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High Temperature Corrosion

At elevated temperatures, an electrolyte is not required to drive the corrosion reaction. Instead, ions within hot gases attack the substrate directly. In high-temperature oxidation, it is oxygen that causes the attack through the formation of an oxide scale on the surface of the component. Initially, the scale may be relatively stable, but as time goes on, the scale continues to grow. Stresses build within the scale and eventually, the stresses become high enough to cause the scale to crack and spall. The process then repeats to the point of failure.

Sulfidation is a similar mechanism to that of oxidation, but the corrosive culprit comes from the presence of sulfur compounds. Sulfidation can be more aggressive than oxidation because these sulfur based scales are less stable than oxides. 

Solutions:

In gas turbine engines the hot turbine sections are subject to high temperature corrosive attack. Oerlikon Metco has long supplied MCrAlY coating materials (M = Metal, generally cobalt, nickel or iron) designed to protect hot section components. MCrAlYs can be applied using atmospheric plasma spray, controlled atmosphere plasma spray or high-velocity oxygen fuel spray. In service, coatings of these materials form a very stable, highly adherent oxide layer that helps prevent diffusion of the corrosive ions. These coatings are also used as stable, corrosion-resistant bond coats in thermal barrier and ceramic clearance control coatings in gas turbine engines. 

Learn more about the coatings for high temperature corrosion

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