STABILITY OF RADIOFREQUENCY MAGNETRON-SPUTTERED CALCIUM-PHOSPHATE COATINGS UNDER CYCLICALLY LOADED CONDITIONS

The stability of radiofrequency (RF) magnetron sputtered calcium phosp hate was studied under cyclically loaded conditions. The coatings were deposited on titanium bars and tested in either dry or wet conditions . X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis and Fourier transform infrared (FTIR) spectroscopy were used to characterize the as-sputtered and tested coa tings. XRD demonstrated that the amorphous structure after annealing a t 650 degrees C changed into a crystalline apatite structure. The resi dual stresses were determined by the XRD cos 2 phi method. These resid ual film stresses were influenced by the coating conditions and the cr ystalline sputtered coating showed the presence of compressive stresse s. SEM demonstrated that, after cyclic loading conditions in air, the crystalline sputter-coated Ti-6Al-4V bars showed a partial coating los s. Furthermore, in wet conditions (simulated body fluid) only the heat -treated sputter-coated bars appeared to be stable. On the other hand, the amorphous coating only showed signs of delamination in the more h ighly stressed regions, while in the less stressed regions a Ca-P prec ipitate was formed. On the basis of these results we conclude that cal cium phosphate coatings subjected to cyclic loading conditions show an important difference in fatigue behaviour when tested in either dry o r wet conditions. (C) 1997 Elsevier Science Limited.