Development of a New 760°C (1400°F) Capable Low Thermal Expansion Alloy

A recently developed 760 o C (1400 o F) capable low thermal expansion alloy, HAYNES 244 alloy, is introduced. The new alloy is intended for use in seal rings and other static parts of future generation gas turbines operating at higher temperatures. The alloy is an improvement over current generation low thermal expansion alloy HAYNES 242 alloy. Its defining feature is the partial substitution of tungsten for molybdenum. Judicious alloying enabled the same age-hardening mechanism to be operative while increasing the thermal stability of the strengthening phase, thus raising the temperature capability of the new alloy. The results of a mill scale-up of this concept are reported with regard to several key performance characteristics: thermal expansion, tensile and creep strength, and thermal stability. While additional product forms such as plate and sheet are being processed, the bulk of the presented results relates to capability pancakes obtained from forged billet. Benchmarking against several current generation low thermal expansion alloys indicates the potential of the new alloy for more demanding operating conditions.