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.
