Properties of DLC Coating
The performance of DLC is between diamond and graphite, which shows both high hardness and excellent friction, as well as good anti-adhesive properties.
◆ Mechanical properties:
High hardness, high elasticity modulus, high thermal conductivity, low thermal expansion coefficient, low density, excellent wear resistance and low friction coefficient.
◆ Electrical properties:
Low electron affinity, high electrical resistivity, low dielectric constant
◆ Optical properties:
High transmittance in the visible light and near-infrared regions, low optical band gap, refractive index is 1.7 to 2.4, high laser damage threshold.
◆ Chemical properties:
Good biocompatibility, ultra-high chemical inertness, acid and alkali resistance, good hydrophobicity.
Problems and Solutions of DLC Coating
◆ High internal stress
Under normal circumstances, the internal stress, elastic modulus and hardness of the coating are directly proportional to each other, so that the higher the hardness of the coating, the greater the internal stress. DLC film has very high hardness, as well as high internal stress, which makes the adhesion of the DLC film to the substrate reduces, and also, it limits the maximum thickness of a stable film that can be deposited on the substrate. In addition, the uniformity of the film thickness also has an effect on the internal stress.
◆ Poor thermal stability
DLC is usually a metastable phase non-crystalline structure. Therefore, during the temperature rising, DLC coating will be graphitized, that is, the sp3 bond turn to the sp2 bond, as a result, the structure and performance of the DLC coating will be changed.
◆ Multilayer film
The deposition of multilayer films Ti/TiC/DLC and Ti/TiN/TiCN/DLC on the substrate can greatly reduce the internal stress between the DLC coating and the substrate.
◆ Gradient film
Deposit gradient transitional layers Cr/CrN/CrNC/CrC/Cr-DLC and Ti/TiN/TiCN/TiC/Ti-DLC by ion source and sputtering deposition technology on the substrate can effectively release stress and effectively improve the strength of the bond between the coating and the substrate.
Doping of non-metal (N, B, Si) can reduce the internal stress of DLC coating and improve its thermal stability. And doping of metal (Cr, Ti, W) can improve the hardness and wear resistance of DLC coating, and reduce its friction coefficient.