Study on Large Plastic Deformation Mechanism of AlCoCrFeNi2.1 Eutectic High-Entropy Alloys Prepared by Laser Additive Manufacturing

In this study, AlCoCrFeNi2.1 EHEA, fabricated through laser additive manufacturing, served as the primary material. We investigated significant plastic deformation through cold rolling combined with various heat treatment methods. Microstructural analysis using SEM and EBSD was conducted on samples post large plastic deformation to elucidate the patterns observed in tensile and microhardness tests. The results of our experiments reveal that the biphasic structure (FCC and BBC) undergoes stretched and twisted following extensive plastic deformation. Additionally, the phase structure size gradually coarsens with increasing heat treatment temperature. Notably, the yield strength, tensile strength, and hardness exhibit an inverse relationship with the temperature of heat treatment, while ductility demonstrates a proportional correlation. At lower heat treatment temperatures (700 °C), sample has the higher tensile strength (1586 MPa) and yield strength (1472 MPa), the lower elongation (7.9%), and the better excellent hardness values (460.46 HV0.3). The primary contributors to strength improvement are the heightened fault density and grain stretched and twisted resulting from substantial plastic deformation. With the increase of heat treatment temperature, the increased dislocation density accelerates static recrystallization process, causing the stretched and twisted grains gradually larger. Consequently, strength decreases, and ductility increases. Furthermore, the elevation of heat treatment temperature facilitates the generation of twins (Σ3) in the FCC phase, contributing to a certain degree of strengthening. This effect counteracts the deterioration of mechanical properties observed after high-temperature heat treatment.