Microstructural Features and Mechanical Behaviors of Al_0.5Cr_0.8CoFeNi_2.5V_0.2 High-Entropy Alloys Fabricated by Selective Laser Melting Technique

In this work, high strength and ductile Al_0.5Cr_0.8CoFeNi_2.5V_0.2 high-entropy alloys (HEAs) were fabricated by the selective laser melting (SLM) technique. After orthogonal experiments, it was verified that a wide SLM processing parameter window can be used to produce crack-free samples for the investigated HEAs. All the printed HEA samples exhibit good densification higher than 98.3%. It was found that obvious epitaxial growth leads to the formation of the cylindrical and equiaxed ordered face-centered cubic (FCC) crystals, displaying the characteristics of sub-cylindrical and sub-cellular microstructures. The low-angle grain boundaries (LAGBs) prefer appearing around subgrain structures, while the high-angle grain boundaries (HAGBs) tend to form around coarse grains. Two HEA samples with high and low apparent densities were selected to observe their mechanical properties, which exhibit Vickers hardness higher than 263 HV and do not fail during compression. With increasing densification, the strength gradually rises. According to the engineering stress–strain curves during compression, the yield strength is higher than 530 MPa, while the strength near 40% engineering strain is larger than 1840 MPa. During deformation, a large density of dislocations becomes popular within subgrain structures together with the pre-existing dislocations from rapid solidification, leading to the formation of planar and cross slip bands. Within coarse cylindrical crystals, some deformation twins are also induced together with the appearance of a distinct copper-type texture during deformation. As a result, the as-printed samples display better mechanical properties than the as-cast counterpart. The present studies provide a very good HEA candidate for the SLM process, but more work should be conducted to achieve excellent comprehensive properties.