Microstructure and Properties of the As-cast and Annealed Al0.8CoCrFeNiTi0.2 High-Entropy Alloys

Al0.8CoCrFeNiTi0.2 high entropy alloys were prepared by vacuum arc melting and then were treated by vacuum annealing at 600, 800 and 1000 degrees C for 10 h. The microstructure, hardness, mechanical properties and corrosion resistance of the as-cast and annealed alloys were studied using XRD, OM, EPMA, hardness tester, universal testing machine, and electrochemical workstation. Microstructure analysis shows that the annealing treatments change the phase composition and microstructure morphology of the alloys. The as-cast alloy consists of bcc and fcc solid solutions, while the 600, 800 and 1000 degrees C annealed alloys consist of bcc, fcc and a phase. In the 800 degrees C annealed alloy, the a phase precipitates the most. During the annealing process, the single-phase solid solution dendrites in the as -cast shift to the thin layer-flake two-phase mixed structure. In the temperature range of 800 degrees C and below, the higher the annealing temperature, the finer the mixed structure and the better the composition uniformity. But the 1000 degrees C-annealed alloy has a large block single-phase solid solution precipitation, causing elements segregation to intensify. Hardness and compression tests show that all of the as-cast and three kinds of annealed alloys have high hardness, yield strength, fracture strength and plastic deformation, showing good comprehensive mechanical properties and resistance to temper softening. The 800 degrees C-annealed alloy has the highest hardness, yield strength and fracture strength, but the as-cast alloy have the best plasticity. Electrochemical corrosion tests show that the as-cast and three kinds of annealed alloys all have good corrosion resistance in the 3.5 wt% NaCl solution and 0.5 mol/L H2SO4 solution and the corrosion resistance of the 800 degrees C-annealed alloy is best.