Formation and characterization of circular δ-hydride in Zircaloy-4 under ion irradiation

Abstract Zircaloy-4 with 200 wppm hydrogen was irradiated with 3 MeV Fe11+ ions and the microstructural evolution of δ-hydride precipitation under ion irradiation was investigated. TEM observation of unirradiated sample shows the needle-like δ-hydride and the orientation relationship between α-Zr matrix and δ-hydride is (0002)α//(1 1 ¯ 1)δ, [2 1 ¯ 1 ¯ 0]α//[011]δ. After ion irradiation, both and -type dislocation loops were observed in α-Zr matrix. Some circular structures with obviously different contrast from the α-Zr matrix were observed in the irradiated Zircaloy-4-200 wppm H samples. The circular structures were identified as δ-hydrides with an fcc structure by indexing the FFT patterns of HRTEM images. There is an orientation relationship of (01 1 ¯ 1 ¯ )α//(200)δ, [01 1 ¯ 2]α//[011]δ between the circular δ-hydride and α-Zr. The formation of circular δ-hydride is related with ion irradiation and the formation process is explained by the hydrogen trapping mechanism.