NOVEL OXIDE-DISPERSION-STRENGTHENED COPPER-ALLOYS FROM RAPIDLY SOLIDIFIED PRECURSORS .1. MICROSTRUCTURAL DEVELOPMENT

ZrO2, Y2O3, and rare earth oxides with related structures are attractive candidates for dispersion strengthening of copper alloys but pose significant processing challenges owing to the low solubility of the oxide-forming elements in Cu. It is shown that the problems may be circumvented by a synthesis approach coupling rapid solidification and internal oxidation, followed by standard powder metallurgy consolidation. Cu-Zr and Cu-Y alloys were melt spun into ribbons similar to 50- to 150-mu m thick and internally oxidized at 1023 to 1223 K to yield similar to 1 vol pet of ZrO2 or Y2O3 particles ranging in size from less than or similar to 5 nm up to similar to 150 nm. The coarser oxides result from direct oxidation of the intermetallic segregate, whereas the finer ones are generated by a dissolution-reprecipitation process. The relative proportions of fine and coarse oxides and the homogeneity of the distribution are related to segregation scale in the melt-spun ribbon and the relative permeabilities of oxygen and the oxidizable element in the alloy, which depend on the internal oxidation temperature. The oxide dispersoids were mostly cubic zirconia or cubic yttria and exhibited predominantly cube-on-cube orientation relationships with the matrix. Analysis of particle shapes revealed that the dominant interfaces are of the type {001}(Ox) parallel to {001}(Cu) and {1(1) over bar1$}(Ox) parallel to {1(1) over bar1$}(Cu) and could be explained by image charge interaction concepts. Extrusion produced an elongated grain structure but no significant changes in the oxide distribution.