Structure and immersion behavior of plasma-sprayed apatite-matrix coatings

The microstructure and properties of a series of plasma-sprayed coatings fr om sinter-granulated powders fabricated from SiO2, CaO, P2O5 and Na-2 O-con taining HA composite powders on Ti-6Al-4V substrate were reported. The imme rsion behavior of these coatings in a simulated body fluid (SBF) was also i nvestigated. The results showed that sinter-granulated apatite-matrix powde rs were irregularly shaped and appeared quite similar. XRD patterns showed that during fabrication of the powders, P2O5 and SiO2 enhanced the decompos ition of HA structure, while CaO and Na-2 O did not. Reasonably high bond s trengths (45-50 MPa) were obtained from all coatings. The plasma spray proc ess itself enhanced the decomposition of apatite and chemical reactions amo ng different phases. When immersed in SBF, the intensities of such phases a s alpha- and beta -TCP in all coatings decreased with immersion time and an apatite precipitation took place on all coating surfaces. The immersed SiO 2- and CaO-containing HA (HSC) coating had the highest rate of apatite prec ipitation among all coatings. The variations in calcium ion concentration i n simulated body fluid indicated that the HSC-immersed solution reached its maximal Ca concentration the earliest, while the HSCP (HA, SiO2, CaO and P 2O5)-immersed solution reached its maximum the latest. (C) 2001 Elsevier Sc ience Ltd. All rights reserved.