Fracture Toughness of Microplasma‐Sprayed Hydroxyapatite Coating by Nanoindentation

We report the fracture toughness ( K I c ) 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 I c at a scale comparable with that of the local microstructure of the coating. In spite of high porosity (∼11 vol%), the coating showed a toughness (∼0.6 MPa m 0.5 ) comparable to typical literature data (∼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.