Effect of FCC anti-ferromagnetic ordering on the stability of phases in Fe60-xMn30Cr10Cox high entropy alloys

Abstract

The FCC-HCP martensitic transformation in High-Mn steels is strongly affected by the magnetic ordering of the FCC austenite which stabilizes this structure. This manuscript extends the analysis of relative phase stabilities and the effect of magnetic ordering to the FeMnCrCo high entropy alloys recently developed. The effect of Co addition on the martensitic transformation temperatures and magnetic order temperature has been experimentally determined. The substitution of Iron by Cobalt atoms leads to an increase of the martensitic transformation temperature as Co content increases. However for Co contents smaller than approximately 3 at % the FCC-HCP transition is completely inhibited. It is shown that the austenitic FCC structure in the quaternary Fe–Mn–Cr–Co system presents a para to antiferromagnetic transition and that the Néel temperature linearly decreases with the addition of Co. In the same way as in ternary Fe–Mn-X based alloys, it is shown that the antiferromagnetic state of the FCC phase stabilizes this structure. However, this stabilization is less strong in the present quaternary alloys, and -by specific heat measurements-we show that this effect can be rationalized by a decrease of the magnetic entropy change when Co is added. The present results and conclusions are important to design new High Entropy Alloys with a larger number of components.