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 permanentorthopedic implants, however, the release of metallic ions from debris due to tribocorro-sion is the main drawback for its extended application. In this paper, we propose the useof the ball burnishing process to improve the surface properties of the CoCrMo alloy. A 32factorial design of experiments (DoE) was conducted to achieve a basic understanding of therelationship between the surface hardness, roughness and corrosion current (response vari-ables) and the force and number of passes of the burnishing tool (input factors). Statisticalanalysis 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 wasdecreased by 72.7% and the corrosion rate was noticeably reduced by 92.4%. Microscopy andX-ray diffraction analysis showed that ball burnishing introduces changes in the microstruc-ture, generating a surface layer with improved properties. It is concluded that the ballburnishing process is suitable for improving the surface properties of the CoCrMo alloyunder an appropriate combination of experimental conditions.