THE INTRINSIC DEGRADATION BEHAVIOR OF THE LAVES PHASE ALLOY ZR0.9TI0.1CR0.9FE1.1 UPON TEMPERATURE-INDUCED HYDROGEN ABSORPTION DESORPTION CYCLING

The intrinsic degradation behaviour of the Zr-based Laves phase alloy Zr0.9Ti0.1Cr0.9Fe1.1 upon temperature-induced hydrogen absorption-desorption cycling is investigated by pressure-composition isotherm measurements, X-ray diffractometry and thermal analysis on the degraded samples. After 7000 thermal cycles between room temperature and 270-degrees-C the reversible hydrogen absorption capacity decreases by about 15%. As the cycling temperature and/or applied hydrogen pressure increase, the degradation phenomenon becomes more severe. The cause of the intrinsic degradation is found to be a stable crystalline hydride phase with a higher Cr content than the original matrix. Under severe cycling conditions it is observed that transformation to an amorphous phase is also a possible reason for the degradation. These structural modifications are strongly activated by the internal accumulation of elastic strain due to the repetitive hydrogenation treatments and the applied thermal energy. It is suggested that the corresponding mechanism is related to the motion of Cr and Fe atoms.