The investigation of selected NpZr alloys by X-ray diffraction up to 700 °C

Abstract

High temperature X-ray diffraction analysis of two NpZr (25 and 33 at.% Np) binary alloy specimens prepared by arc melting was performed to help elucidate important features of the NpZr phase diagram, several features of which have not been resolved. Temperatures in these studies ranged from 25 to 700 °C. The NpZr specimens were characterized as consisting of different combinations of Np, Zr and NpZr2 phases at the different temperatures. The results obtained for this Zr-rich portion of the phase diagram diagram suggest that there is not a continuous mutual solubility between γ-Np and β-Zr, as known to exist in the UZr binary system. The solubility of Zr in γ-Np was estimated to be ca. 4% at 600 °C. Only the α form of Zr was observed in these studies, indicating that there was insufficient Np dissolved in the Zr phase to stabilize its β phase below the normal α-β transition temperature of 850 °C. The hexagonal NpZr2 was detected up to 550 °C; above this temperature it appeared to decompose. Diffraction lines for the α, β and γ forms of Np were observed as a function of the temperature. Diffraction lines for Np disappeared above 650 °C, presumably because of its “localized” melting in micro-domains.