A Rolls-Royce Trent 900 engine on a China Southern Airlines A380. © Airbus 2011
Superalloys are a group of polymetallic high performance alloys that possess very high melting temperatures, high strength, and considerable resistance to wear in corrosive and oxidizing environments. Because of their high strength and minimal thermal creep at high temperatures (above 800ºC), the majority (85%) of superalloys find application as investment castings and directionally solidified and single crystal turbine blades in the hot sections of gas turbines used as aerospace engines and to generate industrial power (IGT). In 2015 the total superalloy sector consumed approximately 400t of tantalum and 2200t of niobium (excluding revert), some 20% and 4% of total production respectively.
For a special report on superalloys see our newsletter Bulletin #167.
Superalloys are typically used in the hottest parts of gas turbines because they offer a unique combination of very high melting temperatures, high strength, and considerable resistance to wear in corrosive and oxidizing environments. They can be nickel-, cobalt- or iron-based alloys and will contain variable amounts of chromium, tungsten, molybdenum and a range of other elements, including tantalum and niobium. While the term superalloy is nominally reserved for those alloys which are used at service temperatures of above 800ºC, in practice it is also used for alloys developed for corrosion and wear resistance. Superalloys were developed for applications where high tensile, thermal, vibratory and shock stresses are encountered and where oxidation resistance is frequently required, particularly in the aerospace and energy industries.
The development of superalloys has been driven by the requirements of gas turbine technology and still today the majority of superalloys are consumed in manufacturing gas turbine aero engines (55%) and industrial gas turbines (IGT) (30%), the latter used mostly for electricity generation, and also for powering terrestrial and marine vehicles (see Figure 1). The balance of superalloys are used by the petroleum and petrochemical industries as well as in space vehicles, nuclear reactors, and steam power plants. The superalloy market is a global one, with particular concentrations in North America, Europe, Russia, China, Japan and Australia. The USA and the EU produce most superalloys and also consume the greatest quantities, estimated at between two-thirds and three-quarters of total demand.