Hi Nadiir,

It all depends on what is required to coating. Here are a few typical examples:

1. Thermal barrier coating from 8Y2O3-ZrO2 (YSZ) for gas turbine blades. For this coating is porosity the primary parameter for optimization, which should be 10-15%. If the porosity is significantly lower, the coating will rebound off the substrate, if more, then it will rapidly degrade as a result of erosion. Also coating thickness is important. The effectiveness of spraying coating YSZ is of secondary importance, and adhesion to the substrate in all cases only a very weak (< 20 MPa).

2. Wear resistant coating Mo-NiCrBSi for the piston rings. In this case need the maximum adhesion with minimal porosity. To achieve the goal to work with a very powerful, hot and high velosity plasma guns with low flow of powder (low spraying efficiency for powder and energy). The coating thickness is less important parameter in this case (coating anyway to be machined).

3. Coating of the Сr2О3 or Al2O3-TiO2 for large rolls of the printing industry. In this case, the high performance spray becomes a major factor. Adhesion, thickness and porosity are also important, but are not as important as in the previous examples.

I would go one step further. What you write in a few examples is called specification. Each coating produced should have one. And, in the well working workshop, the specifications exist and the operators try to stick to them.

But, when you start with a development of a new coating, you have to start with a, statistically speaking, screening of parameters. And adhesion strength seems to me te be a good property to fix. It is clear that without adhesion there is no coating. Such screening can be done with a few spray parameters (spray distance, working gazes, substrate preheating temperature...)

One time we get a useful coatings after such screening, we can start a statistical DOE. And, in this stage it is possible to specify a couple of functions/properties to be optimized by the regression equation.

Dear Nadiir

    I suggest to perform corrosion test for uncoated and coated specimens and then calculate the protection efficiency and porosity percentage.

Best Regards

Rana Anaee

Dear Dr Vadim,

Thank you for providing me all these essential specifications of each type of coating in such a concise way. I'm taking note.

Dear Dr. Lech,

I really appreciate your extended suggestion and clearing up my doubt in choosing the adhesion strength only as a performance parameter, for a start - at least, to maximize the latter through a statistical approach.

Thank you!

Dear Dr. Rana,

I'll implement your idea of protection efficiency (but my coating is not to protect against corrosion) and porosity percentage.

Thanks.

Dear Nadiir Bheekhun

Adhesion strength test is a good choice as a main response in your experimental.

You can find Standard D4541 - 09e1 “Standard Test Method for Pull-Off Strength of Coatings Using Portable Adhesion Testers”, that is available via the link below!

http://www.astm.org/Standards/D4541.htm

Dear Nadiir 

Adhesion strength is crucial test for determining quality of coating.

You can use ASTM C633−13 Standard “Standard Test Method for Adhesion or Cohesion Strength of Thermal Spray Coatings”.

Good luck