Properties of new C&W superalloys for high temperature disk applications

The enhancement of efficiency in gas turbine engines requires the development of new superalloys capable of withstanding higher temperatures. The development of novel industrial cast and wrought (C&W) disk alloys with required combination of strength, creep and fatigue resistances at 700°C is particularly desired due to the expensive cost of powder metallurgy. In this context, new C&W disk alloys were recently developed to fulfill these requirements. TMW4 shows higher properties than the current C&W disk alloy despite an expensive cost due to its high cobalt content, where as 718Plus presents a moderate cost with restricted creep properties at 700°C compared to the current U720Li disk alloy. The new nickel base superalloys developed by Aubert & Duval were therefore designed to offer a better compromise between high temperature properties at 700°C and cost. This paper describes the alloys metallurgical features and the alloys design partly based on phase diagrams modeling. The study was firstly carried out on small ingots of 6kg to optimize the chemistry before forging by industrial processes 200kg ingots. The ability to be processed by the conventional cast & wrought route and the control of the highly expensive elements contents confer to the alloys an attractive cost comparable to that of 718Plus alloy. The high amount of gamma prime and the molybdenum-tungsten levels insure higher creep and tensile properties than those obtained with 718Plus. Tensile, creep, fatigue, long-term aging tests show that the new alloys have high mechanical properties up to 700°C. Based on these results, it should be possible to extend performance capabilities, in terms of cost and mechanical properties, of most current C&W superalloys for turbine disks. (AU) © 2010 by The Materials, Metals, & Materials Society. All rights reserved.