EFFECT OF SPECIMEN THICKNESS ON CORROSION FATIGUE CRACK GROWTH BEHAVIOUR IN TITANIUM ALLOYS

摘要

Fatigue tests were conducted on β Ti-15Mo-5Zr-3Al alloy and (α + β) Ti-6A1-4V alloy in room air and in 3%NaCl solution in order to clarify the effects of specimen thickness and environment on fatigue crack propagation (FCP) behaviour. Specimens with three different thicknesses of 0.5, 2 and 10mm were used. In Ti-15Mo-5Zr-3Al alloy, FCP rates were identical for all the thicknesses in high ΔK region, but were enhanced in low ΔK region with decreasing thickness in both environments. In Ti-6Al-4V alloy, the da/dN - ΔK relationships in room air were almost similar for all the thicknesses, while in 3%NaCl solution, FCP rates were accelerated markedly in high ΔK region. It was found that the FCP resistance of Ti-15Mo-5Zr-3Al alloy was inferior to that of Ti-6Al-4V alloy.