The Effect of Zirconium Hydride on the Corrosion and Mechanical Behavior of Zirconium Base Metal: Experimental and Simulation Studies

In this study, the corrosion and mechanical behavior of zirconium hydride on zirconium alloys in 1% LiOH solution were studied. The electrochemical method was used to create the hydride phase. In this method, the hydrogen atoms were surface-adsorbed, followed by penetration into the bulk, causing the formation of the Zirconium-hydride phase. X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM) studies were done to investigate the hydride microstructure. Results of XRD and SEM observations confirmed the formation of the hydride phase. According to the crystallographic parameters, the volume of the hydride primitive unit-cell (i.e. for one Zirconium atom) is approximately 12% larger than that of the metallic phase, creating micro-cracks once formed. Therefore, this phase was observed as cracks in the microstructure. Besides, the formation of cracks significantly reduces mechanical properties and increases the corrosion rate due to the ionic and electronic changes in the oxide layer (about 80 times). Results of the atomic simulation showed the initial preferential growth of the cracks was due to the anisotropy of the eigenstrain of the hydride phase which was attributed to the volumetric difference between the hydride phase and the zirconium matrix. Atomistic simulations also show that the formation and growth of the crack occurred in the α-Zr basal planes in the direction with the least elastic energy.