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A distinction is often made between those alloys that are primarily used for high-temperature strength, commonly referred to as superalloys, and those that are primarily used for corrosion resistance. High performance alloys are defined, in the present context, as Ni, Ni-Fe and Co base alloys able to operate at higher temperatures than 550oC and high pressures. Fe, Co and Ni are transition metals with consecutive positions in the Periodic Table. The relative order of abundance decreases as Fe, Ni, Co.A modern and comprehensive document on the subject is the second edition of the classic CORROSION BASICS textbook.
The Fe-Ni-base high performance alloys are an extension of stainless steel technology and generally are wrought, whereas Co-base and Ni-base high performance alloys may be wrought or cast depending upon the application or composition involved. Appropriate compositions of all high performance alloy base metals can be forged, rolled to sheet or otherwise formed into a variety of shapes. The more highly alloyed compositions normally are processed as castings. Typical high performance alloys have modulus of elasticity around and above of 200 GPa. The principal microstructural variables of high performance alloys are:
The precipitate amount and its morphology
Grain size and shape
Carbide distribution
Monel (also called Monell) is a patented Nickel/Copper alloy (66/29) plus significant additions of cobalt, manganese, iron, silicon, carbon and aluminum. It is named after the Canadian metallurgist Ambrose Monell who developed it. (Mr. Monell died in 1921.) Its resistance to air oxidation and reaction with carbon dioxide makes it reasonably worry free. When corrosion does occur it is at the boundary where the crystals of nickel and copper join. This would suggest that some batches of Monel might have better resistant to corrosion than others. Monel is also a very hard and wear resistant alloy.
