Complementary Techniques for Quantification of $\alpha$' Phase Precipitation in Neutron-Irradiated Fe-Cr-Al Model Alloys


The substandard performance of Zircaloy LWR cladding materials under loss-of-coolant accident (LOCA) conditions has prompted the search for a more well-suited material for these conditions. Initial investigations of Fe-Cr-Al alloys have demonstrated their superior high temperature oxidation and corrosion resistance compared to Zr-based alloys [1]. However, questions still remain regarding the radiation tolerance of Fe-Cr-Al alloys which, similar to other high-Cr ferritic alloys, are susceptible to embrittlement due to the precipitation of a Cr-rich $\alpha$ʹ phase. Quantification of $\alpha$ʹ phase precipitation has historically been limited to bulk average analysis using small angle neutron scattering (SANS) techniques, as no contrast is seen using conventional TEM imaging techniques due to the semi-coherency of the $\alpha$ʹ phase with the $\alpha$-Fe matrix [2]. However, the advent of local electrode atom probe tomography (APT) and improvements in STEM/EDS chemical mapping have allowed for a more localized investigation of the morphology and composition of these precipitates. Coupling of these techniques allows one to overcome the individual limitations of each approach, resulting in a more comprehensive determination of precipitate evolution and structure. A greater understanding of the mechanisms underlying this precipitation phenomenon allows for a more informed alloy development process as well as the formulation of increasingly robust predictive models of radiation response.

In: Microscopy and Microanalysis, pp. 1470–1471