Analysis of hydrogen behaviour in crack growth tests of γ-TiAl by means of the hydrogen microprint technique

To elucidate the mechanism of hydrogen embrittlement, the behaviour of hydrogen in metals is investigated by the hydrogen microprint method. This is an attractive method in that it enables the hydrogen released from the metal surface during plastic deformation to be observed. The hydrogen behaviour in fatigue and sustained-load crack growth of γ-TiAl intermetallic compounds has been studied by means of the hydrogen microprint technique. Both fatigue crack growth and sustained-load crack growth were accelerated by the hydrogen. The region of hydrogen accumulation could easily be observed by the hydrogen microprint technique. In the case of sustained-load crack growth, it is found that hydrogen is released from the surface in the high hydrostatic stress field around the crack tip. The hydrogen microprint technique revealed that the effect of the hydrostatic stress is very large in the hydrogen accumulation around the crack tip. In fatigue crack growth, the amount of silver precipitation is discussed, which is correlated with the amount of hydrogen accumulation.