In Situ TEM Observation of Precipitation of Zirconium Hydrides in Zircaloy-4 under Hydrogen Ion Implantation
The formation of hydrides in zirconium alloy has been one of the essential matters of discussion to maintain mechanical strength of nuclear fuel cladding tubes. In this work, we examined the precipitation process of zirconium hydride by transmission electron microscopy under hydrogen ion irradiation. Zircaloy-4, which has been used extensively as nuclear fuel cladding, was irradiated with hydrogen ion at room temperature to achieve enough hydrogen concentration for precipitation. The growth of hydrides accompanied with dislocations around hydrides was observed under hydrogen implantation. The observed hydride was the γ-hydride phase with fct structure and the orientation relationship was <110>γ ||<1120>α as reported previously. As the hydride grew, the dislocations were generated gradually. This process can be explained using a ratchet mechanism suggested by Carpenter. The growth rate became lower according to the approach of other hydrides. This behavior is considered to be influenced by the strain field caused by other hydrides.
Young Won Chang, Nack J. Kim and Chong Soo Lee
Y. Shinohara et al., "In Situ TEM Observation of Precipitation of Zirconium Hydrides in Zircaloy-4 under Hydrogen Ion Implantation", Materials Science Forum, Vols. 561-565, pp. 1765-1768, 2007