Phase reversion kinetics of thermally decomposed (α + γ′) phases to γ-phase in U – 10 wt% Mo alloy

Abstract Thermally induced phase reversion kinetics of decomposed α + γ′ phases to γ phase was investigated for the U – 10 wt% Mo (U–10Mo) hypoeutectoid alloy using X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The as-cast U–10Mo alloy was homogenized to the γ phase at 1073 K for 96 h, and decomposed at sub-eutectoid temperature of 773 K as a function of time from 240 to 1200 h. The decomposition of γ phase initiated via two mechanisms: (1) discontinuous precipitation (DP) or cellular precipitation along the grain boundaries and inclusions; and (2) continuous precipitation (CP) within the γ grains as γ′ needles. After 720 h at 773 K, the DP colonies completely consumed the continuous γ matrix, after which discontinuous coarsening (DC) was observed. The completely-decomposed U–10Mo alloy samples were then annealed at 843, 853, and 863 K as a function of time to document the kinetics of α+γ’ → γ phase reversion. The reference intensity ratio analysis was employed to XRD patterns to quantify the phase amount after each heat treatment. A combinatorial kinetic model, consisting of the classical JMAK nucleation and growth, and spherical particle dissolution, was employed to describe the α+γ’ → γ phase reversion as a function of time and temperature. This phenomenological model provided a good approximation for the phase reversion within the temperature and time ranges examined in this study. Furthermore, a diffusion enhancement approach was employed for a set of typical irradiation parameters to estimate the irradiation effect on the α+γ’ → γ phase reversion kinetics.