Microstructure Stability and Its Influence on the Mechanical Properties of CrMnFeCoNiAl0.25High Entropy Alloy

The effect of long-term thermal exposure at 700 degrees C on the microstructure and mechanical behavior of as-cast CrMnFeCoNiAl(0.25)was investigated. Results indicated that microscopically, the as-cast alloy was not an equilibrium alloy to maintain a single FCC structure after long-term aging. The strip-like sigma phase (Cr-rich sigma phase) and B2 phase (NiAl) precipitated in the FCC matrix and coarsened when the exposure time was increased. Due to the increased volume fraction and the strengthening of these precipitates, the yield strength and Vickers hardness increased considerably with increasing the thermal exposure time up to 2000 h. The yield strength increased from 272 MPa for the as-cast alloy to 993 MPa for the alloy exposed for 2000 h. The hardness increased up to 322 Hv for the alloy exposed for 2000 h. However, the yield strength decreased to 664 MPa for the alloy exposed for 4000 h, owing to the coarsening of precipitates. The alloy maintained a good compressive plasticity after long-term aging. Graphic