Comparison between shot peening and abrasive blasting processes as deposition methods for hydroxyapatite coatings onto a titanium alloy

摘要

Recent studies have shown that combining a compressed air jet with entrained hydroxyapatite(HA) particles with a jet of abrasive particles can be used to deposit a well adhered crystallineHA coatings onto titanium substrates. A similar particle bombardment process utilising aflow of shot peen particles and a flow of suitable powder particles has been used to deposit arange of coatings, though the deposition of bioceramic powders have not yet been reported bythis method. In this study a direct comparison between the shot peen and abrasivebombardment processes has been undertaken to determine which technique yields coatingsexhibiting higher levels of adhesion on titanium alloy substrates. Both processes were shownto effectively deposit a layer of crystalline apatite onto the titanium substrates over a range ofpressures and jet to substrate heights. It was observed that for both processes that an increasein particle kinetic energy producing corresponding enhancements in both deposition rate andsurface roughness. The shot peen process however produced a smooth layer of laminarapatite, which was readily removed from the surface using a scratch adhesion test technique.In contrast the combination of a jet of HA and abrasive powders resulted in an increase insurface abrasion and increased mechanical interlocking of the HA into the metal surface wasobserved. The mechano-chemical affect achieved resulted in a better adhered HA layer. Thesurface morphology obtained using the two treatments was significantly different with anincrease in the average roughness (Ra) of ≈ 70 and 80 % for samples treated with abrasiveparticles over shot peen. This difference in surface treatment is further highlighted by theremoval of the HA using an acid etch. The roughness (Ra) of the underlying titanium layerafter this removal is, on average, >175 % higher for the surface treated with the abrasiveparticles during HA deposition.