In-situ EBSD analysis of hydride phase transformation and its effect on micromechanical behavior in Zircaloy-4 under uniaxial tensile loading

Abstract

In this work, hydrogen charged Zircaloy-4 has been investigated under an in-situ electron backscatter diffraction during tensile loading. Aim were, first, to distinguish the hydride phase type and its spatial distribution, second to determine hydride phase transformation (HPT) and orientation relationship (OR) subjected to uniaxial tensile condition, and third to correlate the hydrides evolution and their effect on the micromechanical behavior, such as slip mode activation and lattice rotation, of Zircaloy-4. Apart from the applied stress, the analysis reveals that hydride reorientation is strongly related to temperature and loading mode. We noted that deformation induced δ-ZrH1.5 transformed to γ-ZrH and ε-ZrH2, and the former follows the confirmed OR {0001}α//{111}δ/γ with <11 2‾ 0>α//<110>δ/γ, while the latter's OR changed to {10 1‾ 0}α//{121}ε with <11 2‾ 0>α//<100>ε after HPT. The coexistence of δ-ZrH1.5 and γ-ZrH or ε-ZrH2 is observed, and the main corresponding OR is {111}δ//{111}γ with <121>δ//<121>γ, and {100}δ//{110}ε with <110>δ//<100>ε, respectively. The characterized microstructure and the measured lattice rotation results indicate that HPT delayed cracking in hydride and promoted deformation in parent grains. As the strain increases, the maintenance of hydride-matrix (H-M) coherent interfaces restricts further lattice rotation. HPT accelerates the hydride decomposition ascribed to the intensification of hydrogen diffusion under stress, and the hydride and the H-M interfaces act as priority sites for initiating microcracks. The sequence of HPT depends on the possibility of activated slip mode among grains. These findings contribute to developing the understanding of the HPT and hydrogen embrittlement.