各種環境下におけるTi-6Al-4V合金の疲労強度へのフレッティングの影響

抄録

Differences in the effect of fretting on fatigue behaviors of annealed and STA heat treated Ti-6Al-4V alloys, whose β phase volume is 15% and 60%, respectively has been studied under a number of environments and discussed in relation to differences in friction coefficient, main crack initiation site at the fretted area, paring of micro cracks by pad, crack growth rate, corrosion pit initiation site and microstructures.
The saturation of fretting fatigue damage occurs beyond a certain number of fretting cycles. The ratio of the smallest number of fretting cycles to the fretting fatigue life for the saturation to occur in air is more than 90%, and that in pure water is about 50% in the STA alloy, but in the annealed alloy that in chloride-containing methanol is almost 0%. The fretting fatigue strengths are lower than the fatigue strengths in air, synthetic sea water, etc. However, in chloride-containing methanol, the fretting fatigue strength is the same as the fatigue strength in the annealed alloy, but the former is higher than the latter in the STA alloy.