Fracture Mode of a Ni-Based Single Crystal Superalloy Containing Topologically Close-Packed Phases at Ambient Temperatur
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Modern Ni-based single crystal superalloys with excellent mechanical properties are strengthened by the increase of refractory alloying additions (such as Mo, Re, and W).[1] However, high levels of refractory alloying elements increase the tendency of microstructural instability, especially the precipitation of topologically close-packed (TCP) phases in addition to the basic phases (FCC—c phase and L12—c¢ phase).[2] Many studies indicated that TCP phases, such as r, l, and P, were detrimental to the mechanical properties.[3–5] These undesirable effects are caused by (1) the damage
QIANYING SHI, Ph.D. Candidate, is with State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083, P.R. China. XIANFEI DING, Assistant Research Scientist, and YUNRONG ZHENG, Research Scientist, are with National Center for Materials Service Safety, University of Science and Technology Beijing. JINGYANG CHEN, formerly Ph.D. Candidate with the State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, is now Engineer with the Science and Technology on Advanced High Temperature Structural Materials Laboratory, Beijing Institute of Aeronautical Materials, Beijing 100095, P.R. China. XIAONA ZHANG, Associate Professor, is with Institute of Microstructure and Property of Advanced Materials, Beijing University of Technology, Beijing 100124, P.R. China. QIANG FENG, Professor, is with National Center for Materials Service Safety, University of Science and Technology Beijing, and also with State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing. Contact e-mail: [email protected] Manuscript submitted June 19, 2013. Article published online February 4, 2014 METALLURGICAL AND MATERIALS TRANSACTIONS A
accumulation or cracking due to the hard and brittle nature of TCP phases; (2) softening of the c matrix due to the depletion of strengthening elements, which form TCP phases.[6] Most of previous studies mainly focused on the composition, morphology, precipitation, and growth behavior of TCP phases in Ni-based single crystal superalloys,[7–11] but there was limited research about the role of TCP phases on fracture features. Investigation difficulty at elevated temperature is mainly caused by the oxidation of fracture surfaces. Meanwhile, although the matching fracture surface can clearly display the relationship between microstructure and fracture, matching the fracture surfaces is difficult due to the large size of conventional specimens used for stress rupture and creep tests. To understand the specific role of TCP phases in the fracture mode, a simple and practical testing method at ambient temperature was developed in this study. A small scale specimen of a Ni-based single crystal superalloy containing TCP precipitates was used to investigate the fracture mechanism at ambient temperature. The advantage of this simple testing method is to conveniently trace the matching fracture surfaces and support the solid e
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