Fracture Toughness of Microplasma-Sprayed Hydroxyapatite Coating by Nanoindentation

We report the fracture toughness (K-Ic) measured by nanoindentation technique at five different loads in the range of 100-1000 mN on the cross section of a highly porous microplasma-sprayed hydroxyapatite (MIPS-HAP) coating. The unique advantage of this technique was that it could evaluate K-Ic at a scale comparable with that of the local microstructure of the coating. In spite of high porosity (similar to 11 vol%), the coating showed a toughness (similar to 0.6 MPa m(0.5)) comparable to typical literature data (similar to 0.5 MPa m(0.5)) on dense HAP coating. Scanning electron microscopy of nanoindents suggested some plausible reasons for achieving a relatively higher toughness in the coating.