Ti-6Al-4V合金の衝撃靭性におよぼす水素添加の影響

抄録

Ti-6Al-4V alloys variously heat treated are hydrogenated by cathodic charging. The impact toughness of these alloys are evaluated using an instrumented Charpy impact testing machine. Then, the relationship between the hydrogen embrittlement and the heat treatment condition, i.e. the microstructural factor is examined.
The reduction ratio of energy (r_i, r_p, r_t) and that of fracture load (r₁) which indicate the degree of hydrogen embrittlement increase with hydrogen charging time. These reduction ratios increase with the width of hydrogen embrittled fracture surface, which is equivalent to the width of hydride precipitated zone, and with the decrease of the areal percentage of primary α in the equiaxed α structure. The width of hydrogen embrittled fracture surface is in linear relationship with the hydrogen content. Ti-hydride precipitates mainly at α-β interface and also in α phase. Hydrogen embrittled cracks propagate mainly along primary α-β interfaces where much hydride exists, and sometimes propagates through primary α in the equiaxed α structure. On the other hand, cracks propagate mainly across acicular α phase in the acicular α structure.