Laser additive manufacturing of CrMnFeCoNi high entropy alloy: Microstructural evolution, high-temperature oxidation behavior and mechanism

Abstract

Bulk CrMnFeCoNi high entropy alloy (HEA) was successfully fabricated via laser additive manufacturing (LAM) in this work. Distributions of microstructure and microhardness in the LAM-fabricated specimen were studied in detail, and oxidation scales were characterized after high-temperature oxidation tests. Results indicated that the mixed columnar dendrites and equiaxed grains were the main microstructure of the LAM-fabricated specimen. High-density dislocations induced by rapid solidification during the LAM process contributed to an excellent microhardness. Oxidation kinetics of LAM-fabricated specimens followed the parabolic rate law over the temperature ranging from 800 to 1000 °C, and the mass gain increased with the increasing temperature. The columnar dendrites and equiaxed grains fully transformed into recrystallized grains, and the dislocation density decreased after high-temperature oxidation. The main compositions of the oxide scale were Mn2O3 and Cr2O3 at 800 °C, while Mn3O4 and (Mn, Cr)3O4 were formed in the oxide scale at 900 and 1000 °C. The diffusion of Mn and Cr along dendrite grain boundaries significantly affected high-temperature oxidation behaviors of LAM-fabricated CrMnFeCoNi HEA. The high-temperature oxidation mechanism was proposed.