Co-Based Corrosion-Resistant Alloys

Differences of the high-temperature mechanical behavior of these materials are shown in terms of stress-rupture curves in Fig. 3.1-122. 

Investment-cast Co alloys are generally used for parts of complex shape such as first- and second-stage vanes and nozzles in gas turbine engines. 

Compared to the heat resistant Co-based alloys, the corrosion-resistant alloys have low C concentrations and 

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Corrosion resistance The corrosion resistance of a copper deposit varies with the conditions under which it is deposited and may be influenced by co-deposited addition agents (see, for example, Raub ). Copper is, however, plated as a protective coating only in specialised applications, and the chief interest lies in its behaviour as an undercoating for nickel-chromium on steel and on zinc-base alloy. Its value for this purpose has long been a controversial issue. 

Nickel containing scales exhibit higher conductivity because of the presence of trivalent nickel ions, which introduce vacancies in the lattice of the scale. Therefore, nickel-based coating can lead to superior conductivity and good protection provided that it is alloyed properly with corrosion resistant elements. Cobalt has a lower solubility in molten carbonate and electroless Co has been successfully used for a variety of corrosion-resistant applications. Electroless plating of Ni-Co gives rise to deposition of uniform layers of nanostructured material, which would result in better protection of the substrate. 

More Mo is consumed annually than any other refractory metal. The major use for Mo is as an alloying element in alloy steels, tool steels, stainless steels, Ni-based and Co-based superalloys. In these materials, it increases the hardenability, toughness, high-temperature strength, and corrosion resistance. Molybdenum is important in the missile industry, where it is used for high-temperature structural parts, such as nozzles, leading edges of control surfaces, support vanes, struts, reentry cones, radiation shields and heat sinks. In the electrical and electronic industries. Mo is... 

As discussed before, hard metal-like composites can be prepared by pressureless sintering of ternary borides with Fe, Ni, or Co melts. Materials with x-phase (M21M2 Bg, where = Fe, Ni, or Co, and M = Zr, Hf, Nb, Ta, or W with M as the matrix phase) have not been developed for technical use but Ni-based alloys with x are in applications as wear- and corrosion-resistant coatings on steels [355]. The x phase is also used for the improvement of the creep resistance of Ni-based superalloys. 

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