Thermal expansion behavior of δ-zirconium hydrides: Comparison of δ hydride powder and platelets

The thermal expansion coefficient of δ hydrides and the evolution of the d-spacing of δ hydride platelets in Zircaloy-4 during heat treatments were investigated by conducting synchrotron x-ray diffraction experiments. Identical experiments enabled a direct comparison of the d-spacing of δ zirconium hydride platelets with the d-spacing of the powder δ hydrides. By analyzing the experimental data of this study and the data available in the literature, the thermal expansion coefficient of pure δ hydrides was determined as 14.1 10−6 °C−1. A direct comparison of the d-spacings of δ hydride platelets in CWSR Zry-4 sheet and the powder δ hydride samples showed an evolution of temperature-dependent strains within the δ hydride precipitates in which the strain components normal to the platelet edges exceed that normal to the platelet face during cooling/precipitation but not during heating/dissolution above approx. 200 °C.