Calcium phosphate invert glass-ceramic coatings joined by self-developmentof compositionally gradient layers on a titanium alloy

A glass-ceramic layer containing beta -Ca-3(PO4)(2) crystals could be joine d easily with a new type of titanium alloy (Ti-29Nb-13Ta-4.6Zr) consisting of a beta -titanium phase by heating the metal, on which glass powders with a composition of 60CaO . 30P(2)O(5) . 7Na(2)O . 3TiO(2) were placed, at 80 0 degreesC in air. Measurement of tensile bonding strength revealed that th e joining between the coating layer and the substrate is very strong. Even after the large deformation (e.g., approximate to 90 degrees in bending ang le) of the titanium alloy, the coating layer was not peeled off from the su bstrate. A compositionally gradient layer in the TiO2-P2O5-Na2O-CaO system is developed automatically on the titanium alloy during the heating, result ing in the formation of the strong joining. By soaking in simulated body fl uid at 37 degreesC, hydroxyapatite phase was formed newly on the surface of the coating layer. (C) 2001 Elsevier Science Ltd. All rights reserved.