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1 2008

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Mechanical surface treatments for improving fatique behavior in titanium alloys

Ludian T., Wagner L.

Advances in Materials Science

2008

Vol. 8, nr 2(16)

44-52

Mechanical surface treatments such as shot peening or ball-burnishing induce high dislocation densities and residual compressive stresses in near-surface regions. In addition, the surface roughness is changed. Micro-hardness and residual stress-depth profiles are evaluated in Ti-6Al-4V as a function of the Almes intensity being the main process parameter in shot peening. In the finite life regime, residual compressive stresses are shown to drastically increase the fatigue life by retarding crack growth from thesurface into the interior. However, in the HCF regime a shift in crack nucleation site occurs from the surface to subsurface regions where residual tensile stresses balance the outer compressive stress field. Therefore, the tensile mean stress sensitivity of the fatigue strength which can largely vary in Ti-6Al-4V needs to be taken into account in order to understand the observed differences in HCF responds to shot peening.