respond to the designer’s desire for higher temperature, as shown in Figure E.2); a constant evolution of understanding how to provide the user with a high degree of confidence in the material; and no show-stoppers or major surprises.

To understand why these materials have been successful, one needs to understand the material’s chemistry and chemical behavior. Nickel has no phase transformation between room temperature and its melting point. Its face-centered cubic structure is amenable to facile processing and alloying. For intermediate temperatures, it can be either solid-solution-strengthened or precipitation-strengthened-solid solution, and it can be precipitation-strengthened for high temperatures. There are a variety of compatible alloying element chemistries, including aluminum, chromium, cobalt, iron, and tungsten. In the case of nickel superalloys, there has been a tremendous synergy between scientific understanding and applications—scientific understanding of the relationships between microstructure and high-temperature properties, and applications that have benefited from this understanding in the form of improved materials and processes. This synergy has been a “perfect storm” for a successful story.

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