On cooling rates dependence of microstructure and mechanical properties of refractory high-entropy alloys HfTaTiZr and HfNbTiZr

Abstract

Structural stability of high entropy alloys (HEAs) at intermediate temperatures during which the configurational entropy loses its dominance is crucial. In this work, we have scrutinized the effects of cooling rates on the phase stability of the HfTaTiZr(Ta1) and HfNbTiZr (Nb1) refractory HEAs (RHEAs). Ta1 exhibited strong microstructure and tensile property dependence on the cooling route, but not Nb1. Ta1 retained the BCC lattice under water quenching but experienced complex phase decomposition upon air and furnace cooling. The different dependence on cooling rates in these RHEAs arises from three main reasons: (i) the wider metastable temperature range in Ta1, (ii) the larger mobility difference between Ta and other constituents, and (iii) the larger electronegativity difference of Nb1. The current work not only sheds new insights into the understanding of the thermal and mechanical stability of HEAs but also provides a new paradigm for the optimization of their overall properties.