Effect of Heat Treatment on Microstructure and Properties of Al0.5cocrfeni High Entropy Alloy Fabricated by Selective Laser Melting

In this study, heat treatment as a post processing was used in order to improve the microstructures and mechanical properties of Al0.5CoCrFeNi high entropy alloy (HEA), which fabricated by selective laser melting (SLM). Compared to the microstructure of SLM-ed Al0.5CoCrFeNi HEA, the strengthening the weakening mechanisms of HEA at different heat treatment temperatures are figured out. Heated at 1073 K for 4 hours, the SLM-ed Al0.5CoCrFeNi HEA shows the highest tensile strength. With increasing heat treatment temperature from 1073K to 1673K, both the dislocation density in Al0.5CoCrFeNi HEA and the content of the precipitated phase decrease, while the size of the precipitated phase increases. Moreover, dislocation network disappearance and recrystallization occur at 1173 K and 1373 K, respectively. The boundaries of the dislocation network, as the nucleation sites of precipitation, promote the formation of precipitation phases and form dislocation network wrapped by precipitation phases at 1073 K, which significantly improves the tensile strength of HEA. The low dislocation density in the recrystallized grains change the morphology of the precipitation phases, and the aspect ratio of the precipitation phases increases, which made the HEA still maintain a certain tensile strength at 1673K.