Investigating the effect of micro-dimpling surface texture on ceramic-on-ceramic hip joints / Taposh Roy

Alumina (Al2O3) is a material with high potential for use in bio-medical implants because of its low wear rate and excellent bio-compatibility. The micro dimpling surface technique is one of the most advanced surface modification techniques available for the optimization of tribological performance. A well-defined dimple surface fabricated on Al2O3 substrate could further improve tribological properties of an implant. In this study, a CNC micro drilling machine was used to create a well-defined micro dimple patterns on Al2O3, and tribology testing was performed to optimize the dimple parameters for better tribological performance. Surface morphology, micro hardness and residual stress of the fabricated micro dimple surfaces were characterized, demonstrating that CNC micro drilling is capable of efficiently fabricating micro dimples with a controllable dimple size and array pattern. The micro hardness very near to the dimple is a little bit lower with compared to the area apart from the dimple periphery and on the dimpled surface it was found compressive residual stress. Tribology experiment was performed in simulated hip joint conditions which revealed an obvious improvement in terms of the friction coefficient and wear rate (in terms of weight loss). The friction coefficient was reduced by between 17% - 23% at 181-257 MPa contact pressures to the where with 15% of the dimpled surface (Ø400 μm, depth 30 μm, area ratio: 15%) compared to non-dimpled surface. Wear rate (in terms of weight loss) was found to be somewhat smaller in magnitude, matched by a reduction in wear particle size. The largest wear debris was found to be approximately 600-700 nm sized (equivalent diameter), a size which could be certainly stored in the dimple, thus reducing their possible abrasive wear effects. In conclusion, CNC micro drilling provides a method for precise micro fabrication of micro dimple arrays on Al2O3 surfaces. Further, a well-defined micro dimple surface can be implemented in ceramic on ceramic hip joints in order to produce a reduction in friction coefficient and removing wear debris from the contact area