Abstract:To investigate the effect of solution treatment and aging process parameters on the microstructure and mechanical properties of TB18 titanium alloy, process optimization research was conducted based on the mixed-level orthogonal experiment design of factor levels. Results show that through range analysis, the significance order of process parameters is determined as follows: solution cooling method>solution temperature>aging time>aging temperature>solution time. Considering the strength-ductility matching and engineering application requirements, the benchmark parameters are selected as solution time of 1 h, solution cooling method of air cooling (AC), aging temperature of 525 °C, and aging time of 4 h. Furthermore, the effects of solution temperature in the range of 790–870 °C on the impact toughness and micro-fracture characteristics of the alloy were studied. The results reveal that the larger the area of shear lip and fibrous zone, and the smaller the area of radiation zone, the better the toughness of the alloy. With the increase in solution temperature, the length of secondary cracks on the fracture surface increases, the number of dimples increases, and the toughness is enhanced. Based on the collaborative optimization of strength and toughness, the optimal heat treatment process for TB18 alloy is determined as 870 °C/1 h, AC+525 °C/4 h, AC.

Abstract:The combustion behavior of Ti-Al-Mo-Zr-Sn-W alloy (TC25G) was studied in a high-temperature and high-speed air flow environment using the laser ignition method combined with ultra-high temperature infrared thermometer, scanning electron microscope, X-ray diffractometer, and transmission electron microscope. The burn-resistant performance of TC25G and TC11 alloys was compared. Meanwhile, the microstructural characteristics, crystal structure, and formation mechanism of the combustion products of TC25G alloy were analyzed in detail. The results show that the high-temperature and high-speed air flow promotes combustion within the air flow temperature range of 200–400 °C and the air flow velocity range of 0–100 m/s. The combustion path advances along the direction of the air flow. The combustion of TC25G alloy mainly relies on the diffusion of the oxygen and the expansion of the combustion area caused by the movement of the melt. Based on the microstructure and composition of combustion product, it can be divided into the combustion zone, the melting zone, and the heat affected zone. During combustion, the formation of microstructures is closely correlated with the behavior of alloying elements and their selective combination with O. The major oxidation products of Ti are TiO and TiO₂. The oxides formed by Mo and W hinder the movement of the melt during the combustion. Al and Zr tend to undergo internal oxidation. Al₂O₃ precipitates on the surface of ZrO₂, forming a protective oxide layer that inhibits the inward diffusion of O. Moreover, the element enrichment at the interface between the melting zone and the heat affected zone increases the melting point on the solid side, hindering the migration of the solid-liquid interface.

Abstract:The effects of channel segregation on the macro- and micro-scale chemical composition, microstructure, hardness, and tensile deformation behavior of Ti45Nb wires were investigated. The results show that wires with severe channel segregation exhibit a macroscopic chemical composition identical to those without segregation, and 3D X-ray imaging result also reveals no abnormalities. After annealing, both types of wires exhibit an equiaxed single-phase microstructure with comparable grain sizes, suggesting that channel segregation has negligible influence on the macroscopic composition and grain size. Metallographic examination reveals that channel segregation manifests as spot-like features in the transverse section and band-like structures in the longitudinal section. EDS analysis identifies these regions as Ti-enriched segregations, with a Ti content higher than that of the surrounding matrix by approximately 4.42wt%. Compared to segregation-free wires, those containing extensive channel segregation demonstrate a 15.5% increase in ultimate tensile strength and a 12.3% increase in yield strength, but suffer a reduction in elongation and reduction of area by 19.8% and 18.9%, respectively. Furthermore, the mechanical properties of wires with segregation show significant fluctuations. Fractographic analysis reveals a larger fracture surface area in segregated wires. Severe dislocation pile-ups occur at the interfaces of these segregated regions, initiating microcrack nucleation. This promotes rapid crack propagation of the Ti45Nb wire, leading to a significant decrease in plasticity and reduction of area.

Abstract:To accurately predict the thermoforming process of TC4 titanium alloy, the high-temperature rheological behavior of TC4 titanium alloy was investigated, and a high-precision thermoforming phenomenological constitutive model was developed. Firstly, high-temperature tensile tests of TC4 titanium alloy were conducted at 973-1123 K with strain rates of 0.01-1 s^-1. Based on the experimental data, two constitutive models were established: an Arrhenius constitutive model with strain compensation and a modified Johnson-Cook constitutive model. Sparrow search algorithm (SSA) was employed to optimize the model parameters. Finally, the predictive abilities of the phenomenological constitutive models for TC4 titanium alloy were assessed using statistical analysis. The results indicate that the Arrhenius constitutive model achieves relatively high predictive accuracy despite limited experimental data. However, it has a restricted parameter optimization space. In contrast, the modified Johnson-Cook constitutive with lower predictive accuracy, offers a larger parameter optimization space. The SSA-optimized modified Johnson-Cook constitutive model provides a good fit with experimental results, serving as a solid foundation for high-precision numerical simulations of TC4 titanium alloy thermoforming.

Abstract:A systematical analysis of the macrostructure, microstructure, composition, and crystal orientation of the bright-band defect was conducted by OM, SEM, and EBSD methods, as well as Gleeble tests, and the formation mechanism of bright-band defect of forged TC18 alloy was studied. The results show that the bright-band defects in the center of TC18 alloy forging stocks correspond to β cube-grains with the size of around 100 mm. During the forging process, an inhomogeneous distribution of temperature and equivalent strain in the forging stocks is caused by adiabatic heating, which is an important reason for the microstructural heterogeneity. The large β cube-grains are formed due to the repeated compression along the orthogonal direction, which results in continuous strengthening of the <100> texture in the center of the forging stocks, and the merging of <100> grains with similar orientations. Through annealing treatment and compression along diagonal direction, it is possible to effectively reduce and avoid bright-band defects in TC18 alloy.

Abstract:The hot deformation response and dynamic recrystallization behavior of two representative initial microstructures (a fully lamellar microstructure and an equiaxed-lamellar bi-modal microstructure) were systematically investigated in a wide-width hot-rolled bloom TC4 alloy using a Gleeble thermal simulation testing system at deformation temperature of 1173 K and strain rates of 10 and 0.01 s?1. Meanwhile, a coupled phase-field and crystal plasticity model was developed to simulate the stress-strain distribution and dislocation density evolution in the α/β phases under different initial microstructural conditions. This model was used to examine how initial microstructure configurations influence the dynamic recrystallization behavior of the α phase. The results indicate that under a high strain rate of 10 s?1 and the deformation of 60%, the fully lamellar microstructure undergoes significant dynamic recrystallization in the α phase, resulting in a uniform fine-grained structure with an average grain size of 0.58 μm. In contrast, in the bi-modal structure, only part of the lamellar α phase exhibits localized recrystallization, while the equiaxed α phase primarily undergoes dynamic recovery. Compared with the fully lamellar structure, the bi-modal microstructure requires greater deformation to activate dynamic recrystallization in both the equiaxed and lamellar α phases. This discontinuous recrystallization behavior is attributed to differences in stress-strain distribution between the equiaxed and lamellar α phases during concurrent deformation. These differences influence dislocation accumulation and subgrain formation, ultimately altering the driving force conditions for dynamic recrystallization.

Abstract:The diffusion behavior of hydrogen in lamellar and bi-modal TC4 alloys was investigated through electrochemical hydrogenation combined with multi-scale characterization techniques. The results show that after electrochemical hydrogen charging, the diffusion surfaces of lamellar and bi-modal samples present a gradient distribution of hydrogen concentration, and the thickness of the hydrogen diffusion layer of two samples is similar. The volume fraction of hydride in the diffusion surface of the lamellar sample is larger, hydrides preferentially form at the α/β interface and grow in the form of twin pairs into the α phase. In the case of the bi-modal sample, due to the relatively large equiaxed α grain size, hydrides cannot fill the entire α grain. Different hydride variants alternate in nucleation and growth near the α/β interface. TEM analysis results indicate that the hydrogenation nucleation in both microstructure samples presents a multi-level structural transformation mechanism regulated by stacking faults.

Abstract:Manganese, serving as a cost-effective and potent stabilizer of the β-phase, plays a pivotal role in the development of economically viable and easily deformable β-type γ-TiAl alloys. In this investigation, we focused on a low-cost and easily deformable Ti-44Al-3Mn-0.4Mo-0.4W-0.1B-0.1C alloy (at%), which was rolled into 12 mm-diameter bars by vacuum induction melting and conventional hot rolling techniques. The effects of high-temperature treatments at 1270, 1220, and 1170 °C on the microstructure and mechanical properties of the alloy bars were studied by EPMA, TEM, and EBSD. The results show that the microstructure of the alloy contains γ, α₂, and β_o phases after heat treatment. Decreasing the temperature of high-temperature treatment under identical aging conditions significantly reduces the α₂/γ lamellar content within the alloy. Moreover, both the size of the lamellar colonies and the spacing between lamellae exhibit pronounced reductions as the treatment temperature decreases. The tensile performance tests demonstrate that as the temperature of high-temperature treatment decreases, the tensile strength at room temperature and 800 °C of the alloys with different microstructures declines. At room temperature, the elongation of the heat-treated alloys shows a trend of first increasing and then decreasing, and the values are all within the range of 0.5%–1.0%. However, at 800 °C, significant variations in elongation are observed in the alloys. Specifically, an increase in equiaxed γ phase content correlates with enhanced alloy elongation. Compared to samples treated at 1270 °C, those treated at 1220 °C exhibit a 280% increase in elongation, while those treated at 1170 °C show a 480% increase. This enhancement is attributed to the improved deformability of the equiaxed γ phase at elevated temperatures. Additionally, greater activation of dislocations within the β_o phase occurs, while the γ/γ and α₂/γ interfaces impede the movement of twins and dislocations. This study provides a comprehensive discussion on the evolution behavior and patterns of different heat-treated alloys, emphasizing their correlation with mechanical properties.

Abstract:By applying different current frequencies during the tensile process of the aerospace TC4 titanium alloy, the flow stress of the material is increased and its maximum yield strength is reduced. The microstructural evolution of the material after electrification and the fracture morphology of the samples were observed. The influence of the electric-assisted forming process on the tensile process was analyzed in combination with the tensile test results. The experimental results show that with the increase in pulse current density, the content of the α phase decreases significantly, while the β phase content increases substantially, and the grain size begins to increase. A small amount of martensitic phase suffers transformation during cooling, resulting in fine acicular α′ phase. As the current density further increases, the primary α phase disappears completely, the β phase grows further, and the size of the transformed α′ phase increases. During tensile deformation, the sample temperature rises sharply at the moment when current is applied. It continues to increase during the tensile process, with rising increment until it reaches a peak value at the moment of fracture. The peak temperature increases with the rise in current density and pulse frequency. As the current density increases, the flow stress of TC4 titanium alloy gradually decreases, and its ductility improves. SEM and TEM results show that with the increase in current density, the dimples in the tensile fracture surface of TC4 titanium alloy sheets become significantly deeper, presenting a honeycomb-like appearance, with tear ridges around the dimples, indicating a typical ductile fracture feature. Compared with that after high-temperature and room-temperature tensile tests, the dislocation density inside the material after electric-assisted tensile tests is significantly reduced, with dislocations appearing more straight and some dislocations orderly aligned in a certain direction, indicating that pulse current promotes dislocation motion.

Abstract:The microstructure evolution of TC4 alloy plates with α martensitic as primary microstructure in dual-phase region during clad rolling and annealing were investigated. The relationship between microstructure evolution (grain size, texture) and strength of the alloy was discussed. The results show that β-quenched alloy exhibits fine lamellae α′ martensite which displays multi-scale and multi-variant distribution. The grain of β-quenched alloy is significantly refined with average grain size of 0.89 μm and <0001>//ND of Basal texture forms after two-phase cross rolling. However, a mixed structure, consisting of fine recrystallized grains and coarse deformed grains, is observed. During annealing process, the rolled samples undergo continuous static recrystallization, resulting in the formation of fine equiaxed grain (approximately 1.86 μm at 720 ℃). Meanwhile, annealing treatment do not change the texture type, while the intensity of Basal texture is slightly enhanced. The strong Basal texture makes the Schmidt factor of prismatic <a> slip close to each other along the direction of TD and RD, which results in the decrease in strength difference between transverse and longitudinal direction. The strength of the sheet decreases with the increase in annealing temperature, which is due to the synergistic effect of the increase in grain size and the decrease in dislocation density. The result shows that the fine grained TC4 alloy with Basal texture can be fabricated by using α+β phase cross rolling and annealing, which provides a theoretical basis and technical support for the preparation of fine-grain titanium alloy plates for aerospace applications.

Abstract:The white blocks of TB18 high Mo equivalent metastable β ultra-high strength and toughness titanium alloy were studied. The alloy which was forged in the two-phase region and then solid solution and aging treatment in β region. The formation mechanism and elimination methods of white blocks were analyzed by mechanical property testing, microstructure observation, and further heat treatment experiments. The results indicate that the white blocks in TB18 titanium alloy are β matrix without any precipitation of α phase, with low hardness, high plasticity, and high impact toughness. The reason for the formation of white blocks is not related to the distribution of β-stable elements in the alloy, but mainly caused by the forging process. White blocks can be weakened or eliminated from the macroscopic structure by optimizing forging or heat treatment processes, such as increasing solubility, pre-aging, and extending aging time. However, from a more detailed microstructure analysis, the white blocks in TB18 titanium alloy cannot be completely eliminated but can only be reduced in size, which is determined by the characteristics of the TB18 alloy. The results of this study have a fundamental guiding role in improving the preparation process and optimizing the microstructure of TB18 alloy, and also produce important reference significance for the microstructure and performance analysis of similar alloys.

Abstract:Discontinuously reinforced titanium matrix composites (DRTMCs) exhibit advantages such as light weight, high strength, and heat resistance, demonstrating broad application prospects in aerospace, consumer electronics, and other fields. Inspired by the multi-scale architectures of natural materials, the design of DRTMCs has evolved from uniformly distributed single reinforcements to architecture reinforcement configurations, and further to the coordinated design and regulation of multi-scale reinforcement architectures coupled with hierarchical titanium matrix. This progression has enriched their microstructure, leading to the formation of multi-scale heterogeneous structures. Such structures fully leverage synergistic strengthening mechanisms to enhance strengthening efficiency. Moreover, these composites effectively avoid strain localization to ensure favorable plasticity while maintaining excellent damage resistance. This review summarizes typical configuration design strategies and their evolutionary pathways in DRTMCs, elucidates the underlying strengthening-toughening mechanisms, and proposes future research directions based on current advancements to advance the application of high-performance titanium matrix composites in critical fields.

Abstract:In the practical production and processing of titanium alloys, variant selection frequently occurs during martensitic transformation due to various influencing factors. This preferential behavior causes the crystallographic orientation distribution of α′/α″ phases to deviate from theoretical equiprobability, consequently affecting material anisotropy and mechanical properties. Studies reveal that quenching-induced β→α′ transformation exhibits weak variant selection characteristics. In contrast, stress-induced β→α″ transformation often demonstrates strong variant selection effects with a consistent preference for orientations accommodating maximum external stress. Simultaneously, characteristic self-accommodating morphologies are commonly observed in α′/α″ martensitic microstructures, including triangular, V-shaped, Z-shaped, trapezoidal, and parallel clusters formed by aggregated variants. The emergence of these self-accommodating clusters is one of the critical mechanisms underlying variant selection effects. This paper systematically elaborates on the characteristics and formation mechanisms of martensitic transformation and elucidates the intrinsic nature and influencing factors of variant selection. By integrating the phenomenological theory of martensite and statistical analysis of inter-variant interfaces, the formation mechanisms of self-accommodating microstructures and interface distribution associated with variant selection effects are analyzed comprehensively. Finally, current challenges and future research priorities in this field are identified.

Abstract:Ti-6Al-4V alloy is widely used in aerospace, biomedical, and other fields due to its excellent specific strength, corrosion resistance, and biocompatibility. However, rapid solidification and complex thermal cycling during additive manufacturing often lead to the formation of coarse columnar β grains in titanium alloys, resulting in anisotropic mechanical properties and reduced fatigue performance. Achieving equiaxed microstructure control is crucial for improving the comprehensive properties of additively manufactured titanium alloys. This work reviewed recent advances in achieving equiaxed microstructures of Ti-6Al-4V (TC4) alloy through microalloying, composite fabrication, external field assistance, and heat treatment. The influence mechanisms of α-stabilizing elements, β-stabilizing elements, external field-assisted techniques, and heat treatment processes on the microstructure and mechanical properties of Ti-6Al-4V alloy were discussed. Furthermore, future research directions were outlined, focusing on precise microstructure control, process parameter optimization, and the development of high-performance titanium alloys. The aim of this work is to provide theoretical guidance and technical support for microstructure optimization and performance enhancement of additively manufactured titanium alloys.

Abstract:Titanium matrix composites (TMCs), owing to their high specific strength and high specific modulus, hold great promise for applications in load-bearing aerospace components. However, the strength-ductility trade-off at room temperature significantly restricts their widespread use. The hetero-deformation induced (HDI) hardening effect in heterogeneous structured materials offers a new approach to overcoming the strength-toughness trade-off bottleneck in TMCs. The recent advances in heterogeneous structured titanium and titanium alloys were outlined, then the current research status and compositing strategies of TMCs were summarized and discussed. The failure mechanisms of homogeneous TMCs were elucidated, and the latest developments in configuration and heterostructure design by the pinning effects of reinforcement phases were highlighted. Taking the "hard-in-soft" network structures and "soft-in-hard" granular structures as examples, this work reviewed the design concepts, fabrication methods, classification, and strengthening mechanisms of heterogeneous structured TMCs, providing insights and references for the development of TMCs with a well-balanced strength-ductility relationship.

Abstract:In this study, FeCr?MnAlCu (x=0, 0.5, 1.0, 1.5, 2.0) high-entropy alloys were fabricated using vacuum arc melting, and the corrosion behavior of these alloys in 3.5wt% NaCl solution at room temperature was investigated by electrochemical dynamic potential polarization curves and immersion experiments. The microstructure results show that the high-entropy alloy with x=0 has a body-centered cubic phase structure, whereas the high-entropy alloys with x=0.5–2.0 have a mixed face-centered cubic+body-centered cubic dual-phase structure. The corrosion results show that the corrosion resistance of the high-entropy alloy is increased with the increase in Cr content. Among them, the high-entropy alloy with x=2.0 exhibits the optimal corrosion resistance: the highest self-corrosion potential (E_corr=-0.354 V vs. Ag/AgCl), the smallest self-corrosion current density (I_corr=1.991×10^-6 A·cm^-2), and the smallest corrosion rate (0.0292 mm/a). The composite passivation film of oxides and hydroxides is formed on the surface of the corroded high-entropy alloys, and the Cr₂O₃ content is increased with the increase in Cr content, which effectively improves the stability and protective properties of the passivation film.

Abstract:SiC/Al-based composite foams were prepared by a two-step foaming method. The influence of the SiC content and its distribution uniformity on the foaming stability, cell structure, and mechanical properties of the aluminum foams was investigated. The macro/micro-features of the aluminum foams were characterized and analyzed. Results demonstrate that an appropriate increase in SiC content and the uniform distribution of SiC can improve the foaming stability, optimize the cell diameter and cell wall thickness, ameliorate the cell distribution, and enhance the hardness and compressive strength of the aluminum foams. However, either insufficient or excessive SiC leads to uneven distribution of SiC particles, which is unfavorable to foaming stability and good cell structure formation. With 6wt% SiC, both the foaming stability and cell structure of the aluminum foam reach the optimal state, resulting in the highest compressive strength and optimal energy absorption capacity.

Abstract:To elucidate the deformation mechanisms of γ-TiAl, the nanoindentation experiments and crystal plasticity finite element (CPFE) simulation were employed to investigate the effects of crystal orientations and GBs on the mechanical properties of γ-TiAl alloys. A crystal plasticity constitutive model was developed, and load-displacement curves, hardness, and Young's modulus were obtained for both single grains and GBs in γ-TiAl alloys. Based on the aforementioned model, this study investigated the distribution patterns of surface morphology around the indentation sites of individual grain and GBs. It also analyzed the cumulative shear strain distribution, slip system activation, and the interaction between GBs and dislocation slip for various crystal orientations. The results indicate that the mechanical response and pileup behavior exhibit significant anisotropy due to the interplay among the indenter geometry, material slip systems, and cumulative shear strain distribution. Moreover, the interaction between GBs and dislocation slip substantially alters dislocation distribution, thereby influencing material flow and playing a critical role in the mechanical response and plastic deformation of the material.

Abstract:The Cu0.9Cr0.1Zr alloy was deformed through continuous equal channel angular pressing (C-ECAP) through Route A, followed by liquid nitrogen cryogenic rolling (CR) and aging treated at 450 °C. The microstructure, mechanical properties, and conductivity of the alloy were detected by electron back-scattered diffractometer, energy dispersive spectroscope, X-ray diffractometer, scanning electron microscope, and transmission electron microscope. The evolution mechanism of the texture during the deformation process and its influence on mechanical properties were analyzed. The results show that directional shear bands form in the CuCrZr alloy during the C-ECAP process, and the preferred orientation of the microstructure is consistent with the rolling direction. After deformation, the number of precipitated phases (mainly Cr) increases with the prolongation of aging time, accompanied by the appearance of micro-nanostructured fibrous structure in the alloy. After C-ECAP for three passes, 75% CR deformation, and aging at 450 °C for 2 h, the tensile strength, microhardness, and conductivity reach 538 MPa, 168 HV, and 80%IACS, respectively. CR, aging heat treatment, and formation of recrystallization texture are all conducive to the improvement of conductivity.

Abstract:A series of hot compression tests were conducted on the new heat-resistant alloy SP2215 for supercritical and ultra-supercritical power plant superheater/reheater tubes using a Gleeble 3500 thermal simulation testing machine at 1100–1250 ℃ and the deformation rate of 0.01–10 s^–1 with a deformation amount of 50%. The influence of deformation temperatures and deformation rates on the rheological curve and deformation structure of the alloy was investigated. Furthermore, by modifying the rheological curve based on friction and temperature effects, we established thermal deformation Arrhenius constitutive model, Avrami dynamic recrystallization model, and Yada dynamic recrystallization average grain size model for SP2215 alloy. Additionally, Prasad-Murty-Malas hot working maps were constructed for alloys based on various rheological instability criteria. The results indicate that as the deformation temperature increases, the degree of work hardening decreases while dynamic recrystallization becomes more obvious in SP2215 alloy. Moreover, higher strain rates result in increased flow stress and work hardening rate for this alloy. The recrystallization of the lowest degree occurs at a strain rate of 1 s^–1; however, without certain conditions, mixed crystal phenomenon may occur easily in this alloy. Under experimental conditions in this research, the optimal thermal deformation window for SP2215 alloy is the temperature of 1200–1250 ℃ and the strain rate of 5–10 s^–1.

Abstract:The diesel particulate filter is an effective technology to reduce diesel particulate emissions, and its performance is closely related to catalyst loading. Based on the platform test system of heavy diesel engine, the influence of catalyst amount on the pressure drop, gas state and particulate emission reduction performance of diesel CDPF regeneration was studied. The results show that the exhaust back pressure of catalyst increases linearly with the increase in catalyst loading. When catalyst loading increases from 0 g/ft³ to 5, 10 and 20 g/ft³(1 ft³=0.0283 m³), the average exhaust back pressure increases from 2.94 kPa to 3.44, 3.96 and 4.51 kPa, respectively. The larger the amount of catalyst, the better the emission reduction effect of the catalytic converter on CO and total hydrocarbon (THC). When catalyst loading increases from 0 g/ft³ to 5, 10 and 20 g/ft³, CO emission decreases from 78.94×10^–6 to 71.39×10^–6, 68.12×10^–6 and 63.30×10^–6, and THC emission concentration decreases from 57.34×10^–6 to 48.31×10^–6, 46.93×10^–6 and 44.51×10^–6, respectively. The amount of catalyst has a significant effect on NO oxidation, but not on NO_x emission concentration. Catalyzed diesel particulate filter (CDPF) can achieve a reduction rate of more than 95% for particulate matter and particulate number. Increasing catalyst loading improves the particulate emission reduction effect of CDPF, with a more significant improvement in the reduction effect of nucleation particles. The results of this study have important reference value for the design of high-performance CDPF.

Abstract:To investigate hot working properties and to control microstructure of the extruded novel nickel-based superalloy FGH4113A, the thermal deformation behavior and microstructure characteristics were studied using Gleeble thermal compressing machine, OM, SEM, and EBSD. Hot deformation experiments were conducted within the temperature of 1050–1150 ℃ and strain rate of 0.001–0.1 s^–1. The results indicate that the grain size of extruded FGH4113A superalloy increases after holding at 1150 ℃. Deformation temperature and strain rate have a significant impact on the deformation flow stress and microstructure evolution. It is recommended for the extruded superalloy to undergo thermal deformation at temperature of 1080–1100 ℃ and strain rate of 0.001–0.01 s^–1 within the γ+γ′ microduplex region. After deformation under these conditions, grains are fully recrystallized and size distribution is uniform, with average size controlled within 5 μm. The residual dislocation density within the grain is small, and the misorientation differences are not significant. Recrystallized grain and deformed original grain can be distinguished from multiple dimensions such as LAM, GOS, and IPF.

Abstract:The garnet type polycrystal Ce_xY_3-xFe₅O₁₂ doped with Ce³⁺ was prepared by an optimized sol-gel method (x=0, 0.1, 0.2, 0.3; Ce:YIG). Crystals with no derived impurities and high magneto-optical properties prepared by pre-sintering and sintering in a wide temperature range of 900–1400 ℃ were obtained. Thermogravimetric analysis was used to determine the the crystal synthesis temperature of 890 ℃. XRD results show that the crystal lattice constant varies from 1.237 241 nm to 1.241 210 nm, and the impurity phase CeO₂ appears when x>0.2. SEM analysis shows that the grain size of Ce:YIG increases with the increase in sintering temperature and Ce³⁺ content, and its size distribution ranges from 0.257 to 6.52 μm, which is the maximum size of YIG crystal obtained at present. All Ce:YIG samples were ferromagnetic at room temperature, with saturation magnetization varying from 23.47 to 28.10 (A·m²)·kg^–1. The permeability of Ce_0.1Y_2.9Fe₅O₁₂ crystal sintered at 1200–1300 ℃ is as high as 3.68–3.90. According to the relationship between Faraday rotation angle and permeability, the polycrystal sintered in this temperature range is likely to obtain the best Faraday rotation performance.

Abstract:Zirconium alloy cladding will undergo high-temperature steam oxidation in a loss of coolant accident to make it be brittle, thereby leading to rupture due to absorbing oxygen, which will affect the safe operation of nuclear reactors. The high-temperature steam oxidation behavior of Zr-xSn-0.35Fe-0.15Cr (x=0.5, 0.75, 1.0, 1.2 and 1.5, wt%) alloys at 800–1200 ℃ was studied by a synchronous thermal analyzer equipped with a steam generator. The cross-sectional microstructures of the samples after high-temperature steam oxidation were observed by OM, and the O content was tested by EPMA. Results show that the high-temperature steam oxidation resistance and oxidation kinetics of zirconium alloys show a certain regularity with Sn content at different temperatures, which is mainly related to the action mechanism of α-Zr? β-Zr and m-ZrO₂?t-ZrO₂ phase transformation behavior of zirconium alloys. As the oxidation temperature increases, the oxidized alloy samples present a double-layer structure of ZrO₂ and α-Zr(O), accompanied by the appearance and disappearance of the mixed layer structure of β-Zr+α-Zr(O), which is caused by the effect of O on the α?β phase transformation. The increase in Sn content inhibits the diffusion of O from α-Zr to β-Zr. From the perspective that the increase in Sn content affects the α-Zr?β-Zr phase transformation and inhibits the diffusion of O from α-Zr to β-Zr, the mechanism of the effect of Sn content on the high-temperature steam oxidation behavior of zirconium alloys at different temperatures was discussed.

Abstract:High-entropy alloys, a novel class of materials characterized by the statistical distribution of multiple principal elements on simple crystalline lattices, have emerged as a research hotspot in materials science and condensed matter physics due to their exceptional mechanical properties and unique high-entropy characteristic. Since the discovery of the first high-entropy superconductor in 2014, exploring their superconducting performance and advantages has progressively become a frontier in scientific research. The Ta-Nb-Hf-Zr-Ti system, in particular, exhibits remarkable mechanical robustness, outstanding radiation tolerance, and superconducting performance comparable to the binary NbTi alloy, positioning it as a promising candidate for advanced applications, such as high-field superconducting magnets, superconducting electric motors, and next-generation nuclear fusion reactors. This review systematically summarized global research progress on Ta-Nb-Hf-Zr-Ti-based superconductors, aiming to provide a comprehensive reference for advancing this burgeoning field.