High-purity chromium metal supply issues for gas-turbine superalloys
National Academy Press Washington, D.C. | ISBN : 0387302840 | 190Pages | 1995 | PDF | 7.2 MB
The operating parameters of an aircraft engine are extremely demanding on materials. Metal temperatures within an engine can reach as high as 1200 °C. Materials are subject to rapid oxidation and creep, high centrifugal stresses, high pressures (up to 4 megapascals), and high torque. The alloys used in engines are referred to as superalloys because of their superior combination of low- and high-temperature mechanical properties, as well as their ability to withstand harsh environments. Many of the superalloys contain high levels of chromium metal. Chromium metal limits the coarsening rate of the intermetallic (and usually coherent) precipitates; forms Cr23 C6, which strengthens grain boundaries; plays a critical role in the formation of protective scales; and improves hot-corrosion resistance. Thus a major portion of the gross engine weight consists of chromium-bearing alloys, for which there are currently no substitutes.