Synthesis and characterization of hydroxylapatite-inert ceramic composites and their coatings on biometals

In the first part of this thesis, HAP composites with nearly inert crystalline ceramics (alumina or zirconia) were synthesized to improve their mechanical properties and phase stability. In the second part, these composites were coated on Co-Cr-Mo and Ti-6Al-4V by cold pressing. The best combination of the composites and the metals were identified.; In HAP-α-n-Al₂O₃ composites, HAP decomposed to tri-calcium-phosphate (α, β-TCP) when there was no CaF ₂ present in the composite. When 5wt%CaF₂ was added to the system, it improved the thermal stability of the phases, densification and mechanical properties. No decomposition of HAP and α-n-Al₂O ₃ was observed. A micro-hardness of 10.3 GPa was observed with the 40wt% α-n-Al ₂O₃-5wt%CaF₂-HAP composite. A fracture toughness of 2.8 MPa√m was calculated for the same composite, which is much higher than that of pure HAP (1 MPa√m). Composites with CaF₂ dissolved more slowly than the composites without CaF₂ in the acidic simulated body fluid (SBF).; In HAP-monoclinic (m)-ZrO₂ composites, HAP and ZrO₂ reacted to form CaZrO₃ when there was no CaF₂ present in the composite. Increasing the sintering temperature diminished the p-hardness and fracture toughness because of thermal decomposition. Moreover, m-ZrO ₂ partially transformed to tetragonal (t)-ZrO₂. This partial transformation was probably due to the incorporation Ca2+ ions into ZrO₂ from HAP. When 5wt%CaF₂ was added in to the system, it improved the thermal stability of the phases, densification, hardness and fracture toughness of the composites. No decomposition of HAP and m-ZrO ₂ was observed. m-ZrO₂ completely transformed to CaO doped t-ZrO₂ by incorporating the Ca2+ ions present in CaF₂. Substitution of OH− by F− ions was verified by the change in HAP's hexagonal lattice parameters. There was about 3 times less porosity in these composites than the composites without CaF₂. A μ-hardness of 8.3 GPa was observed with the 40wt% m-ZrO₂-5wt%CaF₂-HAP composite. A fracture toughness of 2.4 MPa√m was calculated for the same composite. Composites with CaF₂ dissolved more slowly than the composites without CaF ₂ in acidic SBF because of the densification of the composites and the thermal stability of the phases in composites with CaF₂. Although MgF₂ and YF₃ improved the zirconia phase transformation from monoclinic to tetragonal, ZrF₄ did not change it.; The second objective of this research was to examine HAP-inert ceramic coatings on Co-Cr-Mo and Ti-6Al-4V alloys. Surface roughness of the metals improved the bonding between the metal and the composite coatings. For Co-Cr-Mo, HAP resulted in as the best ceramic because of its strong binding to Co-Cr-Mo and the formation of very few cracks with small compressive stress. For the Ti-6Al-4V metal, 25 and 40wt% α-n-Al₂O₃-5wt%CaF ₂-HAP composite gave the best results of strong bonding and the matching of the thermal expansion coatings of ceramic and metal.