The precipitation response of corrosion resistant alloys based on the Ni-Cr-Mo phase diagram is complex with both intermetallic and carbide phases being formed during aging in the 650 to 1090 C (1202 to 1994 F) range. Although these phases markedly affect the corrosion resistance, their composition and structure have not been fully defined. Data are presented to show that the precipitating intermetallic phase in Hastelloy alloy C-276 is a (Ni, Fe, Co)3 (W, Mo Cr)2 Mu phase and the carbide is an M6C. Both phases have been shown to significantly increase the anodic dissolution rate of the passive region in boiling 10% sulfuric acid. Intergranular attack on aged alloy C-276 samples occurred due to attack of depleted regions in reducing acids and direct dissolution of precipitates under oxidizing conditions.

Oxidation rates and rate equations off La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Lu„ Y were determined in dry and moist air in the temperature range 100–800 C (212–1472 F) by precision weight gain measurements Oxide structures were examined by both metallographie and x-ray analyses. Observed oxidation characteristics are related to oxide structures and the physico-chemical properties of the rare earth metals.

While nickel has been known for centuries as a material for various uses, including the Ni-Fe expansion alloys that were developed around 1896, the history of the solid-solution-strengthened nickelbased alloys begins with the development of the Ni-Cu alloy Monel ® in 1906. Since that time many other alloys have been developed containing other elements and possessing signifi cantly different corrosion resistance. These developments have also been aided by developments in the metallurgical processing of nickel alloys. This paper will discuss the major nickel alloy developments that have allowed and expanded the use of these alloys in the chemical processing industry.

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