SELECTION OF NEW AGE-HARDENABLE SUPERALLOYS
14 May 2006 - Carpenter Technology Corporation

Superalloys are high-performance materials designed to provide high mechanical strength and resistance to surface degradation at high temperatures of 1200°F (650°C) or above. They combine high tensile, creep-rupture, and fatigue strength; good ductility and toughness, with excellent resistance to oxidation and hot corrosion. Furthermore, superalloys are designed to retain these properties during long-term exposures at the elevated temperatures.

This article focuses on the wrought age-hardenable alloys, which are the most commonly used superalloys. Wrought materials can be formed using hot and cold working operations. Not discussed here are the cast, powder, and oxide dispersion strengthened superalloys that can also offer enhanced properties.

The first age-hardenable, high-temperature alloy dates back to about 1929 when various developers added titanium and aluminum to the standard 80% nickel/20% chromium resistance wire alloy. This was a precursor to the 80A nickel-base superalloy, developed in 1940-1944, but still in use today.

Little was done to advance the original age-hardenable alloys until the time period of 1935-1944 when World War II spurred demand for improved alloys that could be used in the early aircraft gas turbine engines. Alloy development activity exploded in the 1950's and 1960's to keep pace with the demands of the gas turbine engine industry. Progress in superalloy development not only made the jet engine possible, but allowed for constantly increasing thrust-to-weight ratios over the last 60 years.

The primary application for superalloys is still in hot sections of aircraft gas turbine engines, accounting for over 50% of the weight of advanced engines. However, the excellent performance of these materials at elevated temperatures has expanded their application far beyond one industry.

In addition to the aerospace industry, these alloys are used in turbine engines for marine, industrial, land-based power generation, and vehicular applications. Specific engine parts using superalloys include turbine discs, blades, compressor wheels, shafts, combustor cans, afterburner parts and engine bolts.

Beyond the gas turbine engine industries, superalloys are commonly used for applications in rocket engines, space, petrochemical/energy production, internal combustion engines, metal forming (hot-working tools and dies), heat-treating equipment, nuclear power reactors, and coal conversion.

While these alloys are primarily used for service at elevated temperatures above 1000°F (540°C), the characteristics of high strength and excellent environmental resistance have made some superalloys an excellent choice for lower-temperature applications. Examples are prosthetic devices in the medical industry and components for deep sour gas wells in the oil/gas exploration industry.

http://www.cartech.com

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