Densification and strengthening of silver-reinforced hydroxyapatite-matrix composite prepared by sintering

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Ductile-phase reinforcement of hydroxyapatite (HA) was achieved by addition of silver particulates (5–30 vol %) in HA powder and subsequent sintering of HA−Ag powder compacts. A composite made by sintering 10 vol % Ag and the balance HA at 1200 °C for 1 h in air had flexural strength of 75±7 MPa, which was almost double that of pure HA sintered under an identical condition. The density of HA-10 vol % Ag composite was 90±2% of the theoretical density (as calculated from the rule of mixture) and was lower than that (98.7±0.4%) of pure HA sintered at a similar condition. The X-ray diffraction pattern of the composite did not indicate any decomposition of HA or any reaction between HA and Ag. Ag in the composite melted during sintering, but, due to poor wetting, did not spread in between HA particles. The addition of Ag reduced densification and grain growth during sintering of HA−Ag composites. Indentation cracks in the composites went around Ag inclusions and often stopped at Ag inclusions. The increase in the flexural strength of the composites was thought to be due to crack-bridging and crack-arrest by silver particles.