Precipitation suppression of refractory high-entropy alloys at intermediate temperature via adding oxygen

Abstract

Due to the excellent mechanical properties, TiZrNb-based refractory high entropy alloys (RHEAs) show great potential application prospects in aviation, aircraft and petrochemical. However, the RHEAs are usually thermally metastable and brittle phases can be precipitated in intermediate temperature (such as 500–700℃), which severely limit the preparation of large-sized RHEAs ingots in industrial production. In this paper, we propose an alloy optimization strategy to suppress the precipitation of TiZrNb-based RHEAs by adding interstitial atomic oxygen (O). The results show that the precipitation temperature region of brittle phases can be reduced from 500°C∼650°C to 550°C∼600°C after adding oxygen, and the temperature region is reduced by more than 66 %. Moreover, the growth rate of precipitated phase decrease from 4.1 × 10−23 m3/s to 1.9 × 10−24 m3/s after adding oxygen, which is reduced by more than ten times. The analysis shows that adding oxygen inhibits the diffusion rate of Zr at intermediate temperature, thus delaying the formation of Zr-rich phase. Based on this, TiZrNb-based RHEAs with oxygen can well keep the outstanding ductility even after annealing at intermediate temperature for 4 hours, while the TiZrNb-based RHEAs without oxygen show ∼50 % ductility loss after the same annealing treatment. Our results not only provide new insights into the phase stability and mechanical stability of RHEAs, but also provide a new strategy for improving the phase stability of large-size ingots for engineering applications.