TABLE OF CONTENTS Superalloys are heat resistant alloys of nickel, iron nickel and cobalt that frequently operate at temperatures exceeding 1000 F. However, some superalloys are capable of being used in load bearing applications in excess of 85% of their incipient melting temperatures. They are required to exhibit combinations of high strength, good fatigue and creep resistance, good corrosion resistance, and the ability to operate at elevated temperatures for extended periods of time (i.e., metallurgical stability). [1] Their combination of elevated temperature strength and resistance to surface degradation is unmatched by other metallic materials.
Superalloys are the primary materials used in the hot portions of jet turbine engines, such as the blades, vanes and combustion chambers, constituting over 50% of the engine weight. Typical applications are shown in Fig. 6.1. Superalloys are also used in other industrial applications where their high temperature strength and/or corrosion resistance is required. These applications include rocket engines, steam turbine power plants, reciprocating engines, metal processing equipment, heat treating equipment, chemical and petrochemical plants, pollution control equipment, coal gasification and liquification systems, and medical applications. [2]
In general, the nickel-based alloys are used for the highest temperature applications, followed by the cobalt-based alloys and then the iron nickel alloys. A relative comparison of their stress rupture properties is shown in Fig. 6.2. Superalloys are produced as wrought, cast and powder metallurgy product forms. Some superalloys are strengthened by precipitation hardening mechanisms, while others are strengthened by solid solution hardening. For...
