Nickel alloys are industrially important for their resistance to certain types of high-temperature corrosion. For example, the have out-standing resistance to oxidation, and they are generally superior to iron-base and cobalt-base alloys in this mode of attack (Fig. 1). They have low solubility for interstitial atoms, which makes them inherently more resistant to carburization and nitridation attack than other alloys. They also have good resistance to halogen-containing environments, because of the high melting points of the halogen compounds. The compositions of several high-temperature nickel alloys are given in the Table. These are grouped according to their primary elements: Ni-Cr, Ni-Cr-Mo, Ni-Cr-W, Ni-Co-Cr, Ni-Cr-Fe, Ni-Fe-Cr, and Ni-Mo. It is also useful to categorize the high-temperature nickel alloys by whether or not they can be age hardened. Alloys are usually age-hardened by the precipitation of fine gamma-prime or gamma double-prime particles in the microstructure.
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