Effects of feedstock and laser post-spray treatment on plasma sprayed bioceramic coatings

Hydroxyapatite (HA) is a bioactive material with Ca to P ratio similar to that of natural bone. This can encourage early bonding between bony tissues and the implant surface. Plasma spraying is efficient in coating HA onto biomedical implants. However, the biocompatibility of hydroxyapatite (HA) changes after plasma spraying. This paper reports the preparation and characterization of HA coatings using different feedstocks; calcined HA (CHA) that has angular geometry, and spray dried HA (SDHA) that is predominantly spherical in shape. The results indicates that the state of the starting powder adversely influences the coating characteristics. Both types of HA, calcined and crushed HA powders and spray dried HA powders, are plasma sprayed on steel substrates to produce HA coatings. The results indicate that particle cohesion, size range and thermal treatment during thermal spray processing alter the phase and structure of the as-sprayed coatings. Post-spray treatment by pulsed lasers is performed on the coatings to modify the surface characteristics and phase composition of the surface layer. This, in addition, may be necessary to produce a dense and well-bonded coating having the desired biocompatible properties. Laser treatments show overall melting of the HA coating to yield a smooth surface. However, the presence of crack networks is undesirable.