Evolution of the microstructure and mechanical properties of as-cast Al0.3CoCrFeNi high entropy alloys by adding Si content

In this paper, a set of as-cast Al0.3CoCrFeNiSix (values of x is 0, 0.1, 0.2, 0.3, 0.4, 0.5) HEAs were fabricated by arc vacuum melting. The evolutions of microstructure and mechanical properties of alloys were systematically investigated. The results revealed that addition of Si could promote formation of (Al, Ni, Si)-rich phase with B2 structure (BCC1 phase) and (Fe, Cr)3Si phase with L21 structure (BCC2 phase). The microstructure of alloys changed from a single FCC phase to mixed FCC plus BCC1/BCC2 phases with a typical dendritic structure with increasing Si content. Meanwhile, addition of Si could improve the hardness and strength of alloys, the hardness and yield strength of alloys increased from 141 ± 2.0 to 445 ± 6.6 HV and 167 ± 4.3 to 713 ± 5.7 MPa with increasing Si content. According to the relationship between microstructure and mechanical properties, the strengthening mechanisms of current HEAs were evaluated, demonstrating that precipitation strengthening of ordered BCC phase is the dominant strength mechanism.