Age-hardening behavior and phase identification in solution-treated AEREX 350 superalloy
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the latest member of MULTIPHASE** *AEREX is a trademark of SPS Technologies Inc., Jenkintown, PA, **MULTIPHASE is a trademark of SPS Technologies Inc., Jenkintown, PA.
(MP) family, a class of wrought nickel-cobalt base alloys extensively used in high-quality applications including aerospace fasteners, gas turbine engines, and petrochemical industry.[1,2] Due to high-quality requirements, these alloys are produced through a double (VIM 1 VAR) or a triple (VIM 1 ESR 1 VAR) melting route to effectively remove inclusions and achieve optimized ingot structure required for further thermomechanical processing. The MP35N alloy, the original member of the MP family, is mainly strengthened by cold working. Owing to its high rate of work hardening, a common property of all MP alloys, and a characteristic phenomenon known as ‘‘secondary hardening,’’ deformed MP35N may achieve tensile strengths above 1000 MPa.[3,4,5] To improve high-temperature properties, the composition of AEREX 350 has been empirically selected to benefit from cold working, solidsolution strengthening, and, particularly, precipitation hardening. Table I shows chemical compositions of AEREX 350 and MP35N alloys. While the AEREX 350 alloy has been used for several years as a fastener material with superior creep resistance and rupture properties similar to other alloys, very limited research on different aspects of this interesting material has been carried out.[6,7] The alloy is also a suitable raw material candidate for manufacturing more complex gas turbine S. ASGARI, Associate Professor, is with the Department of Materials Science and Engineering, Sharif University of Technology, Tehran, Iran. Contact e-mail: [email protected] Manuscript submitted January 4, 2006. METALLURGICAL AND MATERIALS TRANSACTIONS A
components through thermomechanical processing. This, however, requires a detailed knowledge of microstructure and strengthening mechanisms operating under different process conditions. This article presents results of a completed investigation on precipitation behavior of the AEREX 350 alloy. The main goals of this study have been (1) to characterize the aging response of the material at different temperatures for different aging times and (2) to identify the major strengthening phases produced as a result of aging process and the relative temperature range of formation of each phase. II.
MATERIALS AND EXPERIMENTAL
The AEREX 350 alloy used in this investigation was supplied by SPS Technologies (Jenkintown, PA) in the form of cold-drawn bars. The as-received material was solution treated at 1100 °C for 1 hour in argon atmosphere and subsequently water quenched. For precipitation hardening studies, samples of solution-treated AEREX 350 were aged for different aging times in the temperature range of 500 °C to 1060 °C followed by quenching in water. Aged samples were tested in a LECO† microhardness testing unit after †LECO is a trademark of LECO Corporation, St. Joseph, MI.
being ground and polished. Five indentations were made for each hardness measurem
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