Effects of rare earth additions on structures and properties of rapidly solidified copper alloys

Copper based Cu-RE alloys (where RE represents lanthanum, neodymium, or sam arium) with alloying content up to 16 wt-% were prepared by chill block mel t spinning into ribbons of thickness between 40 and 100 mu m. The melt spun ribbons were heat treated isochronally for 2 h at 300, 400, 500, 600, 700, and 800 degrees C, respectively. The melt spun and heat treated ribbons we re tested for microhardness and resistivity and were characterised by optic al and transmission electron microscopy (TEM) and X-rap diffractometry (XRD ). Microstructures were of the typical zone B type for Cu-1RE and Cu-3RE ri bbons and of the zone B/zone A type for Cu-5RE, Cu-8RE, and Cu-12RE ribbons . Only microstructures of the zone A type were found in Cu-15La ribbons. Th e metastable extended solid solubilities of the rare earth elements were ev aluated by measurements of the lattice parameters of the supersaturated sol id solutions and significant extension from the equilibrium solid solubilit y was found for all three alloys. The secondary phase was identified by TEM and XRD as Cu, RE for all ribbons except Cu-15La ribbons in which metastab le Cu5La and Cu13La phases were also found. Observations using TEM and XRD also showed a reduction in the alpha-Cu grain size of the as spun ribbons w ith increasing alloying content, producing nanosized alpha-Cu grains on the chill side of the ribbons. Heat treatment of the ribbons at 400 degrees C for, 2 h produced no significant coarsening of alpha-Cu grains as the size of these grains was still in the nanometer region. Both alpha-Cu and Cu6RE grains coarsened as a result of heat treatment for 2 h at temperatures of 6 00 degrees C and above for all the alloys.