Phase and Morphology of ZrO<SUB>2</SUB> in Internally Oxidized Dilute Cu&ndash;Zr Alloys

Abstract

Dilute Cu-Zr alloys containing 0.39-1.95 mass%Zr were internally oxidized in the temperature range of 973-1323 K. The phases of dispersed oxides were identified by X-ray diffractometry, and the mean oxide particle sizes were measured by transmission electron microscopy. From X-ray diffractometry of the nitric-acid-treated insoluble residues, the oxide phases precipitated by internal oxidation were monoclinic and tetragonal ZrO2. The amount ratio of monoclinic ZrO2 to the total oxide was increased with the concentration of Zr at a constant internal oxidation temperature. In the case of alloys having the same concentration of Zr, the amount of monoclinic ZrO2 presented the minimum values at about 1223-1243 K. By transmission electron microscopy, it was revealed that large monoclinic ZrO2 particles were precipitated at grain boundaries of Cu and fine monoclinic and tetragonal ZrO2 particles were precipitated inside the Cu grains. The mean particle size of fine precipitates in Cu grains was increased with the distance from the surface. Any difference in the mean particle size of fine ZrO2 inside the Cu grains was not observed among the alloys having different concentrations of Zr, owing to the limitation of solution of Zr into Cu.