Wear properties of zirconia/alumina combination for joint prostheses

While alumina is the only material applied to all-ceramic joint prostheses, zirconia has high potential too, because it has high strength and fracture toughness. However, wear of zirconia/zirconia combination is too high for clinical use. It is likely that a combination of different materials may improve wear properties. In this study, wear tests were carried out with an end-face wear testing apparatus for four material combinations: zirconia/zirconia (Z/Z), zirconia/alumina (Z/A), alumina/zirconia (A/Z), and alumina/alumina (A/A). Mean contact pressures were 5 and 10 MPa, and sliding velocity was 40 mm/s. Wear tests continued for 72 h and total sliding distance was 10 km. After the test, the wear factor defined by (wear volume)/(applied load×sliding distance) was calculated. Worn surfaces were observed with a scanning electron microscope and analyzed by means of Raman spectroscopy. When zirconia was combined with zirconia counterface, the wear factor of zirconia under 5 MPa was about 2.5×10−7 mm3/N m and that under 10 MPa was about 1.9×10−5 mm3/N m. In the case of Z/Z combination, the wear factor was very high due to adhesive wear and the phase transformation. When zirconia was combined with alumina counterface, the wear factor of zirconia under 5 MPa was about 1.7×10−9 mm3/N m and that under 10 MPa was about 1.7×10−7 mm3/N m. In the case of Z/A and A/Z combinations, the wear factor of zirconia decreased drastically as compared with Z/Z combination, because adhesive wear was controlled. Micro cracking and third body abrasion were predominant in this case.