Low Temperature Ageing Behaviour of U-Nb $\alpha''$ Phase Alloys

TL;DR

This study investigates the microstructural and phase evolution of U-5%Nb alloys aged at 150°C over 5000 hours using multiple analytical techniques, revealing defect-driven martensitic tendencies and phase progression.

Contribution

It provides detailed insights into the microstructural changes and phase transformations in U-Nb alloys during low-temperature ageing, utilizing comprehensive surface and bulk analysis methods.

Findings

Crystallographic defects like twinning promote martensitic tendencies.

Lattice resizing and atom shuffling lead to phase transition from α'' to α'.

Ageing induces microstructural evolution detectable by SEM, TEM, XRD.

Abstract

Ageing mechanisms of the U-5\,\%wtNb system have been investigated on samples exposed to temperatures of 150$\,^{\circ}$C for up to 5000\,hours. A variety of surface and bulk analytic techniques have been used to investigate phase, chemical and crystallographic changes. Characterisation of microstructural evolution was carried out through secondary electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDS), electron backscatter diffraction (EBSD), transmission electron microscopy (TEM) and x-ray diffraction (XRD). This investigation suggests crystallographic defects such as twinning furthers the martensitic tendencies with ageing. Resizing of the lattice and shuffling of atoms results in a small progression from the $\alpha''$ towards the $\alpha'$ phase.