Structural modification of high carbon Co−Cr−Mo alloy via chemical etching to enhance hydroxyapatite coating performance Strukturelle Veränderung einer kohlenstoffreichen Co−Cr−Mo-Legierung durch chemisches Ätzen zur Verbesserung der Hydroxylapatit-Beschichtung

Numerous papers have been reported on surface treatment of metallic implant to facilitate positive interaction between the implant and hard tissue interface. In this paper, surface treatment such as chemical etching was done on the biomedical grade cobalt-based alloy prior to hydroxyapatite coating deposition to enhance its biocompatibility. The objective is to investigate which temperature possesses the positive effect in adhesion strength of hydroxyapatite coating without detrimental the surface hardness. Observation showed that acid etched at the highest temperature (80 °C) has successfully roughen the substrate surface from 0.168 μm ±0.1 μm to 1.383 μm ±0.2 μm. Vickers hardness measurement on surface treated at 80 °C exhibit an increment of surface hardness which is about 39 % compared to surface treated at lower temperature. The highest thickness of hydroxyapatite coating layer (~57 μm) was evidently formed on the substrate etched at 80 °C with minimal cracks and no delamination. This phenomenon happened due to chemical reaction were rigorously attack on the substrate surface have provide more micro-pits, pores and deeper craters that trap more efficiently of hydroxyapatite particles for thicker and dense coating formation. It is worth to note that too long acid soaking will also detrimental the material properties.