Effect of hydrogen on the phase–structure transformations in ZrCrNi alloy

The effect of hydrogen—Hydrogenation, Disproportionation, Desorption, Recombination (HDDR) process—for the ZrCrNi alloy on its phase–structure transformations was investigated by means of differential thermal analysis (DTA) and X-ray diffraction (XRD) at the initial hydrogen pressure ∼5.0 MPa and the temperature range from room temperature to 970 °C. The hexagonal C14 (MgZn 2) type Laves phase is the main phase of the alloy. Besides the peak of hydrogen absorption at room temperature, two exothermic (at 535 and 675 °C) and two endothermic (at 791 and 819 °C) effects were determined by DTA during heating of the ZrCrNi–H 2 system. The decomposition (disproportionation) of hexagonal C14 type Laves phase started at the initial hydrogen pressure P H 2 =5.2 MPa and at a temperature of 535 °C. Zirconium hydride, Zr–Ni binary phases (ZrNi 3, Zr 2Ni, Zr 2Ni 7) and chromium are the disproportionation products. Multiphase alloys with different proportions of the cubic C15 (MgCu 2) type and the hexagonal C14 (MgZn 2) type Laves phase, the ZrNi, Zr 7Ni 10, Zr 9Ni 11 binary phases and Cr were obtained depending on the experimental conditions of the HDDR process in the ZrCrNi–H 2 system.