Improved oxidation resistance of ODS-CrFeNi medium entropy alloys by different Y2O3/Ti/Zr additions

Isothermal oxidation tests of four types of oxide dispersion strengthened (ODS)-CrFeNi medium entropy alloys (MEAs) with different Y2O3/Ti/Zr additions, i.e., 1Y alloy (Y2O3), 1YT (Y2O3/Ti), 1YZ (Y2O3/Zr), and 1YTZ (Y2O3/Ti/Zr), were conducted at 1000 & DEG;C and 1100 & DEG;C for 12 h to explore the effects of oxide-forming ele-ments on the high-temperature short-term oxidation resistance. XRD, SEM and EDS analyses were per-formed to characterize the microstructure and phase composition of the oxide layers of the four alloys at different oxidation temperatures. The results showed that the surface oxide layers formed on all ODS-MEAs are mainly composed of hexagonal Cr2O3. The thickness and defects (e.g. pores and microcracks) of the oxide layer strongly depend on the Y2O3/Ti/Zr additions and the oxidation temperature. In general, the thickness of the oxide layer increases with increasing temperature. The oxide layer on 1YZ alloy is very dense and the thickness hardly changes with increasing temperature (0.8 & mu;m at 1000 & DEG;C and 0.9 & mu;m at 1100 & DEG;C), which exhibits the best oxidation resistance and is comparable to that of ODS-FeCrAl. However, 1YTZ alloy shows the worst oxidation resistance at both 1000 & DEG;C and 1100 & DEG;C. The oxide layer is loose together with many pores and microcracks, and the thickness is the thickest among the four alloys. In addition, severe internal oxidation occurs in 1YTZ, which is not obviously observed in the other three alloys. The excellent oxidation tolerance of 1YZ is due to the addition of Zr, which results in the formation of thermodynamically stable oxides Y4Zr3O12, which has the highest number density and smallest oxide size among the four alloys. High-density interfaces between the oxides and the matrix effectively slow down the inward diffusion rate of O and the outward diffusion rate of Cr, and inhibit/moderate the coarsening of the oxides and the formation of volatile CrO3. Therefore, pores and microcracks are effectively suppressed in Zr-containing 1YZ. & COPY; 2023 Elsevier B.V. All rights reserved.