Research On Interface Regulation And Mechanical Properties Of Diamond-like Carbon Films

Diamond-Like Carbon(DLC) films have excellent properties such as high hardness, elastic modulus, low friction coefficient and corrosion. Currently they have been used in mechanical tool,mold, automobile engine parts and other fields. However, high residual stress, poor interface bounding adhesion, unstable friction performance, difficult in uniform controllable preparation and other issues limit the further development of the DLC films. Linear ion beam technology can achieve uniform, long time and stable plasma ionization rate, is currently a large area of highperformance film preparation to the industrialization. Due to the poor adhesion strength between the films and substrate, a suitable buffer layer(W) was added to match the film-substrate suitability between the film and substrate, and the effect of the thickness and types of W transition layer on the structure and mechanical properties of DLC films was studied; in order to meet the demand of industrial applications for high-quality DLC films, the used buffer layer was optimized to improve the film/substrate adhesion performance, and the change of adhesion and frictional properties of DLC films deposited on four substrates with different hardness was also investigated.The DLC films with different thickness of W buffer layers were prepared by linear ion-beam and magnetron sputtering deposition technology. The results showed that with increasing of thickness of the buffer layer, the sp3 content firstly increased then decreased, and hardness and elastic modulus have the same trends; the introduction of the W buffer layer, matched the adaptive membrane-based interface, and reduced the residual stress due to the difference in thermal expansion coefficient; the stress changed from 3.24 GPa of the films without W buffer layer to1.89GPa; when the thickness of W buffer layer was 351 nm,the maximum adhesion strength value was 70 N, which increased by 40% compared to that without buffer layer DLC; friction coefficient showed similar trends.Based on the same thickness of W buffer layer, the components and structure of W buffers were changed, including signal W buffer layer, W-C doped buffer layer, double W layer and three W layers. Results revealed that the films with signal W layer DLC showed the highest hardness of27.4GPa, the residual stress with the increased layers of W decreased from 1.89 GPa to 0.85 GPa. In addition, the DLC film with three W layers had the best toughness and adhesion; the friction performance of the film with W multi-layer structure was also improved obviously.Finally, four commonly used metal materials were chosen as substrate to study the dependence of properties of DLC films with W buffer layer on the hardness of substrate. Results showed that hardness was an important factor affecting the performance of DLC film. The adhesion of film/substrate had a positive relationship with the hardness of substrate. Friction properties of the DLC film with three W buffer layer which deposited on YG8 were stood out under the dry and oil environments, and they showed that on the friction coefficient decreased form0.14 of dry condition to 0.08 of oil condition, and the rate of wear changed from 2.1×10-8mm3/( N·m) to 6.3×10-10mm3/( N·m).