Ni-based alloy powder (NiCrBSi) was applied to prepare coatings on Ti6Al4V by laser cladding to improve the wear resistance of the latter under corrosion. The scanning speed was found to be an essential parameter that could adjust the microstructure of the coatings. Changes in the microstructures of the coatings with the scanning speed were highlighted, and the relationships between the microstructures and microhardness, fracture toughness, corrosion, and corrosion wear resistance of the coatings were established. Results indicated that the matrix changes from Ti2Ni + TiNi to primary γ(Ni) + eutectics (γ(Ni) + Ni3Ti) with increasing scanning speed. Moreover, reinforcement phases changed from TiB2 + TiC (5 mm∙s−1) to TiB2 + TiC + Cr7C3 (11 mm∙s−1) to TiB2 + TiC + Cr7C3 + CrB (17 mm∙s−1). The average microhardness of the coatings first increased and then decreased, and the corresponding fracture toughness showed the opposite trend. The optimum combination of these properties was observed in the coating prepared at 11 mm∙s−1. This coating demonstrated excellent wear resistance in 3.5 wt.% NaCl solution, as well as a high corrosion potential, a low corrosion current density, and a low current density when the electrode initially entered a comparatively stable corrosion state. Moreover, compared with coatings prepared at other scanning speeds, this coating revealed a higher critical potential for oxidation film destruction. The results of this research collectively show that regulating the microstructures of laser-clad coatings by applying different scanning speeds is a feasible strategy to optimize the wear resistance of the coatings under corrosion.

CoCrFeNiAlx (x = 0 and 1.0) high-entropy alloy coatings were synthesized on Ti6Al4V via laser cladding to improve their corrosion and wear resistance under corrosive conditions. Results indicated that the coating (CoCrFeNi) was largely composed of irregular primary α(Ti) and honeycomb-like eutectics of α(Ti) + Ti2Ni as the matrix, with TiC dendrites as the reinforcement. When Al was introduced into the cladding material, irregular α(Ti) grains were transformed into equiaxed grains, besides which the area fraction in eutectics was considerably reduced, and TiC dendrites were also transformed into spherical particles. Compared with the coating without Al, the introduction of Al contributed to the improvement in corrosion resistance because corrosion potential was enhanced from −0.524 V to −0.393 V, whereas corrosion current density and steady current density were reduced from 2.249 × 10−7 A·cm−2 and 1.021 × 10−6 A·cm−2 to 1.260 × 10−7 A·cm−2 and 2.506 × 10−7 A·cm−2, respectively. The substrate was still at the break-in stage during a long-term sliding of 10 h because its wear rate exhibited an approximately linear reduction tendency (2.09 × 10−3 mm3·N−1·m−1 for 2 h and 7.44 × 10−4 mm3·N−1·m−1 for 10 h). With respect to the coatings, they transitioned from the break-in stage into the stable wear stage when the sliding duration exceeded 4 h, during which a comparatively stable wear rate of 2.88 × 10−4 mm3·N−1·m−1 was obtained. The wear mechanism of the substrate was identified as slight microcutting and serious oxidation for the long-term sliding of 10 h. It changed into a combination of slight microcutting, serious oxidation, and moderate brittle debonding for the coatings. Generally speaking, the introduction of Al can refine the microstructure and improve the microstructural uniformity. Moreover, the passive film can be formed more rapidly on the coating surface and presents higher stability when introducing Al. Finally, the introduction of Al also promotes the coating to enter into the stable wear stage more rapidly and causes the decrease in friction coefficient and wear rate.

AlxMoNbTa (x = 0.5, 1.0 and 1.5) refractory high-entropy alloy (RHEAs) coatings were produced on Ti6Al4V by laser cladding. Ti2AlNb as the second phase and the solid solutions with the body center cubic structure (BCC) as the matrix were synthesized in the coatings. The average microhardness of the coatings was increased with the increase in x, along with which the fracture toughness was decreased. Wear resistance of the coatings was investigated by the dry-sliding reciprocating wear tests at room temperature in air (Si3N4 as the counterparts, the 10 N load for 30 min, and the 3 mm/s sliding speed). The wear rate of the coatings was decreased with x enhanced from 0.5 (6.34 × 10−5 mm3/N·m) to 1.0 (5.90 × 10−5 mm3/N·m), then slightly increased with x enhanced to 1.5 (6.18 × 10−5 mm3/N·m). Oxidation resistance was evaluated by the high-temperature oxidation tests at 1000 °C in air for 120 h. The whole mass gain of the coatings showed a slight downward tendency (61.8 mg/cm2 for x = 0.5, 57.8 mg/cm2 for x = 1.0 and 56.3 mg/cm2 for x = 1.5). The change in wear and oxidation mechanism with x was revealed in detail.