Creep behavior of a precipitation-strengthened A2-B2 refractory high entropy alloy

Refractory compositionally complex alloys consisting of a disordered A2 matrix and ordered B2 precipitates mimic the microstructures of state-of-the-art, Ni-based superalloys with A1 matrix and L1 2 precipitates. The former are promising candidates for high-temperature applications because of their high melting points. 27.3Ta-27.3Mo-27.3Ti-8Cr-10Al (in at. %, TMT-8Cr-10Al) is a relevant example where this A2-B2, two-phase microstructure is formed by a precipitation reaction and remains stable even at temperatures close to the precipitate solvus temperature ( T S ). The present study systematically addresses the creep response of polycrystalline TMT-8Cr-10Al at temperatures of 1000 °C and above. Compared to polycrystalline, single-phase A2 and B2 high entropy alloys, a substantially higher compression creep resistance is observed for the two-phase alloy while minimum creep rates comparable to those of state-of-the-art single-crystalline A1-L1 2 CMSX-4 are found. This is specifically remarkable considering the polycrystalline condition of TMT-8Cr-10Al, the open matrix A2 crystal structure and the close proximity of the test temperatures to the solvus temperature with 0.98 T S compared to 0.85 T S for CMSX-4. Consistent with a positive lattice misfit, directional coarsening of precipitates in TMT-8Cr-10Al is noted to be perpendicular to the compression direction after creep in grains with 〈 100 〉 close to the compression direction.