γ/γ′ Nickel-Based Superalloys

Superalloys (that often have an ordered intermetallic phase as the majority component) have a continued important role in high-temperature materials applications. This chapter discusses superalloys, which are an example of at least two phases, one ordered and one disordered. Industrial alloys often have additional phases to the primary disordered and ordered phases but a discussion of the fundamentals of superalloys can be best reduced to a discussion of the common two-phase Y/ Y′ systems. These two-phase systems are often referred to as single crystals in the absence of high-angle grain boundaries. Superalloys that are discussed are single crystals. The early consensus of investigations of creep in superalloys is that slip occurs in directions in both the Y and Y′, particularly below roughly 5% strain.