Paul S. Dunn

Martensitic structures and deformation twinning in the U–Nb shape-memory alloys

Abstract An investigation of the microstructures of four U–Nb alloys has been conducted. The nominal Nb contents are 5, 9, 13 and 18at.% (approximately 2, 4, 5.5 and 8 wt%). The self-accommodating twin structures have been characterized and considered in terms of the lattice parameters of the martensite phases as well as the tetragonal distortion associated with the previously proposed intermediate γ0 phase. In addition, active deformation twinning systems during deformation of the U–13 at.% Nb shape-memory alloy have been identified and are discussed with respect to the α monoclinic distortion and ease of propagation in the microstructure.

Quantification of Large Scale Micro-X-Ray Fluorescence Elemental Images:

Niobium is commonly alloyed with uranium to prevent surface oxidation, and determining how the niobium concentration is distributed throughout a sample is useful in explaining observed material properties. The niobium concentration distribution was determined across the surface of depleted uranium samples using micro-X-ray fluorescence (MXRF). To date, MXRF has been employed primarily as a qualitative tool for determining relative differences in elemental concentrations across a sample surface. Here, a process was developed to convert qualitative MXRF niobium distribution images from depleted uranium samples into images displaying concentration values. Thus, MXRF was utilized to determine elemental concentrations across a surface in a manner similar to that of the established method of electron microprobe X-ray analysis (EMPA). However, MXRF can provide such information from relatively large sample areas many cm2 in size that are too large to examine by the higher spatial resolution technique of EMPA. Although the sample surfaces were polished to the same degree as the standards, little or no sample preparation should be necessary for sample systems where a high energy analyte XRF line can be used for imaging.