Oxidation high temperature resistant metallic coatings

Implantations of yttrium and cerium in 15 % Cr/4% A1 steel and aluminized coatings on nickel-based alloys did not improve the high-temperature oxidation resistance even though conventional yttrium alloy addition had an effect. The differences for the various substrates are attributed to different mechanisms of oxidation of the materials. The austenitic steel forms a protective oxide film and the oxidation proceeds by cation diffusion. Thus, the yttrium is able to remain in a position at the oxide/metal interface. The other materials exhibit oxides based on aluminum. In their growth anion diffusion is involved which means an oxide formation directly at the oxide/metal interface. The implanted metals may, therefore, be incorporated into the oxide and lost by oxide spalling. 

Protective metallic coatings are typically applied to metallic substrates for one of three reasons to aid in corrosion resistance, to furnish high-temperature oxidation resistance, and/or to provide a base for painting. Although metallic coatings could also be applied for other user-specific reasons, such as appearance, to achieve the desired end-use product, the intent of this chapter is to focus on application of coatings to provide protection to the underlying substrate. 

Metallic coatings can also be used to provide high-temperature oxidation resistance for specific applications. Aluminum and aluminum-zinc coatings are well suited for high-temperature applications (up to 675°C). 

High temperature oxidation resistant metallic coatings... 

The heart of corrosion science has been identified as electrochemical science coupled with the thermodynamic and kinetic values. Other limbs are oxidation and high-temperature oxidation of metals, protective coatings, passivity, inhibitors, microbial-induced corrosion, corrosion fatigue, hydrogen embrittlement and corrosion-resistant alloys. Having identified the limbs of corrosion science, it is instructive to examine how the various aspects came into existence over a period of time. 

B. V. Cockeram, R. A. Rapp Oxidation Resistant Boron- and Germanium-Doped Silicide Coatings for Refractory Metals at High Temperature to appear in Mater. Sci. and Eng. 

The use, since 1975, of catalytic converters in automobiles has resulted in increased exhaust gas temperatures, up to 870°C (1600°F), with metal temperatures up to 760 °C (1400 F), as well as increased concentrations of corrosive chemicals, such as sulfuric acid, in the exhaust gas stream. As a result, materials resistant to high-temperature oxidizing conditions, such as hot dip aluminum-coated type 409 stainless steel, are being used in automotive exhaust systems [35-37]. 

T. Ikeda and H. Satoh High-Temperature Oxidation and Wear Resistance of Ti-Al-N Hard Coatings Formed by PVD Method , J. Japan Inst. Metals, 57, 919-925 (1993)... 

Nanociystalline alloy coatings, oxide dispersive alloy coatings and metal oxide composite coatings show superior high temperature corrosion resistance. A Ni-Cr nanocomposite with an average Cr concentration of 11 wt% deposited onto nickel... 

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