As emerging advanced materials, metallic glasses demonstrate impressive high strength (approaching the theoretical strength of the material), fracture toughness, corrosion resistance, and thermoplastic-forming ability because of the absence of long-range atomic periodicity, making them potentially replace commercial materials for micro-electromechanical system applications. Although they possess high hardness, their structural instability upon wearing can cause structural relaxation or crystallization, leading to poor tribological behaviors. Inheriting the advantages of conventional metallic glasses and high-entropy alloys, high-entropy metallic glasses have recently attracted considerable attention. Compared with conventional metallic glasses, one prominent characteristic of high-entropy metallic glasses is higher structural thermostability, i.e., reduced devitrification behavior upon heating, which directly affects its respondent behavior in the thermal-stress coupling field. However, the effect of the structural characteristics of high-entropy metallic glasses on wear resistance, which determines the service life of moving parts under actual working conditions, remains unknown. In this study, the nanoscratch behavior of the TiZrHfCuBe high-entropy metallic glass at different scratching and loading rates was investigated based on nanoindentation and nanoscratch technologies. Moreover, the relationship between the special structural characteristics due to high mixing entropy and the nanotribological properties of the TiZrHfCuBe high-entropy metallic glass was studied. The results show that the microstructure of the TiZrHfCuBe high-entropy metallic glass is uniformly composed of a stiff matrix with sparse defects (i.e., free volumes), and the nanohardness in different regions is close to 90% of the theoretical value. In the nanoscratch experiment, the scratching depth of the TiZrHfCuBe high-entropy metallic glass remained unchanged with increasing scratching rate, but the residual scratching depth gradually decreased. This is attributed to the fact that the increase in the scratch rate retards the activation of the shear transition zone and the subsequent nucleation and expansion of shear bands in the microstructure. This eventually reduces the plowing coefficient and residual scratching depth during the scratch process. However, in the nanoscratch experiment under variable force loading, the hysteresis effect of the shear transition zone activation and the subsequent shear deformation could be relieved by increasing the loading force, thereby increasing the plastic plowing coefficient and scratch depth.

Eutectic high-entropy alloys (EHEAs), as a typical kind of in situ composite, have become a potential alternative for conventional alloys because of their advantages in high-entropy alloys and eutectic alloys. Casting is the conventional preparation method of EHEAs, which is a well-established process with low production efficiency. Laser powder bed fusion (LPBF) is an economical and effective preparation technology that provides a novel way to directly form fine and complex EHEA components. In this study, considering the different application requirements and technical characteristics, AlCoCrFeNi_2.1 EHEA was prepared by vacuum induction melting and LPBF, respectively. The effect of the preparation process on the microstructure of the alloy was investigated. In addition, tensile properties of the samples at 20, 500, and 700°C were investigated. Results showed that as-cast and LPBF-formed AlCoCrFeNi_2.1 exhibited a eutectic structure composed of alternating fcc and bcc/B2 phases. The high heating and cooling rates during the LPBF process were conducive to the formation of ultrafine and uniform eutectic lamellae, which significantly reduced element segregation. During tensile deformation at room temperature, considering the strong phase boundary strengthening and dual-phase synergistic deformation, the ultimate tensile strength of the LPBF-formed sample was enhanced by about 28% compared with that of the as-cast sample, and a satisfactory elongation of 10% was obtained. At 500°C, the mechanical properties of the as-cast and LPBF-formed samples decreased probably because of the severe phase transformation in the alloy. When the testing temperature was increased to 700°C, the mechanical properties of the as-cast sample continued to decrease. The LPBF-formed samples showed a low tensile strength and superior elongation that should be attributed to the eutectic lamellae sliding along the phase boundaries at high temperatures. Meanwhile, the fracture mechanism of the LPBF-formed sample was dominated by ductile fracture. This work could provide a theoretical basis for the optimization of the microstructure and mechanical properties of EHEAs, thereby promoting their industrial application.

Aero-engine turbine blades are operated under harsh conditions such as high temperature, pressure, and load. Therefore, weak grain boundaries at high temperatures should be eliminated from the turbine blades, whereas convection channels inside the blades should be added to dissipate heat. Achieving integrated manufacturing of specialized microstructure in complex components has been a long-term research priority in turbine blade manufacturing. Nickel-based single-crystal superalloys are key materials for manufacturing single-crystal turbine blades for aero-engines, and selective laser melting (SLM) is feasible and technically advantageous for manufacturing complex components with single-crystal microstructures. Owing to the extremely high temperature gradient and scanning speed during SLM, the melt pool is unstable, thereby interrupting directional crystal growth. The metallurgical environment of SLM is further complicated by the large number of overlapping tracks and stacking layers. The quality of the overlaps is critical for the integrity of the single-crystal structure during SLM. Herein, the effects of scanning hatch (h = 0.06, 0.09, 0.12, and 0.15 mm) on the melt track morphology, metallurgical defects, crystal orientation, and microstructure of DD491 fourth-generation nickel-based single-crystal superalloy were investigated. Directionally solidified and solution-aged DD6 single-crystal superalloy rods were used as the substrate, and DD491 powder was coated to a thickness of 40 μm. Electron backscatter diffraction was used to characterize the crystal orientation of the samples. Results show that low power/low speed (S1) and high power/high speed (S4) combinations of laser power and scanning speed provide geometrically and metallurgically stable conditions for directional crystal growth, and the grains at the bottom of the melt track can orient the substrate to achieve [001] directional growth. Different types of crystal orientation defects were observed in different regions, including equiaxed stray grains in the top middle region, [010] and [100] columnar stray grains in the top side regions, and small orientation deviation in the internal region. The scanning hatch affected the crystal orientation in the overlapping regions mainly through the remelted proportion of the old melt pool and the substrate microstructure of the new melt pool during solidification. The higher overlapping ratio with a smaller scanning hatch was beneficial for reducing stray grain defects on both sides of the melt tracks. The role of residual heat on solidification conditions was related to the heat gradient vector of laser input, and multitrack overlapping samples under the S1 process accommodated higher residual heat without causing orientation deviation in the overlapping regions. The multitrack overlapping samples under S1, h = 0.06 and0.09 mm, had maximum pole densities along the y-z plane as high as 47.66 and 46.85, respectively, exhibiting a typical [001] single-crystal structure.

Inconel 718 alloy is widely used in aeronautical fields owing to its excellent mechanical properties and high-temperature resistance. Hot isostatic pressing (HIPing) is a powder metallurgy (PM) processing technology that produces near or net-shape components and solves the problems of macro-segregation and microstructure inhomogeneity. However, the application of PM Inconel 718 alloys has been limited by prior particle boundaries (PPBs), which can negatively impact mechanical properties, such as elongation at elevated temperatures and impact properties. To address this issue, the formation of PPBs can be suppressed during HIPing, or they can be eliminated through subsequent processing. Pre-alloyed powder of Inconel 718 was prepared using the electrode induction melting gas atomization (EIGA) method, and PM Inconel 718 alloys were prepared through the HIPing route. The resulting compacts were subjected to special high-temperature heat treatment, and their mechanical properties were tested. The mechanical properties of PM Inconel 718 test bars were found to be comparable to those of the wrought version of the alloy. However, large and complex components of PM Inconel 718 can contain undesirable PPBs due to mold shielding and insufficient degassing, resulting in poor ductility and impact properties after standard heat treatment. Special high-temperature heat treatment can effectively eliminate the PPBs in the compacts, leading to a substantial improvement in tensile ductility and impact properties. This improvement makes it possible to prepare large and complex components through HIPing with improved mechanical properties.

Zinc-metal alloys with ferrous group metals such as Ni, Co, and Fe have been used for industrial applications due to their better corrosion performance compared to pure Zn. Among them, ternary Zn-Ni-Co alloys, which have superior corrosion resistance and magnetic features, have attracted extensive attention, and have been used as functional films in electro-mechanical system (EMS) devices and magnetic recording media. However, large differences in the reduction peak potential between Zn²⁺, Ni²⁺, and Co²⁺ restrict their codeposition because Zn-competitive adsorption hinders the discharge transfer of Ni²⁺ or Co²⁺. In view of the aforementioned statements, the effects of molar concentration ratios of Ni²⁺ : Co²⁺ : Zn²⁺ and the ascorbic acid (H₂Asc) concentrations in the bath on the surface features and textures of the Zn-Ni-Co alloys were assessed and characterized using FE-SEM, XRD, etc. Results showed that under the optimized condition of Ni²⁺ : Co²⁺ : Zn²⁺ = 4 : 5 : 1, the Ni content in the Ni-Co-Zn deposits reached 12.2%, which was instrumental in grain refinement. From the cyclic voltammetry curves, the potential of the reduction peak positively shifted from -1.47 V to -1.28 V, validating better codeposition with an appropriate H₂Asc concentration. SEM observations depicted a cauliflower-like texture with a crystal size of ~300 nm at a minimum growing stress of 9.04 MPa for the samples with 5 g/L H₂Asc concentration. From EDS analysis, with increasing H₂Asc concentration from 1 g/L to 5 g/L, the Ni + Co content in the Ni-Co-Zn deposits gradually increased but their Zn content decreased, which was attributed to the addition of H₂Asc in the form of [ZnHAsc]⁺ to offer more active sites for Ni or Co growth. Intermetallic compounds such as γ-Ni₅Zn₂₁, CoZn₁₃, and Ni₃Zn₂₂ were determined using XRD. The anticorrosive behavior was evaluated via potentiodynamic polarization (Tafel) tests in a 3.5%NaCl solution. The free corrosion potential (E_corr) positively shifted by ~200 mV for the samples with 5 g/L H₂Asc concentration and their corrosion current density (i_corr) has declined about 75% than those of the samples without H₂Asc. EIS results revealed a capacitive arc followed by a diffusion arc for the samples without H₂Asc, indicating pitting corrosion, and an inductive arc attached to a larger-radius capacitive arc for the samples with different H₂Asc concentrations, showing better corrosion resistance. This was due to the coexistence of the γ-Ni₅Zn₂₁ intermetallic phase and insoluble products [Zn(OH)₄]^2- that fully covered the Zn-dissolved active area to complete the corrosive channels via Cl^- diffusion, thus increasing the corrosion resistance of the Ni-Co-Zn alloys.

Corrosion and cavitation erosion are important indicators for evaluating the performance and reliability of hydraulic machinery. Laser metal deposition (LMD), as an important technique for both surface modification and complex component fabrication, is proven to be effective in enhancing the mechanical properties of materials. In this study, 316L stainless steel (316L SS) samples were fabricated using LMD and the effects of laser power, scanning strategy, surface remelting, and build direction on the electrochemical corrosion and cavitation erosion resistance of the LMD-produced samples were systematically studied. The obtained results were compared with those of a wrought counterpart. The corrosion resistance of the LMD-produced samples in a 3.5%NaCl solution was tested via open-circuit potential measurement and potentiodynamic polarization tests. Also, the cavitation erosion resistance of the LMD-produced samples was studied according to different process parameters. The microstructure of the forged 316L SS sample was characterized with uniformly distributed equiaxed grains, whereas the LMD-produced samples exhibited a process-dependent nonequilibrium microstructure consisting of high-/low-angle grain boundaries, tortuous grains, cellular/dendritic substructures, and processing-related defects. The grain size of the LMD-produced 316L SS sample was much larger than that of the forged 316L SS. By increasing the laser power or changing the sample from horizontally built to vertically built, both the grain size and dendritic arm spacing of the material tended to increase. However, when surface remelting and the 90°-rotation scanning strategy were adopted, the changes in the grain size and dendritic arm spacing of the material were obviously different. Results of a microhardness test showed that the dendritic arm spacing can better match the microhardness evolution than the grain size. This microstructural difference also led to a significantly different electrochemical corrosion and cavitation erosion performance from that of the forged 316L SS. Results of an electrochemical corrosion test showed that the corrosion resistance of the LMD-produced 316L SS sample was much better than that of the forged 316L SS, i.e., the polarization resistance (R_p) of the LMD-produced 316L SS sample under different processing increased by about 2-98 times, while the corrosion current density (i_corr) decreased by one to two orders of magnitude. The test results of an ultrasonic vibration cavitation system showed that the cavitation erosion resistance of the LMD-produced 316L SS sample was better than that of the forged 316L SS. However, stress concentration may be induced in local areas such as pores and grain boundaries, which, in turn, facilitate preferentially cavitation damage in these areas. Also, protrusion topography appeared, and gradually disappeared to form a large number of dimples in the subsequent cavitation erosion process. The cavitation erosion resistance of the material mainly depended on its local mechanical properties. The microhardness test results showed that the hardness of the LMD-produced 316L SS sample was significantly higher than that of the forged sample, so its cavitation erosion resistance was significantly improved. However, because of the heterogeneous microstructure and process-related pore defects formed in the LMD-produced samples, the microhardness contour exhibited a spatially nonuniform distribution characteristic; hence, the surface morphology of the LMD-produced 316L SS sample was seriously eroded in some local areas after cavitation.

Macrosegregation is a typical solidification defect formed during vacuum arc remelting (VAR) process. This defect adversely affects the property of ingots as the defect sustains even in the subsequent heat treatment process. In the industrial production of titanium alloys, VAR is repeated thrice to eliminate inclusions and improve the homogenization of composition. However, the evolution of macrosegregation during the different stages of the triple VAR process remains unclear. In this study, the melt flow behavior and macrosegregation of titanium ingots in the multistage VAR process are examined via solidification simulations, considering both buoyancy and electromagnetic force. The results show that the strong fluid flow in the upper part of melting pool eliminates nonuniform concentration along the radial direction of the electrode. In contrast, the nonuniform concentration along the axial direction can be inherited in the sequential ingot. However, with the increase in the depth of melt pool, the sustained melt flow from the bottom to upside can reduce the axial macrosegregation delivery. In addition, the use of the previous ingot directly as the electrode for the subsequent remelting process results in severe macrosegregation. However, turning the previous ingot upside-down at least once during the three-stage VAR process can substantially reduce the macrosegregation. Overall, the simulated macrosegregation of Al and V elements in TC4 ingot agree well with that observed in experiment.

Biodegradable metallic Zn materials are being considered for orthopedic implant applications because of their moderate degradation rate and potential bio-functionalities. Nevertheless, their clinical use is limited due to inadequate osteogenic properties owing to Zn²⁺ burst release, premature mechanical failure caused by non-uniform corrosion, and poor antibacterial ability. Therefore, to overcome these issues, a metal-polyphenol drug-loaded coating was functionalized on the surface using an alternating chemical deposition method out of tannic acid/metformin molecules and active metallic ions via coordination/chelation reactions. The coating was characterized by homogeneous compactness, which enhanced the corrosion resistance of the Zn substrate, adjusted the corrosion mode, suppressed the release of Zn²⁺, and regulated metformin release. The in vitro pre-osteoblasts (MC3T3-E1) culture results showed that the coated Zn samples exhibited excellent osteogenic ability. The antibacterial assays with coated Zn samples demonstrated strong antibacterial efficiency.

The core issue in the study of giant magnetostriction of Fe-Ga alloy thin sheet is to obtain preferential texture through secondary recrystallization. In this work, the evolution of the texture, precipitation, and grain boundary characteristics of an Fe-Ga alloy thin sheet during the annealing process were investigated using XRD, SEM, EBSD, and TEM. The mechanism of the secondary recrystallization of the Goss ({110}<001>) texture in the Fe-Ga alloy thin sheet was analyzed. The results show that the primary recrystallized thin sheet is composed of strong γ-fibers and has a weak Goss texture. Moreover, high-density MnS and NbC precipitates of size 20-40 nm are dispersedly distributed in the matrix grains after primary recrystallization. The coarsening of the precipitates and a decrease in the volume fraction and density weaken the inhibiting force during the annealing process. The density of the precipitates inside the Goss grains is lower than that of the precipitates in the matrix grains with γ-texture during the process from primary recrystallization to secondary recrystallization. Before the occurrence of secondary recrystallization, Goss grains do not exhibit a number and size advantages over the matrix grains but are surrounded by higher-energy grain boundaries than the matrix grains. The differences between the Goss and matrix grains in terms of precipitation and high-energy grain boundary characteristics during primary recrystallization provide an additional driving force for the secondary recrystallization of Goss grains. Therefore, a perfect secondary recrystallization of the Goss texture with a saturation magnetostriction coefficient of 250 × 10^‒6 is produced in the Fe-Ga alloy thin sheet without the introduction of the surface energy effect using a special annealing atmosphere.

As functional metal materials, immiscible alloys demonstrate wide application prospects in industrial and electronic fields. Immiscible alloys with a uniformly distributed minority phase are a potential substitute for the materials applied in the manufacture of electric contactors and wear-resistant automotive components. Understanding the evolution of various microstructures of immiscible alloys and its correlation with their wear behavior is crucial for their industrial applications. Owing to the liquid-phase separation characteristics of binary Cu-Co and ternary Cu-Co-Fe immiscible alloys, segregation occurred or even a layered microstructure was formed by using conventional casting methods, and obtaining a uniform microstructure was difficult, which seriously limited their applications. This study presents a new strategy for inhibiting the liquid-phase separation and improving the properties of immiscible alloys. Under a high magnetic field, the microstructure of an undercooled alloy was changed, affecting its wear behavior. The experimental results reveal that the microstructures of Cu₅₀Co₅₀ and Cu₅₂Co₂₄Fe₂₄ alloys showed dendritic morphology at modest undercooling without a magnetic field, while the microstructure of Cu₅₀Co₅₀ alloy exhibited a core-shell structure and Cu₅₂Co₂₄Fe₂₄ alloy exhibited an eccentric core-shell structure under large undercooling. Moreover, the application of a high magnetic field resulted in the more uniform microstructure of Cu₅₂Co₂₄Fe₂₄ alloy. With the application of a high magnetic field, the second phases generated by the phase separation of Cu₅₀Co₅₀ and Cu₅₂Co₂₄Fe₂₄ alloys were elongated parallel to the magnetic field direction, and the size of second phases in the alloys decreased significantly in the perpendicular field direction, however, the microstructures of the Cu₅₂Co₂₄Fe₂₄ alloy showed a more uniform distribution. Specimens with large undercoolings in Cu₅₀Co₅₀ and Cu₅₂Co₂₄Fe₂₄ alloys exhibited excellent wear resistance regardless of the application of a high magnetic field. Any alloy that examined abrasive and adhesive wear mechanisms during the wear tests was characterized by rough surfaces generated by material detachment and parallel scratches in the sliding direction. Furthermore, the Cu₅₂Co₂₄Fe₂₄ alloy has a high hardness and a relatively uniform distribution of microstructure under a magnetic field, resulting in the best wear resistance.

Aluminum alloys are widely used in the automobile, rail transportation, and aerospace industries owing to their excellent properties such as low density, high thermal conductivity, and high specific strength. Metal additive manufacturing (MAM) enables the high-quality integrated forming of aluminum alloy components. Among the MAM techniques, droplet and arc additive manufacturing (DAAM) is a newly proposed method that offers advantages, such as high efficiency and low cost. In DAAM process, a droplet generation system is designed above the substrate fixed on a three-dimensional motion platform. Below the droplet generation system, an arc heat source with variable polarity is tilted. During the DAAM process, the metal droplets drop vertically and sequentially into the molten pool generated by the arc heat source to realize metallurgical bonding. Layer-by-layer deposition of aluminum alloy components is achieved by moving the substrate. This study focuses on the DAAM process for 2319 aluminum alloy. The temperature field distribution, microstructure evolution, and epitaxial growth characteristics were investigated. First, the temperature field distribution during the deposition process was calculated using the finite element method combined with element birth and death techniques. Based on the temperature field analysis, the solidification parameters at different positions of the molten pool were calculated. These parameters were then substituted into a phase field (PF) model to determine the growth and evolution of the microstructure at different positions in the molten pool. Columnar crystal structures were formed in the bottom and middle regions of the molten pool. From the bottom to the upper part of the molten pool, the temperature gradient decreased and the solidification speed increased. Therefore, columnar crystals to equiaxed transition occurred in the middle and upper regions. Additionally, misorientation angles were introduced in the PF model to investigate the epitaxial growth characteristics of the solidification process. Larger misorientation angles had a more obvious influence on dendrite morphology and were more likely to be eliminated during competitive growth. Finally, the metallographic analysis showed that from the bottom to the upper part of the deposition layer, the microstructure changed from columnar to equiaxed crystals, and the presence of columnar crystal epitaxial growth agreed well with the simulation results.