Polishing of Co-Cr-Mo Alloy using Photocatalyst and Cathilon excited by Ultraviolet Irradiation

Abstract

The polishing of cobalt alloy processed under ultraviolet (UV) irradiation was investigated to verify the effectiveness of ultraviolet-ray aided machining. Pure cobalt (Co) was immersed in aqueous solutions of TiO₂, cathilon dye, and TiO₂-cathilon due to clarify the chemical reaction. X-ray photoelectron spectroscopy (XPS) was used to quantitatively analyze the surfaces of the immersed Co samples. Inductively coupled plasma spectrometry (ICPS ) analyses were conducted to quantitatively determine the extent of oxidation/dissolution volume of Co, Cr and Mo. These analyses were used to estimate the compounds that are formed/removed by decomposition of cathilon in water during the polishing of Co-Cr-Mo alloy using TiO₂-, cathilon-, and TiO₂-cathilon slurries, all of which included Al₂O₃ powder. The XPS and ICPS measurements indicated that Co does not dissolve in an aqueous solution of TiO₂, whereas the aqueous solution of cathilon dissolves Co at a rate of approximately 10 mg/L. Although Co was dissolved in the aqueous solution of TiO₂-cathilon at a rate of approximately 70 mg/L, Cr and Mo were not dissolved in the same solution. UV irradiation has a more significant effect on Co-dissolution at lower concentrations of cathilon (0.5 and 1.0 wt%) than in an aqueous of 2.5 wt% cathilon, whereby oxide, nitrate, and hydroxides form on the Co. However, Cr and Mo form only their oxides. Chemical-mechanical polishing of the Co-Cr-Mo alloy using the TiO₂-cathilon slurry under UV irradiation resulted in surface roughness of Ra = 2.9 nm and Rz = 83 nm.