Microstructure and mechanical properties of hydride blisters formed on Zircaloy-4 claddings

Abstract

To assess the microstructural and mechanical characteristics of hydride blisters formed on Zircaloy-4 tubes, we employ the electron backscatter diffraction (EBSD) analyses and micro-cantilever failure tests directly on the hydride blister (HB) area. In the HB area, more than 70% of the blister area is characterized to be δ-hydride, and the HB area does not favor the orientation relation ((101¯1)α//(001)δ, [12¯10]α//[1¯10]δ) that is otherwise well-matched in the Zr matrix area. The geometrically necessary dislocation density is observed in the entire blister area, indicating a large amount of strain throughout the blister area. Also, the deformation strain is concentrated in both the hydride and α-Zr phases of HB areas; however, the hydride underwent intensive deformation in the Zr matrix. The average fracture toughness of the hydride blister area obtained through the micro-cantilever test is 1.81 MPam, indicating a brittle fracture that may threaten the integrity of spent nuclear fuel claddings.