AlSi10Mg is a frequently utilized aluminum alloy known for its low density, high specific strength, strong energy absorption capability, and good impact resistance. It holds significant appeal in the aviation, automotive, and machinery sectors and is particularly used as protective structures for critical aerospace components. In particular, in complex application scenarios, these protective structures are often subjected to impacts from foreign objects at different loading rates. This leads to diverse forms of damage and unpredictable damage patterns, ultimately jeopardizing key components and disrupting the normal operation of associated parts. Herein, through extensive research into the preparation, properties, and factors influencing AlSi10Mg porous structures, an understanding of the intrinsic relationship between the porous metal structure and its properties is revealed. This is important for improving material properties, expanding application possibilities, and promoting scientific and technological advancement. Exploring the application potential of AlSi10Mg porous structures across various fields offers theoretical support and technical guidance for its practical utilization. Moreover, this will provide new insights and methodologies for the future development of aluminum alloys with porous structures. By conducting a series of experimental studies, theoretical analyses, and numerical simulations, the load-bearing capacity, damage modes, and damage mechanisms of the optimized AlSi10Mg porous structures under different loading strain rates were examined. The rusults showed that the predominant damage modes in AlSi10Mg porous structures are fracture and shear damages, and the mechanical behavior is unaffected by the loading strain rates. The combination of structural damage analysis and high-precision numerical simulations revealed that under axial compressive loading, the AlSi10Mg porous structures experiences shear damage caused by relative misalignment along the diagonal cross section. This failure mode is the direct cause of the fracture damage of the structure. Furthermore, combined experimental and theoretical analyses indicated that the energy absorption properties of the AlSi10Mg porous structures are maintained at low and medium strain rates when the strain of the structures is less than 10%. When the strain exceeds 10%, the energy absorption properties at medium strain rates slightly improve compared to those at low strain rates. The energy absorption properties of the AlSi10Mg porous structures remain almost unchanged under different strain rates ranging from 378 to 1639 s^-1.

The α + β titanium alloy TC19 (Ti-6Al-2Sn-4Zr-6Mo, mass fraction, %) has shown great application potential in aerospace because of its superior moderate-temperature mechanical properties. The bulk composition of this alloy contains Al, Sn, Zr, and Mo, which are the main alloying elements in the field of high-temperature titanium alloys. Compared with Ti, Al and Sn, which are characterized by lower melting points and densities, can be easily volatilized during vacuum arc remelting (VAR). In addition, Zr has a higher density, and Mo has a higher melting point and density compared with Ti. Therefore, controlling the chemical homogeneity either in the macro- or micro-scale for industrial-scale titanium alloy ingot with complex compositions is challenging. In this study, the macrosegregation behavior and mechanism of Zr and Mo were investigated systematically in a TC19 industrial-scale ingot (ϕ720 mm × 1160 mm) by using a directional solidification technology where samples were solidified under a constant-temperature gradient of approximately 200^oC/cm and a wide range of withdrawal rates (solidification rate) from 3 mm/h to 150 mm/h. Result shows an evident macrosegregation of Zr and Mo, which is primarily attributed to the difference in the solidification rate during solidification. Zr as the negative segregation element was pushed to the front of the solid-liquid interface continuously, whereas Mo as the positive segregation element was enriched in the solid phase at the solid-liquid interface. Consequently, the content of Zr is relatively lower at the center equiaxed crystal zone but higher at the top casting riser in the TC19 industrial-scale ingot. However, Mo exhibits the opposite trend in comparison with Zr. The degree of element segregation decreased with the increase of the solidification rate. Moreover, the “crystal rain” caused by the density difference between liquid and solid phases as well as buoyancy would promote the macrosegregation in industrial-scale ingots. The Lorentz force arising from electromagnetic stirring is the main driving force for the flow of the molten pool during VAR. Electromagnetic stirring plays an important role in accelerating the melt flow in the molten pool, and the strong melt flow is favorable to break the correspondence between the grain structure, thereby weakening macrosegregation. Therefore, the low-temperature gradient and low solidification rate, that is, near equilibrium solidification conditions, primarily cause the macrosegregation in TC19 titanium alloy industrial-scale ingots.

An AZ31 Mg alloy sheet with bimodal non-basal texture exhibits good formability at room temperature. However, its initial yield stress (YS) is relatively low during uniaxial tension along the rolling direction (RD) at room temperature, which limits its potential for further application. Recent studies have demonstrated that introducing {10\overline{\mathrm{1}}2} extension twin (ET) through predeformation can improve the mechanical properties of Mg alloy sheets with a basal texture at room temperature. However, the predeformation process for Mg alloy sheets with non-basal texture has rarely been investigated, along with their subsequent plastic deformation behavior at room temperature. Therefore, to investigate the room temperature deformation behavior and microstructure evolution of an AZ31 Mg alloy sheet with bimodal non-basal texture after predeformation, this work exerted a 5% thickness reduction on the sheet via cryogenic rolling. Then uniaxial tension experiments at room temperature and microstructure characterization experiments were conducted to illuminate the effect of predeformation on the mechanical behavior and microstructure evolution of the fabricated sheet. The findings indicate that when loaded along the RD, the YS and fracture elongation (FE) of the predeformed sample are 212.5% larger and 56.9% smaller than those of the non-predeformed sample. When loaded along the transverse direction (TD), the YS and FE of the predeformed sample are 6.7% smaller and 37.9% larger than those of the non-predeformed sample. The difference in YS in the predeformed samples is primarily attributed to easier activation of basal <a> slip in grains with a TD texture component in the TD sample than in grains with a bimodal non-basal texture component in the RD sample. The difference in FE in the predeformed samples is due to the inhibition of the expansion of preexsiting {10\overline{\mathrm{1}}2} ETs in the RD sample, resulting in the early occurrence of {10\overline{\mathrm{1}}1} compression twins (CTs). In comparison, the expansion of preexsiting {10\overline{\mathrm{1}}2} ETs can be effectively performed in the TD sample. Additionally, some {10\overline{\mathrm{1}}1}-{10\overline{\mathrm{1}}2} double twins (DTs) would be activated at the later stage of tensile deformation to sustain and/or accommodate local plastic strain.

As a new antibacterial metal element, Ga is widely used in the medical field and always added to compounds in ionic form to form Ga complexes for medicinal use. However, related research on the mechanical properties, antibacterial properties, and antibacterial mechanism of Ga-bearing alloys is still very limited. In this work, the effect of Ga addition on the mechanical properties of 304L austenitic stainless steel (304L SS) after solution treatment was investigated via metallographic observations and tensile strength and hardness tests. Moreover, the antibacterial properties of Ga-bearing 304L stainless steel (304L-Ga SS) were tested using plate counting and the activity state of bacteria on the surface of the material was detected using SEM. Based on the known Ga ion sterilization principle, the antibacterial mechanism of 304L-Ga SS was preliminarily discussed using the reactive oxygen species (ROS) fluorescence reaction and ion dissolution results of the material in different solution tests. Results showed that the structure of 304L-Ga SS is still austenitic like that of 304L SS. The Ga addition increases the yield strength and elongation of the material but decreases its tensile strength and hardness. The change in strength and elongation is the result of the synergistic effect of the increase in stacking fault energy and the solid solution strengthening. The Ga addition also slightly increases the lattice constant of stainless steel due to the replacement solid solution effect. In the passive film of 304L-Ga SS, Ga exists in alloy form. Because of their similarity to Fe ions, Ga ions dissolved from Ga in the passive film are inhaled into bacteria cells and cause high expression of ROS in the bacteria, causing oxidative stress, and bactericidal effect. Contact sterilization is one of the main bactericidal mechanisms of 304L-Ga SS. Adequate contact between the bacteria and stainless steel improves the dissolution of Ga due to the proton (H⁺) depletion reaction in the bacteria. At the same time, the production of additional ROS during the proton consumption reaction further enhances the antibacterial effect.

M50 steel is primarily used for manufacturing the main shaft bearings of aero engines. However, the fatigue property of M50 steel affects the service life of shaft bearings owing to their operation in the environment with high temperature, high rotation speed, and high contact stress. Inclusions and large-sized carbides are proved to be the primary reasons that cause fatigue cracking. Nevertheless, inclusions in M50 steel and fatigue failure due to inclusions are substantially reduced with the rapid development of metallurgical technology and metallurgical equipment in recent years. M50 steel contains high fractions of Cr, Mo, and V elements, which are easily enriched and can form primary carbides. The primary carbides in M50 steel are hard and brittle and cause stress concentration under external load, thereby accelerating the initiation and propagation of fatigue cracks. Currently, the large-sized primary carbides in M50 steel play an important role in reducing the service life of bearings and have attracted substantially research attention. The present investigation focuses on the decomposition mechanism of large-sized M₂C primary carbide in M50 steel to reveal the carbide-refinement mechanism during high-temperature heat treatment. In addition, M₂C primary carbide in M50 steel was systematically characterized by SEM, EPMA, and TEM, and its decomposition mechanism at 1160-1250^oC was studied. The difference in chemical composition of different M₂C primary carbides and its effect on the decomposition mechanism were also explored. Three forms of M₂C carbides in M50 steel were revealed: the rod-like carbide, the lamellar-like carbide, and the block-like carbide. In these three M₂C carbides, the content of Fe increased, while the content of Mo decreased successively. The difference in chemical composition and morphology of these three M₂C carbides led to the different microstructure-evolution process when heat-treated at elevated temperature. When the steel was heat-treated at 1160-1180^oC, only the M₂C carbides with high Fe content decomposed and a few of the carbides transformed to MC carbide. The growth rate of MC carbide was extremely low at this temperature. When the steel was heat-treated at 1210^oC, most of the M₂C carbides decomposed after 20 h. The growth rate of MC carbide also increased rapidly, and a large amount of large-sized MC carbides were found. Further heat treatment of steel at 1250^oC resulted in the decomposition of all M₂C carbides and the absence of large-sized primary carbides in the microstructure. However, a large amount of newly born M₂C carbide, formed due to the melting of the matrix and re-solidification, were found in the microstructure.

High nitrogen austenitic stainless steels (HNASSs) are widely used for their good wear resistance and high strength, plasticity, and corrosion resistance. Among these steels, 1Cr22Mn16N HNASS improves the cost effectiveness because of the incorporation of a N element in place of the expensive Ni element. In addition, the overall mechanical properties of the steel are further improved because of the solid solution-strengthening effect of the N element. However, the traditional welding methods such as arc welding, tungsten gas shielded welding, and friction stir welding are not suitable for 1Cr22Mn16N HNASS welding because of the different solubility of N in the liquid and solid phases. N easily spills out during the welding process, which considerably degrades the mechanical properties of the welded joints. Therefore, a new welding method needs to be explored to solve the problems in 1Cr22Mn16N welding. In this work, the bonding technology of plastic deformation was introduced to solve the poor performance problems of 1Cr22Mn16N HNASS welded joints. The experiments were conducted through the Glebble 3500 thermomechanical simulation in the temperature range of 1050-1250^oC and a strain range of 10%-40% with a strain rate of 0.1 s^-1. The microstructure evolution of the bonding interface was characterized and investigated using OM, EBSD, and TEM; the interface healing mechanism was discussed, and the bonding strength of the joint was evaluated by tensile test. The results show that the bonding level of the interface substantially increases with the increase in deformation and temperature. When the deformation temperature reached 1200^oC and the strain reached 40%, the mechanical properties of the bonding interface reached up to the same level as the matrix. During the process of deformation, discontinuous dynamic recrystallization (DDRX) occurred at the interface because of thermomechanical coupling; meanwhile, dislocations accumulated and entanglement occurred under the action of stress, forming a large number of subgrain boundaries within the original grain boundaries near the interface, which, lead to continuous dynamic recrystallization (CDRX). The healing of the interface was achieved by the synergistic effect of CDRX and DDRX.

The service temperature of K4169 superalloy aeronautic turbine disks and other important aeronautic components is generally below the equi-strength temperature, and grain refinement can significantly improve the service performance. Compared with the conventional gravity casting process, the centrifugal casting process as a dynamic grain refinement method plays an important role in grain refinement, feeding, and molten filling of the casting. A precision casting with typical structural characteristics of the K4169 superalloy was prepared using the centrifugal casting process with the mold positive and negative rotation method and the conventional gravity casting process, respectively. The alloy microstructure, element segregation, secondary phase distribution, fracture microstructure, and mechanical properties at room temperature were compared and studied under two process conditions. The as-cast structure of the K4169 superalloy can be significantly refined using the mold positive and negative rotation method. The grain refinement of the experimental alloy was the most significant when the casting mold was reversed for 4 s, and the grain size under gravity casting decreased from (5.37 ± 0.21) mm to (0.27 ± 0.01) mm. Also, the primary phase of the experimental alloy was broken and the dendrite morphology was degraded that the coarse dendrites were replaced by broken dendrites and rose-shaped crystals after positive and negative rotations. Compared with unidirectional rotation, the segregation of alloying elements decreased, the number of Laves phases in the solidified structure was reduced, and the number of carbides was slightly increased. The tensile strength of the K4169 alloy at room temperature under the positive and negative rotation duration of 4 s was 31.4% higher than that under conventional gravity casting.

In recent years, refractory high-entropy alloys (RHEAs) have gained widespread attention owing to their high structural stability and excellent mechanical properties at both room and elevated temperatures. However, their wear resistance at room temperature is often poor due to their fragility. In this study, the effect of adding small amounts of silicon (Si) to NbMoZrV RHEA on its tribological properties and wear mechanism at room temperature have been studied using various techniques including tribometer, SEM, and XPS. The results showed that adding a moderate amount of Si induced the homogeneous precipitation of a eutectic structure composed of Zr-Zr₃Si phase at the bcc matrix grain boundary. This eutectic structure significantly improved the hardness and wear resistance of the NbMoZrVSi_0.1 RHEA. Unlike the poor tribological behavior observed in NbMoZrVSi_0.05 and NbMoZrVSi_0.2 RHEAs, the NbMoZrVSi_0.1 RHEA exhibited stable coefficient of friction and wear rate under dry sliding wear test at room temperature with varying normal loads. The Zr-Zr₃Si eutectic structure effectively inhibited the initiation and propagation of cracks and brittle spalling during the sliding wear test, resulting in only slight abrasive wear of the NbMoZrVSi_0.1 RHEA. Moreover, the mechanism promoted the subsequent homogeneous oxidation of the worn surface.

The addition of Ni to cobalt-based alloys can form the γ′ phase, which can significantly improve their mechanical properties and high-temperature oxidation resistance. The oxidation behavior of quaternary Co-20Ni-8Cr-xAl (x = 3 or 5, mass fraction, %) alloys was investigated in 1.013 × 10⁵ Pa O₂ at 800, 900, 1000, and 1100^oC. Also, the effects of Al and/or Cr contents and temperature on the oxidation properties of the alloys were explored by analyzing the oxidation kinetics of the alloys and the cross-sectional morphology characteristics of the scales, revealing the oxidation mechanism of these alloys. After oxidation, both the alloys formed complex scales with irregular thickness and composition. Alumina scales were generated for each alloy at 800, 900, and 1000^oC and only for Co-20Ni-8Cr-5Al at 1100^oC. The increase in temperature from 800^oC to 900^oC has a negative effect on the oxidation resistance, resulting in greatly accelerated oxidation rates. Conversely, that from 1000^oC to 1100^oC has a positive effect on the oxidation of the two alloys, causing a decrease in the oxidation rate. The oxidation rate of the Co-Ni-Cr-Al alloy decreases when the Al content in the alloy is increased from 3% to 5%, but 5% is still not sufficient to form continuous alumina scales. The simultaneous presence of Cr and Al is beneficial to reducing the oxidation rate of the quaternary Co-Ni-Cr-Al alloys compared with the ternary Co-Ni-Al alloy with the same Al content.

In the advanced-packaging industry, (111)-oriented nanotwinned copper ((111)nt-Cu) offers several advantages over common randomly oriented equiaxed polycrystalline Cu (C-Cu), including high strength, excellent elongation, and promising electrical conductivity. In recent years, (111)nt-Cu has shown potential for becoming a C-Cu replacement in under-bump metallization and redistribution layer applications. This shift is attributed to the escalating demand for thermal stability and enhanced electrical and mechanical performances of Cu materials amid the rapid transition toward three-dimensional electronic packaging. This study proposed that (111)nt-Cu exhibits better oxidation resistance than C-Cu after aging in air at 250^oC. The thickness and composition of (111)nt-Cu and C-Cu oxide layers were analyzed respectively via TEM and XPS. Various grain boundaries on the surface of the prepared (111)nt-Cu and C-Cu substrates were evaluated using EBSD and FIB techniques. The morphology at the interface between the two Cu substrates and their oxide layers was characterized using SEM. In addition, the solderability of the oxidized layers was assessed by measuring the wetting angles and spreading areas of the involved Sn-Cu joint structures. Results show that when the oxidation time was 9 min, the thickness of the (111)nt-Cu oxide layer was 43.2% lesser than that of the C-Cu oxide layer. After 12 min of oxidation, the contact angle between Sn and oxidized (111)nt-Cu was 26.7% smaller than that between Sn and oxidized C-Cu, while the spreading area of Sn on (111)nt-Cu was 24.6% larger than that of Sn on C-Cu. After oxidation, the surface layers of both Cu substrates comprised CuO and Cu₂O nanocrystals coexisting within the same layer. Because oxidation is closely related to the diffusion of Cu atoms through grain boundaries, the grain boundaries of both Cu substrates were investigated in the natural-growth direction. The results show that compared to C-Cu, (111)nt-Cu has a lower surface energy and smaller area fraction of high angle grain boundaries, effectively limiting the outward-diffusion rate of Cu atoms.

High-quality superconducting joints play a key role in the construction and stable operation of superconducting magnets. The preparation of superconducting joints for Nb₃Sn wires is often affected by the presence of an internal tantalum barrier layer. Thus, this study examined the effectiveness of different removal methods of the Ta barrier layer in Nb₃Sn superconducting wire. For this, the superconducting wire prepared by an internal tin method was considered as the experimental object, and the corrosion behavior and characteristics of the wire in HF solution, HF atmosphere, mixed solution of HF and H₂O₂, and mixed solution of HF and HNO₃ were investigated. The microstructure and corrosion morphology of the wire were analyzed using SEM and OM. Furthermore, high-purity Ta sheets were selected as the research object, and corrosion experiments were carried out in the above-mentioned media. The corrosion morphology, phase structure, and valence state of the elements of the specimens were analyzed using OM, XRD, and X-ray photoelectron spectroscopy (XPS) to reveal the corrosion mechanism of Ta. The results showed that the corrosion of the Ta layer was the fastest in the mixed solution of HF and HNO₃, followed by the mixed solution of HF and H₂O₂, the HF atmosphere, and then the HF solution. Based on the effect after corrosion, the mixed solution of HF and H₂O₂ was found to be the best method to remove the Ta barrier layer in Nb₃Sn superconducting wire. Moreover, the presence of an oxidation agent can accelerate the corrosion rate of Ta by HF by accelerating the formation of Ta₂O₅ film on the Ta surface.

Nanocomposites comprising of graphene nanoplatelets (GNPs) and aluminum (Al) have gained tremendous interest over the past few decades owing to their exceptional mechanical, thermal, and electrical properties. The microstructure of GNPs in these composites, such as dispersion, and orientation, significantly affects the loading capacity and thermal properties. However, previous studies on the mechanical properties have overshadowed investigations into the thermal expansion coefficient of GNPs/Al composites with different microstructures. In this study, a three-dimensional model of microscopic GNPs/2009Al composites was established using the finite element method and the software ABAQUS. The effects of the distribution, geometric configuration, and volume fraction of graphene nanoplatelets on the thermal expansion coefficient of the composite were analyzed. Results show that the thermal expansion coefficient of the composite is less affected by the distribution form of graphene nanoplatelets. However, when the distribution form of graphene nanoplatelets is 2 clusters, the thermal expansion coefficient is smaller than other distribution forms. Moreover, the geometry and volume fraction of graphene nanoplatelets have a significant effect on the thermal expansion coefficient. An increase in the volume fraction of graphene nanoplatelets leads to a decrease in the thermal expansion coefficient of the composites. When the volume fraction of graphene nanoplatelets in the composite is 2.5% and the aggregate distribution is bundled, the thermal expansion coefficient decreases the most (by about 27%) compared to the matrix. By comparing with experimental results, the validity of the model is verified. The conclusions of this study can provide a theoretical basis for designing and optimizing the configuration of graphene nanoplatelets/aluminum matrix composites.

With the rapid development of high-speed and heavy-haul railways, the reliability of railway track service performance is becoming increasingly important. Bainite rail steel is widely known for its excellent properties, but solute microsegregation during solidification of molten steel affects the quality of continuous casting bloom, which can damage bainite rail steel components during service. Therefore, studying solute microsegregation of bainite rail steel during the continuous casting process is necessary. Solute microsegregation in steel occurs when solute redistributes between solid and liquid phases during solidification of molten steel. The factors that influence solute microsegregation include the equilibrium distribution coefficient of solute elements at the solid-liquid interface, cooling rate, reverse diffusion strength of solute elements in the solid phase, and dendrite coarsening. Among them, the reverse diffusion strength of solute elements in the solid phase and dendrite coarsening are two important factors that cannot be ignored. In this study, a model of solute microsegregation is established, which takes into consideration both δ/γ phase transformation and dendrite coarsening during the solidification process of bainite rail steel. The effects of cooling rate and C, Mn, S, and P contents on interdendritic solute microsegregation, zero strength temperature (ZST), and zero ductility temperature (ZDT) of steel are analyzed. The results show that S and P are more likely to segregate between dendrites compared to other elements in bainite rail steel. The effect of cooling rate on the microsegregation of solute elements varies with solid fractions. When the solid fraction is 0.99, the segregations of Si, Mn, Cr, Ni, Mo, P, and S increase differently with the increase of cooling rate. C content mainly affects the solidification mode of steel, which then affects the segregation behavior of other elements during solidification. C content has a more significant effect on the microsegregation of S and P compared to other elements in bainite rail steel. In contrast, the contents of Mn, P, and, S have little effect on the microsegregation of other solute elements. The increase in C and Mn contents result in a decrease in ZST and ZDT. However, with an increase in cooling rate and S and P contents, ZST has little change, and ZDT decreases significantly.