Formation of Cr and Cr 2Nb precipitates in rapidly solidified Cu-Cr-Nb ribbon

Abstract

Ribbons of a Cu-Cr-Nb alloy produced by chill-block melt-spinning were examined to determine the phases present in the as-melt-spun material. Combined electron diffraction and EDS analyses determined that the as-melt-spun ribbon contained two precipitate phases. Both elemental Cr precipitates with an average diameter of 18 nm and the hexagonal phase of Cr 2Nb with a bimodal size distribution with average particle sizes of 13 and 5 nm were found. Based upon the spheroidal shape of the particles, their lack of well defined orientation relationships with respect to the copper matrix, and kinetic arguments, the conclusion was drawn that the observed precipitates formed predominantly in the liquid Cu prior to solidification of the ribbon. The formation of these precipitates in the liquid Cu indicates a very strong dividing force for the formation of the elemental Cr and Cr 2Nb phases.