Effects of Water Location in Starting Materials on Bonding Behavior of Hydroxyapatite and Titanium via Hydrothermal Hot‐pressing

Solidification of hydroxyapatite (HA:Ca₁₀(PO₄)₆(OH)₂) and its bonding with titanium (Ti) was achieved simultaneously by using the hydrothermal hot‐pressing method at temperatures as low as 150° C with no special surface treatment of Ti. A mixture of calcium hydrogen phosphate dihydrate and calcium hydroxide was used as the starting powder material for solidifying HA. Three point bending tests were conducted to obtain an estimate of the fracture toughness for the HA/Ti interface as well as for the HA ceramics only. The fracture toughness tests showed that the induced crack from the pre‐crack tip deviated from the HA/Ti interface and propagated into the HA. It is cleared that water in starting materials must be crystallized in starting materials in order to achieve the bonding HA ceramics and Ti by the HHP method. The fracture toughness determined on the bonded HA/Ti specimen was close to that of the HA ceramics only (approximate 0.3 Mpam^1/2).