The cyclic degradation of TiCrV hydrogen storage alloy has been studied by using SEM and TEM. Microstructural analysis indicated that the accumulation of lattice defects such as dislocations and strain field occurred due to volume expansion and shrinkage during cycles, led to a loss of the effective storage capacity. Annealing with minute particles in order to suppress the development of lattice defects during cycles resulted in increase in plateau width during hydrogenation but nothing improved during de hydrogenation. This is probably due to beta hydrides formed during hydrogenation, which is stable with lattice defects and strain field. Fine particles less than several hundred nano meter in size could have a good degradation resistance due to less accumulation of lattice defects and during cycles.
The effect of minor yttrium atom addition on deformation behavior was investigated using Mg X atY (X=0.01, 0.02, 0.03, 0.04 and 0.05) dilute alloys and pure magnesium with an average grain size of about 50 mm. The stress and strain curves in all the alloys showed a sigmoidal shape in the compression tests, which suggested the formation of {10˜12} type twinning due to the lack of slip system. On the other hand, yttrium atom addition of more than 0.03 at was effective to affect the deformation behavior: a large compressive strain of 0.5 was possible to obtain, and the sub grained and fine grained structures were formed even at room temperature in three kinds of alloys. The dominant deformation mechanism in these alloys was the twinning at the beginning of the state and the dislocation slip with further imposed strain.
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