Abstract: Taking Co_xFe₃₅Mn₂₅Cr₁₅Ni₁₀Ti₅ (x=7,11,15) high entropy alloys as the research object(named as Co₇HEA, Co₁₁HEA and Co₁₅HEA, respectively), the effect of annealing process on the microstructure and hardness was studied by means of metallographic microscope, scanning electron microscope, X-ray diffractometer and Vickers hardness tester. The results show that with the increase of Co element, the compatibility between the black network phase and the gray phase in the alloys is improved, leading to precipitation strengthening and recrystallization during annealing. After annealing, the distribution of Cr, Fe, Ni and Ti elements in the alloys is more pronounced than that in the as-cast. The annealing temperatures corresponding to the highest hardness of the annealed alloys are concentrated at 800 ℃. After annealing at 800 ℃ for 12 h, the hardness of the Co₇HEA alloy and Co₁₁HEA alloy is 422.4 HV0.3 and 778.3 HV0.3, respectively, while the hardness of the Co₁₅HEA alloy is 325.8 HV0.3 after annealing at 800 ℃ for 8 h. When the annealing temperature reaches 1000 ℃, the Co_xFe₃₅Mn₂₅Cr₁₅Ni₁₀Ti₅ alloys undergo varying degrees of recrystallization.

Key words: Co_xFeMnCrNiTi high entropy alloy, annealing, microstructure, hardness