Microstructural changes and mechanical behaviour of a near lamellar γ-TiAl alloy during long-term exposure at 700 °C |
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| Affiliation: | 1. School of Materials Science and Engineering, Southwest Jiaotong University, Chengdu, Sichuan, 610031, PR 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, PR China;1. State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083, China;2. National Center for Materials Service Safety, University of Science and Technology Beijing, Beijing 100083, China;1. State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing, 100083, China;2. National Center for Materials Service Safety, University of Science and Technology Beijing, Beijing, 100083, China |
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| Abstract: | Ti-44Al-5Nb-1W-1B with a near lamellar microstructure was exposed at 700 °C for up to 10000 h in air. The changes in microstructure were investigated using scanning and transmission electron microscopy. It has been found that the combined addition of Nb and W can restrict parallel decomposition of α2 lamellae into ultrafine γ lamellae, but causes prevalent precipitation of fine β(B2+ω) particles from α2 lamellae and precipitation/growth of ω particles from β(B2) grains. However, although 3/4 of α2 lamellae dissolved and majority of them transformed to β(B2+ω), tensile ductility is reduced only by 30% while the strengths remain essentially unchanged for the thermally exposed alloy. This is attributed to the widespread distribution of β(B2+ω) particles. On the other hand, fatigue limit was found to decrease during the first 5000-h exposure but finally increased by 11% after 10000-h exposure. The reasons for the decrease and increase of fatigue strength at different exposure stages are discussed by considering two contradictory effects on the exposed alloy: 1) exposure-induced embrittlement due to microstructural changes (harmful); 2) annealing of fatigue samples in a warm air environment for prolonged time (beneficial). |
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| Keywords: | Intermetallics Mechanical properties Thermal stability Casting Electron microscopy Scanning Electron microscopy Transmission |
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