Intragranular thermal transport in U-50Zr

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 gamma phase, the low temperature delta phase, and the metastable omega 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 d phase exhibits significant thermal anisotropy. The gamma phase has the highest thermal conductivity. The higher conductivity of the gamma phase is thought to be due to the presence of Zr precipitates that slightly change the stoichiometry of the gamma matrix. The highly disordered omega phase appears to be thermally isotropic and has a lower conductivity than the delta phase. Both observations are likely due to the presence of delta domains that reside between u domains. This supposition is supported by the presence of thermal heterogeneities that appear as noise in the measured signals. (C) 2020 Elsevier B.V. All rights reserved.