Control of microstructure and hardness of ODS-CrFeNi MEAs by Y2O3/Zr addition

Abstract

Oxide dispersion strengthened (ODS)-CrFeNi medium entropy alloys (MEAs) with different addition amounts of Y2O3/Zr were prepared by mechanical alloying (MA) and spark plasma sintering (SPS) to reveal the influence of Y2O3/Zr amounts on microstructure and mechanical properties. The microstructure was characterized by XRD, BSE, EBSD, HRTEM, and the micro-hardness was tested. The results show that ODS-CrFeNi MEA with 1 wt% Y2O3/Zr addition (1YZ alloy) mainly consists of face-centered cubic (FCC) matrix, body-centered cubic (BCC) phase and high-density nanoscale oxides Y4Zr3O12 while in ODS-CrFeNi MEA added 3 wt% Y2O3/Zr (3YZ alloy), additional [Ni, Zr] phase is formed except for FCC matrix, BCC phase and nanoscale Y4Zr3O12. The average size and number density of Y4Zr3O12 depend on the addition amount of Y2O3/Zr, which are 9.8 nm/3.9 × 1021/m3 and 24.6 nm/3.3 × 1021/m3 in 1YZ and 3YZ alloys, respectively. The average grain size of 1YZ and 3YZ alloy are 127 nm and 344 nm, respectively. The effective grain refinement in 1YZ alloy results in the higher hardness, which is 474 HV. The hardness of 3YZ alloy is 368 HV. The detailed strengthened mechanisms are discussed.