Ultrafine-grained Cu50(FeCo)50 immiscible alloy with excellent thermal stability

Abstract

This work deals with the microstructural characterization of bulk Cu50(FeCo)50 immiscible alloy prepared by mechanical alloying and spark plasma sintering. The microstructure evolution is investigated from milled powder through sintering to annealing at temperatures of 800 °C and 980 °C for 3 h. Despite the immiscibility of Cu with Fe and Co, the FCC supersaturated solid solution was formed upon mechanical alloying. During sintering, the supersaturated solid solution decomposed into a fine microstructure composed of Cu-rich and FeCo-rich phases. However, the equilibrium microstructure was not reached even during annealing when, in addition to FCC Cu-rich phases and BCC FeCo-rich phases, FCC FeCo-rich phases with increased Cu content were present in the microstructure. The average grain size of 0.35 μm after sintering increased to 0.85 μm after annealing at a temperature corresponding to 90% of the melting point. Thus, the Cu50(FeCo)50 alloy exhibits excellent thermal stability compared to other ultrafine-grained materials, which is caused due to its immiscible nature.