Microstructure, Mechanical Properties, and Friction-Wear Mechanisms of NbMoTaWV Refractory High-Entropy Alloy Coatings Fabricated via Laser Cladding

In this study, NbMoTaWV RHEA coatings were fabricated via laser cladding, and X-ray diffraction (XRD), scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy (SEM/EDS), microhardness tester, nanoindentation system, digital image correlation (DIC) testing system, and friction and wear tester were employed to characterize and analyze the phase constituents, microstructural features, microhardness, elastic modulus, evolution of tensile strain distribution, friction coefficient, volume wear rate, and three-dimensional profile of wear scars. The results indicate that certain post-heat treatment of the laser-clad RHEA coatings can lead to the formation and homogeneous dispersion of a certain amount of hard Laves intermetallic compounds and ceramic carbides within the matrix phase, which may significantly enhance the microhardness of the coatings. The solidification microstructure of the laser-clad RHEA coatings is predominantly composed of cellular crystals and equiaxed dendrites. Furthermore, the plasticity and toughness of the laser-clad RHEA coatings on the Inconel 718 nickel-based substrate are notably improved. Both types of laser-clad RHEA coatings initially develop high-strain regions in local areas, which gradually evolve into several narrow high-strain bands. Additionally, at room temperature, the wear mechanism of both the SUS321 substrate coating and the Inconel 718 substrate coating is abrasive wear. At an elevated temperature of 800 °C, the wear mechanism of the SUS321 substrate coating transforms to oxidative wear, whereas the Inconel 718 substrate coating exhibits a mixed wear mechanism of abrasive wear and adhesive wear. At 800 °C, the volume wear rate of the laser-clad NbMoTaWV refractory high-entropy alloy coating ranges from (0.20 to 0.27)×10⁻⁵ mm³/(N·min).