Influence of microstructure degradation induced by pretreatment on the creep behavior in Ni-based single-crystal superal
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Influence of microstructure degradation induced by pretreatment on the creep behavior in Ni-based singlecrystal superalloy with different orientations Wenyan Gan1, Hangshan Gao1, Yanchao Zhao1, Zhixun Wen2,a), Guangxian Lu1, Bo Jiang1, Zhufeng Yue2 1
School of Mechanics, Civil Engineering and Architecture, Northwestern Polytechnical University, Xi’an 710072, People’s Republic of China School of Mechanics, Civil Engineering and Architecture, Northwestern Polytechnical University, Xi’an 710072, People’s Republic of China; and Shaanxi Key Laboratory of Structure Strength and Reliability for Aeroengine, Northwestern Polytechnical University, Xi’an 710072, People’s Republic of China a) Address all correspondence to this author. e-mail: [email protected] 2
Received: 24 September 2019; accepted: 27 January 2020
The effects of stress-free and stress-assisted pretreatments at a relatively high temperature on the creep properties of [001] and [011] oriented Ni-based single-crystal superalloys are investigated in this article. The results show that the creep life of the pretreated samples is shorter than that of the original samples. The variation of the c/c9 morphology during the creep process is characterized by the microstructure period. Based on the interaction between the dislocations in the c matrix channel and the c9 phase, the difference in creep properties of the two oriented alloys after pretreatment is analyzed. Combined with the crystal plasticity theory and the number of activated slip systems observed in the experiments, it can be concluded that the two oriented alloys after pretreatment show obvious creep anisotropy and that the creep life increases with the number of activated slip system.
Introduction Nickel-based single-crystal superalloys are among the widely used materials for turbine blades because of their excellent mechanical properties at high temperatures and good creep and fatigue resistances. The alloys have excellent creep resistance because of their unique microstructure, which consists of order c9 precipitates (L12) with a high volume fraction that are coherently embedded in the disordered c phase [1, 2, 3]. The preferred growth direction of nickel and other facecentered cubic (FCC) alloys is the [001] crystal orientation [4]. Although the preferred orientation of Ni-based singlecrystal superalloy blades is the [001] direction, the dispersion of process parameters and geometric complexity of these blades often result in a deviation between the longitudinal axis of the blades and the [001] direction. The crystal orientation therefore has a considerable impact on the mechanical properties of materials, including yield [5, 6], creep [7, 8], fatigue [9, 10, 11, 12], and creep–fatigue interaction [13]. The creep anisotropy of Ni-based single-crystal superalloys has been extensively studied. Sass et al. [14, 15] reported that
ª Materials Research Society 2020
the CMSX-4 alloy exhibited a weak creep anisotropy at 980 °C/ 350 MPa, and the decrease in creep anisotropy between [001] and [011] crystals
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