Selective laser melting of an equiatomic AlCrCuFeNi high-entropy alloy: Processability, non-equilibrium microstructure and mechanical behavior

An equiatomic AlCrCuFeNi high entropy alloy (HEA) is fabricated successfully from the alloy powders using selective laser melting (SLM). Microstructural characteristics and mechanical behavior of SLMed AlCrCuFeNi samples under optimal SLM processing parameters are studied in detail. It is revealed that the SLMed AlCrCuFeNi HEA shows high crack sensitivity, and the optimum processing window is narrow. The formation of FCC phase is inhibited, resulting in a simple BCC solid solution to accommodate high lattice distortion and elastic strain induced by rapid cooling rate for the SLMed AlCrCuFeNi HEA. Moreover, unique fine columnar grains containing multiple ultrafine sub-grains structures appear within the molten pool and present a <100> preferred orientation. Nano-scale Cu-rich phases precipitate and exhibit chain-like at HAGBs while granular shape at LAGBs. Also, anomalous alternating bright and dark structures containing B2 and A2 phases with the width about 22 nm appear at the sub-grain boundaries due to rapid solidification. The SLMed AlCrCuFeNi HEA possesses superior properties with a compression strength of 2052.8 MPa and a fracture strain of 6.8% compared to the corresponding casting material. Fracture analysis indicates that the SLM (0°) specimen exhibits quasi-cleavage fracture while the SLM (90°) specimen shows intergranular fracture. The grain boundary strengthening effect, <100> preferential growth orientation of BCC grain and the existing microcracks are proposed to explain the anisotropy of compression properties.