Texture Evolution Under Fast Heating and Cooling Rates of Zirconium Alloys Studied In-Situ by Synchrotron X-Ray Diffraction

Abstract

In-situ synchrotron x-ray diffraction (SXRD) was used to study the texture evolution of a recrystallized (RX) Nb-containing Zr-alloy and a cold-worked (CW) Nb-free Zr-alloy under fast β-thermal cycles, which are characteristic of loss-of-coolant accidents (LOCA) in light-water nuclear reactors. When using a fast heating rate of 100oCs -1 , it was found that the α-microstructure and α-texture developments during the early stage of heating, prior to noticeable phase transformation, and the β-texture in the two-phase regime are greatly affected by the RX and CW conditions. During transformation on heating, variant selection does not occur and the β-texture is weak, but different for both starting conditions. During β-grain growth in the single β-phase regime, the β-texture strengthens. During transformation on cooling, variant selection occurs early in the nucleation of the α-phase. However, there is no or little variant selection in the CW condition. A difference in chemical composition between the zirconium alloys does not affect transformation textures and variant selection. The findings provide accurate inputs of texture for zirconium fuel claddings when modelling their mechanical behaviour in LOCA. The link between deformation, fast heating rates and microstructure evolution might also be relevant for other processes like additive manufacturing and forging in the two-phase region.