Evolution in Wear and High-Temperature Oxidation Resistance of Laser-Clad AlxMoNbTa Refractory High-Entropy Alloys Coatings with Al Addition Content

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.