Shot Peening of a Titanium Alloy for Medical Implant Applications with Ziirconia Shot

Shot peening with steel shot followed by a cleaning process with glass beads is commonly used as surface finish in the production of modular hip endoprostheses. The induced compressive residual stresses increase the resistance against fatigue and fretting fatigue. The surface roughness can be adjusted in a range that enhances the physiological acceptance I compatibility of monolithic ~rnplants. However, an increasing number of publications show that there is a significant contamination of residual glass fragments at the finished surfaces. Latest research suggested an association between glass particle contamination and increased corrosion or fretting fatigue, respectively of the morse taper junction. The particles cause damage of the natural passivation layer of the Ti-alloy since the Ti-oxldes show relatively poor me chanical properties. There are also hints that particle contamination causes local osteolysis of the surrounding femur. The aim of this study was to evaluate the effects of shot peening with zirconia shot in comparison with glass andlor steel shot. Zirconia beads offer higher hardness and strength I fracture resistance than glass beads, The surfaces of TiA16V4 rods were shot peened with zrrconia shot using different Almen intensities and coverages. A field emission scanning electron microscope was used for the detection of the residual particle contamination on the surfaces. The near-surface residual stress distributions induced by the shot peening processes were measured by X-ray diffraction. The results of the scanning electron microscopy and X-ray residual stress analyses are discussed with respect to application of the shot peening processes as finish of monolithic and modular hip endapros!heses.