Superalloys: Alloying and Performance
Superalloys are among the most compositionally complex alloys ever developed, containing a multiplicity of alloying elements and producing multiple phases with important mechanical effects. A few key alloying elements produce the dominant phases, while a variety of adjunct elements, often in trace amounts, can modify the properties; in some cases, the modification is profound. The topic of superalloys is ripe for research, especially experimental research, and new effects, sometimes subtle, continue to be discovered.
The primary purpose of Superalloys: Alloying and Performance is to examine the role of alloying elements in superalloys, ultimately for understanding the suitability for a particular application. The main target audience for the book is mechanical, materials, and metallurgical engineers and technologists in industry involved in the design, specification, or application of superalloys. It would also be of interest to academia, where students and researchers may find it useful as a broad reference and succinct summary of research in the field. The book attempts to fill a niche for a concise, practical, readable summary of the topic of superalloys.
The book is quite descriptive, without mathematical rigor, and stands alone sufficiently for anyone with a basic knowledge of materials science to grasp. It is not envisioned to be a book of interest to the layman, but by virtue of its descriptive nature, the layman is not shut out. The book is accessible to anyone requiring a detailed knowledge of the chemistry, phases, and microstructure of superalloys.
The gas turbine engine, with its high temperatures and stresses, is the dominant application that drives the superalloy industry, continually demanding that the mechanical performance boundaries be advanced. The big metallurgical advances enabled the development of the jet aircraft. Minor metallurgical advances continue to gradually push the temperature envelope, enabling higher efficiencies and/or greater component longevity in the gas turbine engine. Other applications have arisen as the technology evolves, with the application base of superalloys now extending to such areas as nuclear reactors, biomedical devices, petrochemical equipment, and high-temperature furnaces.
The book presents an overview of the subject of superalloys and summarizes current research in the field. It discusses the phases present and the effect of many alloying elements on developing those phases and their effect on mechanical performance. Abundant citations to the references support the text. Few other books address the compositional effects on microstructure and mechanical properties so broadly. The book is not meant to be an exhaustive or deep discussion of the field; rather, the authors strived to produce a brief, focused summary that invites the reader with specific interests to consult more specialized works.
The economic importance of the gas turbine engine spurs continued research in the field. The dominant mode of research continues to be experimental because the metallurgical complexity of superalloys, coupled with the computational sophistication of accurate quantitative prediction of the behavior of such materials, renders theoretical investigation valuable only in the sense of gaining a cursory understanding. Accumulating the body of knowledge and detailed understanding of interrelated effects of many alloying elements, often in trace amounts, by experiment is slow, painstaking work and continues to be new research ground for the application of practical talents; hence, the field evolves slowly.