Delayed hydride cracking (DHC) in products from Zr-based alloys under tensile loading is considered as a texture-dependent phenomenon. DHC development is anisotropic due to crystallographically regulated operation of plastic deformation mechanisms within zones of stress concentration near moving cracks. As applied to both plain and notched samples from Zr-l%Nb sheet, it was shown by X-ray study, that α-Zr crystallites under tensile loading change their initial orientation in different manners by means of slip or twinning depending on the direction of this loading. Features of the plastic deformation zone at the tip of moving crack vary in accordance with operating mechanisms. The revealed regularities of local reorientation are valid in the case of DHC in channel CANDU tube from Zr-2.5%Nb alloy as well. The orientation of S-hydrides, observed near the fracture surface, testifies that they reprecipitate in α-Zr matrix both by its initial texture and after twinning. The proposed mechanism of DHC involves the twinning by {10.2} planes within the plastic deformation zone near the crack tip, formation of the distinct boundary between deformed and undeformed regions with the increased gradient of lattice distortion, the intense diffusion of hydrogen to this boundary, the preferential precipitation of stress-oriented hydrides at its favorably positioned sections, and the growth of hydrides both inside and outside the plastic deformation zone till the next step of the crack between boundaries, decorated by hydrides. The known anisotropy of DHC reflects variation of the capacity of the α-Zr matrix to deform by twinning depending on the direction of tensile loading.
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