polymer-based nanocomposites reinforced with halloysite nanotubes, for high-performance promising applications. The qualities of the nanofiller can be changed by chemically modifying exterior surface and interior lumen. Chemical alteration of the halloysite nanotube surface, in particular, results in nanoarchitecture with targeted affinity through functionalization of the outer surface and potential for drug transport through functionalization of the nanotube lumen. The various functionalization techniques of altering the nanofillers to allow interaction with polymers are discussed. The significance of filler dispersion in the polymeric matrix is also featured. The consequences of functionalized nanofillers on the microstructure and morphology, mechanical strength, thermal stability, drug encapsulation and sustained release abilities, and flame retardancy as well as barrier properties can be summarized. Subsequently, the challenges, key problems, future prospects, and feasible mechanism for polymeric clay nanocomposites are also reviewed. [ABSTRACT FROM AUTHOR]

Understanding the effects of in-service microstructural changes in metal alloys on the mechanical performance and remaining life of equipment is a critical part of integrity management in industrial plants. However, the effects of processes such as carburization or nitridation are not accounted for in industry-standard life assessment methodologies such as those provided in the API 579-1/ASME FFS-1: Fitness-For-Service standard. This is problematic for the austenitic stainless steel Alloy 800H, which typically operates in the creep regime and has been reported to suffer nitriding during high-temperature service in air. Despite this being one of the most common service environments for 800H, the impact of nitriding on in-service performance and implications for remaining life assessment have not been well-studied for this alloy. In this work, we characterize the microstructures of as-received, aged, and nitrided Alloy 800H tube material, and correlate observations with room-temperature tensile properties and high-temperature creep behavior. We show that while the creep properties of aged 800H material can be captured by the widely-used MPC Project Omega creep model and API 579-1 Omega properties for 800H, nitrided material properties fall outside of the expected bounds, and therefore remaining life cannot be reliably predicted using this method without experimental data. [ABSTRACT FROM AUTHOR]

The degradation of components resulted from wear is unavoidable in service, which could be partly solved by applying surface treatment technique. Stellite-6 cobalt-based alloy is considered as a potential cladding material to improve the wear resistance of base materials owing to its excellent hardness and strength. The microstructural evolution and local mechanical properties of Co-rich matrix and Cr-rich eutectic carbide of Stellite-6 cladding with different aging times at 900 °C are investigated by optical microscopy, field emission scanning electron microscope and nanoindentation testing. The tribological characteristics of the matrix and eutectic carbide itself are systematically investigated using the single-pass nano-scratch testing. In the matrix region, the carbide precipitations occur after 5 h and coarsens after 10 h aging. The nanoindentation results indicate that the hardness of the matrix regions is significantly increased due to the presence of dispersed carbide and fine stripe-like precipitations. The nano-scratch tests depict that the wear resistance is improved with higher matrix hardness to support eutectic carbide based on aging treatment. Potential improvement on tribological performance through the aging treatment procedure is proved based on the micromechanical and wear behaviors of matrix and eutectic carbide were identified. [ABSTRACT FROM AUTHOR]

For the welded joints of S690QL high-strength steel, determining the local brittle zone (LBZ) in dissimilar weld metal, understanding the microstructure evolution caused by multiple welding thermal cycles and element diffusion is significant to evaluate the safe service. However, microstructure evolution in weld root is ignored in previous studies. Here in this article, we utilized various characterization methods to elucidate the effect of multiple thermal cycle on weld root microevolution. The results of the impact test and the crack tip opening displacement (CTOD) test show that there is an LBZ in the root weld pass. The effects of welding multiple thermal cycle and base metal element dilution on the microstructure evolution of root zone were analyzed. The results indicate that although the microhardness of root zone is intermediate between SAW zone and SMAW zone, the impact energy of root zone is ~ 92 J compared with SAW zone (~ 133 J) and SMAW zone (~ 121 J), which is the LBZ. Due to the dilution of the base metal, C, Cr, and Ni elements diffuse into the root pass. Meanwhile, under multiple thermal cycles, the grain coarsens, the proportion of high-angle grain boundaries decreases, and martensite-austenite (M-A) constituents grow and evolve into large-size blocks, which has two types substructure, contributing to the impact toughness reduction of root zone. Furthermore, M-A constituents show different fracture behaviors under fast loading and slow loading. This study not only reveals the evolution behavior of M-A constituents, but also provides a design reference for the microstructure optimization and property improvement of 690 MPa grade high-strength steel welded joints. [ABSTRACT FROM AUTHOR]

Ti–B4C system is one of the most important reaction material systems for preparing TiB2–TiC composite coatings, but the difficulty of densification in preparing TiB2–TiC composite coatings by plasma spraying Ti–B4C system composite powder has greatly limited its application. In order to remove the inherent defects of the microstructure and properties of the coatings prepared by plasma spraying Ti–B4C system composite powder, the TiB2–TiC composite ceramic coatings were prepared on the surface of TC4 titanium alloy substrate by plasma spraying reaction synthesis process with Ti–B4C as the base system and adding appropriate graphite additive. The influence of graphite additive on the microstructure and mechanical properties (hardness, scratch resistance, erosion and wear resistance) of the coatings prepared by plasma spraying Ti–B4C system composite powder was investigated. It was found that the main phases of the coating obtained by plasma spraying Ti–B4C–C system composite powder were TiB2 and TiC, and the density of the coating was increased. The TiB2–TiC composite coating prepared by plasma spraying Ti–B4C–C system composite powder had higher microhardness, better scratch resistance, erosion resistance and wear resistance. The reason is that the addition of graphite improved the melting state of the composite powder during the plasma spraying process, accelerated the reaction rate of the spraying system, and increased the density of the resulting coating. The results of this study will provide a theoretical basis for the microstructure control and optimization of TiB2–TiC composite coating synthesized by plasma spraying Ti–B4C system composite powder. [ABSTRACT FROM AUTHOR]

Linear friction welding of equiaxed Ti17 titanium alloy with great strength–plasticity matching was carried out in this study and the microstructure evolution, tensile property and impact toughness of this joint were investigated in detail. Results show that α dissolution (α → metastable β transformation) takes place in both thermo-mechanically affected zone (TMAZ) and weld zone (WZ). The metastable β in TMAZ near base metal (BM) is affected by stress during welding, resulting in concentrated orientation and high dislocation density. Dynamic recrystallizations of α and metastable β phases occur in TMAZ near WZ, leading to fine recrystallized α grains and equiaxed recrystallized β grains. Complete α dissolution and total dynamic recrystallization appear in WZ owing to the effect of strong thermomechanical coupling. Above microstructure evolution causes significant work hardening and fine grain strengthening effects, counteracting the weakening effect induced by α dissolution, and resulting in the tensile strength (1250.0 MPa), elongation (12.2%) and impact toughness (28.8 J/cm2) of the joint are higher than those of the BM. In addition, the tensile strength and elongation of the equiaxed Ti17 joint are increased compared to those of bimodal as well as basketweave Ti17 joints. [ABSTRACT FROM AUTHOR]

The need for 2219 aluminum alloy and 2195 Al–Li alloy dissimilar friction stir welding (FSW) arises as the conventional 2219Al alloy was gradually replaced by the novel 2195Al alloy in fabrication of fuel tanks. However, the systematic investigation about the effect of welding parameters and material positioning on the microstructure evolution and mechanical properties of dissimilar FSW 2219Al/2195Al joints is lacking. In the present study, 2219Al-T8/2195Al-T8 plates were subjected to FSW under rotation rates of 800–1200 rpm and welding speeds of 200–800 mm min−1 with placing 2219Al-T8 alloys on the advancing side (AS) and retreating side (RS), respectively. The results showed that sound FSW joints were obtained under all the welding conditions. Welding parameters and material positioning affected the joint strength and fracture failure behavior. The FSW thermal cycle resulted in low hardness zones (LHZs) on both the 2219Al-T8 and 2195Al-T8 sides. The LHZ on the 2219Al-T8 side, characterized by partial coarsening of θ′ (Al2Cu) precipitates and dissolution of the residual precipitates, showed the minimum hardness in the entire FSW joints. When 2219Al-T8 alloy was placed on the AS, the LHZ on the 2219Al-T8 side experienced higher peak temperature, and therefore more dissolution of θ′ than that on the RS, thereby obtaining higher tensile strength. The tensile strength of the FSW joints at room temperature and − 196 °C largely increased as the welding speed increased from 200 to 400 mm min−1. The FSW joints presented much higher tensile strength at − 196 °C than that at room temperature under the identical welding parameters and material position. The FSW joints fractured along the LHZ on the 2219Al-T8 side during tension. For the bending testing, the up and down bending failure angles were about 91–117° and 88–109°, respectively, with the weak zone appearing in "S" line or HAZ on the 2195Al-T8 side. [ABSTRACT FROM AUTHOR]

Hafnium (Hf) was added as an alloying element to enhance the strength in the NiCoCrAlYMoHf alloys, and the effects of Hf content on constituent phases, microstructural characteristics, and mechanical properties of the as-cast alloy were investigated. The experimental results showed that microstructure of the alloy with 1.0 wt.% Hf was composed of β phase and γ′ phase. The experimental results showed that microstructure of the alloy with 1.0 wt.% Hf was composed of β phase and γ′ phase. With increase in Hf content, the β phase content increased, while the γ′ phase content decreased, and σ phase gradually appeared and precipitated at grain boundary, which resulted in an increase in the hardness of alloys from 429 to 586 HV. The indentation hardness, Young's modulus, and compressive strength of NiCoCrAlYMoHf alloy with 4.0 wt.% Hf could reach 7.12 GPa, 185.52 GPa, and 2659 MPa, respectively, which means that more addition of Hf is beneficial for improving performances of NiCoCrAlYMoHf alloys. The microhardness value is 1.95 times higher than that of the Hf-free alloy. Furthermore, the nanoindentation hardness and Young's modulus are 1.05 and 1.75 times higher, respectively, than those of the Hf-free alloy. [ABSTRACT FROM AUTHOR]

In this study, the gradient microstructure of Mg-Y-Nd-Zr alloy processed by an ultrasonic surface rolling process (USRP) is characterized by electron backscatter diffraction analysis and transmission electron microscopy. The mechanism of microstructure evolution and its effect on mechanical properties of the alloy are discussed in detail. The grain size and orientation of Mg-Y-Nd-Zr alloy after USRP treatment changed gradually along the processing depth. The grain refinement mechanism was elucidated as follows: First, the coarse-grained matrix was subdivided by dislocation slip and twins and further refined into sub-structures by multiple techniques, such as mutual intersection and fragmentation between twins, the interaction between twins and dislocations, and the entanglement of dislocations. Finally, equiaxed nanocrystals with high-angle grain boundaries were formed by sub-grain rotation and recrystallization. The strength improvement of the alloy was mainly attributed to the contributions of grain refinement and dislocation strengthening. The synergistic deformation between the gradient structures is the main reason for the excellent strength and plasticity matching of the alloy. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) needled ZrC–SiC-modified C/C composites (C/C–ZrC–SiC composites) as cutting-edge materials for throat or expansion section of rocket nozzle are mainly subjected to complex loads conditions of internal pressure and axial force. The coupled axial compression and internal pressure experiments of 3D needled C/C–ZrC–SiC composites thick-walled cylinder were carried out to study the damage modes and failure mechanisms combing with the optical microscope and micro-computed tomography (micro-CT). A meso–macro-finite element model considering local needling fiber regions was also established to investigate the failure process of the thick-walled cylinder under the complex loads. The predicted strength, failure strain and ultimate crack morphologies obtained by the proposed model were in good agreement with the experimental results. The effect of needled region distribution on the crack evolution and damage mechanisms was further analyzed. The non-uniform distribution of needled fiber region can induce the stress concentration of no needled regions under circumferential tension, which can trigger crack initiation and deflection. This study can be helpful of establishing the relationship between the structural behavior of ultra-high-temperature ceramics-modified C/C composites nozzle and the 3D needled composites design. [ABSTRACT FROM AUTHOR]

TiB whisker-reinforced Ti2AlNb (TiBw/Ti2AlNb) composites with a network architecture were fabricated by the spark plasma sintering (SPS) technique at the temperature ranging from 950 to 1250 °C with the pressure range of 15–50 MPa for 5–30 min and followed by furnace cooling. The effects of SPS parameters and the volume fraction of TiB2 on the microstructure, densification, phase composition and mechanical properties of the sintered composites were studied in detail. The results revealed that the microstructure of TiBw/Ti2AlNb composites was related to the degree of in situ reaction, which was linked to sintering temperature, time, pressure and the volume fraction of TiB2. The TiBw/Ti2AlNb composite exhibited the highest strength and plasticity at room temperature with the sintering process of 1200 °C/15 min/50 MPa/2.5 vol. % TiB2, and its ultimate tensile strength was nearly 240 MPa higher than that of SPS sintered Ti2AlNb-based alloy. However, its high-temperature mechanical properties were lower than those of SPS sintered Ti2AlNb-based alloy, which is due to the fact that the bonding strength between high-strength TiB whiskers and Ti2AlNb matrix was worse during hot deformation, the interface deboned before fracture, and the strengthening effect of TiBw decreased. Compared with the traditional TiBw-titanium alloys system, this work systematically discussed the influence of various parameters on the microstructure and mechanical properties of the composites under TiBw-Ti2AlNb-based alloys system, which can eventually enrich the application of network architecture in the field of powder metallurgy to improve the mechanical properties of materials and provide guidance for the optimization of process parameters. [ABSTRACT FROM AUTHOR]

Zirconia toughened alumina (ZTA) ceramics are commonly used in various industries. Adding suitable additives is an effective way to improve the performance of ZTA ceramics. However, the common reinforcement in ZTA, chromia (Cr2O3), tends to volatilize at high temperature in the presence of oxygen, limiting ceramic densification. Consequently, additional amounts of Cr2O3 are typically limited to below 1 wt%. In this study, spark plasma sintering was utilized to inhibit the volatilization of Cr2O3. Dense ZTA ceramics with high Cr2O3 content (from 1 to 10 wt%) were prepared at 1350 °C. The impact of the solid solution on the structure and properties of the ceramics was investigated. The findings demonstrate that the high Cr2O3 solution can regulate the grain size in the matrix, leading to an enhancement in both hardness and fracture toughness. The optimum performance of the sample was obtained with a 5 wt% dosage of Cr2O3, where the maximum values of Vickers hardness and fracture toughness were 20.66 GPa and 6.37 MPa m1/2, respectively. [ABSTRACT FROM AUTHOR]

The preparation of component with 2219 aluminum alloy consists of hot/warm forming and the subsequent heat treatment, inducing complex microstructure evolution. The microstructure simulation in forming and solution treatments is investigated using cellular automata (CA) models, consisting of initial microstructure generation model, static recrystallization (SRX) model and thermal–mechanical treatment model. The effect of parameters (temperature, strain, strain rate and pass interval time) on the microstructure characteristic is analyzed. SRX occurs during the pass interval time by the transformation from low-angle grain boundaries into high-angle grain boundaries. Low temperature, large strain and strain rate during the hot compression contribute to the SRX process during pass interval time due to the resulted higher dislocation. Warm forming is beneficial for the increased dislocation density and sub-grain structures, which change to equiaxed grains after solution treatment, indicating the total recrystallization. The increased strain and strain rate, and lower temperature in the warm forming process contribute to the grain refinement and acceleration of the velocity of the SRX process after solution treatment. Experiments of hot compression, warm compression followed by solution treatment are conducted. The CA simulated flow stress and microstructure agree with the experimental results. The CA models established can provide guidance for the microstructure evolution for the hot/warm forming and the subsequent heat treatment of aluminum alloy. [ABSTRACT FROM AUTHOR]

The microstructure and mechanical properties of a novel Cr and Si co-alloying Fe–0.6C–15Mn steels, labeled as 2Cr(3Si), 4Cr(3Si), 6Cr(3Si), and 4Cr(0Si), were investigated. All samples for mechanical property test and microstructure analysis were subjected to solution treatment at 1100 °C for 1 h after forging. The results indicate that the microstructure for the 2Cr(3Si), 4Cr(3Si) and 4Cr(0Si) steels mainly consists of the full austenite, and grain size is about 100 μm, whereas the microstructure of the 6Cr(3Si) steel exhibits austenite and some undissolved Cr7C3 carbides. The refined austenite grain size of 48 μm is obtained in 6Cr(3Si) steel. The strength and elongation of the experiment steels with Si and Cr increase significantly with the Cr contents. Among the steels, the 6Cr(3Si) steel has the maximum yield strength, tensile strength and elongation of 490 MPa, 987 MPa and 41.5%, respectively. And the impact toughness is 151 J cm−2. The Si-free steel (4Cr(0Si)) exhibits a low yield strength (372 MPa) and a high tensile strength (992 MPa). The high elongation of 74.8% and impact toughness of 320 J cm−2 are obtained. The results also demonstrate that the Cr and Si co-alloying in high-Mn steels is beneficial to improve work hardening capability, and the work hardening capability increases with the increase of Cr content. According to the results analyzed by the electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM), the strain-induced ε-martensite is dominant at the low strain level and the content of ε-martensite increases with the increase of the tensile strain. The maximum amount of the ε-martensite is found in the 6Cr(3Si) steel. With the strain increasing, α'-martensite appears in microstructure, which is formed on the ε-martensite. In addition, the stacking faults (SF) and mechanical twins (MT) are also observed. [ABSTRACT FROM AUTHOR]

Resistance heating (RH) has broad prospects in hot stamping due to its rapid heating rate and high energy efficiency. In this work, the ultra-high strength boron steel was heated by high current and then water quenched (without soaking). The effects of heating temperature and current density on mechanical properties and microstructure were explored. The results indicated that resistance heating method can significantly shorten the heating time, and even the soaking stage can be ignored when overheating is adopted; thus, the whole heating period can be reduced from 5 min to 15 s. Besides, the oxide scale is inapparent on the uncoated sheet with rapid heating, which improves the surface quality evidently. Furthermore, the mechanical properties of the boron steel after resistance heating are better than those after furnace heating (FH), including both strength and elongation. The microscopic characterization confirms that the grain size of the resistance heating sample is obviously finer than that of the furnace heating, showing a mixed microstructure of coarse and fine grains, and the final structure includes a certain amount of retained austenite. These characteristics ensure that the boron steel has excellent properties after resistance heating and quenching. [ABSTRACT FROM AUTHOR]

Understanding the oxidation of Ni-based single crystal (SX) superalloys is significantly important because oxidation can damage the microstructure and eventually lead to failure of the alloy. Using advanced scanning/transmission electron microscopy, oxidation effects on the microstructure of a SX superalloy during heat treatment and simulated service (stress/temperature coupling) conditions are systematically investigated in order to reveal oxide microstructures and oxidation mechanisms. Heat treatment in argon results in less weight loss, thinner γ′-free layer and fewer internal oxidation than that treated in air. But the oxide layer structures and influence depths of oxidation in both atmospheres are similar. External tensile stress not only accelerates the oxidation of alloy but also affects the oxide microstructures. Moreover, stress effects on the oxidation microstructure depend on temperature. At 750 °C, Ni–Co oxides are formed on the alloy surface, followed by the inner layer of Ni–Co–Mo–Re–W oxides at the location of original γ phase under stress free condition. As the stress increases, an oxide layer mainly containing Al, Cr, Nb, Mo and Re elements is formed between the above two oxide layers. When temperature increases to 1050 °C, as applied tensile stress increases, the thickness of oxide layer increases but the structure of oxide layer is not obviously changed. [ABSTRACT FROM AUTHOR]

René 65 is a high strength cast & wrought (CW) Ni-base superalloy with thermomechanical performance tailored toward intermediate temperature and stress conditions (677 °C/690 MPa). René 65 Turbine disk rotor forgings are typically subject to a sub-solvus heat treatment utilized to retain a uniform and fine-grained microstructure that confers a high level of fatigue performance and strength at the expense of high-temperature creep resistance. However, the processing of René 65 via laser powder bed fusion (LPBF) can enable this material to exhibit intermediate or coarse-grained microstructures after heat treatment that possess improved creep resistance. The effect of the difference in the processing route in conjunction with heat treatment on the resulting microstructure is presented and correlated to the creep behavior (at 677 °C/690 MPa) and stress relaxation behavior (700 °C). A good correlation of relaxation and creep behaviors was found, with LPBF processed René 65 exhibiting overall improved resistance to high-temperature deformation. The primary factor with regards to microstructural difference toward the stress relaxation/creep behavior of René 65 has been identified to be the size and volume fraction of tertiary γ' present resulting from the chosen processing pathway. [ABSTRACT FROM AUTHOR]

The preparation of SA508 Grade 3 steel was innovatively realized based on laser powder bed fusion (LPBF). On this basis, the influence of processing parameters on the microstructure as well as the mechanical properties of SA508 Grade 3 steel was studied. The effect of the high cooling rate brought about by LPBF on the microstructure and mechanical properties of the specimens was investigated. Defects such as unfused powders and lack-of-fusion defects were observed in specimens prepared at excessively low volumetric energy density. Defects in specimens prepared at excessively high volumetric energy density were predominantly keyhole-shaped defects. The range of the volumetric energy density for obtaining defect-free specimens with a high relative density (99.4 ± 0.3%) was determined to be 111–133 J/mm3. The cooling rate provided by LPBF is much higher than the critical cooling rate for martensitic transformation, resulting in a uniform distribution of fine martensite with an average grain size of about 3 μm in the specimens. The strength of the specimens reached 1.041 GPa, which was much higher than that of the specimens prepared by the traditional process. The high strength of the specimens can be attributed to the Hall–Petch relationship provided by the fine grains. The proposed strategy in this work provides a new technical approach for the additive manufacturing of a high-performance low-carbon and low-alloy steel. [ABSTRACT FROM AUTHOR]

The high-temperature deformation behavior and fracture mechanism of Fe–Ni-Cr superalloy under high strain rates from 1 to 100 s−1 were studied by hot tensile experiments at a temperature range of 900–1150 °C. The results manifest that the high strain rate has significant influence on the microstructure evolution and local instability fracture behavior of the superalloy. At high strain rates, the flow behavior of the alloy shows obvious dependence on the strain rate and temperature. With the increase of strain rate, a higher ratio of low-angle and low-energy grain boundaries can be obtained while keeping fine and uniform equiaxed grain microstructure, yet the control window of hot deformation microstructure of the alloy is obviously narrowed. After deforming at temperatures of 950–1000 °C and strain rates of 10–50 s−1, the fine equiaxed grains with average grain size less than 10 μm can be controlled at high deformation rates. Under high strain rates and higher deformation temperature, it has been found that the plastic strain induced by recrystallization nucleation and growth at the original high angle grain boundary (HAGB) of the alloy is not enough to coordinate the rotation of the original grain and the sliding of the original HAGB during deformation, resulting in intergranular cracking. This is the fundamental reason for the abnormal change of thermal deformation power dissipation behavior, higher strain rate sensitivity, flow instability and fracture when the alloy is hot deformed at high strain rates. [ABSTRACT FROM AUTHOR]

The hot compression test, with a true strain of 0.9, was carried out at a temperature of 1100–1250 °C and a strain rate of 0.001–1 s−1 by a Gleeble3800 thermal simulation testing machine for the as-cast TNM alloy. The stress–strain curves were recorded to measure the deformation resistance and deformation uniformity of the whole specimens, and the microstructure was analyzed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) from the perspectives of the extent of recrystallization and the orientation and size of the grains. At lower strain rates, the strain is more uniform within the specimen. At higher temperatures, a complete recrystallization microstructure showing an equiaxed nearly lamellar (NL) structure with a weak texture can be obtained at a low strain rate, and a microstructure showing an elongated fine-grained NL structure without texture can be obtained at a high strain rate. The deformation mechanisms were analyzed, and the processing parameters were optimized by constructing empirical hot processing maps. The parameters 1200–1250 °C and 0.1–0.01 s−1 are recommended for deformation to obtain a uniform fine grain structure economically without cracking of the specimen. [ABSTRACT FROM AUTHOR]

The effect of hot deformation parameters on the flow behavior of newly developed 18Cr–12Ni–4Si has been studied. Hot compression tests were carried out in temperatures 1173–1473 K with varying strain rates from 0.01 to 10 s−1. The flow curves exhibited strain-hardening, strain-softening, and steady-state characteristics at different thermomechanical processing conditions. Constitutive modeling of the flow behavior has been carried out using a hyperbolic sinusoidal Arrhenius equation-based kinetic model to correlate the changes in the flow stress with temperature and strain rate. Due to low values of strain rate sensitivity, the proposed constitutive equation was less accurate at the lowest temperature and highest strain rate conditions. The dynamic materials model approach was adopted to identify the stable hot workability regimes using the processing maps. The regimes for optimum hot workability were found at 1222–1473 K/0.01–0.04 s−1; 1173–1473 K/0.04–0.36 s−1; and 1383–1473 K/3.89–10 s−1. Subsequently, the microstructural characterization using EBSD confirmed the occurrence of dynamic recrystallization (DRX) and was found to be the dominant recrystallization mechanism. The microstructures were segmented using the grain orientation spread analysis to distinguish between the deformed grains and the recrystallized grains. Avrami equation for DRX has been utilized for elucidating the DRX kinetics and prediction of recrystallized grains volume fraction at different strain rates and temperatures. The percentage of recrystallized grains that was obtained experimentally was in good agreement with the predicted results. It was discovered that, at a given strain, the recrystallization kinetics accelerates with the increasing temperature, while the reverse trend was observed with increasing strain rate. [ABSTRACT FROM AUTHOR]