Dynamic relaxation characteristics and stress relaxation behavior of Pd-based<sub> </sub>metallic glass

Abstract

As a potential functional and structural material, high-entropy metallic glasses have aroused tremendous research interest in condense matter physics and mechanics. The correlation between macroscopic mechanic properties and microstructure heterogeneity of high-entropy metallic glasses is one of the most important scientific issues in glassy solids. In the present research, Pd<sub>42.5</sub>Cu<sub>30</sub>Ni<sub>7.5</sub>P<sub>20</sub> metallic glass and Pd<sub>20</sub>Pt<sub>20</sub>Cu<sub>20</sub>Ni<sub>20</sub>P<sub>20</sub> high-entropy metallic glass are selected as the model alloys. Dynamic mechanical analysis (DMA) and stress relaxation are used to investigate the influences of temperature and physical aging on dynamic mechanical relaxation process and microstructure heterogeneity of the model alloys. The dynamic mechanical analysis results demonstrate that the Pd<sub>42.5</sub>Cu<sub>30</sub>Ni<sub>7.5</sub>P<sub>20</sub> metallic glass and Pd<sub>20</sub>Pt<sub>20</sub>Cu<sub>20</sub>Ni<sub>20</sub>P<sub>20</sub> high-entropy metallic glass both exhibit evident <i>β</i> relaxation process. In addition, the atomic mobility of model alloys is reduced in these processes, and the <i>β</i> relaxation shifts toward higher temperatures. In the stress relaxation process, the Gibbs free energy is reduced due to the high configurational entropy. This is the potential reason that high-entropy metallic glass possesses higher activation energy. In parallel, high-entropy metallic glass is more difficult to activate and needs to break through a higher energy barrier. With the increase of physical aging time, the flow unit in high-entropy metallic glass becomes smaller. This also benefits from the high-entropy effects that bring sluggish diffusion into high-entropy metallic glass. The change of activation volume under physical aging of high-entropy metallic glass is less sensitive to stress relaxation than that of metallic glass.