Microstructure and texture analysis of δ-hydride precipitation in Zircaloy-4 materials by electron microscopy and neutron diffraction

This work presents a detailed microstructure and texture study of various hydrided Zircaloy-4 materials by neutron diffraction and microscopy. The results show that the precipitated delta-ZrH1.66 generally follows the delta(111)//alpha(0001) and delta[1 (1) over bar0]//alpha [11 (2) over bar0] orientation relationship with the alpha-Zr matrix. The delta-hydride displays a weak texture that is determined by the texture of the alpha-Zr matrix, and this dependence essentially originates from the observed orientation correlation between alpha-Zr and delta-hydride. Neutron diffraction line profile analysis and highresolution transmission electron microscopy observations reveal a significant number of dislocations present in the delta-hydride, with an estimated average density one order of magnitude higher than that in the alpha-Zr matrix, which contributes to the accommodation of the substantial misfit strains associated with hydride precipitation in the alpha-Zr matrix. The present observations provide an insight into the behaviour of delta-hydride precipitation in zirconium alloys and may help with understanding the induced embrittling effect of hydrides.