ISOTHERMAL TRANSFORMATION OF U-14 AND U-16 WT % Mo ALLOYS AT 550 C. Interim Report

Abstract

Isothermal transformation kinetics studies of nominal U-14 and U-l6 wt% Mo alloys were carried out to determine the limits of gamma-phase stability in these alloys at 550 deg C. Vacuum induction melted and homogenized samples were gammatized in vacuum at 900 deg C for 72 hr and ice-water quenched. The gamma phase was retained in each sample. The gammatized samples were then isothermally heat treated in vacuum for specified intervals, icewater quenched, and examined by x-ray diffraction, metallographic, and microhardness techniques for evdence of transformation. The retained and metastable gamma phase in U-l4 and U-l6 wt % Mo alloys began to transform to the alpha plus gamma prime and gamma prime phases after 20 and l6 hr, respectively, as indicated by x-ray diffraction and metallography. However, a transition phase, believed to be of alpha phase U-Mo, appeared in the alloys after 0.3 hr in U-l4 Mo and 0.1 hr in U-16 Mo. A plot was made of the variation in time at 550 deg C for the beginning of equilibrium transformation and molybdenum content. U-10 wt% Mo alloys are more gamma stable at 550 deg C than other alloys in the range of about 5 to l6 wt% Mo. However, U- 16 wt% Mo alloys transform to a stable gamma prime equilibrium phase, a promising structure for high temperature, high burnup reactor service. (auth)