FCC-L12 ordering transformation in equimolar FeCoNiV multi-principal element alloy

The ordered L 1 2 phase generally appears as dispersed precipitates in FCC multi-principal element alloys (MPEAs). In this work, a single L 1 2 ordered intermetallic is obtained in the annealed equimolar FeCoNiV alloy. Experiments show that the FCC to L 1 2 ordering transformation occurs below 778±2 °C, accompanied by lattice contraction, anti-phase boundaries (APBs) formation and low-temperature magnetic moment decrease. A strong linear strain hardening rate up to 5.0 GPa is obtained during the tensile deformation for L 1 2 ordered alloy at room temperature. The ab initio calculations based on the exact muffin‑tin orbitals in combination with coherent potential approximation predict that V atoms prefer to occupy the cubic corner positions of L 1 2 sublattice, and the FCC phase becomes more stable with respect to L 1 2 phase above 849 °C considering the competition between enthalpy and entropy. The ab initio molecular dynamic simulations indicate that V atoms prefer to bond with the unlike atoms (Fe, Co and Ni) in liquid FeCoNiV, which is consistent with the cubic corner site occupation of V in L 1 2 ordered structure. The present work demonstrates a new design strategy of MPEAs which focus on single phase ductile intermetallic compounds.