EFFECT OF AGING ON THE DEPENDENCE OF FATIGUE CRACK GROWTH BEHAVIOR ON MEAN STRESS (STRESS RATIO) IN THE β- TITANIUM ALLOY: Ti-10V-2Fe-3Al

摘要

The effect of mean stress or stress ratio, R, on fatigue crack growth (FCG) behavior of α-aged and ω-aged microstructures of the beta titanium alloy Ti-10V-2Fe-3Al was investigated. While the mean stress had a negligible effect on the FCG behavior of the α-aged microstructure, a strong effect was observed in the ω-aged microstructure. In particular the values of threshold stress intensity range (ΔK_(th)) exhibited a strong dependence on R in the ω-aged microstructure, while this dependence was weak in the α-aged microstructure. These effects seem to arise primarily from fracture surface roughness induced crack closure. Crack closure levels for the α-aged microstructure were found to be very low compared to those for the ω-aged microstructure. Transmission and scanning electron microscopic studies of microstructures and fracture surfaces were performed to gain insight into the deformation characteristics and crack propagation mechanisms, respectively in these microstructures. The microstructure- induced differences in fatigue crack growth behavior are rationalized in terms of the effect of aging on slip and crack closure.