Effect of substrate BIAS on electrochemical corrosion of amorphous carbon nitride thin films

Diamond like carbon thin films were deposited on medical grade CoCrMo alloys by glow discharge sputtering method with different substrate biasing and gas flow. The corrosion potential of the a-C:N coated samples was shifted towards more positive values and the range of current density was smaller compared to uncoated samples. This indicates that the tendency towards corrosion for coated samples has become weaker. The highest value off Ecorr for CoCrMo substrate was measured on the coating deposited with substrate bias around -0.6 kV. The shift of Ecorr to more positive values was approximately 350 mV. All of the coatings after polarization tests seemed to have less or more noticeable surface degradation. SEM micrographs showed a small amount of surface localized shallow wide pits with vertical grain attack and surface solid products which usually agglomerate around the defects or pores. Hardness of the coated samples was dependent on the value of connected negative substrate bias. The highest hardness on CoCrMo substrates was measured for negative bias between 1 kV and 2 kV, where the Raman spectroscopy showed the lowest ID/IG ratio and G peak position. (authors)