Intragranular thermal transport in U–50Zr

Abstract

A thermoreflectance method was used to measure intragranular thermal diffusivity and conductivity of samples having a composition of U-50 wt%Zr (U–50Zr). Three phases at this composition were investigated: the high temperature γ phase, the low temperature δ phase, and the metastable ω phase. This approach uses a tightly focused laser to inject micron scale thermal waves and a second tightly focused laser to monitor the temperature distribution. The thermal properties are extracted by comparing experimental temperature profiles to an analytical heat diffusion model. The probe laser can monitor the temperature field in orthogonal directions along the surface of the sample and is well suited to measure thermal anisotropy. We show that the δ phase exhibits significant thermal anisotropy. The γ phase has the highest thermal conductivity. The higher conductivity of the γ phase is thought to be due to the presence of Zr precipitates that slightly change the stoichiometry of the γ matrix. The highly disordered ω phase appears to be thermally isotropic and has a lower conductivity than the δ phase. Both observations are likely due to the presence of γ domains that reside between ω domains. This supposition is supported by the presence of thermal heterogeneities that appear as noise in the measured signals.