Effect of Solution Temperature on the Microstructure and Mechanical Properties of a Newly Developed Superalloy TMW-4M3
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INTRODUCTION
ADVANCED polycrystalline Ni-base superalloys are used widely in gas turbines for high-pressure rotor disks because of their excellent mechanical properties.[1] Generally, superalloys rely on a combination of solid solution strengthening and precipitation hardening to provide high-temperature mechanical properties. Solid solution strengthening is achieved by the introduction of solutes such as W, Mo, Co, and Cr, whereas precipitation hardening is obtained by the precipitation of large volume fractions of intermetallic phases such as c¢. Heat treatment has a profound effect on the microstructure, such as modified c¢ characteristics, thereby influencing the mechanical properties of Ni-base superalloys. Considerable efforts[1–5] have been made to investigate the influences of heat-treatment conditions on the microstructures of various superalloys in the past decade. For instance, the effect of heat treatment on the microstructure of U720Li (developed by Special Metals CorporaZHIHONG ZHONG, YONG YUAN, and TOSHIO OSADA, Postdoc Researchers, YUEFENG GU, Senior Researcher and Group Leader, TADAHARU YOKOKAWA and TOSHIMITSU TETSUI, Senior Researchers, and HIROSHI HARADA, Senior Researcher and General Director, are with the High Temperature Materials Unit, National Institute for Materials Science (NIMS), Tsukuba, Ibaraki 305-0047, Japan. Contact e-mails: [email protected]; gu. [email protected] CHUANYONG CUI, Researcher, is with the Institute of Metal Research, China Academy of Science, Shenyang 110016, P.R. China. Manuscript submitted November 29, 2010. Article published online October 12, 2011 METALLURGICAL AND MATERIALS TRANSACTIONS A
tion, Huntington, WV) was studied by Jackson and Reed.[2] The effect of the cooling rate on c¢ morphology and c/c¢ mismatch in several superalloys has been studied recently by Mitchell et al.[3] Monajati et al.[4] investigated the influence of various heat-treatment conditions on the kinetics of c¢ dissolution, reprecipitation, and growth in a wrought superalloy. Recently, Hwang et al.[5] characterized the compositional and microstructural variation of different generations of c¢ precipitates during continuous cooling in Rene 88DT (Rene 88DT is a trademark of General Electric Aircraft Engines, Cincinnati, OH). In all the preceding studies, the focus has been on the microstructure, with minimal on mechanical properties. The effect of heat treatment on the mechanical properties of superalloys is significant, that even small changes in the condition of heat treatment could lead to great changes in mechanical properties. The effect of heat treatment on the mechanical properties is also complicated: The time-dependent properties (creep and fatigue crack growth [FCG] resistance) at high temperature can be maximized with coarse grain microstructures produced by solution heat treatment above the c¢ solvus temperature; however, the strength-dependent properties (tensile strength, low cycle fatigue [LCF] resistance) can be maximized with fine grain microstructures produced by solution heat tre
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