Abstract:This study systematically investigated the influence of cerium (Ce) addition on the microstructure and mechanical properties of Al-Cu-Mn-Mg alloys through multi-scale characterization techniques, including OM, SEM, TEM, and XRD. The results reveal that the addition of Ce leads to the formation of two distinct Ce-containing intermetallic compounds. One is the primary Al₂₀Ti₂Ce phase formed during solidification, which induces grain coarsening by consuming the effective grain-refining element Ti in the melt. The other Ce-containing phase is Al₁₆Cu₄Mn₂Ce, which forms through a eutectic reaction at the final stage of the solidification process. Unlike Al₂Cu, this phase is unstable at high temperatures and undergoes transformation into Al₂₄Ce₃Cu₈Mn and Al₂₀Cu₂Mn₃ during heat treatment. Consequently, Cu and Mn from Al₁₆Cu₄Mn₂Ce phase cannot dissolve into the Al matrix, resulting in a reduction in supersaturation degree. Furthermore, the minor addition of Ce retards the phase transformation from θ′′ to θ′ in the Al matrix. Thus, with the identical heat treatment, the primary strengthening phase is θ′′ phase in the Ce-containing alloy, whereas the strengthening phase is θ′ phase in the alloy without Ce addition. These changes in the microstructure and phase composition directly influence the mechanical properties of alloys: with Ce content increasing from 0wt% to 0.3wt%, the ultimate tensile strength and yield strength are decreased by 95.0 and 45.5 MPa, respectively, and the elongation is reduced by about 50%, compared with those counterparts of the alloy without Ce addition.

Abstract:Zr-0.75Sn-0.35Fe-0.15Cr-xNb alloys were investigated, and static autoclave tests were conducted in deionized water at 360 ℃ and 18.6 MPa for 580 d. Secondary ion mass spectrometry was employed to characterize the concentration gradient distribution of carbon from the oxide film surface to the oxide/matrix interface, and X-ray photoelectron spectroscope was used to analyze the valence states of carbon on the substrate surface. The experimental results show that the C concentration in the oxide film on the rolling surface (S_N) of the Zr-0.75Sn-0.35Fe-0.15Cr alloy was significantly higher than that on the surface perpendicular to the transversal direction (S_T). Adding 0.15wt% Nb can considerably decrease the C concentration in the oxide film and reduce the difference in carbon concentration distribution among oxide films on different surfaces. The C/Zr ratio on the S_N surface of the Nb-free alloy increases more obviously with the rise of temperature, suggesting a potential competitive relationship between Nb and Zr in C binding. In conjunction with experimental observations of corrosion anisotropy of the Zr-0.75Sn-0.35Fe-0.15Cr alloy, this study explored the relationship between C and anisotropic corrosion from the perspective of the effects of Nb on impurity C distribution.

Abstract:The microstructure evolution and mechanical properties of the N08120 superalloy rolled at 780 ℃ and deformed through the cumulative reduction of 40%, 60%, and 80% with the single pass reduction of 10% were investigated. The experimental results show that MC and M₂₃C₆ carbides precipitate at grain boundaries and within the grains during deformation. These finely dispersed carbides effectively hinder dislocation motion, thereby enhancing the strength of the material. Dynamic recovery is identified as the predominant softening mechanism during hot rolling, where dislocations progressively reorganize into dislocation cell structures through slip and recombination. Owing to the strong pinning effect of grain boundaries on dislocations and their high interfacial energy, dislocations preferentially accumulate near grain boundaries, inducing localized recrystallization and the formation of fine recrystallized grains. With increasing deformation amount, the alloy texture transitions progressively from Rotated Goss {110}<110> to Rotated Cube {110}<112> and finally to the Copper {112}<111> type. After 40% deformation, work hardening is significant, with the yield strength increasing from 322 MPa to 867 MPa and the microhardness rising from 196 HV_0.5 to 337 HV_0.5. Beyond 40% deformation, both yield strength and microhardness tend to stabilize. This is mainly attributed to the evolution of carbides, dislocation density, substructure, and recrystallization in N08120 superalloy during hot rolling.

Abstract:In Al/Cu friction stir welding (FSW) T-lap joints, the hook-shaped structure present in the nugget zone (NZ) serves as a crack initiation site, which severely compromises the performance of the joints. In this study, FSW of 6061 aluminum alloy and pure copper in a T-lap configuration was performed employing an eccentric progressive pin. Two types of welding wires with different chemical composition were pre-set at the corner die, and the applicability of three tools for T-lap joints was examined. The research was intended to improve the bonding quality between the hook-shaped structure and the base material to obtain high-quality welded joints. Two optimal welding tools were selected. The influences of these tools on the grain morphology at the Al/Cu interface and the morphology of intermetallic compounds (IMCs) were analyzed, and the mechanical properties of the joints along the skin and stringer directions were evaluated. The results reveal that the tool with a small eccentric pin reduces the thickness of the interfacial IMC layer, simultaneously thinning the tip of the Cu hook and enlarging the volume of the NZ, and achieving metallurgical bonding between the periphery of the Cu hook and the matrix, thus improving the welding quality. For the M800Al welding tool equipped with a small eccentric pin and three cutting surfaces, its periodic shearing action facilitates the formation of a vortex-like interlocking interface. Meanwhile, more fragments scraped from the Cu hook are distributed throughout the NZ. This phenomenon not only refines the grain structure but also promotes discontinuous dynamic recrystallization and geometric dynamic recrystallization. The ultimate tensile strength of the M800Al joint along the stringer direction reaches 176 MPa, marking a 23.9% increment compared with that of the joint produced using a non-eccentric tool. This work provides a feasible solution for improving the performance of FSW T-lap joints of dissimilar metals.

Abstract:Coatings with strong corrosion resistance and high electrical conductivity on bipolar plates are urgently required for large-scale applications of proton exchange membrane water electrolysis (PEMWE). High-performance TaTiN coatings were fabricated via magnetron sputtering. Results show that TaTiN coatings with preferred (111) planes and refined grains show higher corrosion resistance and better electrical conductivity. On the one hand, the closely-packed (111) plane favors a dense texture; moreover, grain refinement can smooth the surface and facilitate the formation of a continuous, compact passive layer, thereby improving corrosion resistance. On the other hand, the small lattice mismatch between TaTiN (111) and Ti (0001) enhances interfacial bonding and thus electrical conductivity across the interface, resulting in lower interfacial contact resistance (ICR). The optimized TaTiN coating shows a low corrosion current density of 6.56×10^-7 A·cm^-2 and an ICR of 9.11 mΩ·cm², indicating the strong potential of TaTiN coatings to protect metallic bipolar plates in PEMWE systems.

Abstract:γ-TiAl alloys feature superior high-temperature performance and low-density properties. However, the inherent brittleness of γ-TiAl alloys poses significant challenges to precision machining. As a highly promising machining approach, water lubrication enables temperature reduction and mitigates frictional heat accumulation, tool wear, and crack-associated defects. This work investigated the effects of nano-scratching speed on scratching force, temperature evolution, plastic deformation, and surface quality of single-crystal γ-TiAl alloy under water lubrication. The results show that the coupling effect between scratching speed and water lubrication governs the machinability and surface quality of single-crystal γ-TiAl alloys. An increase in scratching speed substantially elevates scratching force and frictional heat, which further induces local temperature rise and stress concentration. In comparison, a 1-nm-thick water lubrication layer yields minor temperature fluctuation of the substrate and delivers favorable cooling capacity. At a scratching speed of 400 m/s, water lubrication alleviates surface plastic deformation and damage, promotes chip accumulation, and reduces surface roughness. Experimental observations further confirm that scratching speed exerts a pronounced effect on surface quality.

Abstract:Research on high-performance and low-cost hydrogen evolution reaction (HER) catalysts is of great significance for the large-scale development and practical application of hydrogen energy. Using cheaper metals instead of platinum (Pt) to reduce catalyst costs while ensuring HER performance is a current challenge. In this work, we used a facile and controllable method, the spray-drying technique combined with thermal decomposition reduction, to synthesize the catalyst of ruthenium-nickel atomic cluster supported on carbon black (RuNi-ac/C) at a reduction temperature of 300 ℃ in H₂. The results show that as-synthesized RuNi atomic clusters are uniformly distributed on the carbon black, with the particle size distribution ranging from 0.5 nm to 2.5 nm. Electrochemical tests indicate that the HER overpotential of RuNi-ac/C is only 37 mV at a current density of 10 mA·cm^-2 in 0.5 mol/L H₂SO₄ electrolyte. The overpotential is increased by only 2 mV after 4000 cyclic voltammetry cycles in the stability test, demonstrating excellent electrochemical stability. Compared with synthesized Ru/C-300 ℃, Ni/C-400 ℃, and RuNi/C (200, 400, and 500 ℃) catalysts, the RuNi-ac/C has the best HER performance. Furthermore, the RuNi-ac/C has better HRE activity as well as lower cost compared with the commercial Johnson Matthey Pt/C catalyst, providing a new idea for the industrial application of low-cost and high-efficiency HER catalysts.

Abstract:Cu-Ti alloys, owing to their excellent mechanical strength, have been widely applied in aerospace, electrical engineering, and rail transit. However, issues including relatively low electrical conductivity (EC), Ti element segregation, oxidation, and discontinuous precipitation have constrained the enhancement of their comprehensive performance and engineering applications. This research reviewed recent progress on the evolution of microstructure and performance regulation of Cu-Ti alloys, with a focus on the analysis of the formation mechanism of precipitates and their influence on the mechanical properties and EC of the alloys. The composition design strategies, advanced preparation technologies, and thermo-mechanical treatment were also summarized. On this basis, it is proposed that constructing a heterogeneous structure with multiscale and multiphase strengthening is a feasible technical path to further improve the yield strength, ultimate tensile strength, and EC of Cu-Ti alloys through improvements in composition design, hot treatment process, and microstructure control. This work is expected to develop copper alloys with good processability, high strength, and high EC to meet the rapid development of high-end manufacturing fields such as electrical engineering and aerospace.

Abstract:The crack propagation performance of the independently-developed 3rd-generation powder metallurgy superalloy FGH4113A was studied, including the effects of preparation process, temperature, and frequency on crack propagation performance, and a comparison was made with similar superalloys. The preparation process involved a combination of hot isostatic pressing, hot extrusion, isothermal forging (ITF), and heat treatment. Test temperatures included room temperature, 650 ℃, and 700 ℃, with test frequencies of 0.33 and 20 Hz. The effects of process, temperature, and frequency on the high-temperature crack propagation performance of the alloy were analyzed. The crack propagation performance of similar alloys with grades such as FGH95, FGH96, FGH97, FGH98, ME3, and LSHR was compared. The results show that prior particle boundary (PPB) and coarse primary γ′ phase around the grain boundary are unfavorable factors for the crack growth performance of the alloy, and increasing the grain size is beneficial to reducing the crack propagation rate. Extrusion and forging process can effectively eliminate PPB, thereby enhancing the crack propagation resistance of the alloy. The crack propagation rate at room temperature is much lower than that at 650 and 700 ℃, and the crack propagation rate at test frequency of 0.33 Hz is significantly higher than that at 20 Hz. Increasing the temperature and decreasing the test frequency will increase the crack propagation rate of the alloy. In the stable crack propagation stage, the FGH4113A alloy in ITF state exceeds FGH98, LSHR, and ME3 alloys, and reaches the advanced level of the 3rd-generation powder metallurgy superalloy.

Abstract:This study investigated the powder metallurgy superalloy FGH4113A, focusing on the design and implementation of precisely controlled cooling during the solid solution state. The effect of cooling path on microstructural evolution and tensile properties at 800 ℃ was examined. The results show that the cooling path significantly affects the strength-ductility synergy. At a conventional continuous cooling rate of 150 ℃/min, the alloy exhibits a yield strength of 920±7 MPa, an ultimate tensile strength of 1079±9 MPa, and an elongation of 13.4%±2.9%. In contrast, a two-stage cooling process (CP2), combining an initial slow cooling (44–75 ℃/min) with a subsequent fast cooling (459–594 ℃/min), enhances the yield strength and ultimate tensile strength to 978±7 and 1112±5 MPa, respectively, while also improving the elongation to 14.6%±1.1%. Further optimization of the process parameters to an initial cooling rate of 48–65 ℃/min followed by a second-stage rate of 275–326 ℃/min (CP3) achieves an elongation of 18.5%±0.8% while maintaining high strength levels (yield strength of 975±10 MPa and ultimate tensile strength of 1108±6 MPa). Microstructural characterization shows that the staged cooling strategy effectively produces grain structures with low orientation spread and low dislocation density by promoting dislocation recovery via slow cooling at high temperature and then freezing the low-defect structures through fast cooling at medium temperature. Furthermore, analysis of γ'' precipitation behavior indicates that the primary cooling rate governs the size of secondary γ'' phase, the secondary cooling rate influences the size of tertiary γ'' phase, and the cooling transition temperature regulates the volume fraction of tertiary γ'' phase. Through this multiscale cooperative distribution of γ'' phases, moderately-sized secondary γ'' phase enhances strain hardening capacity by promoting the Orowan bypassing mechanism, while the finely-dispersed tertiary γ'' phase compensates for the strength loss associated with coarsened secondary γ'' phase through shearing mechanism. This work demonstrates that precisely controlled staged cooling is an effective pathway for synergistically optimizing the strength and ductility of FGH4113A superalloy at 800 ℃ without altering its chemical composition, providing both a theoretical basis and practical guidance for the heat treatment design of this alloy.

Abstract:Zirconium alloys have garnered significant attention and widespread application in the nuclear industry due to their exceptional corrosion resistance and low thermal neutron absorption cross-section, particularly in dissolver equipment for highly corrosive environments. This study investigated the diffusion bonding interface microstructure between Zr-3 alloy and refractory metal tantalum as well as their mechanical properties. The effect of diffusion bonding temperature on the shear strength of zirconium/tantalum joints was examined. Additionally, the interface structure and fracture surface morphology of the joints were analyzed, and a preliminary study on the corrosion resistance of the joint was conducted. Results show that the typical interface structure of the joint is Zr/α-Zr+β-(Zr,Ta) solid solution/Ta, with the thickness of the diffusion layer increasing gradually as the bonding temperature rises. The shear strength of the joint initially increases and subsequently decreases with rising temperature. Under the bonding conditions of 900 °C-30 min-10 MPa, the joint strength reaches its maximum value of 385 MPa, with the fracture surface exhibiting mixed fracture characteristics. Furthermore, the zirconium/tantalum diffusion bonding joint demonstrates excellent corrosion resistance.

Abstract:The effect of trace element Zr addition on the microstructure and mechanical properties at room temperature and high temperature of K492M superalloy was investigated. The Zr content in the experimental alloys ranged from 0.006wt% to 0.058wt%. The results show that the addition of element Zr does not change the main phase constitution of the as-cast and heat-treated K492M superalloys. The microstructure of the as-cast K492M superalloy mainly consists of γ matrix phase, γ'' precipitated phase, MC carbides, and (γ+γ'') eutectic phase. After heat treatment, the (γ+γ'') eutectic phase is nearly eliminated, accompanied by the precipitation of M₂₃C₆ carbides. The addition of element Zr significantly refines the grain structure of the as-cast and heat-treated K492M superalloys. When the Zr content is 0.016wt%, both the as-cast and heat-treated superalloys exhibit the most significant grain refinement. With the increase of Zr content from 0.006wt% to 0.058wt%, the MC carbides in both as-cast and heat-treated superalloys tend to be refined, while element Zr addition has a minor effect on the volume fraction and size of γ'' phase. The variation of Zr content has little effect on the tensile properties at room temperature and the tensile strength at high temperature (760 ℃) of the heat-treated superalloy, but significantly influences the ductility at 760 ℃ and stress rupture life at 760 ℃/662 MPa. The superalloy with 0.016wt% Zr content demonstrates the highest high-temperature elongation and the stress rupture life, which are 53.8% and 16.8% higher, respectively, compared to the 0Zr alloy.

Abstract:Based on the Gleeble thermal compression simulation tester, the hot deformation behavior of the homogenized GH4975 superalloy was investigated at strain rates of 0.1 and 1 s^–1 with deformation temperature ranging from 1140 ℃ to 1200 ℃. EBSD and SEM were used to observe the microstructure evolution of the homogenized alloy to study the dynamic recrystallization (DRX) mechanism of GH4975 superalloy. The results show that the main DRX mechanism of GH4975 superalloy at low temperature is discontinuous dynamic recrystallization (DDRX) at grain boundaries. As the temperature increases, the mechanism gradually transitions to particle stimulated nucleation, where secondary phase particles promote the nucleation of new grains. This evolution is associated with the morphology and distribution of the precipitates. In the GH4975 superalloy, the γ′ phase promotes DRX. As the deformation temperature increases, the γ′ phase partially dissolves back into the matrix, and the sparsely distributed γ′ phase contributes to a well-developed dynamically recrystallized grain structure. Additionally, the surfaces of the (γ+γ′) eutectic phase can serve as nucleation sites for recrystallization, thereby further promoting DRX.

Abstract:Solution-aging treatment is a critical approach for optimizing the microstructure and enhancing the mechanical properties of laser directed energy deposition (LDED)-fabricated Ti6Al4V alloys. The results show that as-deposited Ti6Al4V alloys consist of primary β columnar grains with width ranging from 200 μm to 500 μm. The intragranular features include grain-boundary α phase, Widmanst?tten structure at grain boundaries, and basket-weave microstructure. The ultimate tensile strengths in the directions perpendicular and parallel to the printing direction are 1010 and 996 MPa, with corresponding elongations of 8.1% and 11.2%, respectively. After sub-β-transus solution treatment followed by intermediate-temperature aging, the microstructure consists of discontinuous grain-boundary α phase, short rod-like α phase, and transformed β phase (composed of retained β phase and secondary α phase). Solution treatment above the β-transus causes pronounced grain coarsening and coarse Widmanst?tten structure. The treatment of 850 °C/2 h+500 °C/4 h with air cooling (AC) yields the excellent strength-ductility balance at room temperature. The ultimate tensile strengths perpendicular and parallel to the printing directions reach 1033 and 1007 MPa, respectively, with corresponding elongations of 12.1% and 15.8%. The strength-plasticity synergy originates from the multiscale α/β structure formed by sub-β-transus solution combined with intermediate-temperature aging. Specifically, the grain-boundary α phase transforms from a continuous to a discontinuous/spheroidized morphology, thereby weakening the cracking propagation channels along boundaries. The intragranular α phase is moderately coarsened and evolves from acicular to short-rod morphology, which improves deformation compatibility. Meanwhile, the secondary α phase dispersed within the transformed β phase and the residual β phase jointly promote slip transfer and work hardening.

Abstract:The effect of B₄C addition on the high-temperature compressive creep behavior of a β-solidified γ-TiAl-based alloy under the conditions of 250 MPa/800?850 ℃ and 850 ℃/200?250 MPa was investigated. The results show that the reinforcement of the Ti-43Al-6Nb-1Mo-1Cr alloy with B₄C significantly enhances its high-temperature compressive creep property. This improvement is reflected by a reduction in steady-state creep rate of 38.42% and a decrease in creep strain after 50 h of 46.32%. The steady-state creep rate of alloys as a function of stress and temperature follows the Norton-Bailey power-law model. With the addition of B₄C, the stress exponent increases from 1.96 to 4.16, and the creep activation energy rises from 335.02 kJ/mol to 368.52 kJ/mol. This change indicates a transition in dominant deformation mechanism from grain-boundary sliding to dislocation climb. The remarkable enhancement in compressive creep resistance is attributed to multiple strengthening effects. The precipitated rod-like TiB acts as a hard second phase that strengthens the matrix by hindering dislocation motion and pinning grain boundaries. In synergy with C dissolved in the matrix, it also refines the lamellar clusters. The addition of 0.2at% B₄C notably suppresses dynamic recrystallization, thereby delaying degradation of the lamellar structure and mitigating the softening effect induced by recrystallization. Furthermore, Ti₂AlC and Ti₂Al particles precipitate dynamically during high-temperature compressive creep, pinning at the α₂ phase interfaces and within the B2 phase, respectively. These precipitates strengthen the crystal structure and improve the microstructural stability of the alloy.

Abstract:The stress rupture properties at 550 ℃ and the microstructure and hardness of the grip and gauge sections from ruptured specimens of a silicon-enhanced 9Cr ferritic/martensitic steel (denoted as H-Si steel) were investigated by SEM, TEM, EBSD and Vickers hardness tester. A comprehensive investigation was conducted, which included the microstructure evolution of H-Si steel under the coupling effect of temperature and stress and its influence on the creep behavior. The results show that H-Si steel exhibits good stress rupture properties and the stress rupture life is 2252 h under the conditions of 550 ℃ and 167 MPa. The fracture modes under experimental stress conditions are all ductile fracture. The grip section of H-Si steel exhibits relatively stable microstructure under different stresses, with a lath width ranging from 380 nm to 440 nm and the hardness being approximately 230 HV. However, the microstructure of the gauge section undergoes obvious degradation due to the stress, with the rapid decrease in dislocation density and the significant widening of laths. Correspondingly, the hardness drops obviously due to significantly decreasing dislocation strengthening and interface strengthening. The hardness of the 167 MPa@2252 h specimen decreases to 193 HV, which induces a lower high-temperature stress rupture property compared to 9Cr-1Mo-V-Nb martensitic steel (P91).

Abstract:A flexible Ni-based tungsten-carbide metal cloth, which was prepared by mixing WC powder, NiCrBSi powder and the binder, was coated on the surface of Q235 steel by vacuum brazing. This flexible metal cloth can be arbitrarily cut and folded, enabling the preparation of coatings with controllable thickness on the surfaces of curved and irregularly shaped structural components. The effects of brazing temperature on the microstructure, shear strength, microhardness and wear resistance of the Ni-based WC coatings were explored. The results show that increasing brazing temperature does not change the microstructure composition of the coating. The interface between Ni-based tungsten-carbide coating and steel substrate is mainly composed of Fe solid solution, Ni₃B and Ni₃Si compounds, while the brazing seam zone is mainly composed of Ni solid solution, WC, W₂C, CrB and Cr₇C₃ compounds. With the increase in brazing temperature, the porosity and average pore area of the coatings gradually decrease, while the density gradually increases. Consequently, the microhardness and wear resistance of the coating are enhanced. This is mainly because after the flexible Ni-based tungsten-carbide metal cloth melts, as the brazing temperature increases, the ability of the molten NiCrBSi alloy to encapsulate WC particles and fill the gaps between them is enhanced. This reduces the porosity in the coatings, improves the density, thus endowing the coatings with higher hardness and wear resistance. The bonding strength between Ni-based tungsten-carbide coating and steel substrate increases first and then decreases with the increase in brazing temperature. When the brazing temperature is 1080 ℃, the shear strength of the coating reaches the maximum value of 336.5 MPa. This is because the thickness of the compound layer at coating/substrate interface increases from 4.7 μm to 9.2 μm when the brazing temperature increases to 1080 ℃, and the compound layer with appropriate thickness increases the bonding strength between the coating and the substrate. However, the thickness of the interface compound layer increases to 13.9 μm when the brazing temperature increases to 1140 ℃, and the compound layer with the excessive thickness leads to a decrease in bonding strength of the coating.

Abstract:To enhance the comprehensive performance of magnesium alloy surfaces, Ni-based composite layers added with zero-dimensional material nano-diamond (ND) and one-dimensional material carbon nanotubes (CNTs) were prepared on the surface of AZ91D magnesium alloy by nano-composite electrodeposition technique. The results show that the synergistic effect of the combination of ND and CNTs optimizes the microstructure of the deposited layer and enhances its comprehensive performance. ND, as a heterogeneous nucleation core, promotes the preferred orientation growth of Ni grains along the (111) plane, reduces the surface roughness of Ni-based deposition layers, and enhances their microstructure uniformity and density. The high specific surface area and excellent electrical conductivity of CNTs further optimize the microstructure and properties of the deposited layer. The combination of two carbon-based nanomaterials exhibits an excellent synergistic effect: the grain refinement effect of ND and the electrical conductivity enhancement effect of CNTs complement each other, significantly optimizing the deposited layer in terms of structural density, grain orientation stability, and interfacial bonding strength, further enhancing wear resistance and corrosion resistance. When the addition amounts of ND and CNTs are 12 and 0.15 g/L, respectively, the microstructure of the deposited layer is uniform and dense, the hardness reaches 1212.7 HV, the coefficient of friction decreases to 0.34, the self-corrosion current density decreases to 1.458×10^?7 A·cm^?2 (three orders of magnitude lower than that of the magnesium alloy matrix), and the resistance to Pseudomonas aeruginosa is good. The antibacterial rate is as high as 90%. This study provides a theoretical basis and process reference for the synergistic reinforcement of composite deposition layers on high-performance magnesium alloy surface with low-dimensional materials.

Abstract:The GH4151 alloy samples after different heat treatments were tested using instrumented impact testing, and the effects of microstructural characteristics and grain boundary features on the impact toughness of GH4151 alloy were analyzed through metallographic microscope, scanning electron microscope, transmission electron microscope, and phase diagram calculations. The results show that the percentage of primary γ′ phase decreases with the increase in solid solution temperature, while the average grain size gradually increases and the impact toughness of the solution-treated alloy also gradually increases. The results of phase diagram calculation by JMatPro depict that there is a certain amount of μ phase (a type of TCP phase) at grain boundaries and M₂₃C₆. Analyses of the instrumented impact curves and fracture surfaces reveal that for the alloy subjected to solution treatment only, the elastic deformation work (E_e), plastic deformation work (E_p), and tearing work (E_c) are all relatively large, indicating a good resistance to crack initiation and propagation and a high impact toughness. After solution treatment followed by two-stage aging, both the E_e and E_p become significantly smaller, and the E_c even approaches zero, resulting in a substantial decrease in impact toughness. Compared with the sample subjected to solution treatment only, the significant reduction in impact toughness of sample after two-stage aging is primarily attributed to grain refinement and the synergistic precipitation of grain boundary μ phase and M₂₃C₆ carbides during aging, while showing relatively little correlation with the grain boundary characteristics of the matrix.

Abstract:Rare-earth magnesium alloys, as a new type of high-strength lightweight structural material, have become increasingly widespread in the aerospace industry. However, issues related to casting defects have grown more prominent. Fluorescent linear defects are a typical defect found in this class of alloys. Nevertheless, their formation mechanism remains unclear, and there is a notable lack of precise control methods to mitigate them. This study systematically characterized the composition, morphology, and microstructure of fluorescent linear defects in a sand-cast low-pressure ZM6 (Mg-Nd-Zr) alloy casing component, and revealed the defect evolution mechanism through numerical simulations of the filling flow field. The results show that fluorescent defects are formed by multi-scale and multi-morphology double-layer oxide films. Meanwhile, the oxide film in ZM6 consists of porous MgO as the matrix, containing Nd₂O₃ particles. This film exhibits poor toughness and is prone to fragmentation, resulting in the formation of small-sized oxide inclusions around the oxide film. Combined with the analysis of the casting structure and filling flow field, it is found that the convergence and backflow of the melt during the filling process cause the oxide film on the melt surface to fold and be incorporated, thereby generating double-layer oxide film that can be displayed by fluorescent inspection.

Abstract:A NiCrBSi coating was fabricated on 304 stainless steel substrate using high-velocity oxygen-fuel (HVOF) spraying. The tribological behavior of the coating was investigated at room temperature (RT), 200 °C, 400 °C, and 600 °C to reveal the effect of elevated temperatures on its wear mechanisms. The effects of temperature on the microstructure and mechanical properties of the coating were analyzed by scanning electron microscope and high-temperature microhardness tester, respectively. The morphology and chemical composition of the wear tracks were characterized using white light interferometer and Raman spectroscope. The results show that the NiCrBSi coating exhibits a distinct crystallization exothermic peak at approximately 505 °C. Above this temperature, the crystallinity and microstructure of the coating are significantly improved. As the temperature increases, both the porosity and microhardness of the coating generally decrease, with a relatively gentle decrease below 505 °C and a sharp drop beyond it. The combined effect of mechanical action between the coating and the counterpart ball and the high-temperature environment induces oxidation during friction, generating oxides such as NiO, Cr₂O₃, and NiCr₂O₄. At temperatures below 505 °C, the high-temperature environment leads to a certain reduction in friction coefficient. With a further increase in temperature, the lubricating effect of the oxides further contributes to the decrease in friction coefficient. Meanwhile, the wear rate of the coating continuously increases with temperature, rising from 2.0×10^-5 mm³/(N·m) at RT to 11.3×10^-5 mm³/(N·m) at 600 °C. At RT, the dominant wear mechanism is fatigue wear. As the temperature increases to 600 °C, the marked decrease in coating microhardness leads to the generation of substantial debris, making abrasive wear the predominant mechanism. In engineering applications, the determination of the amorphous transition temperature of NiCrBSi coatings provides essential data for the design of coating service temperatures and the formulation of heat treatment processes.

Abstract:Binder jetting is a potential low-cost near-net-shape forming method for large-scale complex-shaped W-Ni-Fe alloy components. Nonetheless, it faces challenges such as billets cracking during curing and debinding. Developing the manufacturing process for high-strength W-Ni-Fe alloy billets is an inevitable requirement. In this study, a series of 93W-4.9Ni-2.1Fe alloy billets were prepared by binder jetting with variables including powder particle size, binder material, binder saturation, and single-layer printing thickness. The compressive strength of the billets was tested, and the effects of material characteristics and process parameters on the quality of 93W-4.9Ni-2.1Fe billets was analyzed. The results show that the compressive strength of binder-jetted 93W-4.9Ni-2.1Fe alloy billets exhibits a negative correlation with powder particle size and single-layer printing thickness, which improves continuously with the increase in higher binder saturation. By employing a water-based alcohol binder, the 93W-4.9Ni-2.1Fe powders with a D₅₀ particle size of 7.65 μm, a binder saturation of 70%, and a single-layer printing thickness of 60 μm, the binder-jetted 93W-4.9Ni-2.1Fe alloy billets achieve a balance between good strength and dimensional accuracy.

Abstract:Accident tolerant fuel (ATF) can further improve the safety and economics of commercial nuclear reactors. At present, Cr-coated zirconium alloy cladding is the most promising candidate for near-term industrial application as an ATF cladding. This paper provides a comprehensive review of Cr-coated zirconium alloy cladding, covering its development status, preparation processes, microstructural characteristics, and service performance. Initially, the worldwide development of Cr coating is introduced. Subsequently, the main preparation processes of Cr coatings, including cold spraying, laser cladding, and physical vapor deposition, are described, and the characteristics and microstructure of different processes are analyzed. Afterwards, the corrosion, irradiation, and mechanical properties of Cr-coated zirconium alloy cladding are summarized, and the corrosion oxidation mechanism, irradiation damage mechanism, and plastic deformation mechanism are deeply analyzed. Finally, the key challenges in current research are identified, and future development directions are proposed.

Abstract:High-entropy alloys (HEAs) are composed of five or more principal elements in equimolar or near-equimolar ratios, and exhibit distinctive properties including high-entropy effects, lattice distortion, sluggish diffusion, and cocktail effects. Platinum-group metal high-entropy alloys (PGM-HEAs) combine outstanding catalytic activity with superior corrosion resistance, and also exhibit notable functional properties in superconductivity and magnetocaloric refrigeration, which have rendered them a significant branch of HEA research. This review surveys the state of the art in PGM-HEAs, proceeding from compositional design through fabrication techniques to functional applications. In terms of compositional design, the review outlines multi-scale design methods based on phase-diagram calculations, first-principles calculations, and machine learning-assisted screening, with emphasis on the application of machine learning in adsorption energy prediction. For bulk PGM-HEAs, major fabrication techniques including vacuum melting, powder metallurgy, and laser additive manufacturing are summarized, followed by an assessment of research progress concerning mechanical properties, superconductivity, shape memory effect, and magnetocaloric performance. For nanostructured PGM-HEAs, both “top-down” and “bottom-up” synthesis strategies are categorized, and their application and mechanisms in electrocatalytic reactions, including fuel cells and water electrolysis for hydrogen production are discussed in detail. Finally, persistent challenges related to high material cost, scalable production, and compositional homogenization are analyzed, while future research directions including low-PGM alloy design, green synthesis methodologies, and multi-scale computational modeling are discussed.

Abstract:Graphite is widely used in aerospace, nuclear energy, and electronic heat dissipation due to its many excellent properties, and it plays an increasingly important role in modern industry. Achieving reliable connections among graphite, alloys, and metals is of great significance for achieving complementary performance of heterogeneous materials and expanding application fields. However, there are some urgent problems to be solved in the welding process between graphite and dissimilar materials, mainly including poor wetting of the brazing material, control of formation of brittle phases at interface, and alleviation of interface stress. This study reviews the research progress on brazing of graphite, alloys, and metals, and elaborates on the effects of direct and indirect brazing methods on the joint performance of graphite and metals. It focuses on analyzing the solutions to the problem of poor wetting of graphite using various brazing methods, and finally provides prospects for the connection of dissimilar materials.

Abstract:Inertial friction welding (IFW), as an advanced solid-state welding process, has been widely applied in the manufacturing of aero-engine rotor components due to its green, efficient, and superior welding quality. This review systematically summarizes the research achievements in recent years regarding the microstructure, mechanical properties, and numerical simulation of IFWed joints of aviation titanium alloys and superalloys. It also summarizes the large-tonnage, high-precision IFW equipment for aerospace and their application in various types of advanced aero-engine rotor components. Future research should focus on addressing key technical challenges in the engineering application of new materials and new structures. This review also presents prospects for future development, highlighting that continuous innovation of IFW technique will provide critical technical support for achieving the high performance, lightweight design, and enhanced reliability of the new generation of aero-engines.