Digital twin technology has attracted the extensive attention owing to the unique advantages in intelligent manufacturing. In-depth research and widespread applications have been carried out on the conceptual models, theoretical frameworks, and practical deployment. The application of digital twins in metal additive manufacturing is receiving the increasing attention, serving as a bridge connecting the physical and digital worlds. By integrating the multi-physics simulation, internet of things perception, artificial intelligence, and big data analysis technologies, the virtual models precisely mapped to physical entities are constructed to achieve the real-time monitoring of the metal additive manufacturing production process, and to achieve the precise regulation and closed-loop optimization of the entire process, including materials, processes, and structures. The compatibility of digital twin technology with metal additive manufacturing was discussed in this article, the application scenarios of digital twin in metal additive manufacturing were investigated, and the challenges and development trends faced by digital twin and metal additive manufacturing were summarized.
High-entropy alloys (HEAs), designed based on the multi-principal element concept, break through the traditional alloy design strategy dominated by one or two principal elements. Owing to the superior comprehensive properties, including high strength, high hardness, excellent corrosion resistance, and remarkable thermal stability, HEAs have attracted the extensive attention in recent years. With the rapid development of powder metallurgy and additive manufacturing technologies, the powder-metallurgy-processed HEAs have emerged as a research hotspot in the field of advanced materials. Compared with the conventional casting methods, powder metallurgy can effectively improve the compositional homogeneity and microstructural refinement, enable the near-net-shape fabrication, and expand the capability for producing complex components. The fundamental theories and core effects of HEAs were systematically reviewed in this paper, with emphasis on the powder preparation techniques, such as mechanical alloying, gas atomization, electrode induction melting gas atomization, plasma rotating electrode process, and plasma spheroidization, as well as the consolidation and forming technologies, including spark plasma sintering, hot extrusion, hot isostatic pressing, and additive manufacturing. Furthermore, the strengthening mechanisms and performance advantages of powder-metallurgy HEAs in terms of mechanical properties, corrosion resistance, high-temperature stability, and irradiation resistance were summarized. The potential applications in nuclear energy, aerospace engineering, marine environments, and high-performance coatings were also discussed. Finally, the future challenges and development directions, including cost reduction, process optimization, and materials genome engineering design, were proposed.
Ti-based amorphous alloys exhibit the unique disordered structure, combining with the high specific strength, excellent corrosion resistance, and distinctive physicochemical characteristics, which endow them with broad application prospects in aerospace, biomedical engineering, and precision manufacturing. However, the limited glass forming ability and room-temperature brittleness remain the key bottlenecks restricting the engineering applications of Ti-based amorphous alloys. The structural characteristics and the thermodynamic and kinetic conditions for formation of Ti-based amorphous alloys were summarized in this paper, and the detailed introduction to the principles and applicable scenarios of various preparation methods was provided, including melt spinning, copper mold suction casting, mechanical alloying, and powder metallurgy. On this basis, the effects of structural regulation approaches, such as post-heating crystallization, electropulsing treatment, and deep cryogenic cycling treatment, on the microstructure and mechanical properties were systematically discussed, and the central roles of free volume and shear transformation zones in plastic deformation were elucidated. Furthermore, the corrosion behavior and corrosion resistance mechanism of Ti-based amorphous alloys in acidic and physiological environments were introduced. Finally, focusing on the cutting-edge field of irradiation effects, the critical conditions for irradiation-induced crystallization, the regulation mechanism of irradiation on mechanical properties, and the unique surface morphology evolution behavior were thoroughly analyzed.
The aligned short carbon fiber reinforced titanium matrix composites with the carbon fiber mass fractions ranging from 0.3% to 0.9% were fabricated by direct-write 3D printing combined with hot-pressing sintering. The rheological properties of composite slurries and the effects of carbon fiber content on the microstructure and mechanical performances of composites were systematically investigated. The results reveal that the viscosity and shear stress of composite slurries decrease with the increasing carbon fiber mass fraction. Carbon fibers are aligned along the printing direction under extrusion shear field, and the TiC interfacial coating layers form through the interfacial reaction between carbon fibers and Ti matrix during hot-pressing sintering. The tensile strength and yield strength of the composites first increase and then decline with fiber content rising, reaching the maximum values at carbon fiber mass fraction of 0.7%. By contrast, the hardness continuously increases while the elongation after fracture decreases monotonically. The evolution of mechanical properties is governed by the competitive mechanism among fiber directional strengthening, TiC interfacial strengthening, and the proliferation of pore defects at high fiber contents. The surface grooves generated by nitric acid etching and the in-situ formed TiC layers jointly construct a dual interfacial strengthening structure of mechanical interlocking plus metallurgical bonding, which guarantees the efficient load bearing of carbon fibers.
To systematically reveal the influence of rotating speed on the particle size distribution and powder properties of IN625 alloy powders prepared by plasma rotating electrode process (PREP), five rotating speed levels ranging from 18000 to 28000 r·min‒1 were set for PREP experiments. The results indicate that as the rotating speed increases, the particle size distribution undergoes a structural transformation: the proportion of fine powders (‒270 mesh, mass fraction) increases from less than 15% to over 60%, while the span of particle size distribution gradually narrows. The dominant role of ligament disintegration mode in the atomization process is significantly enhanced with increasing rotating speed, and the more sufficient ligament disintegration directly promotes powder refinement. The powder sphericity remains above 0.96 throughout, but the defect type changes from the elongated irregular particles caused by insufficient ligament disintegration at low rotating speed to the satellite particles formed by collision and adhesion of fine and medium particles at high rotating speed. As the rotating speed increases, the oxygen and nitrogen contents (mass fraction) of the as-produced IN625 powders increase slightly, while the flowability and apparent density decrease modestly, which is partially related to the increased proportion of fine powders (−270 mesh). The suitable rotating speed windows were identified for the different particle size requirements: the rotating speeds≥26000 r·min‒1 can achieve a relatively high proportion of fine powders, while 18000~22000 r·min‒1 is favorable for obtaining the as-produced powders with the excellent flowability and apparent density.
Ti(C,N)-based cermets have become the important candidate materials for the conventional and high-temperature structural components due to the excellent comprehensive properties. In recent years, the research on Ti(C,N)-based cermets has gradually shifted from the composition design and fabrication processes to the microstructure control and gradient materials. By introducing the novel binder phases, such as high-entropy alloys and intermetallic compounds, the “core-ring” structure modulation, the synergistic enhancement of strength and toughness, and the construction of gradient structures have been achieved through the advanced techniques as spark plasma sintering, microwave sintering, and additive manufacturing. The recent advances in Ti(C,N)-based cermets were systematically reviewed in this article, regarding binder phase optimization, gradient microstructure control, and green sintering. The low-cobalt/cobalt-free bonding systems, the multi-scale gradient structures, and the regulation mechanisms on the microstructure and properties by atmosphere sintering, spark plasma sintering, and 3D printing were mainly discussed.
The coprecipitation method enables the atomic-level homogeneous mixing of metal ions, effectively mitigating powder composition segregation and enhancing doping uniformity. The non-doped indium zinc oxide (IZO) nanopowders were synthesized by coprecipitation with In:Zn atomic ratio of 1:1 in this study, the effects of final precipitation pH and calcination temperature on phase composition and morphology were investigated, and the optimal process parameters were established. Subsequently, the rare-earth-doped PrIZO, NdIZO, and TbIZO nanopowders were prepared with rare earth (Pr, Nd, Tb):In:Zn atomic ratio of 0.01:1.00:1.00. Thermogravimetric-differential scanning calorimeter (TG-DSC) was adopted to analyze the thermal decomposition, phase transformation, and crystallization behavior of the precursors. Phase structure and composition of both precursors and calcined powders were characterized by X-ray diffraction (XRD). The scanning electron microscope (SEM) and transmission electron microscope (TEM) were utilized to examine the micro-morphology and particle size distribution, while the elemental composition and distribution were verified by energy disperse spectroscopy (EDS) and Fourier transform infrared spectroscopy (FT-IR). The results demonstrate that, the rare earth doping effectively modulates the thermal behavior, crystallization, and microstructure of IZO powders. Uniform, the well-dispersed and high-sphericity doped IZO nanopowders are successfully fabricated, and the influencing mechanism of rare earth elements on the structural and microscopic properties of IZO precursors and calcined powders is clarified.
High-entropy alloys (HEAs) exhibit the outstanding properties, owing to the multi-principal-element design and high-entropy effects. Nevertheless, the conventional forming processes of HEAs fail to produce the complex shapes while maintaining the microstructural uniformity, hindering the industrial application. Additive manufacturing (AM) provides the revolutionary solution for complex component forming and microstructure precision control. The research status of mainstream additive manufacturing technologies used for high-entropy alloy preparation was systematically reviewed in this paper, such as laser powder bed melting and directional energy deposition. The typical systems, microstructure characteristics, mechanical properties, and functional properties of additive manufacturing high-entropy alloys were summarized. The AM technology can refine grains, inhibit harmful phases, promote the formation of metastable phases, and significantly improve material properties through rapid solidification and thermal cycling. However, the challenges still remain, such as complex process parameters, crack sensitivity, high preparation cost, and insufficient multi-scale simulation. In the future, the machine learning should be actively used to optimize the process-organization-performance relationship, develop new AM technology and post-treatment process, design low-cost alloy system, and realize the intelligent design combined with cross-scale simulation.
Fe-based amorphous alloy composite coatings were deposited on Q235 steel substrates via laser cladding. The influence of laser power on coating morphology, dilution rate, phase composition, microstructure, thermal stability, and mechanical response was systematically characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), differential scanning calorimetry (DSC), and Vickers microhardness testing. In the results, the coatings predominantly consist of α-Fe, Cr/Mo-enriched carbide/boride precipitates, and amorphous matrix. Laser power markedly affects both the dilution and the amorphous-phase retention. At 1200 W as the optimal laser power, the amorphous content (mass fraction) is 24.04%, the crystallization onset temperature is 732 K, and the amorphous formation capability parameter (a) is 0.618, indicating the superior thermal stability. The maximum microhardness reaches HV 1480 in the central region of coatings, roughly ninefold that of the Q235 substrates, attributed to the synergistic grain refinement and the homogeneous dispersion of strengthening precipitates.
High-entropy amorphous soft magnetic alloys integrate the multi-principal-element design with the advantages of amorphous structures, overcoming the traditional trade-offs between “strength and plasticity” and between “high saturation magnetization and low coercivity” in soft magnetic materials. The research progress of high-entropy amorphous soft magnetic alloys was systematically reviews in this paper, focusing on the application of ordering regulation strategies in constructing amorphous-nanocrystalline transition structures. The development history and theoretical foundations was outlined, and the composition design principles were summarized, including the optimization of Fe, Co, and Ni ratios to maximize local magnetic moments, the use of metalloids B and Si to tune glass-forming ability and magnetostriction, and the role of trace elements (Cr, Mo, Nb, and V) in controlling nanocrystal precipitation and improving corrosion resistance. Finally, the FeCoNi-based alloys, one-step fiber fabrication, and additive manufacturing techniques were reviewed, and the future directions were discussed, including machine learning-assisted design, precise microstructural control, and industrial applications.
The near-net-shape forming of alloy rings is regarded as the promising approach for manufacturing critical components in aero-engines. The FGH2907 alloy powders were prepared by plasma rotating electrode process, and the FGH2907 alloys were fabricated by hot isostatic pressing. The specimens were subjected to solution and aging heat treatments for 1 h, 2 h, and 4 h, respectively. The effects of aging time on microstructural evolution and mechanical properties of the FGH2907 alloys were investigated. Results show that, with the prolonged aging time, the tensile strength initially increases and then decreases, while the ductility first decreases and then slightly recovers. After 1 h of aging, the γ′ phases are uniformly and finely dispersed within the matrix, and the ε phase content is low, resulting in the optimal balance between strength and ductility. After 2 h of aging, the needle-like ε phases and the spherical γ′ phases coarsen significantly, leading to the marked increase in strength but the sharp decline in ductility. After 4 h of aging, the secondary nucleation of the ε phases and γ′ phases occurs, weakening the precipitation hardening, leading to the reduce in strength and the slight recovery in ductility.
High-entropy alloys, leveraging the four core effects as high entropy, lattice distortion, sluggish diffusion, and cocktail effect, possess the advantages such as high activity, excellent selectivity, corrosion and heat resistance, and structural stability, effectively compensating for the scarcity and high cost of the traditional noble metal catalysts. The high-entropy alloy catalysts have been widely applied in electrocatalysis, photocatalysis, and thermocatalysis, which exhibit the outstanding performance in reactions such as hydrogen evolution, oxygen evolution, CO2 conversion, and organic pollutant degradation. The mainstream preparation techniques of high-entropy alloy catalysts were systematically reviewed in this paper, including mechanical alloying, carbothermal shock, and rapid moving-bed pyrolysis, and the advantages, disadvantages, and applicable of these preparation techniques were analyzed. By leveraging the computational materials science and advanced characterization techniques, the bottlenecks of high-entropy alloy catalysts in terms of alloy design, catalytic mechanism, stability, cost, and process could be addressed, which is expected to enable the large-scale industrial applications in hydrogen energy, fuel cells, and resource utilization of greenhouse gases, thereby contributing to the green development of the energy and environmental industries.
Al/Mg bimetallic materials combine the excellent properties of aluminum and magnesium alloys, offering the promising application prospects in aerospace and other fields. Diffusion bonding is one of the most effective methods for fabricating the bimetallic materials. However, the tendency for brittle Al–Mg intermetallic compounds to form at the interface significantly reduces the bonding strength. To address this issue, the Ni/Cu composite interlayers were introduced at the Al/Mg bimetallic interface to achieve the solid/liquid diffusion bonding. The effects of holding time on the interfacial microstructural evolution and bonding strength were systematically investigated. The results show that at the bonding temperature of 500 ℃, the eutectic reaction occurs between the Mg matrix and the Cu foils, promoting the liquid-phase diffusion at the interface, while the solid-state diffusion takes place between the Ni foils and the Al matrix. As the holding time increases from 15 min to 30 min, the Cu foils are gradually consumed and eventually disappear. When the holding time reaches 45 min, the wavy interface morphology begins to form. The maximum shear strength of 53.78 MPa is achieved after holding for 60 min, the interfacial structure is composed of Al/Al3Ni2+Al3Ni/Ni/Mg2Ni/Mg3AlNi2/Mg, and the fracture occurs near the interface between Mg2Ni and Mg3AlNi2.
Soft magnetic composites (SMCs) have emerged as the critical materials in high-frequency power electronics due to the superior high-frequency low-loss characteristics and three-dimensional formability. The FeSiCr and Fe-based amorphous/nanocrystalline soft magnetic composites represent the current mainstream systems. As the core processing step, the insulating coating technology directly determines the comprehensive properties of soft magnetic composites, including electrical resistivity, permeability, core losses, and mechanical stability. The compositional design, fabrication processes, and application-specific adaptability of FeSiCr powders, Fe-based amorphous powders, and Fe-based nanocrystalline powders were systematically reviewed, and the inorganic, organic, and hybrid inorganic-organic coating methodologies were discussed. The material systems, processing routes, and underlying mechanisms governing microstructure evolution and macroscopic performance were further elaborated on. By comparing the coating effects on eddy current suppression, thermal stability enhancement, and interfacial bonding, the nonlinear coupling relationships among coating thickness, uniformity, and magnetic properties were revealed. Additionally, the common characterization on coating performance were introduced, offering the theoretical foundations and technical references for the engineered development of high-performance soft magnetic composites.
The (WMoCrTa)Si2 coatings were prepared by two-step process, involving slurry sintering followed by halide-activated pack cementation, with the silicide powders as the raw materials. The oxidation resistance at 1400 ℃ of the coatings on tantalum surface was investigated. In the results, the four-layer structure is present in the final coatings: the porous high-entropy silicide layers, the chromium-tantalum silicide layers, the TaSi2 interlayers, and the innermost Ta5Si3 layers with the overall thickness of 186 μm. Under the static air oxidation at 1400 ℃, the coatings can protect the tantalum substrate for over 14 h, with the mass gain curves showing a three-stage behavior as slow growth, rapid gain, and gradual stabilization. In the initial stage, the dense SiO2 scale is formed rapidly, Cr is preferentially oxidized to Cr2O3, which further reacts with Ta2O5 to form CrTaO4, and the synergy enhances the stability and oxygen-blocking ability of the coatings. In the later stages of oxidation, the protective performance of the coatings finally deteriorates due to the SiO2 spallation and the internal pore proliferation.
Based on the patent data for high-entropy alloy catalysts, the relationship between the patent application trend and technological life cycle, the target country and region, and the major research institution were analyzed in this study. The preparation techniques, application areas, and catalytic performance of high-entropy alloy catalysts were summarized. In the results, both the number of patent applications and applicants show the rapid growth. China is the primary target country for these patents, and Chinese research institutions hold the dominant position in terms of both the number and ranking of patent filings. The main preparation methods of high-entropy alloy catalysts disclosed in patents include the magnetron sputtering, electrospinning, electrochemical deposition, wet chemistry, dealloying, high-energy rapid reaction, and mechanical alloying. The application fields of high-entropy alloy catalysts span the energy conversion and storage, the environmental catalytic treatment, the chemical synthesis and transformation, and the advanced materials development. The research directions of high-entropy alloy catalysts focus on optimizing the catalyst composition, improving the preparation conditions, and expanding the application domains.
Rhenium powders are prepared by hydrogen reduction in tubular push-boat furnace,using ammonium perrhenate as the raw materials.The effects of ammonium perrhenate particle size,reduction temperature,hydrogen flow rate,and boat loading amount on the rhenium powder morphology,particle size,and oxygen content(mass fraction)were investigated.Furthermore,the vacuum deoxidation treatment was performed on the rhenium powders,and the effects of reduction temperature on the metallic impurity content(mass fraction)were analyzed.The results show that,after the primary hydrogen reduction at 350℃,the ammonium perrhenate is primarily converted into rhenium powders,with only trace amounts of intermediate oxides remaining;after the secondary reduction,the ammonium perrhenate is completely transformed into the rhenium powders.The ammonium perrhenate undergoes significant particle refinement during reduction;however,the particle size of rhenium powders primarily depends on that of the raw ammonium perrhenate.Rhenium powders prepared from medium and large-sized ammonium perrhenate mainly consist of the irregular flaky particles,along with a small amount of fine particles.Ultrafine ammonium perrhenate(approximately 5 μm)yields the rhenium powders composed of micro-nano particles after reduction.Reduction temperature is the primary factor affecting the oxygen content in rhenium powders.As the reduction temperature increases,the oxygen content in rhenium powders decreases.However,higher reduction temperature also enhances the tendency of rhenium powders to sinter and agglomerate.To obtain rhenium powders with lower oxygen content,the vacuum degassing is performed on the rhenium powders in vacuum furnace to reduce the oxygen partial pressure.The vacuum treatment of secondary reduced rhenium powders(oxygen mass fraction is 0.160％)is performed at 900℃ under 10-3Pa for 2 h,reducing the oxygen mass fraction in rhenium powders to 0.063％.During the high-temperature reduction of ammonium perrhenate,the impurities from the furnace tube and boat may be introduced into the rhenium powders.The content of metallic impurities in the rhenium powders is independent of the reduction temperature and remains extremely low.
High-density ultrafine-grained molybdenum was prepared using ultrafine molybdenum powder (0.40 μm) with the two-stage sintering method of hydrogen deoxidation pre-sintering and spark plasma sintering (SPS). It is found that by pre-sintering at 1000 ℃ in hydrogen for 2 hours, the mass fraction of oxygen in ultrafine molybdenum powder decreased from 0.237% to 0.066%. After pre-sintering, a large number of sintering necks are formed, but the grain size does not significantly increase. Then, the pre-sintered samples sintered by SPS at 1200 ℃ under 50 MPa for 10 min undergo the densification sintering and the relative density reaches 99.2%. Due to the relatively low sintering temperature (1200 ℃), the average grain size is 0.88 μm, the growth of grain size is not significant. Benefiting from the low oxygen content, high relative density, and small grain size, the Vickers hardness and bending strength of the Mo samples are HV 300 and 523 MPa, respectively. However, reducing the SPS sintering temperature to 1100 ℃ may result in the insufficient sintering with the relative density being only 91.3%, and the Vickers hardness and bending strength dropping to HV 215 and 343 MPa, respectively. Increasing the SPS sintering temperature to 1300 ℃ may caused the grain size to increase significantly to 6.95 μm, and the Vickers hardness and bending strength decreases to HV 197 and 467 MPa, respectively.
Closed-cell foam materials are the structural-functional integrated materials with the combined properties of lightweight, high specific strength, high energy absorption, vibration, and thermal isolation. As an auxiliary research method, the numerical simulation can offer the solution to the issues in experiment research, such as structural variation between samples and high costs of experiment. A large number of research studies have been performed on the properties and mechanisms of the closed-cell foam materials by experiments and numerical simulations. Modeling is the core issue in the numerical research of the closed-cell foam materials, because the credibility of numerical results relies heavily on the reasonable simulation model. The modelling of the closed-cell foam materials was comprehensively discussed in this paper. The existing foam models were summarized and classified into several types, including the continuous models, two-dimensional porous models, three-dimensional periodic foam models, three-dimensional reconstruction models, and three-dimensional random foam models. The advantages, disadvantages, and applicable scopes for each type of modeling methods were then analyzed thoroughly. The future trends in the modeling method were also proposed as achieving the balance between cost and simulation accuracy in the modeling of closed-cell foam materials and integrating the machine learning algorithms into the simulation modeling.
Using diamond,high-purity tungsten powders,and tungsten oxide powders as the raw materials,the tungsten coatings were fabricated on the diamond surfaces by thermal diffusion method.The microstructure,phase composition,and element distribution of the coatings were characterized by scanning electron microscopy(SEM),X-ray diffraction(XRD),and energy dispersive spectroscopy(EDS).The coating mechanism was analyzed,and the effects of coating temperature and raw material mass ratio on the coating quality were investigated.The results show that,the uniform,continuous,and dense tungsten coatings can be formed on the diamond surfaces by thermal diffusion method,showing the gradient structure of WC-W2C-W.The relative density of the coatings increases with the rise of coating temperature,and the optimal coating quality is obtained at 1150℃.The mass fraction of tungsten in the coatings first increases and then decreases as the proportion of tungsten in raw materials rises.When the raw material mass ratio(diamond,high-purity tungsten powders,tungsten oxide powders)is 1.0∶1.2∶1.0,the coatings on the diamond show the uniform and dense structure with fine and closely arranged grains,delivering the excellent overall quality.The optimal preparation parameters are determined as the coating temperature of 1150℃,holding time of 1 h,and raw material mass ratio of 1.0∶1.2∶1.0.The coatings prepared under these conditions possess the best comprehensive properties.
