Effect of annealing temperature on the microstructure and mechanical properties of Al0.2CrNbTiV lightweight refractory high-entropy alloy

The DSC analysis and heat treatment of the newly proposed Al0.2CrNbTiV 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 degrees C, 850 degrees C and 1050 degrees C for 12 h were analyzed. The results show that the Al0.2CrNbTiV high-entropy alloy could maintain stable BCC solid solution structure from room temperature to 800 degrees C. The alloy annealed at 650 degrees C exhibited simple BCC structure with coarse equiaxed grains; after annealing at 850 degrees 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 degrees C. With the increase of annealing temperature, the microhardness of the Al0.2CrNbTiV alloy increased first and then decreased, reaching the maximum value of 692 HV after annealing at 850 degrees C. Due to the high dislocation density and the formation of kink bands, the alloy annealed at 650 degrees 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 degrees C and 1050 degrees C. However, the wear resistance of the alloy also improved with the presence of the hard phase. The friction coefficient of Al0.2CrNbTiV alloy annealed at 650 degrees C is 0.67, with the abrasive wear acting as the main wear mechanism, and the alloy after annealing at 850 degrees C shew the best wear resistance, with the friction coefficient of 0.63, and delamination wear mechanism.