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罗诚, 袁荒. 基于张量化微结构表征的筏化镍基单晶高温合金疲劳寿命评估. 力学学报, 待出版. DOI: 10.6052/0459-1879-23-609
引用本文: 罗诚, 袁荒. 基于张量化微结构表征的筏化镍基单晶高温合金疲劳寿命评估. 力学学报, 待出版. DOI: 10.6052/0459-1879-23-609
Luo Cheng, Yuan Huang. Fatigue life evaluation of rafted nickel-base single crystal superalloys based on tensorial microstructure characterization. Chinese Journal of Theoretical and Applied Mechanics, in press. DOI: 10.6052/0459-1879-23-609
Citation: Luo Cheng, Yuan Huang. Fatigue life evaluation of rafted nickel-base single crystal superalloys based on tensorial microstructure characterization. Chinese Journal of Theoretical and Applied Mechanics, in press. DOI: 10.6052/0459-1879-23-609

基于张量化微结构表征的筏化镍基单晶高温合金疲劳寿命评估

FATIGUE LIFE EVALUATION OF RAFTED NICKEL-BASE SINGLE CRYSTAL SUPERALLOYS BASED ON TENSORIAL MICROSTRUCTURE CHARACTERIZATION

  • 摘要: 镍基单晶高温合金的微观组织在长时高温服役下会发生粗化和筏化等微结构演化, 导致力学性能衰减, 影响航空发动机的服役寿命. 文章研究了粗化和筏化镍基单晶DD6合金的低周疲劳行为, 通过高温热暴露和预蠕变处理分别制备了粗化和筏化合金, 针对具有不同微结构状态的合金开展了980 °C下的等温低周疲劳试验, 发现粗化和筏化合金的疲劳寿命相比初态合金显著下降. 基于电子扫描显微镜和光学显微镜对试件断口表面进行了微观表征, 揭示了筏化组织对低周疲劳损伤机理的影响. 裂纹扩展路径受微结构状态影响, 相比初态合金, 粗化和筏化合金中I型微裂纹会更早发生偏折, 沿晶体学面扩展而导致更早的疲劳失效. 基于组构张量及其张量分解方案对合金的微结构进行了量化表征, 提取了微结构的特征参数, 进一步提出了一种新的微结构敏感的等温疲劳寿命预测模型. 通过分别关联γ-基体相和γ′-强化相组构张量的独立分量, 解耦了粗化和筏化对寿命的影响. 在新模型中, γ/γ′ 微结构形态对低周疲劳的影响得到了较好描述, 预测结果的准确性和保守性得到了显著提高. 研究结果可为工程中镍基单晶涡轮叶片的强度设计和寿命评估提供理论指导.

     

    Abstract: The microstructure of nickel-base single crystal superalloy undergoes coarsening and rafting during long service at high temperature. Microstructural evolution leads to mechanical degradation and affects the service life of aero engines. The present work studied low cycle fatigue (LCF) behavior of coarsened and rafted DD6 alloys by fatigue tests, fracture analysis and life modelling. Coarsened and rafted DD6 alloys were prepared through thermal exposure and pre-creep treatments, respectively. Isothermal LCF tests were carried out at 980 °C under strain control on the alloys with different microstructure states. It was found that the fatigue lives of the coarsened and rafted alloys reduced significantly compared with the virgin-state alloy. Fracture surfaces and longitudinal sections of the tested specimens were characterized by SEM and optical microscope. The effect of rafted structure on the LCF damage mechanism was revealed. It was found that the crack propagation path would be affected by the microstructure state. In the coarsened or rafted alloys, mode I microcracks would deflect from its propagation path early, develop along the crystallographic planes and thus lead to faster failure when compared with that in the virgin-state alloy. Based on the fabric tensor and tensor decomposition method, the microstructure was quantitatively characterized and the characteristic parameters of both γ-matrix phase and the γ'-strengthened phase were extracted for life modelling. A new microstructure-sensitive isothermal fatigue life prediction model was proposed. The effects of coarsening and rafting on life reduction were decoupled by correlating with the independent components of the fabric tensors of the γ-matrix phase and the γ'-strengthened phase, respectively. Under the new model, the influence of γ/γ' microstructure morphology on LCF was well described. The accuracy and conservatism of prediction results were significantly improved. This research can provide theory basis for the strength design and life assessment of nickel-base single crystal turbine blades in aero engines.

     

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