Microstructural evolution and mechanical enhancement of Co-free AlCrFeNi3 eutectic medium entropy alloy via heat treatment after selective laser melting

Abstract

The as-printed Co-free AlCrFeNi₃ eutectic medium entropy alloy (EMEA) was fabricated by selective laser melting (SLM). Heat treatment as a post processing was used to improve the mechanical properties of the as-printed samples, which were subjected to solid solution treatment at 400 °C–1200 °C for 1 h in this work. The microstructure and mechanical properties of the as-printed and heat-treated samples were examined in detail. No visible cracks and pores were found in the as-printed samples and the highest relative density is up to 99.57 %. The as-printed AlCrFeNi₃ EMEA is consisted of FCC, B2, and intergranular BCC phases, showing a typical fish scale-like structure with ultrafine cellular and columnar substructures. There are significantly preferred orientation and a strong texture in the molten pool, exhibiting obvious anisotropy, which affects the mechanical properties of the as-printed alloy in different directions. The ultimate tensile strength and elongation of the as-printed alloy with relatively optimal printing parameters are 1146.9 MPa and 7.6 %, respectively. Additionally, as the heat treatment temperature increases, the morphology of the matrix structure and intergranular BCC phases changed significantly, and the mechanical properties of the samples improved accordingly. When the solid solution temperature reaches 1000 °C, the intergranular BCC phases disappeared, and the second phases are uniformly distributed in the matrix, while the ultimate tensile strength and elongation of the sample are 1335.5 MPa and 12.3 %, respectively, demonstrating an 188.6 MPa increase in strength and 4.7 % increase in ductility compared to the as-printed alloy. Mechanical properties of the as-printed alloys are improved objectively due to grain refinement and second phase strengthening. Theoretical analysis and experimental guidance were provided in this work for the further application and performance improvement of printing alloys in additive manufacturing, such as aerospace, wear-resistant coatings, and energy applications.