On the mechanism of plastic deformation in metastable TiZrHfNb_x refractory high entropy alloys during tensile and sliding friction at 500 °C

Revealing the deformation mechanisms and their corresponding effect on the mechanical performance of the metastable TiZrHfNb_x refractory high entropy alloys (RHEAs) is of great significance for the current engineering applications. A series of metastable TiZrHfNb_x RHEAs was developed by applying the metastable engineering. The tensile and tribological properties were investigated at 500 °C systematically. The deformation mechanisms induced by the tensile stress and wear were elaborated in detail. From the experimental results, the Nb_0.4 sample performs remarkable comprehensive performance with 445 MPa of YS, 937 MPa of UTS and 58.5 % of EL while Nb_0.2 sample performs excellent tribological performance with lowest friction of coefficient and wear volume. It is concluded that metastable engineering with decreasing the Nb content successfully makes the matrix BCC phase unstable and improves the tensile properties and wear resistance at 500 °C. For the tensile tests, deformation bands, phase transformation and slip bands are regarded as the dominant deformation mechanisms. The co-deformation of the dual-phase microstructure for TiZrHfNb_0.4 RHEA leads to excellent tensile performance. For the wear tests, the low-angle grain boundaries and nanocrystalline layer are reasonable for the lowest coefficient of friction and wear volume at 500 °C. This study not only developed a series of RHEAs with excellent tensile and tribological properties, but also expanded the understanding of the deformation mechanisms induced by stretching and friction.