Effect of vapor-flame treatment on plasma sprayed hydroxyapatite coatings

A vapor-flame treatment was developed to modify the crystallinity of the as-sprayed hydroxyapatite (HA) coatings. The effects of the treatment on composition, structure, and properties of HA coatings were investigated. Results showed that the vapor-flame treatment is simple and efficient to adjust the crystallinity of as-sprayed HA coating. Its crystallinities can be raised from 53.5 to 98.7% in 3-7 min. The porosities of coatings increased with an increase in the vapor-flame treating time. The microhardness of coating decreased as a result of this treatment. It may be explained in terms of the extent of microcracks caused by recrystallization of amorphous HA and relaxation of stress of the coating. The porosity, bonding strength, and hardness of HA coatings treated for 7 min were 15.7%, 32.0 MPa (300 microm thickness), and 1.9 GPa, respectively.