greeting,
I have faced a major problem about the golden color in a same chamber. we apply decorative TiN coat by cathodic arc pvd. after each pass, the samples at the top of the chamber are darker than those in the bottom or vice versa. in fact, 3 different theme of golden color is seen in a same chamber. I will be really grateful if anyone help me to solve the problem and get a similar color in a chamber of pvd.
thank you in advance
Dear Saba Khoramkhorshid,
In order to obtain a gold coating, it is necessary to vary the amount of nitrogen as well as the pressure in the chamber during the application process. In order to achieve uniform coverage along the entire length, the evaporator must be larger than the detachable part. The distance from the product to the sample has a strong influence on the uniformity of the coating. As the distance between the sample and the evaporator decreases, different shades of coating are observed. As the distance from the sample to the evaporator increases, the coating throughout the sample becomes uniform. However, this reduces the growth rate of the coating. Coverage time will need to increase. In the presence of small distances from the product to the camera, shadows of lower coverage are often obtained. Probably in the technical parameters of the installation are written the requirements for the distance between the sample and the evaporator, current, operating voltage, amount of gas, overall dimensions of the products.
Dear Saba Khoramkhorshid,
This is a strange problem I haven't encountered so far. I have seen similar problems with other coatings, but not with TiN.
I think there are two possibilities.
First, you mention that the coatings are "decorative". Probably, they are thin and deposited for a very short time. If you have a Ti adhesive layer below, using very thin TiN layer above, this Ti base will be partially seen through the TiN and will affect the final color. Thus, the thickness of the TiN coating will affect the color (I tried it in the past). If the coating is very thin and non uniform (with various thickness), it could have a different color. The CAD is one line-of-sight process, the thickness is formed under the so-called cosine law, where the evaporation angle and the distance to the target are important. Solution: try to deposit thicker coatings. Then the thickness unevenness won't affect the color.
The second possibility is less likely. It is possible there is a lack of enough N in the chamber, which in combination with other circumstances (e.g. poor flow stabilization) could theoretically cause a similar effect. This, rather may explain a different color among the work cycles, but not in one cycle (chamber). Solution: try to work with higher N pressure (flow). This should not be a problem for the CAD method and, certainly, the color will be stabilized, being quite close to that of real gold.
These two are just assumptions because of the lack of enough information about the technological process.
Dear Saba Khoramkhorshid,
The problem you faced on is the substrate material. As you mentioned it is ABS, which is composite material, consisting synthetic rubber. During the deposition your substrates are heated up and significant desorption of hydrocarbon gases occurs. In this case you can't deposit stoichiometric TiN, but some kind of TiCN.
One possible solution is to deposit Cr before the TiN, thus Cr sublayer will reduce the hydrocarbons desorption.
Another solution is to change the deposition technology to magnetron sputtering, but again Cr sublayer will help.
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