The role of ternary alloying elements in eutectoid transformation of U–10Mo alloy part II. In and ex-situ neutron diffraction-based assessment of eutectoid phase transformation kinetics in U-9.8Mo-0.2X alloy (X = Cr, Ni or Co)

Abstract

Exploring the effects of minor ternary alloying additions, typically impurity elements, on the phase stability of U–10Mo is important for preventing undesirable phase decomposition during processing or during service. This work examines the influence small ternary additions of Cr, Ni, and Co. Both in-situ and ex-situ neutron diffraction measurements made during and after high temperature (450–525 °C) exposures were used to better define the influence of these elements on the time-temperature-transformation (TTT) behavior of U–10Mo, providing information which is complementary to electron microscopy investigations of the same alloy systems performed in the first part of this work. Minor additions of Ni and Co decrease the γ-phase stability at all temperatures investigated. Signatures of U6X (X = Ni or Co) compounds were shown to be present in amounts of up to 6 wt% in the heat treated alloys, suggesting that the initial precipitation of this phase may catalyze further γ-phase decomposition. On the other hand, the Cr containing alloys were observed to have nearly the same, and in some cases slower, phase transformation kinetics when compared to the binary U–10Mo control samples. The results of the study have enabled preliminary estimates of the TTT curves for the ternary alloys.