Tribological studies of microplasma sprayed hydroxyapatite coating at low load

Abstract

For bioactive prosthetic implant applications, the present work reports the tribolgical behaviour of the recently developed, microplasma (e.g. plasmatron power <1·5 kW) sprayed (MIPS) hydroxyapatite (HAp) coatings on Ti6Al4V substrates at low constant normal load, e.g. 200 mN. Conventionally, the macroplasma (e.g. plasmatron power <25 kW) sprayed (MAPS) HAp coatings are used for such purpose. The phase analysis and microstructural studies of the HAp coatings were carried out by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. Further, the single pass scratch tests were conducted on both the bare substrates and the HAp coatings at an applied normal load of 200 mN. The average coefficient of friction (COF, μ) of the HAp coatings developed by MIPS (e.g. μ∼0·7) was slightly higher than that (e.g. μ∼0·5) of the bare Ti6Al4V substrates. The characteristic, high variability of the μ data of the HAp coatings developed by MIPS; was explained in terms of the intrinsic microstructural heterogeneity and the local differences in orientations of the splats.