Influence of synthesis method on microstructure and mechanical behavior of Co-free AlCrFeNi medium-entropy alloy

The influence of synthesis method on a Co-free equiatomic medium-entropy alloy (MEA), AlCrFeNi, has been systematically investigated in the present study. Three synthesis methods, melting and casting, spark plasma sintering (SPS) of the mechanically alloyed powders and direct SPS of the mixture of elemental powders, were respectively used to prepare bulk samples. All bulk samples primarily consisted of a disordered body-centered cubic (BCC, A2) phase and an ordered BCC (B2) phase, suggesting that synthesis method had a negligible influence on the phase compositions. However, the synthesis method showed a significant influence on the microstructure of the AlCrFeNi MEA, leading to altering the mechanical properties. A rare chrysanthemum-like eutectic microstructure was obtained in the as-cast sample, while a spinodal decomposed microstructure was observed in the SPS sintered samples. All bulk AlCrFeNi samples exhibited a relatively high yield strength (> 1040 MPa) with a fairly high strain-to-failure (> 28%). The CALPHAD (Calculation of Phase Diagrams) approach was used to explain the phase formation and stability in the bulk AlCrFeNi samples. In addition, the microstructural evolution and microstructure-property relationship were also investigated deeply.