Comparison of Mechanical Properties of TMW Alloys, New Generation of Cast-and-Wrought Superalloys for Disk Applications
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Turbine disks are the parts holding the rotor blades while rotating at a high speed, which require that the materials for the disk have excellent properties in fracture toughness, creep, and fatigue resistance.[1–3] Nickel-based alloys with c/c¢ two-phase structure are generally employed for the turbine disks. To meet the high requirements of modern engines for mechanical properties, the latest disk alloys such as Rene 95, RR1000,[4] and ME3[5] have a high volume fraction of c¢ phase and heavily solid-solution-hardening elements, which make them produce only via the powder metallurgy process route.[4–6] However, the high requirement for clean powder and the cost of thermomechanical processing steps set the limit to their applications. Recently, in the High Temperature Materials 21 Project led by the Japanese National Institute for Materials Science, we proposed an innovative concept to design disk alloys.[7–16] This concept is based on
Y.F. GU, Senior Research and Group Leader, C. CUI, Research Fellow, H. HARADA, Senior Researcher and General Director, T. YOKOKAWA, Senior Researcher, and J. FUJIOKA, Y. KOIZUMI, and T. KOBAYASHI, Research Fellows, are with the High Temperature Materials Center, National Institute for Materials Science, Ibaraki 305-0047, Japan. Contact e-mail: [email protected] T. FUKUDA, Staff Member, and A. MITSUHASHI, Director, are with the NonFerrous Alloys Research and Technology Laboratory, Mitsubishi Materials Corporation, Kitamoto, Saitama 364-0023, Japan. Manuscript submitted May 8, 2009. Article published online October 27, 2009 METALLURGICAL AND MATERIALS TRANSACTIONS A
combining the characters of two kinds of c-c¢ two-phase alloys (Ni-base and Co-base alloys), where Ni-base alloys offer basic mechanical properties required for disk applications and added Co-base alloys have beneficial effects on increasing the middle temperature (600 C to 800 C) strength and on widening the C&W processing window of the mixed alloys.[8] We named these C&W Ni-Co–base materials TMW alloys. In this article, we report the investigations on mechanical properties of some TMW alloys (TMW-2, TMW-24, and TMW-4M3) and a commercial C&W Nibase disk alloy (U720Li alloy). The chemical compositions of the tested alloys are listed in Table I. All specimens used were cut from the pancakes (440 mm in diameter and 65 mm in thickness) produced by a conventional C&W processing route including triple melting, billet making, and pancake forging at Mitsubishi Materials Corporation. The specimens were heat treated in the standard heat-treated condition reported for U720Li alloy (1100 C/4 h followed by oil quench (OQ) and then aging at 650 C/24 h/OQ + 760 C/16 h/OQ). All mechanical property tests were carried out at Kobe Materials Testing Laboratory, the first material testing laboratory in Japan accredited to Nadcap. (Nadcap is the only worldwide standard accreditation program of special processes and products required by aerospace prime contractors.) The tests were performed according to ASTM E8/E21, ASTM E139, ASTM E606, and
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