Refractory high-entropy alloys (RHEAs) typically exhibit a body-centered cubic (BCC) structure with excellent strength but poor ductility, which limits their practical applications. In this study, we designed BCC/FCC dual-phase RHEAs through phase diagram calculations and neural network modeling. The analysis of the binary phase formation relationships among alloying elements enabled the preliminary screening and inclusion of 13 liquid-phase-separated BCC/FCC dual-phase RHEAs in the training dataset for the machine learning model. Two strategic binary classifications of this dataset were conducted on HEAs to identify their “multiphase” and “solid solution” structures. Consequently, two neural network models were trained, achieving accuracies of 89.52% and 89.83%, respectively. These models predicted 51 BCC/FCC dual-phase RHEAs among 504 novel RHEAs, representing the first successful compositional design of metastable BCC/FCC dual-phase RHEAs. The arc-melted alloys exhibited refined dendritic structure. This study provides valuable insights for the tailored design of novel multi-phase RHEAs to achieve specific targeted properties.

A laser additive and subtractive hybrid manufacturing technology was proposed to repair Inconel 718 cracks in this paper. Microstructures and the mechanical properties such as the micro-hardness, the tensile strength, and the friction-wear of the repair zone were investigated in detail. The microstructure analysis showed that a metallurgical bonding could be achieved between the repair zone and the matrix. The typically columnar and dendrite crystal appeared in the repaired zone, and the crystal epitaxial grew along the deposition direction, and the heat-affected zone in the groove boundary was coarse equiaxial crystal. The mechanical test result showed that the micro-hardness and tensile strength of the repaired tissue was about 87% and 89% of the original Inconel 718 wrought substrate. And, the wear resistance of the repaired zone was similar to that of the substrate. It was found that the surface quality of the repair zone for laser polishing is better than that for mechanical milling.

Refractory high-entropy alloys (RHEAs) exhibit outstanding softening resistance and thermal stability at elevated temperatures. Unfortunately, poor ductility at room temperature has remained the critical issue for their processability and practical application. In this study, an original-type fabrication method of RHEA was proposed, using multi-walled carbon nanotubes (MWCNTs) to enhance the alloy prepared via laser melting deposition (LMD) technology. The processing optimization, microstructure evolution and mechanical properties were systematically investigated for LMD processing of CNTs/CoCrMoNbTi_0.4 RHEA. The results have shown that CNTs/CoCrMoNbTi_0.4 RHEA have a polycrystalline structure (BCC, HCP, and TiC). As the optimal LMD-processing parameters of laser linear energy density of 3.6 J/mm were applied, owing to the formation of high densification and an ultrafine microstructure, the fully dense LMD-processed alloy exhibited high microhardness of 1015 HV_0.5, fracture strength of 2110.5 MPa, and fracture strain of 2.39%. The solid solution strengthening and load transfer are considered as the main strengthening mechanisms occurring simultaneously during compressive tests at room temperature, leading to excellent mechanical properties of LMD-processed CNTs/CoCrMoNbTi_0.4 RHEA, which explores the potential application of RHEAs.

The design of the resonant ultrasonic vibration-assisted laser cladding (R-UVALC) setup involved employing finite element analysis (FEA) to simulate the ultrasonic transducer, horn, and workpiece in a resonance state. The impact of R-UVALC on AlCrFeMnNi high-entropy alloys was assessed using various ultrasonic vibration amplitudes of 0, 5, 10, and 15 µm, with a constant frequency of 20 kHz. Ultrasonic vibrations reduced pores and cracks and increased the clad breadth, melt pool wetting angle, and laser-clad layer consistency. The columnar elongated grains in proximity to the substrate surface underwent a size reduction and transformed into grains with a more equiaxed shape with the utilization of ultrasonic vibrations at an amplitude of 5 µm. Laser cladding performed without ultrasonic vibrations yields two phases: face-centered cubic (FCC) and body-centered cubic (BCC). However, when the coating is exposed to ultrasonic vibrations with an amplitude of 5 µm, it forms a solitary body-centered cubic (BCC) phase. The microhardness tripled compared to the substrate, and the most significant microhardness value was achieved at 5 µm of ultrasonic vibration. The friction coefficient was assessed at an ambient temperature, revealing that an ultrasonic amplitude yields the lowest friction coefficient, demonstrating the excellent wear resistance properties of the coating. The analysis of the 3D surface profile of the wear indicates that the use of ultrasonic aid with a 5 µm amplitude leads to reduced depth of scars, and the primary wear mechanism observed is abrasive and oxidative wear with fewer grooves and debris. In addition, XPS analysis revealed the presence of metal components in an oxidized condition, suggesting that the wear process is oxidative in nature. Integrating the R-UVALC setup into a resonance state can significantly enhance the efficiency of the laser cladding process in the laser cladding field.

The present study effectively produced a high-entropy alloy (HEA) coating of AlCrFeMnNi on AISI 304L steel using resonant ultrasonic vibration-assisted laser cladding (R-UVALC). An investigation was conducted to examine the impact of dilution rate on the phase composition, microstructure, and mechanical and tribological properties of AlCrFeMnNi coatings. The coating, which was created utilizing the appropriate dilution rate, was thoroughly characterized using EDS mapping and TEM investigation. The results suggest that a higher dilution rate causes a change in the AlCrFeMnNi coating, transforming it from a single solid solution phase (BCC) into a two-phase solid solution containing both FCC and BCC phases. The analysis conducted using transmission electron microscopy (TEM) reveals that the AlCrFeMnNi coating, when diluted at an optimal rate of around 37%, is predominantly composed of a disordered body-centered cubic (BCC) phase and an ordered BCC (B2) phase featuring a spinodal decomposition structure. The AlCrFeMnNi coating has an average microhardness of approximately 540 HV, which is over 2.5 times higher than the microhardness of the substrate. Additionally, it was also established that the dilution rate has an impact on the occurrence of phases, which subsequently affects the mechanical and antifrictional properties of the coating. The integration of ultrasonic vibration in laser cladding enhances quality and improves mechanical and tribological properties, thereby reducing material costs and promoting an environmentally friendly process when compared to conventional cladding.

To address the critical applications of heterogeneous structures involving nickel-based superalloys (IN718) and copper alloys (CuSn10) under extreme operating conditions, and to address the limitations of traditional joining techniques in terms of interfacial brittleness and geometric constraints, this study employs Laser Powder Bed Fusion (LPBF) technology, specifically multi-material LPBF (MM-LPBF). By precisely melting IN718 and CuSn10 powders layer by layer, the study directly fabricates multi-material IN718/CuSn10 joint specimens, thereby simplifying the complexity of traditional joining processes. The research systematically investigates the interfacial microstructure and mechanical property evolution laws and underlying mechanisms. It reveals that sufficient element diffusion and hardness gradients are present at the IN718/CuSn10 interface, indicating good metallurgical bonding. However, due to significant differences in thermophysical properties, cracks inevitably appear at the interface. Mechanical property tests indicate that the strength of the IN718/CuSn10 joint specimens falls between that of IN718 and CuSn10, but with lower elongation, and fractures primarily occur at the interface. This research provides theoretical support for establishing a process database for LPBF formed of nickel–copper heterogeneous materials, advancing the manufacturing technology of aerospace multi-material components.