Correlation between the microstructure and corrosion performance of the HIPIMS nitrided bio-grade CoCrMo alloy

•HIPIMS nitriding significantly improves corrosion resistance of the CoCrMo alloy.•Nitriding potential influences microstructure and eventually corrosion resistance.•Diffusion based S-phase layer clearly enhances corrosion resistance.•Selective dissolution of grain boundaries and ϵN phase grains evident.•Precipitation of Cr based nitrides compromises the corrosion protection offered.