Temperature effects on the serrated behavior of an Al_0.5CoCrCuFeNi high-entropy alloy

Compression experiments of the Al_0.5CoCrCuFeNi high-entropy alloy (HEA) under displacement control were conducted at different temperatures ranging from 673 K to 873 K with a strain rate of 5 × 10⁻⁵/s to study its serration behavior. Samples after compression tests were investigated, using the synchrontron-diffraction technique and transmission-electron microscopy. By comparing the stress-strain curves at different temperatures, two opposite directions of serrations were observed, named the upward serration appearing at 573 K and 673 K and the downward serration at 773 K and 873 K. The different directions of serrations were discussed in terms of not only the relationships among the stress vs. strain, stress vs. time, and strain vs. time, but also the interactions among dislocations, atoms, and nanoparticles. Finally, the temperature effect on the flow serration is discussed by referring to a theoretical framework for the initiation of the serrated flow. Beyond a critical high temperature, the initiation of the serrated flow becomes swiftly difficult, and ultimately the plastic flow in the full deformation range turns smooth. The theoretical prediction of the normal behavior is essentially in qualitative agreement with the experimental observation in the present work, i.e., the critical strain to initiate the serration decreases with increasing the temperature.