Characterization of zirconium hydrides in Zircaloy-4 cladding with respect to cooling rate

In order to characterize the habit planes and crystallographic relation between the α-matrix and various kinds of Zr hydrides, three different Zr hydrides including δ-hydride, γ-hydride, and surface hydride are produced by controlling the cooling rate from 0.5 to 300 °C/min. Analysis of SAED patterns and TEM images of the Zr hydrides demonstrates representative habit planes and crystallographic relation according to the hydride morphologies. The macroscopic δ-hydride has two kinds of habit planes such as {101¯7}α and {0002}α, while microscopic δ-hydride has the habit plane of {0002}α at the cooling rate of 0.5-10 °C/min. The microscopic γ-hydride has the major habit plane of {101¯7}α at the cooling rate of 300 °C/min in which the crystallographic relation between the γ-hydride and the α-Zr matrix as (111¯)γ‖(011¯1)α;(111)γ‖(0001)α;[11¯0]γ‖[112¯0]α.