Residual stress relaxation in shot peened Timetal 21s

Selective surface aging treatments (mechanical surface treatment followed by aging) on β-titanium alloys can result in higher endurance limits than conventional mechanical surface treatments. An explanation of fatigue behaviour of selectively surface aged parts should not only consider preferential precipitation strengthening but also take into account the remaining residual stresses. The β-titanium alloy Timetal 21s with two oxygen contents (0.15 and 0.30 wt%), in two solution treated conditions (fully and partially recrystallized) was aged at temperatures between 350 and 500°C after shot peening. Microhardness and X-Ray measurements allowed the determination of the degree of precipitation strengthening and relaxation of residual stresses, respectively, in the near surface regions during aging.