Microstructural characterization and corrosion behaviour of SLM CoCrMo alloy in simulated body fluid

CoCrMo base alloys are widely used for the production of orthopaedic implants because of their excellent mechanical properties and high corrosion resistance in biological fluids. However, despite the advances in this sector, untimely implant failures and dissatisfaction are still observed in patients. The fabrication of customized implants by Selective Laser Melting should permit to overcome some common problems, like mismatch between the joint prosthesis and the natural joint conformation, non-physiological load transfer and scarce osteointegration. However, some parameters related to the process optimization in terms of final density and mechanical properties are critical and the evaluation of their influence on corrosion resistance of the components is reputed fundamental. In this work SLM technique was used to produce two types of samples based on ASTM F1527 CoCrMo alloy by using different process parameters. The corrosion behaviour of the two materials was investigated by recording the EIS spectra and the polarization curves during 15 days of immersion in Phosphate-Buffered Saline (PBS) solutions at pH 7.4. The samples showed a fine microstructure, characterized by Mo enrichment at the cell boundaries. Both types of samples showed low corrosion rates in the studied environments because of the formation of a very protective oxide film on the sample surfaces with high resistance to localized corrosion, but the finer microstructure ensured slightly higher corrosion resistance.