Comprehensive evaluation of cryogenic processing on functional and structural behaviour of biomedical alloy CoCr28Mo6

The biomedical cobalt-chromium-molybdenum (CoCrMo) group of alloys has long been recognised as effective biomaterials, particularly for orthopaedic joint replacement implants. These alloys still face challenges related to corrosion and wear resistance, long-term durability, and metal ion release. In the last years, deep cryogenic treatment (DCT) has shown potential in enhancing the microstructural and surface properties of various alloys, but its effects on CoCrMo alloys remain mainly unexplored. This study investigates the influence of DCT on biomedical-grade wrought low C CoCrMo alloy. The effect of DCT is evaluated in correlation to the microstructure, surface micro-residual stresses, microhardness and electrochemical response. For comparison, CoCrMo samples were subjected to conventional heat treatment (CHT) and subsequently treated with DCT at -196 °C for 24 and 48 hours. Characterisation and testing were performed using scanning electron microscopy (SEM), X-ray diffraction (XRD),), XRD micro-residual stress analysis, corrosion behaviour (potentiodynamic measurements), Raman shift spectroscopy for oxide formation analysis, and Vickers microhardness testing. The findings reveal the potential of DCT to improve the performance of wrought CoCrMo alloys for biomedical applications with respect to the evaluated properties, in particular corrosion resistance, surface micro-residual stresses and microhardness. • Wrought CoCrMo alloys benefit from deep cryogenic treatment (DCT) • DCT increases corrosion resistance and raises microhardness values • Micro residual stresses are changed to compressive character • DCT demonstrates potential to enhance long-term implant performance