Fatigue response of a grain refined TiAl alloy Ti-44Al-5Nb-1W-1B with varied surface quality and thermal exposure history |
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| Affiliation: | 1. School of Materials Science and Engineering, Southwest Jiaotong University, Chengdu, Sichuan, 610031, China;2. School of Metallurgy and Materials, The University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK;3. State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing, 100083, China;1. State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi''an, Shaanxi 710072, China;2. National & Local Joint Engineering Research Center for Precision Thermal forming Technology of Advanced Metal Materials, Northwestern Polytechnical University, Xi''an, Shaanxi 710072, China;3. LEM3, CNRS UMR 7239, Université de Lorraine, Ile du Saulcy, 57045 Metz Cedex 1, France;4. DAMAS (Laboratory of Excellence on Design of Alloy Metals for low mass Structures), Université de Lorraine, Ile du Saulcy, 57045 Metz Cedex 1, France;1. School of Materials Science and Engineering, Taiyuan University of Technology, Taiyuan 030024, PR China;2. School of Materials Science and Engineering, Inner Mongolia University of Technology, Hohhot 010051, PR China;3. National Key Laboratory for Precision Hot Processing of Metals, Harbin Institute of Technology, Harbin 150001, PR China;1. School of Materials Science and Engineering, Taiyuan University of Technology, Taiyuan 030024, PR China;2. Shanxi Key Laboratory of Advanced Magnesium-based Materials, Taiyuan University of Technology, Taiyuan 030024, PR China;3. National Key Laboratory for Precision Hot Processing of Metals, Harbin Institute of Technology, Harbin 150001, PR China;1. National University of Science and Technology "MISIS", Leninsky pr. 4, 119991 Moscow, Russia;2. The E.O. Paton Electric Welding Institute, 11 Bozhenko str., 03680 Kyiv, Ukraine |
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| Abstract: | Fatigue specimens with four types of designed surface (EDM plane-sited, EDM notched, shot peened, electropolished) were assessed under three exposure conditions (no exposure, block exposure, individual exposure-oxidation at 700 °C for 10000 h) to quantify the effects of surface roughness, stress concentration, oxidation and inner microstructural embrittlement on fatigue behaviour of a grain refined TiAl alloy Ti-44Al-5Nb-1W-1B. With the yield strength of 568 MPa, fatigue is found to occur under a loading condition of σmax<σ0.1. Local plastic deformation is difficult to occur. The alloy becomes sensitive to surface damages but not to V-notch because the small surface area sampling the highest stress significantly reduces the EDM impact. Electropolishing rather than shot peening is found to be more effective in improving fatigue strength for the high strength alloy. When subjected to block exposure, both annealing effect (beneficial) and microstructural embrittlement (detrimental) occurred on all the surfaces, and the latter was dominant in governing fatigue behaviour except for EDM surfaces. After individual exposure-oxidation, fatigue performance deteriorated significantly for the shot peened and moderately for the electropolished but not for EDM surfaces. The mechanism for specific fatigue behaviour is discussed individually based upon whether or not the beneficial effects outweigh the detrimental effects. |
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| Keywords: | Titanium aluminides Electron microscopy Fatigue behaviour Oxidation Phase transformation Thermal stability |
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