Improving the surface integrity of the CoCrMo alloy by the ball burnishing technique

The CoCrMo alloy is a biomaterial that has been employed for the production of permanent orthopedic implants, however, the release of metallic ions from debris due to tribocorrosion is the main drawback for its extended application. In this paper, we propose the use of the ball burnishing process to improve the surface properties of the CoCrMo alloy. A 3(2) factorial design of experiments (DoE) was conducted to achieve a basic understanding of the relationship between the surface hardness, roughness and corrosion current (response variables) and the force and number of passes of the burnishing tool (input factors). Statistical analysis showed that force is the most significant factor for changing the surface properties. At the best experimental conditions, hardness was improved by 41.4%, the roughness was decreased by 72.7% and the corrosion rate was noticeably reduced by 92.4%. Microscopy and X-ray diffraction analysis showed that ball burnishing introduces changes in the microstructure, generating a surface layer with improved properties. It is concluded that the ball burnishing process is suitable for improving the surface properties of the CoCrMo alloy under an appropriate combination of experimental conditions. (C) 2020 The Author(s). Published by Elsevier B.V.