Papers by Keyword: Nickel-Base Single Crystal Superalloy

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Authors: T. Li, Zhu Feng Yue
Abstract: The possibility of the life prediction model for nickel-base single crystal blades has been studied. The fatigue-creep (FC) and thermal fatigue-creep (TMFC) as well as creep experiments have been carried out with different hold time of DD3. The hold time and the frequency as well as the temperature range are the main factors influencing on the life. An emphasis has been put on the micro mechanism of the rupture of creep, FC and TMFC. Two main factors are the voiding and degeneration of the material for the creep, FC and TMFC experiments. There are voids in the fracture surfaces, and size of the voids is dependent on the loading condition. Generally, the rupture mechanism is the same for creep, FC and TMFC. If the loading can be simplified to the working conditions of the turbine blades, i.e. the hold time is at the top temperature and maximum stress, a linear life model is satisfactory to the life prediction of nickel-base single crystal superalloy from the experimental study in this paper. The temperature and the stress level of the nickel-base single crystal (SC)blades are not uniform. To predict the life of SC blades, one should consider the cycles of the temperature and stress as well as the oxidation simultaneously. In the past 30 years, there are many works on the mechanical behavior and description, such as the inelastic constitutive relationships, plastic, fracture, isothermal creep and fatigue and thermal fatigue as well as oxidation [1-3]. There are also special software (program) to analyze the deformation and life of nickel-base single crystal structures, such as blades. In order to apply to the engineering more conveniently, there should be a life prediction model for the blades. The model should not be too complex, but take more influential factors as possible into consideration.
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Authors: De Long Shu, Su Gui Tian, Xin Ding, Jing Wu, Qiu Yang Li, Chong Liang Jiang
Abstract: By means of heat treatment and creep property measurement, an investigation has made into the creep behaviors of a containing 4.5% Re nickel-base single crystal superalloy at high temperature. Results show that the elements W, Mo and Re are enriched in the dendrite arm regions, the elements Al, Ta, Cr and Co are enriched in the inter-dendrite region, and the segregation extent of the elements may be obviously reduced by means of heat treatment at high temperature. In the temperature ranges of 1070--1100 °C, the 4.5% Re single crystal nickel-based superallloy displays a better creep resistance and longer creep life. The deformation mechanism of the alloy during steady state creep is dislocations slipping in the γ matrix and climbing over the rafted γ′ phase. In the later stage of creep, the deformation mechanism of alloy is dislocations slipping in the γ matrix, and shearing into the rafted γ′ phase, which may promote the initiation and propagation of the micro-cracks at the interfaces of γ/γ′ phases up to the occurrence of creep fracture.
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Authors: Su Gui Tian, Ming Gang Wang, Xing Fu Yu, Xu Dong Lu, Ben Jiang Qian
Abstract: By means of the calculation of the elements diffusion mobility, an investigation has been made into the influence of the elements interaction on the rates of the elements diffusion and  phase directional coarsening during creep of single crystal superalloys. Results show that the elements diffusion and  phase directional coarsening during creep are related to the applied stressed and elastic modulus. And the rate of  phase directional coarsening is enhanced with the applied stresses. Due to the interaction between the elements, the rates of the elements diffusion and  phase directional coarsening decrease with the increment of the elements Ta+Mo gross and Ta/W ratio. In the diffusion field of the elements during creep, the Al, Ta atoms with bigger radius are diffused to {100} planes to form the N-type rafted structure along the direction vertical to the applied stress axis, and the change of the strain energy density in the interfaces of the cubic  phase is thougth to be the driving force of the elements diffusion.
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