Pin-on-disk wear tests using biomedical CoCrMo alloy pins and alumina disks were conducted in Kokubo and 1% lactic acid solutions. The mass loss and elution of metallic ions were measured and the surface of the pin was observed after the wear test. Mass loss of the alloy pins in 1% lactic acid solution was 10 times higher than the mass loss in Kokubo solution. In Kokubo solution, the as-cast pins exhibited higher mass loss and higher total amount of eluted ions than solution-treated pins. The Cr and Mn ion content in Kokubo solution was lower than expected, based on the chemical composition of the alloy. The incorporation of Cr and Mn ions into the calcium phosphate detected on the wear track of disks is the possible reason for the small amount of these ions in Kokubo solution.

The surface modification of commercially pure titanium (CP Ti) by pack cementation treatment at 973 K using tetracalcium phosphate (Ca4(PO4)2O, TTCP) slurry was investigated. An HAp phase and a CaTiO3 phase were observed on the reaction layer of the CP Ti substrate after pack cementation treatment at 973 K for 86.4 ks. TTCP powder decomposed to HAp and CaO, and CaO reacted with TiO2 to form CaTiO3. The reaction layer on the CP Ti substrate consisted of inner and outer layers and the particles were in the outer reaction layer. The pores observed on the reaction layer were formed by the detachment of particles from the outer layer. The bonding strength of the reaction layer was 68.1 MPa. Apatite completely covered the surface of the pack-cementation-treated CP Ti after immersion in Kokubo solution for 21.6 ks; such rapid apatite formation suggests that pack cementation treatment improves the biocompatibility of titanium.