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 6xxx-series Al alloys have been used for decades because of their favorable strength-to-weight ratio, corrosion resistance, and fatigue performance. However, conventional welding techniques often induce localized weakening, as thermal effects modify the microstructure and compromise structural integrity. For nearly 70 years, AA4043 welding wire has been the primary choice for joining 6xxx-series Al alloys. Nevertheless, microstructural and mechanical property mismatches between the base metal and weld region remain key factors contributing to premature failure, while welding-induced defects further increase rupture susceptibility. Microalloying has emerged as an effective strategy for enhancing both the mechanical and thermal properties of aluminum alloys. In this study, rare-earth (RE) elements La and Ce were introduced into the AA4043 system to exploit their grain refining and mechanical strengthening capabilities. In addition, the effects of Sr modification were examined and compared with La-Ce addition. This work aims to elucidate the strengthening mechanisms associated with La-Ce-Ti microalloying in AA4043 welding wire, a topic that has rarely been systematically investigated. With 0.019Ti-0.02La-0.03Ce additions, the modified wire exhibited significant performance improvements, achieving an UTS of 204 MPa and a YS of 191 MPa—representing increases of 10.3% and 18.6%, respectively.