Creep strength of refractory high-entropy alloy TiZrHfNbTa and comparison with Ni-base superalloy CMSX-4

Despite the decade-long worldwide interest in refractory high-entropy alloys (RHEAs) for high-temperature applications, their tensile creep properties have not been published, making it difficult to assess their true potential. Here, we report the tensile creep behavior at 980°C and 1,100°C of TiZrHfNbTa, a body-centered cubic (BCC), solid solution RHEA, and compare it with single crystals of a leading precipitate-strengthened Ni-base superalloy, CMSX-4, as well as its solid solution matrix. The superalloy is 25 times stronger in creep than the RHEA at 980°C and 70 times stronger at 1,100°C. Even the single-phase matrix of CMSX-4 has three times the creep strength of the RHEA at 980°C. We also find that the microstructure of the RHEA is unstable and undergoes phase decomposition during creep. In light of these observations, we discuss the temperature ranges where RHEAs may or may not be competitive with Ni-base superalloys. • Creep strength of TiZrHfNbTa is lower than Ni-base superalloy CMSX-4 • TiZrHfNbTa is also weaker than the face-centered cubic matrix of CMSX-4 • Faster diffusion in the body-centered cubic TiZrHfNbTa accounts for this weakness • Precipitate strengthening may be required to overcome the diffusion penalty Gadelmeier et al. demonstrate that significant hurdles, including poor strength and microstructural instability, must be overcome for the refractory high-entropy alloy TiZrHfNbTa to become competitive with state-of-the-art Ni-base superalloys for demanding high-temperature applications.