Effect of additive elements on cold workability in FeCo alloys

Abstract

Addition of various elements to equiatomic FeCo alloys and changes in ratio of iron and cobalt have been examined in order to study mechanisms for the improvement of ductility in the alloy. It has been revealed that Fe30Co70, one of the alloys having a different Fe/Co ratio, and alloys having additive elements such as carbon, vanadium, chromium, nickel, niobium, molybdenum, tantalum and tungsten ranging from 0.5 to 2 at %, are effective in improving ductility; whereas aluminium, beryllium, boron, copper, gold, manganese, silver, silicon, titanium and zirconium are ineffective. A common feature is found in the effective alloying elements: the elements combine with cobalt to form an Co3X type compound that can be produced only by diffusion; for instance, Co3C, Co3V, Co3Cr, Co3Ni, Co3Nb, Co3Mo, Co3Ta and Co3W. It is suggested, as a way of explaining this common feature, that as a result of the formation of the Co3X compound, the zones, difficult to cause the order lattice may be produced around the compound particles, and thus resulting in ductility.