PVD coatings: color control

A. Questions of this kind appear quite frequently. But there is no simple answer or prescription to obtain a specified colour which depends on many factors like atomic ratios of different elements elements present, texture of the coating, coating thickness, substrate properties, specific PVD technique used, bias applied, deposition rate etc. For example by varying the composition Ti:N:C one can obtain colours varying from nearly golden, brass, bronze, copper-ish etc. Coatings based on sputtering techniques are generally smoother and shinier than the ones based on arc techniques. Even when the technique is same different manufacturers would have their own variants. I am afraid every user has to develop his/her own recipe.

A. Your question is way too general, as noted by HR. Decorative coatings for faucets, for example, are deposited on nickel/chrome plated brass at low temperatures. They do not have to be very hard or thick, so a wide variety of colors are possible. On the other hand, if your coating also has to be wear resistant, such as would be applied on a stainless steel orthodontic bracket, the coating has to be much thicker and harder, limiting the range of available colors but allowing for much higher deposition temperature.
You need to realize that PVD is a commercial process, so how to achieve specific colors and other performance parameters is generally regarded as proprietary information and almost never published. Suggest you either experiment on your own or hire a consultant.

A. Maybe can use PVD + Anodizing, it's easier to get the color you want.

A. Gold and brass colors are usually formed from zirconium nitride with small admixture of carbon. Chromium nitride yields silver. I don't know of any commercial work in red and blue, but would assume one can get blue by depositing titanium oxide. Erbium oxide yields a pinkish gray. The most common deposition process is by cathodic arc. Coatings are very thin -- around 200 nm.

A. I've some PVD plated steel samples that are in blue, black, grey and bronze colours, but I'm not sure the composition of the layer. Some French and Taiwanese platers can achieve those colours.

I've also read on the web that purplish red can be achieved by plating TiAlCN. You can surf the web for details. The plating is applied on tooling for wear resistance and high temp properties.

A. Silicon nitride is bright blue. Also oxides can be deposited (or metals such as niobium can be anodized) that give a red or blue appearance. You just have to ensure the oxide thickness is uniform to give a homogeneous colour.

Best regards,

Based on my superior language skills, I'll guess that is French for "me too" :-)

A. Hello Shoaib,

Variation in the nitrogen gas level gives change in color of Ti coating. TiN is generally gold in color, if you go up to 500 sccm of nitrogen with lowest bias you get a reddish golden color. Including chrome in Ti material, i.e., TiCr with only Nitrogen gas in coating gives Blue color.

A. We can get violet to red colors in TiCN by varying the Methane to Nitrogen gas ratio. Ratios are preferable like Methane:Nitrogen = 1:5 Red-ish yellow, like 1:4, 1:3, 1:2, 1:1(gray color).

A. PVD color depends primarily on the target material and the reactive gas mix. For example, you get yellow gold with a titanium target and nitrogen gas. Adding methane or acetylene darkens the finish, going to reddish gold to gray to black. There is no general recipe, just recipes that work for a specific PVD system design.

A. PVD coating is not just about colouring. It is a technique to deposit metals, metal oxide, nitrides, carbides, etc., which is generally not possible by other means. They are used for their exceptional mechanical properties such as hardness, and also for their chemical, electrical and optical properties. The process goes something as follows:

The machine basically consists of a vacuum chamber in which solid cathodes like titanium, zirconium, aluminium, chromium, etc., are installed as per users' requirement. The parts to be coated are thoroughly cleaned, degreased and dried and then loaded inside the vacuum chamber. The chamber is then evacuated and often heated to a temperature in the range of 200 °C - 400 °C. Then a plasma is created on the surface of cathodes by processes like vacuum arc, dc magnetron discharge, rf magnetron discharge, etc., which can vary from machine to machine depending on users' requirement. The intense plasma on the cathode generates ions/atoms of the cathode material. These ions travel in straight lines and condense as a film on any surface in their path forming a coating. The parts to be coated are placed strategically in the chamber and are also rotated so that they are uniformly coated. They are also biased to suitable voltage to improve adhesion and quality of the film. If during the coating process a gas like nitrogen/acetylene/oxygen is injected at appropriate rate, nitrides/carbides/oxides can be deposited. The colour depends on the composition of the film you are depositing. For example titanium nitride has somewhat golden yellow colour. Thin transparent films can have rainbow colours.

The process is, in fact, more complex and many details are missing in the above brief description. There are many websites and review article which describe various aspects.

A. Hi Farooq. Mr. Prabhakara is an expert who is welcome to reply to you if he chooses ... but free advice by definition never comprises 'expert opinion' :-)

You probably should retain the services of a consultant specializing in that field. Surely requirements like "14 targets" is simply a number from one particular supplier for one specific machine/package, not an inherently more valid number than 12 targets or 15; trying to evaluate anything from sales pap is usually hopeless -- but good luck!

Regards,

A. My Dear Mr. Farooq Muhammad,

Following links (which you might have already seen) may be of some help.
(1)Sputtering Physical Vapour Deposition (PVD) Coatings: A Critical ... https://www.mdpi.com/2079-6412/8/11/402/htm

(2)https://www.svc.org/Education/SVC-Education-Program.cfm

I cannot make any comment on the specific machine you have mentioned. It appears to be of Chinese or some similar origin.
I understand they are relatively less expensive compared to machines from Europe, USA etc. In the initial stages you may face some technical issues as I have heard from a couple of users of similar machines. My suggestion is that you get one or two batches of the medical instruments coated by the supplier of the machine and satisfy yourself. You would also need some additional equipment for cleaning the parts before coating.
Regarding the size of the machine, well, it depends on the number of parts you want to process per/batch/day/month. But the manufacturer seems to be offering his standard product.
It may be a good idea to visit their factory and learn more about the machine and its operation.

? What coating are you depositing, and what method are you using to deposit the coating?

A. Based on some work my son has done, I think it is possible to deposit blue and red coatings by a form of PVD. However, it is a very difficult process requiring very special equipment, as well as quite a bit of research work, and even then it might not be commercially viable. If you do find a way to do it, let me know -- there are many people interested in these colors.

A. This could occur if the bias on your substrates is not right. You should clean your racks or fab new racks, as build-up of coating on the racks can affect the actual voltage on the parts as they draw current (higher resistance through the racks).