Special Engineering Topics
This article reviews some of the trends in superalloy development as they relate to U.S. strategic materials availability and the aerospace industry. It discusses the supply sources and availability of strategic materials and summarizes the status of U.S. resources and reserves. The article presents a list of several superalloys that have been used in gas turbine engines or that are emerging as replacements because of the promise of increased operating temperatures and higher efficiencies for the aircraft of the future. It concentrates on the objectives, results, and methodology of the NASA Conservation of Strategic Aerospace Materials (COSAM) program.
A significant amount of the worldwide demand for metals is met with recycled materials acquired by metal producers in the form of purchased scrap. This article focuses primarily on the methods and technology used to process and repurpose the vast amounts of purchased scrap that recirculate in the industrial supply chain. It describes the U.S. market for iron and steel scrap, providing information on scrap use by industry, factors influencing demand, and the purchased scrap supply. Iron and steel recycling is discussed separately from stainless steel and superalloy recycling in this article, as the scrap industry treats them differently. The scrap processing of iron involves collection, separation and sorting, size reduction and compaction, detinning, blending, and incineration. The recycling of stainless steels and superalloys follows the same process, but requires several additional steps, including secondary nickel refining, degreasing, and separation of metallurgical wastes.