Formation mechanism of in-situ nanostructured grain in cast Cu–10Sn–2Zn–1.5Fe–0.5Co (wt.%) alloy

Abstract

In-situ nanostructured grain (NG), with numerous iron-rich nanoparticles dispersed within refined copper grains (20–40μm), was achieved in Cu–10Sn–2Zn–1.5Fe–0.5Co (wt.%) alloy fabricated by centrifugal casting. NG structure resulted in excellent combination of high strength and high ductility. Formation mechanism of NG structure in the alloy was studied. Iron-rich nanoparticles were confirmed to in-situ precipitate in the melt prior to copper solidification. Grain refinement is attributed to the high potency, suitable size, appropriate size distribution and adequate number density of the nanoparticles. Based on the high potency of the nanoparticles, nanoparticle encapsulation model was proposed to interpret the nanoparticle-matrix interactions during solidification. Some encapsulated nanoparticles (i.e. iron-rich nanoparticle encapsulated by initial copper layer) catalyze the nucleation of copper grains, promoting the fine equiaxed non-dendritic grains growth, others are incorporated into copper grain by spontaneous capture. Moreover, a pathway was summarized for fabricating bulk nanostructured alloys, wherein favorable NG structure formed by the interactions between in-situ nanoparticle and the matrix during solidification was used to achieve good ductility and high strength.