Microstructural analysis of the thermodynamically controlled hydride phases grown in the ZrNi-H2 system

The microstructure evolution induced by hydrogen absorption in the ZrNi compound was investigated during the activation process. A rigorous control of the thermodynamic parameters during the hydride phases growth allowed to prepare two samples of overall composition ZrNiH0.746 and ZrNiH2.55. First, the formation of fine platelets of the monohydride β-phase was investigated by X-ray diffraction, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). A shear mechanism is proposed to explain the microstructure, the orientation relationship and the habit plane of the β-phase in the ZrNi-Hx α-phase matrix. Then, for the first time, a monohydride/trihydride compound was analysed by transmission electron microscopy. This allowed us to determine the morphological and crystallographic characteristics of the trihydride γ-phase.