Abstract:The TiB+TiC dual-reinforced B₄C/TC4 composite was in-situ fabricated via incorporating 0.5wt% B₄C reinforcement during the laser melting deposition process. Different heat treatments of annealing and solid solution were used to regulate the microstructure, mechanical properties, and corrosion properties of B₄C/TC4 composite. Results show that with the increase in temperature from 500 °C to 800 °C, partial lamellar α-Ti in the as-deposited sample is gradually transformed into equiaxed α-Ti, accompanied by the disappearance of basketweave microstructure. At 1100 °C, a small portion of TiC phase suffers fusion. This composite exhibits the optimal combination of strength and plasticity after annealing at 500 °C for 4 h followed by furnace cooling, which is attributed to the stress release effect and the refined basketweave microstructure. However, this composite shows a decline in corrosion resistance after various heat treatments due to grain coarsening and micro-galvanic corrosion.

Abstract:The fatigue crack growth rate of a novel Ti-6Al-4V-1Mo titanium alloy, which is developed for laser directed energy deposition technique, was investigated before and after cyclic heat treatment (CHT). Changes in microstructure, fracture surfaces, and crack growth paths were analyzed before and after CHT. Results indicate that in the stable crack growth region, the growth rates for the as-deposited and cyclic heat-treated specimens follow the relationships da/dN=1.8651×10^-8(ΔK)^3.2271 and da/dN=1.4112×10^-8(ΔK)^3.1125, respectively. Compared with that at the as-deposited state, the microstructure after CHT is transformed from a uniform basket-weave microstructure to a dual-phase microstructure consisting of near-spherical α and β-transformed matrix phases. The cyclic process also disrupts the continuity of the grain boundary α (α_GB) at the primary β-phase grain boundary. The coarsening of primary α and the disruption of α_GB continuity are the primary factors to release stress concentration and promote crack deflection, thereby decreasing the fatigue crack growth rate. Additionally, the increased occurrence of crack branching, secondary cracking, and crack bridging in cyclic heat-treated specimens further reduces the crack driving force and slows the fatigue crack growth rate.

Abstract:Refractory metals, including tungsten (W), tantalum (Ta), molybdenum (Mo), and niobium (Nb), play a vital role in industries, such as nuclear energy and aerospace, owing to their exceptional melting temperatures, thermal durability, and corrosion resistance. These metals have body-centered cubic crystal structure, characterized by limited slip systems and impeded dislocation motion, resulting in significant low-temperature brittleness, which poses challenges for the conventional processing. Additive manufacturing technique provides an innovative approach, enabling the production of intricate parts without molds, which significantly improves the efficiency of material usage. This review provides a comprehensive overview of the advancements in additive manufacturing techniques for the production of refractory metals, such as W, Ta, Mo, and Nb, particularly the laser powder bed fusion. In this review, the influence mechanisms of key process parameters (laser power, scan strategy, and powder characteristics) on the evolution of material microstructure, the formation of metallurgical defects, and mechanical properties were discussed. Generally, optimizing powder characteristics, such as sphericity, implementing substrate preheating, and formulating alloying strategies can significantly improve the densification and crack resistance of manufactured parts. Meanwhile, strictly controlling the oxygen impurity content and optimizing the energy density input are also the key factors to achieve the simultaneous improvement in strength and ductility of refractory metals. Although additive manufacturing technique provides an innovative solution for processing refractory metals, critical issues, such as residual stress control, microstructure and performance anisotropy, and process stability, still need to be addressed. This review not only provides a theoretical basis for the additive manufacturing of high-performance refractory metals, but also proposes forward-looking directions for their industrial application.

Abstract:Soft magnetic alloys are extensively used in various power electronic devices due to their advantageous properties, including high saturation magnetic induction, low coercivity, and high permeability. In certain applications, complex-shaped components are increasingly required for performance enhancement. Additive manufacturing technique, particularly selective laser melting (SLM), has emerged as an effective method for fabricating such complex-shaped soft magnetic components. SLM, a laser-based additive manufacturing technique, employs high-power-density lasers to melt and fuse metal powders within a powder bed selectively. This approach enables rapid prototyping, precise geometrical control, and the integration of multi-material designs. This review highlights recent advancements in the application of SLM technique for the production of soft magnetic alloys, focusing on Fe-Si, Fe-Ni, Fe-Co, and amorphous alloy systems. Moreover, it explores the implementation of SLM in manufacturing processes and evaluates both the opportunities and challenges associated with SLM-based production of soft magnetic alloys.

Abstract:To address the issues of TiC particle agglomeration and pore defects of TiC particle-reinforced Al-Cu alloys prepared by wire arc additive manufacturing (WAAM), this study proposed a novel ultrasonic-frequency pulse (UFP)-assisted WAAM process. By modulating arc thermal characteristics, this method enhanced convective and turbulent behaviors in the melt pool, transitioning from a conventional Marangoni-driven flow to a more uniform dual-vortex structure. A computational fluid dynamics model was developed to trace TiC particle motion and revealed their improved mixing mechanism with the matrix under UFP conditions. Simulation results were validated by real-time melt pool imaging. Results showed that compared to conventional VPTIG, the UFP-VPTIG technique can significantly refine grains and improve homogeneity. Dispersed TiC particles are more uniformly, and porosity and segregation defects are reduced. This study offers a promising route for manufacturing high-performance Al-Cu alloy components.

Abstract:The printing process and the debinding sintering process were carried out step by step to realize the pure copper processing with high laser reflectivity and high thermal conductivity. The process parameters of pure copper binder jetting additive manufacturing were studied. The effects of powder layer thickness and inkjet density on green parts forming performance were studied. At the same time, the effects of sintering atmosphere and sintering temperature on the densification process of the parts were studied. The results show that the combination of powder layer thickness of 75 μm and inkjet density of 50% can ensure the density and compression strength of green parts, resulting in high dimension precision and high surface quality. The driving force in hydrogen atmosphere is stronger than that in vacuum, and the surface oxide layer can be effectively reduced by the introduction of hydrogen. The compactness of sample treated at 1060 ℃ is 77.70%, the carbon residue forms pores to restrain the sintering process, and the compactness of sample treated at 1070 ℃ is 93.94%. It points out the direction for further optimizing the manufacturing process of binder jetting with pure copper.

Abstract:With the urgent demand for high-performance thermal management components in aerospace field, multifunctional components that combine efficient heat dissipation with excellent mechanical load-bearing capacity have become a focus of research. Using finite element simulation and experimental characterization methods, this study systematically investigated the influence of volume fraction on the forming quality, mechanical response, and heat exchange performance of AlMgScZr alloy Primitive lattice structures formed by selective laser melting (SLM) technique. The results indicate that although the SLM-formed Primitive structure exhibits surface roughness and dimensional deviations, its overall forming quality meets functional requirements. In terms of mechanical properties, an increase in volume fraction significantly enhances the mechanical performance of the lattice structure. When the volume fraction reaches 25%, the compressive modulus reaches 1664.06 MPa, the peak plateau stress is 42.85 MPa, and the energy absorption per unit volume increases significantly with increasing volume fraction. In terms of heat exchange performance, the Nusselt number (Nu) of the Primitive lattice structure with a volume fraction of 25% increases by 41.6% compared to that with a volume fraction of 10%. The increase in Reynolds number (Re) further enhances convective heat transfer efficiency, but this is accompanied by an increase in friction factor (f). This study achieved synergistic regulation of heat exchange and mechanical properties through volume fraction optimization, providing a reference for the application of Primitive lattice structures in thermal management components.

Abstract:This work investigated the forming process optimization, microstructure and properties of the GH4099 alloy fabricated by binder jetting 3D printing (BJ3DP) to meet the needs of forming accuracy and service performance of complex components. The effects of layer thickness, binder saturation, roller traverse speed and drying time on the surface quality of green samples were analyzed through orthogonal experiments. The results reveal that binder saturation is the main control factor. The optimized parameters significantly improve the forming uniformity and dimensional stability. In addition, the influence of sintering temperature on microstructure and properties was also investigated. It is found that when the sintering temperature is 1345 ℃, the relative density of the sample reaches 98.4%, and a large amount of coherent L1₂-Ni₃(Al,Ti) phase are precipitated in this sample. Under this condition, the optimum mechanical properties are obtained, i. e., tensile strength of 669 MPa and yield strength of 590 MPa. The work establishes the mechanism of the synergistic regulation of GH4099 microstructure-property by printing and sintering parameters of BJ3DP, providing new ideas and theoretical support for achieving high-performance complex components of nickel-based alloys.

Abstract:1wt%ZrO₂-0.2wt%GNPs/2024Al composites were prepared by laser powder bed fusion (LPBF) process. The phase composition and microstructure evolution of the as-deposited and heat-treated (475 ℃ solution treatment for 1 h+140 ℃ aging treatment for 12 h) composites were characterized to reveal the changes in mechanical properties. Results show that compared with that of the as-deposited samples, the microhardness of the composites is maximally enhanced under the heat treatment regime of 475 ℃/1 h+140 ℃/12 h. The second phases precipitated in the samples are mainly in the form of Al₂Cu strips and Al₂CuMg plates. The tensile strength and yield strength are increased from 382 MPa and 269 MPa to 624 MPa and 522 MPa, respectively, but the elongation is decreased from 16% to 5.6%. The strength enhancement is mainly attributed to the dislocation and load transfer strengthening effects caused by heat treatment, which has a much greater influence than the coarsening of the second phase and grain growth caused by heat treatment. The decrease in plasticity is mainly due to the coarse Al₂Cu and Al₂CuMg second phases which are prone to fracture and detach from the Al matrix, promoting to the premature formation of local shear bands and voids.

Abstract:IN625 superalloy was used to repair the surface of EA4T axle steel by laser cladding. The phase composition, microstructure, grain size and mechanical properties of different areas of IN625 laser cladding samples were analyzed by X-ray diffractometer, scanning electron microscope, Vickers hardness tester and universal experimental machine, respectively. The results show that the bottom of the IN625 laser cladding layer is the columnar crystal structure with multiple growth directions, the middle is the columnar crystal structure with single growth direction and the grain size is the largest, and the top is the mixed crystal region dominated by equiaxial crystal. The interdiffusion of Ni, Cr and Fe occurs between the cladding layer and the substrate, and the diffusion region is about 9 μm. The microhardness is 295 HV_0.2, the tensile strength is 888 MPa and the elongation is 38.0%.

Abstract:To address the challenges of integrated shell molding in precision investment casting of titanium alloy closed impellers and the prolonged cycle time of conventional methods, a fabrication process for titanium alloy closed impellers based on stereolithography 3D printing has been developed. By optimizing powder bulk density by multilevel particle gradation and using ammonium citrate dispersants of 1.5wt% combined with alkaline environment of pH=10.0, a stable aqueous slurry with 62vol% solid content and 394 mPa·s viscosity was achieved, effectively suppressing Y₂O₃ hydration-induced slurry instability. The effect of key process parameters on molding performance was systematically investigated: the green body exhibits 18.9 MPa flexural strength at 62vol% solid content, which increases to 25.4 MPa after two vacuum impregnations with 20wt% nano-Y₂O₃ dispersion. Stereolithography 3D-printed resin prototypes combined with gel casting enable one-step fabrication of yttria molds with complex flow channels. Vacuum gravity casting successfully produces fully formed titanium alloy closed impellers, with no chemical sand adhesion observed after mold removal, and the microstructure characteristics and α layer thickness of the casting are essentially identical to those of ZTC4 casting produced by traditional investment casting process. Experimental results demonstrated that this process significantly shortens the lead time compared to traditional investment casting, providing a novel approach for cost-effective precision casting of high-performance titanium alloy components with complex geometries.

Abstract:Dense and uniform high-entropy alloy AlCoCrFeNi gradient composite coating with different WC content was prepared on 45# steel substrate by laser cladding technology. The effect of ceramic particle content on the microstructure evolution and mechanical properties enhancement mechanism of high-entropy alloy gradient coating was quantitatively analyzed in order to improve the surface wear resistance of metal parts. The results show that with the increase in WC content, the grain size of the coating decreases from 20.16 μm to 7.71 μm, and the grain shape changes from cellular to dendrite and equiaxed. In addition, the microhardness of the gradient composite coating is significantly increased, which is 3 times that of the substrate, and 1.4 times higher than that of the high-entropy coating without adding WC. The coating mainly consists of body-centered cubic phase and metal carbide, and the corresponding diffraction peak intensity increases gradually with the increase in WC content. The wear performance test results show that the coating exhibits the best wear resistance when the WC content is 20wt%, and the friction coefficient and wear amount are 0.4680 and 0.16 mg, respectively, which are lower than the coating with 40%wt WC which has the highest average hardness, indicating that maintaining appropriate toughness while improving the hardness of the coating is the key to achieve the optimization of the coating performance. This study provides a certain reference value for the study of the optimization of high entropy alloy coatings prepared by laser cladding.

Abstract:The development of additive manufacturing (AM) has brought innovative opportunities for the precision forming of high-melting-point refractory metals (such as tungsten, molybdenum, tantalum, niobium, and their alloys). However, due to the inherent properties of refractory metals such as high melting point, their AM processes exhibit significant particularities different from those of other metal materials. Based on the metal powder bed fusion (PBF) AM techniques represented by selective laser melting (SLM) and selective electron beam melting (SEBM), this paper systematically reviewed the research progress of tungsten, molybdenum, tantalum, niobium, and their alloys in AM field. The research focused on the powder preparation technique of refractory metals, as well as the microstructure regulation strategies of typical process defects (such as pore, cracking, grain coarsening) during the forming process and mechanical properties of these alloys. In addition, this paper also summarized the key faced in the industrialization process of refractory metals prepared by AM and prospected the future development trends.

Abstract:To investigate the influence of Al-Zn-Mg-Cu alloy with as-homogenized and as-rolled initial microstructures on the tensile flow behavior, isothermal tensile tests were conducted on a GLEEBLE-3500 isothermal simulator at temperatures of 380–440 °C and strain rates of 0.05–1 s^-1. The Johnson-Cook model, Hensel-Spittel model, strain-compensated Arrhenius model, and critical fracture strain model were established. Results show that through the evaluation of the models using the correlation coefficient (R) and the average absolute relative error, the strain-compensated Arrhenius model can represent the flow behavior of the alloy more accurately. Shear bands are more pronounced in the as-homogenized specimens, whereas dynamic recrystallization is predominantly observed in as-rolled specimens. Fracture morphology analysis reveals that a mixed fracture mechanism is prevalent in the as-homogenized specimen, whereas a ductile fracture mechanism is predominant in the as-rolled specimen. The processing maps indicate that the unstable region is reduced in the as-rolled specimens compared with that in the as-homogenized specimens. The optimal hot working windows for the as-homogenized and as-rolled specimens are determined as 410–440 °C/0.14–1 s^-1 and 380–400 °C/0.05–0.29 s^-1, respectively.

Abstract:Dual-layer thermal barrier coatings (TBCs) with ultrahigh temperature resistance were prepared on the surface of molybdenum-rhenium alloy hot-end components. The preparation of the MoSi₂-Gd₂Zr₂O₇ dual-layer TBCs was designed based on the coefficient of thermal expansion and the coating functionality, and it was completed using atmospheric plasma spraying technique. The microstructure, mechanical properties, and thermal properties were analyzed. Results indicate that the adhesion of the prepared dual-layer composite TBCs is excellent, and no noticeable cracks appear at the interface. Compared with the MoSi₂ coating with a low fracture toughness (0.88 MPa·m^1/2), the Gd₂Zr₂O₇ coating exhibits higher fracture toughness (1.74 MPa·m^1/2) and stronger resistance to crack propagation. The prepared MoSi₂-Gd₂Zr₂O₇ composite coatings have a high porosity (39%), low thermal conductivity (1.020 W·(m·K)^-1, 1200 °C), and low thermal diffusivity (0.249 mm²/s, 1200 °C). Additionally, they possess a high oxygen-vacancy concentration, which ensures excellent insulation performance.

Abstract:The influence of homogenization parameters on element segregation, dendritic structure, and the precipitate evolution in the GH3535-0.08wt% Y alloy was investigated. Additionally, some specific homogenization parameters were maintained constant throughout the experiments. Results indicate that the heat treatment at 1150 °C for 10 h is the optimal homogenization condition. Following this optimal treatment, dendrite structures and element segregation are eliminated. Furthermore, both SiC and Y₅Si₃ precipitates in the as-cast alloy decrease significantly. Conversely, the homogenization at 1188 °C induces overheating defects within the alloy. Although SiC and Y₅Si₃ phases also decrease, some large M₆C phases can still be observed, adversely affecting subsequent forging processes.

Abstract:Nb-22Si-20Ti-6Mo-xTa (x=0, 1, 2, 3, 4, at%) alloys with different contents of Ta were prepared by vacuum non-consumable arc melting method, and effects of Ta content on phase constitution, microstructure and mechanical properties of Nb-22Si-20Ti-6Mo-xTa alloys were investigated. Results show that addition of Ta does not change the phase composition Nb-22Si-20Ti-6Mo-xTa alloys. All alloys consist of Nbss and β-Nb₅Si₃, and Ta is mainly dissolved in Nbss. Microstructure of alloys consists of bulk primary β-Nb₅Si₃ phase and Nbss/β-Nb₅Si₃ eutectic. Addition of Ta refines the microstructure, and the grain size of primary β-Nb₅Si₃ phase decreases from 26.84 μm to 14.65 μm. In addition, the amount of primary phase is decreased with increasing the Ta content, and the amount of eutectic structure is increased. Room-temperature compressive strength of Nb-22Si-20Ti-6Mo-xTa alloys is improved with increasing the Ta content, and it is increased from 2261 MPa to 2321 MPa with increasing the Ta content from 0at% to 4at%. Fracture strain of Nb-22Si-20Ti-6Mo-xTa alloys first decrease and then increase with increasing the Ta content. Fracture strain of NST-0Ta alloy is 9.9%, that of NST-1Ta alloy is 9.7%, and that of NST-4Ta alloy increases to a maximum of 10.6%. Compressive strength improvement of alloys is contributed to solid solution strengthening and grain refinement strengthening by the addition of Ta. Due to refinement of alloy microstructure and the increase in eutectic structure, fracture strain of alloy is increased.

Abstract:Zirconium and its alloys have recently received considerable attention as candidate materials for dental implants due to its low modulus of elasticity, good corrosion resistance, and excellent biocompatibility. In this work, Zr-30Ti-xCu (x=0, 3, 7, wt%) alloys were designed by the valence electron concentration theory. The microstructures of the alloys were characterized using SEM/EDS and TEM/EDS. The mechanical properties, corrosion behavior, biocompatibility, and antibacterial activities of the alloys were characterized through microhardness testing, room-temperature tensile testing, electrochemical testing, contact angle testing, and antibacterial performance experiments. Results show that after quenching at 650 ℃/15 min, three alloy matrices are mainly composed of β phase. In the Cu-containing alloys, Zr₂Cu second phase precipitates and the number of Zr₂Cu particles increases with the increase in Cu content. With the increase in Cu content, the Vickers microhardness increases by 37%, and the contact angle decreases from 98.49° to 74.21°, indicating the surface wettability improvement which shows a significant inhibitory effect on Escherichia coli and Staphylococcus aureus. Besides, the corrosion resistance of the alloy in physiological saline solution is enhanced. Three alloys have low elastic modulus (67.8–78.9 GPa) and cytotoxicity, but their relationship with Cu content is not obvious. It can be seen that Zr-30Ti-xCu alloy exhibits excellent comprehensive properties, which can provide theoretical basis and guidance for the selection of new dental metal implants.

Abstract:The microstructure of high-purity copper targets has a significant impact on the quality of sputtered films. This study investigated the evolution of the microstructure and dynamic recrystallization mechanism of copper targets from the perspective of hot working. The hot deformation behavior of high-purity copper at temperatures ranging from 500 ℃ to 650 ℃ and strain rates from 0.01 s^–1 to 10 s^–1 was studied through isothermal compression experiments. The results show that the evolution of the microstructure and the recrystallization mechanism are closely related to the Zener-Hollomon parameter Z. As the temperature increases and the strain rate decreases, the lnZ decreases, and the average grain size decreases, both the microstructure homogenization and dynamic recrystallization enhance, and the texture transitions from a strong deformation texture of Cube ND{001}<110> to Cube{001}<100> and Goss{011}<100>. The dynamic recrystallization mechanism changes at different lnZ values. Local recrystallization occurs at high lnZ values, which is a discontinuous dynamic recrystallization (DDRX) mode. At middle lnZ value, the degree of recrystallization increases, the orientation difference increases uniformly and the lattice rotates gradually. At low lnZ values, continuous dynamic recrystallization (CDRX) of progressive rotation of lattice and geometric dynamic recrystallization (GDRX) of grain "pinching" occur. At low lnZ value of 650 ℃, 10 s^–1, homogeneous fine microstructure and weak texture strength are obtained. The research can provide theoretical guidance for the optimization of hot working technology of high purity metal sputtering targets.

Abstract:IMI834, as a high-performance titanium alloy resistant to 600 ℃, faces limitations in its application due to issues such as a narrow processing window, weak deformation ability, and high deformation resistance. Although it is feasible to control the sheet's microstructure and texture by adjusting the rolling thickness and post-rolling heat treatment, related research remains insufficient. In this study, the effects of deformation and solution treatment temperature on the microstructure and texture of IMI834 sheets was investigated by scanning electron microscopy and back scattered electron diffraction techniques. The results indicate that as the rolling deformation increases, the sheet's microstructure gradually transforms into banded and equiaxed fine-grained structures, in which the banded structure exhibits an RD texture. Additionally, reversing the rolling direction can increase the proportion of equiaxed fine-grained structures. Appropriate solution treatment can effectively weaken the basal texture, thereby reducing the sheet's deformation anisotropy.

Abstract:The effect of decreasing the homogenization temperature on the microstructure and mechanical properties of 2024-T3 alloy was investigated. The results show that the area fractions of the residual coarse secondary phases of alloys after homogenization at 430 or 460 ℃ for 24 h followed by rolling are similar, and they are higher than those of the alloys homogenized at 490 ℃ for 24 h. The latter treatment is routinely used in the industry. The alloys with homogenization of 430 ℃/24 h or 460 ℃/24 h and solution treatment have higher recrystallization fractions and finer grain sizes due to the particle stimulated nucleation (PSN) effect of the coarse secondary phase. Hardness tests and tensile tests show that the peak hardness, tensile strength, yield strength, and elongation of the three alloys are relatively similar to each other. Therefore, appropriately decreasing the homogenization temperature can improve the uniformity of grain size, reduce the cost, and maintain the excellent tensile properties of 2024-T3 plates. Whereas the high-temperature homogenization of 490 ℃/24 h can make the 2024-T3 sheet have relatively good plasticity and toughness.

Abstract:To further investigate the effects of void defect on the plastic deformation behavior of α-Fe under tensile load, the molecular dynamic models of the α-Fe samples with the void defects were established and related simulations under uniaxial tension were carried out for a series of models. The results show that overall, the deterioration of tensile mechanical properties of the sample with void is positively related to the void size. The larger the void size, the easier the occurrence of plastic deformation stage for sample. Overall, the Young's modulus, yield stress, ultimate tensile strength and tensile elongation of the samples containing void decrease with increasing the radius of void. The plastic deformation mechanism is of a mixture of the tensile stress-induced structural phase transition and the dislocation slip. However, the characteristics of stress-strain curves change significantly with increasing the radius of void, the plastic yield stage and strain hardening stage of the sample become shorter, and the strain hardening stage even vanishes. The research deepens the understanding of the effects of void defect on the mechanical properties and plastic deformation mechanisms of metals and lays a useful foundation for the subsequent analysis and study of the physical and mechanical properties of polycrystalline α-Fe materials under various conditions.

Abstract:In order to explore the effect of multi-directional forging on the microstructure and mechanical properties of aluminium alloy, this paper took the homogenized Er7050 aluminum alloy as the research object. The alloy samples were subjected to multi-directional forging of three kinds of forging passes at 400 ℃, namely three-time upsetting and three-time cross stretching (3U3CS), 6U6CS and 9U9CS. Subsequently, the samples were subjected to solid solution treatment, water quenching and T6 aging treatment. The microstructure and mechanical properties of the samples were analyzed. Comparison of the mechanical properties of the samples obtained by the different forging processes reveals that the sample treated by the 9U9CS forging process has the best mechanical properties, which is attributed to its fine grains and dense precipitated strengthening phases. The average tensile strength of the sample under this forging process is 621.4 MPa, the average yield strength is 545.4 MPa, and the average elongation is 13.58%, which indicates that the optimized forging process significantly improves the mechanical properties of the alloy.

Abstract:To investigate the influence of mold temperature on the temperature field and equivalent stress field of Mg alloy processed by inverse temperature field equal channel angular pressing (ITF-ECAP), a thermal mechanical coupled finite element analysis model was established for ITF-ECAP processing of B2 alloy (Mg-1.5Bi, wt%). Combined with experimental research, the processing process of B2 alloy at different mold temperatures was analyzed. The results show that during the ITF-ECAP, the temperature of the billet significantly increases at the corner of the mold channel, which facilitates smooth plastic deformation. After severe deformation, the temperature gradually decreases, thereby inhibiting coarsening of recrystallized grains. The stress concentration of the billet mainly occurs at the corner of the channel and near the mold outlet, and it significantly decreases with the increase in mold temperature. The experiment verification finds that when the mold temperature is low (200 ℃), the surface cracking of B2 alloy billet occurs after one-pass ITF-ECAP processing. In contrast, the surface of B2 alloy can be ITF-ECAP processed for four passes without surface cracking when the mold temperature is set as 300 ℃. Further microstructural characterization reveals that a bimodal grain structure composed of fine and ultrafine grains is formed after four-pass ITF-ECAP deformation, leading to a simultaneous improvement in both strength and ductility.

Abstract:The synergistic evolution mechanism of microstructure and texture of Ti-3Al-5Mo-4.5V (TC16) alloy bar was revealed under rolling-drawing-different annealing cooling (water quenching (WQ), air cooling (AC) and furnace cooling (FC)). The results show that the initial lamellar structure of TC16 titanium alloy bar has a dual-phase structure composed of equiaxed α and β phases through dynamic recrystallization and α phase growth during two-phase rolling and annealing. The β phase and α phase form the axial silk texture of <110>//bar and //bar, respectively. Although hot drawing does not change the texture type, the hot drawing deformation leads to a significant increase in the internal grain orientation gradient, which in turn significantly weakens the texture intensity. The annealing cooling rate has a significant effect on the content of α phase, and the content of equiaxed α phase increases from 36.8vol% (WQ) to 74.9vol% (FC). The texture types of β phase and α phase at different cooling rates are consistent with the drawn texture. The α→β phase transition in the annealing heating stage retains and strengthens the original β phase texture through the Burgers orientation relationship. During the cooling process, the β→α phase transition triggers the selection of variants due to the adaptive effect, resulting in an increase in the texture strength of the α phase. It can be seen that heat treatment can retain and strengthen the rolling-drawing texture, rather than reconstruct its type. This study provides reference and guidance for the optimization of microstructure and texture of titanium alloy through the synergistic control strategy of hot processing and cooling.

Abstract:Platinum group metals have high melting points, strong corrosion resistance, stable chemical properties, and low oxygen permeability in high-temperature oxygen-containing environments. As thermal protective coating materials, they have gained essential applications in the aerospace field and have excellent prospects for application in frontier military fields, such as protecting hot-end components of hypersonic aircraft. This research reviewed the latest research progress of platinum group metal coatings with high-temperature oxidation resistance, including coating preparation techniques, oxidation failure, and alloying modification. The leading preparation techniques of current platinum group metal coatings were discussed, as well as the advantages and disadvantages of various existing preparation techniques. Besides, the intrinsic properties, failure forms, and failure mechanisms of coatings of single platinum group metal in high-temperature oxygen-containing environments were analyzed. On this basis, the necessity, main methods, and main achievements of alloying modification of platinum group metals were summarized. Finally, the future development of platinum group coatings with high-temperature oxidation resistance was discussed and prospected.

Abstract:In recent years, clean nuclear energy has developed rapidly. Zr alloys are commonly used as fuel element cladding materials in water-cooled nuclear reactions due to their good corrosion resistance and low neutron absorption cross-section. The nuclear fuel is usually sealed in a Zr alloy envelope by welding, so its weld quality is particularly critical. The high heat input of traditional fusion welding leads to large deformation, and the porosity and intermetallic compounds (IMCs) in the brazing process tend to damage the joint performance, and low-temperature diffusion bonding of Zr alloys can avoid the above problems. Therefore, this paper analyzed the weldability of Zr and its alloys, reviewed the research status of their welding technologies including fusion welding, brazing, and diffusion bonding, briefly introduced two kinds of pre-welding optimization methods, namely surface mechanical attrition treatment (SMAT) and thermo-hydrogen processing (THP). Finally, it summarized and prospected the applications in low-temperature diffusion bonding of Zr alloys.