Fracture Toughness Analysis of Advanced Ceramic Composite for Hip Prosthesis

The fracture behavior of a zirconia-toughened alumina-matrix composite (added with small amounts of mixed oxides) for ceramic hip joint prostheses has been evaluated with emphasis placed on the effect of environmental surface degradation in moist environment. Accelerated aging tests were performed up to 300 h in an autoclave operating at 121 degrees C (under 0.1 MPa pressure) in vapor environment, which represents a quite severe environmental testing condition. Besides conventional fracture mechanics characterizations, including different types of fracture toughness test, microscopic insight into the effect of environmental surface degradation on toughness could be obtained according to Raman and fluorescence microprobe spectroscopy. The main outcomes of this study were as follows: (i) after 10-h autoclaving (according to ISO standard recommendation) no significant change of monoclinic volume fraction and fracture toughness could be detected; (ii) after very long exposure time (300 h) the monoclinic phase content increased and the surface fracture toughness decreased by approximately 30%, although it was still above the toughness level of pure alumina; and (iii) the bulk toughness was unaffected by autoclave exposure, independent of exposure time elongation.