Dispersion strengthening of copper by internal oxidation of rapidly solidified Cu-RE alloys

Abstract

Combination of rapid solidification and internal oxidation was used for producing a fine dispersion of rare earth oxide particles in the copper matrix. An overall microstructural analysis has shown that the internal oxidation temperature, the rapidly solidified microstructure and its changing ahead of the internal oxidation front strongly influence the mechanism of the internal oxidation process and the resulting microstructure. The internal oxidation in a Cu-Yb alloy took place mainly by direct oxidation of intermetallic particles. Contrary to this, in a Cu-Er alloy two mechanisms of internal oxidation have been clearly observed: (i) Dissolution of intermetallic particles ahead of the internal oxidation front and oxidation of the erbium from the solid solution and (ii) direct oxidation of the Cu-Er intermetallic particles. While a reasonable optimum combination of processing conditions at internal oxidation in the solid state, yielding suitable oxide dispersions, seems to have been identified for the Cu-Er alloy, the same was not true for the Cu-Yb alloy. However, the internal oxidation of the Cu-Yb alloy in the semisolid state, which occurs by alternation of two processes - Yb oxides precipitation and Cu matrix solidification - led to a relatively uniform dispersion of Yb oxide particles.