Unusual deformation-induced martensitic transformation in Fe-Co-Ni-Cr-Mn high entropy alloy thin films

Abstract

Deformation-induced martensitic transformation in Fe-Co-Ni-Cr-Mn high entropy alloy (HEA) thin film with nanocolumnar growth feature are revealed to readily occur at intermediate deposition power rather than low and high deposition power ranges. The high probability of deformation-induced martensitic transformation from face-centered cubic (FCC) to hexagonal close-packed (HCP) phase in 150 W-film results in low nanoindentation hardness and compressive yield strength, in comparison with 60 W- and 210 W-films. Dependence of the martensitic transformation probability has been explained in terms of the competition between grain size effect and nanocolumn cohesion effect on the phase metastability. The increased grain size with deposition power favors the mechanical instability of FCC parent phase caused by the weakened slip obstruction, while the enhanced nanocolumn cohesion with deposition power hinders the formation of HCP martensite due to the increased activation energy for martensitic transformation. The grain size effect is dominated over the cohesion between nanocolumn at low deposition power range, while column cohesion effect is dominant at high deposition power range, which gives rise to the crossover of FCC-to-HCP with deposition power. This work might provide a deeper understanding in phase metastability of sputtered films, for instance, the effect of deposition power on deformation-induced martensitic transformation.