Microstructure and mechanical properties of plasma sprayed HA/YSZ/Ti–6Al–4V composite coatings
K.A. Khor, Y.W. Gu, D. Pan, P. Cheang
Biomaterials
Abstract
Plasma sprayed hydroxyapatite (HA) coatings on titanium alloy substrate have been used extensively due to their excellent biocompatibility and osteoconductivity. However, the erratic bond strength between HA and Ti alloy has raised concern over the long-term reliability of the implant. In this paper, HA/yttria stabilized zirconia (YSZ)/Ti 6Al 4V composite coatings that possess superior mechanical properties to conventional plasma sprayed HA coatings were developed. Ti 6Al 4V powders coated with ?ne YSZ and HA particles were prepared through a unique ceramic slurry mixing method. The so-formed composite powder was employed as feedstock for plasma spraying of the HA/YSZ/Ti 6Al 4V coatings. The in?uence of net plasma energy, plasma spray standoff distance, and post-spray heat treatment on microstructure, phase composition and mechanical properties were investigated. Results showed that coatings prepared with the optimum plasma sprayed condition showed a well-de?ned splat structure. HA/YSZ/ Ti 6Al 4V solid solution was formed during plasma spraying which was bene?cial for the improvement of mechanical properties. There was no evidence of Ti oxidation from the successful processing of YSZ and HA coated Ti 6Al 4V composite powders. Small amount of CaO apart from HA, ZrO2 and Ti was present in the composite coatings. The microhardness, Young s modulus, fracture toughness, and bond strength increased signi?cantly with the addition of YSZ. Post-spray heat treatment at 600 C and 700 C for up to 12h was found to further improve the mechanical properties of coatings. After the post-spray heat treatment, 17.6% increment in Young s modulus (E) and 16.3% increment in Vicker s hardness were achieved. The strengthening mechanisms of HA/YSZ/Ti 6Al 4V composite coatings were related to the dispersion strengthening by homogeneous distribution of YSZ particles in the matrix, the good mechanical properties of Ti 6Al 4V and the formation of solid solution among HA, Ti alloy and YSZ components.
keywords:Plasma spraying; Hydroxyapatite; Composite coating; Mechanical property; Yttria stabilized zirconia; Ti alloy
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