Influence of Mechanical Surface Treatments on Notched Fatigue of Various Titanium Alloys

The effects of shot peening and ball -burnishing on the fatigue performance of various titanium alloys belonging to the alpha, alpha+beta and beta alloy classes will be presented. Tests were done on Ti -2. 5Cu (alpha), TIMETAL-54M (alpha+ beta) and TIMETAL LCB (beta). Smooth (k(t)=1) as well as notched (k(t) =2. 5) specimens of these alloys were prepared and the surface layer properties such as micro -hardness depth profiles and residual stress depth profiles were determined. The HCF performance was done by rotating beam loading (R=-1) in air at a frequency of 50Hz. The improvements in notched fatigue performance after mechanical surface treatments were most pronounced in the alpha alloy Ti 2. 5Cu. Results on TIMETAL LCB indicated much less improved performance while intermediate improvements were observed on alpha+ beta alloy TIMETAL-54M. These results will be interpreted on the basis of process -induced micro -hardness depth profiles and residual stress -depth profiles.