Improvement in mechanical properties of nano-structured HA/TiO2 multilayer coatings deposited by high velocity suspension flame spraying (HVSFS)

In order to improve mechanical properties of HA coatings, nano-structured HA/TiO2 multilayer coatings composed of TiO2 bond layer, HA/TiO2 intermediate layer with different TiO2 contents and HA top layer were prepared by a high velocity suspension flame spraying (HVSFS) method using nano-sized HA and TiO2 powders. Phase constitution, compositions and microstructures were characterized by XRD, XPS, FTIR and SEM. Mechanical properties of multilayer coatings were investigated in comparison with the pure HA coating. Results show that multilayer coatings were mainly composed of HA and TiO2 phases, and presented well-bonded coating/substrate interfaces and porous surfaces as well as graded chemical compositions in coating thickness. Microhardness and Young's modulus of HA/TiO2 intermediate layers were increased with the TiO2 contents due to its reinforcement, and HA/TiO2 multilayer coatings revealed gradual mechanical properties from the TiO2 bond layer to HA top layer. Tensile strengths of HA/TiO2 double-layer coatings were improved due to TiO2 reinforcement in comparison with the pure HA coating. Wear properties of HA/TiO2 multilayer coatings were tested by a pin-on-disc method and were improved due to the presence of intermediate layers resulting in lower wear rates than that of the pure HA coating.