New evidence on the phase transformation of HfNbTaTiZr high-entropy alloy at intermediate temperatures

Refractory high-entropy alloys (RHEA) are promising structural materials for high-temperature thermal-harsh environment. The HfNbTaTiZr RHEA is a good example that shows a rare combination of high strength and good ductility. In real-world applications, high-temperature alloys have to maintain a high phase stability not only at high temperatures, but also for a wide range of temperatures for a prolonged service time. While the HfNbTaTiZr RHEA is generally regarded as a single-phase BCC solid solution, recent studies by Senkov et al suggest phase decomposition after cold-rolling at 800 °C. Controversy still exists for the phase stability of the HfNbTaTiZr RHEA at intermediate temperatures. In the present work, we investigated the phase decomposition of the RHEA at different temperatures (500–1000 °C). The formation of BCC Ta-Nb-rich and HCP HfZr-rich precipitates, as well as their preferred orientation to the BCC matrix, are elucidated from experiments. Thermodynamic modeling shows good agreement with experiments.

"Phase transformations of HfNbTaTiZr high-entropy alloy at intermediate temperatures", Scripta Materialia, 158, 50-56 (2019) [PDF]