"DLC" is the abbreviation of the word "Diamond-like carbon". DLC is composed of a carbon element, similar in nature to diamonds, and has a structure of graphite atom composition of the substance. Diamond like carbon (DLC) is an amorphous film that is very suitable for wear-resistant coating due to its high hardness and high modulus of elasticity, low coefficient of friction and abrasion resistance and good vacuum tribological properties. At present, there are many ways for preparing DLC thin films. The carbon sources of different preparation methods and the ion energy on the surface of the matrix are different. The structure and properties of the deposited DLC films are quite different, and the tribological properties are different.
1. Mechanical property
(1) Hardness and elasticity modulus
The hardness and elastic modulus of DLC films prepared by different deposition methods are quite different. The DLC film with hardness exceeding or even exceeding diamond can be prepared by magnetic filtered cathode arc. The composition of the film has a certain impact on the hardness of the film, and the addition of Si and N can improve the hardness of the DLC film. The DLC film has a higher modulus of elasticity, although it is lower than that of diamond (1100GPa), but it is obviously higher than the modulus of elasticity of the general metal and ceramics.
(2) Internal stress and adhesive strength
The internal stress and adhesive strength of the film determine the stability and service life of the film, which are two important factors that affect the performance of the film. The DLC film with high internal stress and low adhesive strength is easy to produce cracks, folds or even shedding in applications, so the DLC films prepared preferably have moderate internal stress and high adhesive strength. Most studies show that the adhesive strength of the DLC film deposited directly on the substrate with the substrate is generally low.
2. Friction performance
DLC film not only has excellent wear resistance, but also has very low friction coefficient. Generally, less than 0.2 is an excellent surface wear resistance modified membrane. The friction coefficient of DLC varies with the preparation process and the change in the composition of the film, and the friction coefficient can be as low as 0.005. Doping metal elements may reduce the friction coefficient, but the addition of H can improve the lubrication, and the environment also has a certain effect on the friction coefficient. Compared with the traditional hard thin films, the DLC films have obvious advantages in terms of the coefficient of friction, and the friction coefficient of these traditional hard films is above 0.4. Therefore, it is possible for DLC films to replace these traditional hard coatings in a lot of tribological fields.
3. Thermal stability
Due to the metastable material of DLC, the poor thermal stability is an important factor limiting the application of DLC membrane. The SP3 bond transition to the SP2 bond occurs when the annealing is above 300? C. It has been found that the addition of Si can obviously improve the thermal stability of the DLC film, and the DLC film containing 20 at%Si show sp3 bond to sp2 bond transition at 740? C. Similarly, the addition of metal (such as Ti, W, and Cr) can also improve the thermal stability of the DLC film, and we are investigating this aspect.
4. Corrosion resistance
The pure DLC film has excellent corrosion resistance, all kinds of acid, alkali and even aqua regia can hardly erode it. However, the corrosion resistance of DLC films doped with other elements has decreased, which is due to the first erosion of the doped elements, thus destroys the continuity of the film.
5. Surface states
The surface of DLC film is usually relatively smooth, which has little effect on the surface finish of the substrate, but as the film thickness increases, the surface finish will decrease. The surface finish of the DLC film obtained by different deposition methods is also different.
The DLC film has good anti-adhesion, especially for non-ferrous metals (such as copper, aluminum, zinc, etc.), and also have anti adhesion properties to plastics, rubber, ceramics and so on.