The boundary between the hydroxyapatite coating and titanium substrate

The effect of the heating of a Ti substrate to 300 and 550°C on the microhardness of a hydroxyapatite (HA) plasma coating, Ti, and their interface is investigated in specimens in different states (as sprayed, after hydrothermal (650°C, 3 h) and vacuum heat treatment (800, 1000, 1100°C, 3 h)). It is shown that the preliminary heating of the substrate to 550°C leads to the interface microhardness increasing from 2.32 to 3.07 GPa, while the following heat treatment has a weak influence on that. After the heat treatment, the microhardness of the HA coating is increased from 3.0 to 3.8 GPa and the microhardness of the Ti substrate near the boundary is increased from 2.5 to 6.9 GPa. A slight effect of the heat treatment on the interface microhardness is explained by preservation of the interface structure formed under HA plasma spraying on the heated substrate. The distribution of chemical elements near the interface between the coating and substrate is studied by Auger electron spectroscopy (AES).