Stress-induced reorientation of hydrides in Zr-1Nb-0.01Cu cladding tube studied by synchrotron X-ray diffraction and EBSD

High-energy X-ray diffraction and electron backscatter diffraction techniques were employed to investigate the hydride precipitation in Zr-1Nb-0.01Cu cladding tube under different internal pressures up to 30 MPa. Hydride reorientation occurs when the internal pressure exceeds 10 MPa. Higher internal pressure applied to the cladding tube induced plastic deformation, which significantly increases the nucleation sites of the δ-hydrides.

The different evolutions of the (111) d-spacing with the azimuth angles indicated that the δ-hydrides precipitated from the cladding tubes under different internal pressures possessed different residual stress fields. Detail analysis of stereo-graphic projections confirmed that both the circumferential and radial δ-hydrides precipitated under different internal pressures followed the {0001}α-Zr // {111}δ-hydride and <110>α-Zr // <110>δ-hydride orientation relationship with their parent α-Zr matrix.

The δ-hydride {111}<11> twins may form when the Shockley partial dislocations glide on the alternate close-packed (0001) basal planes and the alternating distribution of δ-hydride twins may result in a deflection of hydride packet. The δ-hydride precipitates along the radial direction of the cladding tube under internal pressure is more adaptable to the volume expansion induced by phase transformation.