Papers by Keyword: Single Crystal Superalloy

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Authors: Zhi Yuan Yu, Zhu Feng Yue, Wei Cao, Xin Mei Wang
Abstract: Nickel-based single crystal superalloys have been widely used in modern aircraft, which is related to its high temperature mechanical strength and creep properties. And the initial cubic γ′ precipitates start to coarsen directionally during high temperature creep, which results in the degradation of the mechanical properties, especially the creep properties. Therefore, it is essential to figure out the mechanism of directional coarsening during the period of high temperature creep. In this article, a broad review of rafting mechanism of nickel-based single crystal superalloys is provided. The major work of this critical review is to introduce several experiments and numerical simulations which are used to analyze the evolution of rafting. For three different numerical simulations, their performance, advantage and disadvantage are discussed in detail. Through methods above, the effect on creep properties is summarized.
Authors: Zhi Ping Ding, Ming Li, Teng Fei Wang, Rong Hua Yang
Abstract: Based on micro structure of Ni-based single crystal superalloy, a γ/γ’ two-phase unit cell finite element model was established, and its cyclic stress-strain was simulated under tension/torsion cyclic loading. A low cycle fatigue (LCF) life prediction model of single crystal superalloy was proposed by using cyclic plasticity strain energy as a parameter based on energy dissipation theory. Calculation results of macro finite element model and γ/γ’ two-phase unit cell micro finite element model, and multiaxial LCF test data of CMSX-2 Ni-based single crystal superalloy along [001] orientation were applied to fit the LCF life model by multiple linear regression. The results show that the unit cell model not only reflects the microstructure characteristics of single crystal Ni-based superalloy, but also is better than the macro model in accuracy of analysis, and greatly improve the accuracy of fatigue life prediction. Almost test data fall into the factor of 2.0 scatter band.
Authors: Jia Rong Li, Kai Guo Wang, Yu Shi Luo, Shi Zhong Liu, Mei Han, Chun Xiao Cao
Authors: Zhi Xun Wen, Nai Xian Hou, Zhu Feng Yue
Abstract: Based on the microstructure change and damage characteristics of single crystal, a two-state-variable crystallographic creep damage constitutive model has been developed to investigate crack growth behaviors of single crystal compact tension specimen at 760 for two crack orientations: (001)[100] and (011)[100]. Numerical simulation results show the crack-tip stress fields are dependent on crack crystallographic orientation. Observations performed on the real single crystal specimens reveals that the macroscopic crack growth path appears as zigzag wave. The creep deformation at crack tip takes place in specific slip plane, and the deflection angles of crack initiation direction from the crack plane are 45º or 135 º and 53.7ºor 127.3º in the crack orientations (001)[100] and (011)[100]. A good agreement between experimental observations and numerical results is found.
Authors: Yun Song Zhao, Yan Fei Liu, Jing Xuan Zhao, Xiao Tie Zhang, Yan Yang, Hao Chen, Hua Jiang, Yu Shi Luo
Abstract: Intermediate temperature creep properties are considered a key indicator of single crystal superalloys used for turbine blades of aircraft engines. The interrupted and ruptured creep tests were carried out in a second generation single crystal superalloy under the conditions of 760°C/785MPa. The creep rupture life as well as minimum creep rate were also in the same level of those in CMSX-4 and PWA1484. The microstructural evolution at different creep stages were analyzed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results showed the γ’ phases kept the cuboid morphology mostly until the creep rupture, and super lattice stacking faults (SSFs) extended along [-1 1 0] and [-1-1 0] orientations within the γ’ precipitate were the typical dislocation configuration.
Authors: Qing Wu Wang, Mao Pang, Shi Hui Zhang
Abstract: Single crystal nickel base superalloys, such as Chinese material DD6 have been used in gas turbine blade in China more and more widely. In order to make better use of single crystal superalloys with many excellencies, constitutive models have been developed. In this paper, general method of crystallographic constitutive modeling was summarizes and a new constitutive model, based on crystallographic theory was proposed with phenomenological models' advantages. Based on crystallographic slip system principle, the basic slip-based viscoplasticity theory equations were set up on 12 octahedral slip systems and 6 cubic slip systems, total 18 slip systems. In micro-level slip system, the general unified constitutive formulations were used as the flow equations and hardening law. In the model, scalar forms were applied for constitutive equations on slip systems and the number and types of active slip systems were used to describe the material anisotropy, which was satisfied automatically by slip systems not anisotropic tensors and. The experimental and calculation results of two kind single crystal superalloys PWA1480 and DD6 were compared. The model had the capability to predict many mechanical response and analyze structure of single crystal superalloys. The modeling procedures and results showed that this crystallographic model had more clear physical meaning and was exact.
Authors: N.J. Simms, A. Encinas-Oropesa, John R. Nicholls
Authors: Caroline M. Charles, Gemma A. Drew, Stephen Bagnall, Catherine M.F. Rae
Authors: Fabienne Touratier, Bernard Viguier, Christophe Siret, Sandrine Lesterlin, Eric Andrieu
Abstract: The creep behaviour of MC2 single crystal superalloy has been studied at 1150°C/80 MPa, with an applied load along [001] axis. The resulting dislocation microstructures were examined by transmission electron microscopy. The occurrence of a[010] type dislocations (with a zero Schmid factor) within the ordered γ' precipitates is often observed. It is shown that those dislocations moved by a climb process, based on a mechanism involving two dislocation systems and vacancy exchanges, as proposed in the literature. We calculate the vacancy fluxes associated with such a mechanism and show that the vacancy transportation can be easily insured by a simple diffusion process. This calculation shows that the diffusion and climbing steps do not seem to be the creep rate controlling mechanisms for those situations in MC2 alloy.
Authors: Li Rong Liu, Jing Sheng Huang, Guo Qing Zu
Abstract: Recrystallization behavior after indentation loading and heat treatment at different temperatures of the as-cast and solution-treated alloy was investigated. The results showed that slip deformation occurred in the as-cast and heat treated samples after deformation and apparent slip line can be observed. Slip lines of heat treatment state was significantly more than that of the as-cast samples. Neither equiaxed nor cellular recrystallization occurred in the surface of the as-cast and solution-treated samples after heat treatment at 1120; Slip traces were examined in the vicinity of indentation and M6C carbide precipitated on the slip line in heat-treated samples, while cellular recrystallization occurred in the internal part and MC carbides became the nucleation centers. Equiaxed recrystallization occurred simultaneously in samples of the two states with the heat treatment at 1310 after deformation and the recrystallization area increased with the processing time; after heat treatment with same time and temperature, recrystallization area of the cast samples were less than that of heat-treated samples.
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