Creep-Fatigue Cracking Near the Welded Interface in Friction Welding Dissimilar Superalloys INCONEL 718 and MAR-M247
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INTRODUCTION
NICKEL-BASE superalloys have emerged as the candidate materials for high-temperature applications, where resistance to fracture under static, fatigue, and creep conditions is decisive.[1,2] In gas turbines, for instance, the blades operate at high temperature and, thus, require outstanding creep resistance. On the other hand, the disks operate at lower temperatures but higher loading conditions and, thus, require excellent fatigue resistance.[1,2] Therefore, there are several advantages from the development of a multifunctional single component. Such a component can work well under distinct temperature regimes and loading conditions, e.g., turbine blisks. Recently, to meet these requirements, there have been a number of new trends in superalloys and processes. NASA designed the dual-microstructure heat-treatment technology in which the microstructural and property variation can be achieved within any given component.[3,4] Another favorable way different superalloys are joined into one structure.[5–8] As a suitable method of joining dissimilar alloys, friction welding is generally accepted as an alternative process in this hybrid approach.[5–13] Friction welding has been used recently to join a cast MAR-M247 with a forged INCONEL 718.* They are
candidate superalloys for turbine blisks.[1,2,14] The mechanical properties of the welding were experimentally investigated under various loading conditions by Okazaki et al.[6] The welding was strong under monotonic and fatigue loadings. When the dissimilar joint is addressed to use at elevated temperatures, the so-called creep fatigue and thermomechanical fatigue need to be investigated. Here, several mechanical and metallurgical factors are simultaneously considered. From a metallurgical aspect, the dissolution or coarsening of the main strengthening precipitates and the recrystallized microstructure might be the important issues.[11,12,15–18] From a mechanistic viewpoint, the stress concentration resulting from the incompatibility of mechanical properties could be a critical concern. The objective of this work is to explore the role of the stress multiaxiality induced by the inhomogeneous properties along the welding. For this purpose, the creep-fatigue behavior of the welding was assessed by the experiments. Then the stress field in the welded zone was numerically analyzed using a visco-elastic model, employing two kinds of damage parameters proposed by Huddleston[19] and Spindler.[20]
II. *INCONEL is a trademark of Special Metals Corporation, New Hartford, NY.
TRAN HUNG TRA is with Nha Trang University, 02 Nguyen Dinh Chieu, Nha Trang, 058, Vietnam. Contact e-mail: [email protected] MASAKAZU OKAZAKI is with Nagaoka University of Technology, Kamitomioka-Machi 1603-1, Niigata, 940-2188, Japan. Manuscript submitted September 23, 2016.
METALLURGICAL AND MATERIALS TRANSACTIONS A
EXPERIMENTAL PROCEDURES
A dissimilar friction joint (denoted DFJ) between cast polycrystalline MAR-M247** (denoted MM247) and **MAR-M247 is a trademark of Martin Marietta.
forged INCO
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