The effects of peening conditions on the surface characteristics and fatigue life of titanium alloy was investigated using microshot peening, ultrasonic shot peening, and multiple shot peening. The use of microshot peening technology with minute media has become more widespread in consideration of the reduction of the notch effect in the material surface. The ultrasonic shot peening that uses media of several millimeters in size with ultrasonic vibration has attracted attention as a means to reduce the surface roughness. In the present study, an air-type and an ultrasonic type machine were used. In the microshot peening process, the media used was high-carbon cast steel and the hard powder, with an average diameter of 0.1 mm. The workpiece was commercial titanium alloy Ti-6Al-4V. In the microshot peening (MSP), work hardening was evident to the depth of approximately 0.3 mm from the surface. This depth was approximately three times the diameter of the media. However, the influence of the peening time on the hardness distribution was not great. In the ultrasonic shot peening (USP), work hardening was deeper in the material. This is because the diameter of the media used for ultrasonic machining was large. On the other hand, in the combined shot peening (CSP), a degree of hardness was higher at the top surface. However, the hardness patterns and values were pretty much identical to ultrasonic shot peening. The fatigue limit was thought to be greater in the microshot peening experiment because the work-hardened layer was formed near the workpiece surface.
Surface work hardening of pure niobium induced by water polishing.
