The mechanism of hydrogen induced delayed crack in EBW of Ti55 alloy is the diffusion of hydrogen up a stress gradinent to form hydride TiH 2 which precipitates at the crack tip.

• 裂纹尖端应力场诱导氢原子扩散导致氢化物TiH2 析出是Ti5 5合金电子束焊缝氢致延迟裂纹扩展的主要机制