Coupling effects of tungsten and molybdenum on microstructure and stressrupture
properties of a nickel-base cast superalloy |
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Authors: | Tongjin Zhou Wei Feng Huibin Zhao Yu Meng Huaxia Zhang Hongsheng Ding and Zichen Wang |
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Institution: | 1. National Key Laboratory for Precision Hot Processing of Metals, Harbin Institute of Technology, Harbin, Heilongjiang 150001, China;2. Beijing Institute of Aeronautical Materials, Beijing 100095, China |
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Abstract: | In order to comprehensively understand the forming mechanism of abnormal phases solidified in a nickel-base cast superalloy with additives of tungsten and molybdenum, the coupling effects of W and Mo on the microstructure and stress-rupture properties were investigated in this paper. The results indicated that the precipitation of primary α-(W, Mo) phase depended tremendously on the amount of W and Mo addition. When the total amount of W and Mo was greater than 5.79?at%, α-(W, Mo) phase became easily precipitated in the alloy. With increasing of Mo/W ratio, the dendrite-like α-(W, Mo) phases were apt to convert into small bars or blocky-like phases at the vicinities of γ′/γ eutectic. The morphological changes of α-(W, Mo) phase can be interpreted as the non-equilibrium solidification of W and Mo in the alloy. Since the large sized α-(W, Mo) phase has detrimental effects on stress-rupture properties in as-cast conditions, secondary cracks may mainly initiate at and then propagate along the interfaces of brittle phases and soft matrix. During exposing at 1100?℃ for 1000?h, the α-(W, Mo) phases transformed gradually into bigger and harder M6C carbide, which results in decreasing of stress-rupture properties of the alloy. Finally, the alloy with an addition of 14W-1Mo(wt%) maintained the longest stress lives at high temperatures and therefore it revealed the best microstructure stability after 1100?℃/1000?h thermal exposure. |
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Keywords: | Superalloy Tungsten and molybdenum Cast Microstructure Stress-rupture properties |
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