A Study On Tribological Films With High Load-Bearing And Low Elastic Modulus For Biomedical Applications

Due to the increasing concerns of human beings to their own health, the study of biomedical materials receives more and more attention. Nowadays, the surface modification of hard tissue replacement materials is a hot topic, while friction/wear is an important resource that leads to the failure of hard tissue replacement. In view of this subject, the present works and obtained innovative achievements on titanium substrate for this dissertation are as follows:（1） SiC （silicon carbon） films and DLC （diamond like carbon）/SiC （SiC as interlayer） double-layer films with high load-bearing and good friction/wear properties were successfully developed through optimized magnetron sputtering techniques. When sliding against Si3N4 （silicon nitride） under Kokubo simulation body fluid （SBF） condition and 500 g loads, the SiC and the DLC films both exhibited superior friction/wear properties without film fracture and interface delaminating, with the friction coefficient respectively of about 0.215 and 0.1, the special wear rate of 10-5 mm3/Nm and 100^-6～10^-7 mm3/Nm. It is found that the submicron-scale domains features and the low sp³/sp² lead to that the SiC and DLC films have high toughness. The large and gradual element diffusions among films and substrate, as well as the low elastic modulus ensure the good adhesions and high load-bearing capacity of the interface. The excellent corrosion-resistance of the films and the good tribochemistry behavior of the friction system ensure the low friction coefficient and wear rate of the films. This study provides advanced surface modification films and its preparation technology for high load-bearing hard tissue substitute, such as artificial hip joint. （2） A conception of film material with ultra-low elastic modulus and excellent friction/wear properties was put forward. The SiC and DLC/SiC （SiC as the under layer） films with ultra-low Young’s modulus and good friction/wear properties were successfully developed by using Mg films as interlayer, with all the films deposited through magnetron sputtering techniques. The SiC films have the microstructures of submicron-scale shell domains, which makes it exhibits the ultra-low elastic modulus （15.75 GPa） within the human bone’s modulus range （4～30 GPa） and the ultra-high hardness-to-modulus ratio （0.149） like those of such as fullerene/fullerene-like materials. The DLC films have an ultra-low sp³/sp²（0.13） and a lower elastic modulus （47.69 GPa）. When sliding against Si3N4 （silicon nitride） under Kokubo SBF condition and 200 g loads, the SiC and the DLC films both exhibited good friction/wear properties without film fracture and interface delaminating, with the friction coefficient respectively of about 0.26 and 0.1, the wear rate of 10-5～10-6 mm3/Nm. This study provides advanced film materials and its preparation technology for the artificial hard tissue devices of artificial joint stem, bone plate, fastener, et al.（3） Nano-crystallization of the substrate would greatly influence the microstructure and properties of films, as well as the adhesions between the films and the substrate. This study proposed surface nano-crystallization of materials, which named high energy shot peening technology. This technology involved in using heavy-pressure-air driven hard-particles to bombard the surface of substrate. It is found that the surface nano-crystallization can improve the surface hardness of titanium enormously, by 61.7%. The study on SiC （SiC in SiC-High Energy Shot Peening Ti） films showed that surface nano-crystallization of the substrate can obviously improve the content of the C-C bonds. All the above researches established a technique foundation for preparing film materials with high load-bearing capacity and low elastic modulus, as well as the theoretical basis, for the surface modufication of hard tissue replacement materials.