Effect of heat treatment on microstructure and properties of Al0·5CoCrFeNi high entropy alloy fabricated by selective laser melting

Abstract

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 h, the SLM-ed Al0·5CoCrFeNi HEA shows the 1419 MPa tensile strength. With increasing heat treatment temperature from 1073 K to 1673 K. The content of BCC phase decreases from 34.4% to 14.6%. The average size of BCC phase at grain boundaries increases from 0.497 μm to 2.271 μm, and the average size of BCC phase inside the grains increases from 0.037 μm to 1.216 μm. 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 precipitated phases and form dislocation network wrapped by precipitated phases at 1073 K. The precipitated phases and the dislocation network wrapped by precipitated phases increase the tensile strength of SLM-ed HEA by 65.8%. The low dislocation density in the recrystallized grains change the morphology of the precipitated phases, and the aspect ratio of the BCC phases increases, which made the HEA still maintain a certain tensile strength at 1673 K.