Ti-6Al-4Vの低応力拡大係数域における大気中疲れき裂伝播特性の解析

抄録

Fatigue crack growth property in air in three kinds of Ti-6Al-4V was analyzed at stress intensity range less than 30 kgf/mm^3/2. The following results were mainly obtained.
1) α phase shows cleavage-like fracture at low stress intensity range. The fracture mode of β phase depends on the shape of a precipitated in β phase. Fracture surface of β phase in which fine a particles precipitated is flat and featureless, and that in which lath like a plate formed is cleavage like.
2) Microstructure influences fatigue crack growth rate, which depends on the volume of a phase, shape of a particles in β phase etc.
3) ΔK threshold decreases with increase of stress ratio until more than 0.9.
4) The effective ΔK threshold is about 7.5 kgf/mm^3/2 without reference to microstructures, because the mode of fracture is intergranular at ΔK close to the ΔK threshold and is same among the three kinds of specimens.