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Question
#1427
Subject: Best practices for diffusion coating low carbon steel
I would like to know about a new method of diffusion coating and a best practice for coating low carbon steel with aluminum, zinc, chromium, silicon.
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#1428
Author: Charles A. Bishop, C.A.Bishop Consulting Ltd.
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Subject: Best practices for diffusion coating low carbon steel
Diffusion coating is a method of modifying metals by using heat to diffuse another metal into the surface. This requires both metal surfaces be clean and sufficient tolerance of the part to allow diffusion to take place. This technique has included clamping plates of material together where the surface is completely flat. In the case of complex shapes, the parts have been immersed in a powder of the metal that is to be diffused into the surface. In this latter case there is the problem of oxidation so this process would be carried out under vacuum or a reducing atmosphere.
With the advent of vacuum coating, it is possible to coat the outside of the part in a vacuum system and then use the same vacuum system as a vacuum furnace to diffuse the coating into the surface. In some other cases, it is possible to use a gas such as nitrogen as the diffusing material and, thus, by using a plasma and temperature to nitride the surface to harden it. The same can be done using hydrocarbons for carburizing the surface, again to surface harden the metal part.
If you're considering vacuum coating to supply the metal for diffusion coating then it may be worth considering a high-performance coating such as titanium nitride or aluminum-carbo-nitride or other materials of this class, which would out-perform most diffusion coatings.
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