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

This work deals with the microstructural characterization of bulk Cu-50(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 degrees C and 980 degrees 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 FeCorich 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 mu m after sintering increased to 0.85 mu m after annealing at a temperature corresponding to 90% of the melting point. Thus, the Cu-50(FeCo)(50) alloy exhibits excellent thermal stability compared to other ultrafine-grained materials, which is caused due to its immiscible nature.