Effect of arc current on microstructure, texturing and wear behavior of plasma sprayed CaZrO3 coatings

Abstract

In order to enhance the biocompatibility of metallic implants, various ceramic coatings are currently in vogue. CaZrO3, a promising candidate material, was deposited through plasma spraying on stainless steel (316L) substrates at arc currents of 400, 500 and 600A. The coatings were characterized using a SEM, XRD, surface profilometers and a tribometer. It was found that the arc current had profound effects on the thickness, microstructure, phase evolution, crystallinity and wear behavior of the coatings. The cross-sectional images and fractographic analysis showed that a denser coating with better inter-splat fusion was produced at arc current of 600A. The average roughness (Ra) of the coatings increased from 3.62 to 6.68μm as the arc current was increased from 400 to 600A. The feedstock (powder) and the coatings were predominantly composed of CaZrO3 along with a minor amount of CaZr4O9 phase. The rise in the arc current resulted in a slight increase in the relative proportion of the CaZrO3 phase. Also, the coating produced at arc current of 600A exhibited highest crystallinity. The detailed XRD analysis of (002) and (200) reflections of the ferroelectric CaZrO3 revealed the preferred orientation of crystals in the coatings. The presence of this texture is explained on the basis of shifting the unstable Zr4+ ion in oxygen octahedral cage preferably in one direction. The increase in the arc current decreased the coefficient of friction and, as a result, relatively better wear resistance was observed for the coating produced using higher arc current. Moreover, the coating fabricated using arc current of 600A reduced the volumetric weight loss by 13 times during the wear test as compared to the substrate. Plasma sprayed CaZrO3 coating not only enhanced the wear resistance of the stainless steel but also showed the potential to furnish a bioactive surface.