Everyone knows that the type of coating for a job is the most important thing to consider. Right?
Obviously, using a diamond type of coated tool on a steel part is a bad idea, as the carbon from the diamond will readily dissolve into the steel. So in the case of chemical incompatibility / misapplication, I guess what everybody knows is correct.
But after listening to George Korenyi-Both of Dayton Coating Technologies, I found myself agreeing with his 3 factors to understanding tool coatings.
According to George, the three factors are Adhesion, Thickness and Morphology.
IN THAT ORDER.
- The Adhesion of the coating is 10,000 times more important than the type of coating, according to George.
- The Thickness of the coating is 1000 times more important than the type of coating.
- The Morphology of the coating is responsible for about 10 times the advantage over the type of coating.
What good is a high tech coating to your job if it won’t stay on the tool when you need it?
If it isn’t thick enough to be effective?
At that point, does it really matter what type of coating it is? Or what its structure is?
This is an over-simplification which can lead to erroneous conclusions. For example, adhesion plays only a minor role in machining soft, abrasive materials, such as graphite, some aerospace composites, or hyper-eutectic aluminum alloys. There the temperatures generated and the cutting forces are typically low, and tool life is defined by abrasion resistance, that is, the hardness of the coating, and the thickness of the coating at the location of maximum abrasive wear.
Also, note that adhesion and thickness are different types of properties than morphology (which is the form or structure of the film). Adhesion, thickness, hardness, and strength (resistance to brittle fracture, or resistance to crack propagation) are “macroscopic” properties which ultimately define the performance of a specific coating in a specific application, on a practical level. The underlying properties, such as composition, atomic and molecular bond strength or the type of the chemical bonds, the composition and composition-modulation within the structure, the conditions of meta-stability and stress levels, in turn will define the practically applicable “macroscopic” properties.
Thank you George. Always appreciate well thought out comment. Your comments are probably correct regarding the materials you describe. Those materials, graphite, some composites and Hypereutectoid aluminum, are not routinely machined in our world of contract parts manufacturing. Our audience is primarily dealing with metal alloys, often heat treated steels, and some materials with high nickel content. Thanks for sharing your comment regarding coatings on the other materials that you mentioned. Recognizing assumptions is a key to critical thinking. Our post was regarding coatings for the materials routinely encountered in our NAICS 332721 Precision Machining Contract Manufacturing shops.
What…Huh…? Too much for me to take in on a Monday morning.
Anyway, Great discussion guys!