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

The ordered L1(2) phase generally appears as dispersed precipitates in FCC multi-principal element alloys (MPEAs). In this work, a single L1(2) ordered intermetallic is obtained in the annealed equimolar FeCoNiV alloy. Experiments show that the FCC to L1(2) ordering transformation occurs below 778 +/- 2 degrees 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 L1(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 L1(2) sublattice, and the FCC phase becomes more stable with respect to L1(2) phase above 849 degrees 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 L1(2) ordered structure. The present work demonstrates a new design strategy of MPEAs which focus on single phase ductile intermetallic compounds. (c) 2019 The Authors. Published by Elsevier Ltd.