Effect of annealing temperature on the microstructure and mechanical properties of Al_0.2CrNbTiV lightweight refractory high-entropy alloy

The DSC analysis and heat treatment of the newly proposed Al_0.2CrNbTiV lightweight refractory high-entropy alloy prepared by vacuum arc melting was investigated, and the evolutions of the microstructure and mechanical properties of the alloy after homogenization annealing at 650 °C, 850 °C and 1050 °C for 12 h were analyzed. The results show that the Al_0.2CrNbTiV high-entropy alloy could maintain stable BCC solid solution structure from room temperature to 800 °C. The alloy annealed at 650 °C exhibited simple BCC structure with coarse equiaxed grains; after annealing at 850 °C, fine acicular and irregular block-like C14 Laves phases were uniformly precipitated in the grain and grain boundaries, meanwhile, the C14 Laves phase get coarser with the annealing temperature increased to 1050 °C. With the increase of annealing temperature, the microhardness of the Al_0.2CrNbTiV alloy increased first and then decreased, reaching the maximum value of 692 HV after annealing at 850 °C. Due to the high dislocation density and the formation of kink bands, the alloy annealed at 650 °C showed a good combination of plastic and strength, with the work hardening ability strengthened simultaneously, the compressive yield strength could be up to 1454 MPa, with strain >50 %. Due to the precipitation of the hard and brittle C14 Laves phase, the load-bearing capacity of the alloy was reduced after annealing at 850 °C and 1050 °C. However, the wear resistance of the alloy also improved with the presence of the hard phase. The friction coefficient of Al_0.2CrNbTiV alloy annealed at 650 °C is 0.67, with the abrasive wear acting as the main wear mechanism, and the alloy after annealing at 850 °C shew the best wear resistance, with the friction coefficient of 0.63, and delamination wear mechanism.