Effects of laser power and Y2O3/Ti contents on microstructure and hardness of ODS-CrFeNi medium entropy alloys by additive manufacturing

Oxide dispersion strengthened (ODS)-CrFeNi medium entropy alloys (MEAs) were prepared by laser engineering near-net forming. The effects of varying laser power (1800 W, 2000 W, 2200 W and 2400 W) and Y2O3/Ti contents (0.5 wt%, 1 wt% and 1.5 wt%) on the microstructure and hardness of the alloys were investigated. The results showed that the ODS-CrFeNi MEA is mainly composed of FCC-structured FeNi-rich matrix, plate-like FeCr-rich a phase and Cr-rich phase with a BCC structure. The volume fractions of the Cr-rich phase and the a phase are found to be closely related to the laser power and the oxide content. With the increasing laser power, the volume fraction of the Cr-rich phase decreases while that of the a phase increases. The addition of Y2O3/Ti effectively refines the solidification microstructure. With the increasing Y2O3/Ti content, the volume fraction of Cr-rich phases increases and the a phase decreases. The alloy with an optimized laser power of 2000 W and a Y2O3/Ti content of 1 wt% exhibits the lowest porosity, the highest density and hardness. Its hardness reaches 629 HV. The mechanism by which laser powder and Y2O3/Ti additions affect the microstructure and hardness has been elucidated.