Study on Mechanical Properties and Blood Compatibility of Carbon Nitride Film Deposited on NiTi Alloy

Ti/CNx (x .26), as well as Ti/DLC (Diamond-Like Carbon) and Ti/TiN gradient films were deposited on NiTi alloy substrates using DC (direct current) magnetron sputtering method. The mechanical properties concerning hardness and cohesion of the above three films were tested by using microhardness tester and scratch tester, respectively. The surface hydrophilicities of the three films were measured using contact angle measurement. The blood compatibilities of the substrate and the films were evaluated by hemolysis test and platelet adhesion test. The results indicate that the cohesion between Ti/CNx film and NiTi alloy substrate is excellent (63.6N). The hardness of the CNx film (23.01GPa) is nearly equal to that of the TiN film, which is somewhat higher than that of the DLC films. The results of surface hydrophilicity test and platelet adhesion test demonstrate that the hydrophilicity and blood compatibility of NiTi alloy are improved effectively by the modification with the Ti/CNx film. In comparison with Ti/TiN and Ti/DLC gradient films, Ti/CNx film has the minimum hemolysis ratio of 1.12%. Among the above gradient films, the Ti/CNx film has the best blood compatibilities, as indicated by the minimum amount of conglutinated platelets and the least deformation.