镍基变形高温合金热疲劳损伤机制多尺度研究

Focusing on the service reliability and accurately predicting service life of wrought nickel-based superalloys for aerospace engines, it is proposed to explore the thermal fatigue damage behavior evolution mechanism of wrought nickel-based superalloys from multiple scales in this project. The thermal fatigue damage behavior of wrought nickel-based superalloys is systematically studied under coupling multi-parameter effects. The in-situ TEM and molecular dynamics simulations are used to explore the evolution microscopic mechanism of interface structure and performance under coupling effects of temperature field, elastic stress field and interface local strain field in thermal fatigue process. Based on in-situ synchrotron radiant thermal fatigue experiments, the nucleation and growth theory models of micropores are established to reveal the evolution microscopic mechanism of micropores under the condition of the changing interface structure in thermal fatigue process. On this basis, combining the theory of GNT model, Paris law, Gleiter-Hornbogen dislocation cut-off and Orowan dislocation bypass mechanisms, comprehensive considering the interface structure evolution and the influence of its change on the nucleation and growth of mesoscale micropores under the micro-nano-scale multi-field coupling effects in the service process of wrought nickel-based superalloys. An across-scale theoretical model is constructed to accurately predict the thermal fatigue service life of wrought nickel-based superalloys. The implementation of the project will provide a scientific theoretical basis for service life prediction of aerospace engines.

本项目针对航空发动机用镍基变形高温合金服役可靠性和服役寿命精确预测难题，提出从多尺度探究镍基变形高温合金热疲劳损伤行为演化机制。系统研究多参数耦合作用下镍基变形高温合金热疲劳损伤行为，结合原位透射和分子动力学模拟探究热疲劳过程中温度场、弹性应力场与界面局域应变场耦合作用下界面结构与性能演化的微观机制，基于原位同步辐射热疲劳实验，建立界面结构变化条件下热疲劳过程中微观孔洞形核和长大理论模型，揭示界面结构变化条件下热疲劳过程中微观孔洞演化微观机理，在此基础上，基于GNT模型、Paris定律、Gleiter-Hornbogen位错切过和Orowan位错绕过机制理论，综合考虑镍基变形高温合金服役过程微纳尺度多场耦合作用下界面结构的演化及其界面结构变化对介观尺度微孔形核与长大的影响，构建精确预测镍基变形高温合金热疲劳服役寿命的跨尺度理论模型。项目的实施将为航空发动机服役寿命预测提供科学的理论基础。

本项目针对航空发动机用镍基变形高温合金服役可靠性和服役寿命精确预测难题，提出从多尺度探究镍基变形高温合金热疲劳损伤行为演化机制。系统研究多参数耦合作用下镍基变形高温合金热疲劳损伤行为，结合实验和分子动力学模拟探究热疲劳过程中温度场与应变场耦合作用下微观结构与疲劳性能演化的微观机制，考虑疲劳极限和晶粒尺寸的影响，建立了一种新型的疲劳寿命预测模型，揭示热疲劳失效机制。通过分析循环应力响应曲线和疲劳滞后回线研究了镍基高温合金高温低周疲劳过程中的循环变形行为。合金的峰值应力、疲劳寿命、循环硬化及软化行为与总应变幅紧密相关。考虑晶粒尺寸影响的疲劳寿命模型的预测精度高于Ostergren能量法寿命模型和Manson-Coffin寿命模型，具有普遍的适用性。为了研究镍基高温合金的低周疲劳断裂机理，观察并分析了低周疲劳后的滑移带、位错组态和断口形貌。断口分析表明合金在低应变幅时以脆性断裂为主，高应变幅时以韧性断裂为主。微观结构分析表明合金低周疲劳变形存在平面变形和非平面变形两种机制。随着总应变幅增加，位错的密度显著增加，位错严重剪切γ′相使得γ′相对基体强化作用迅速下降。此外，位错在晶界或者孪晶界处塞积，产生的应力集中导致其开裂，随后微裂纹长大并扩展，最终导致合金疲劳断裂。依据镍基高温合金微观组织特点建立了Ni/Ni3Al/Ni原子夹层模型，并选用包含Ni-Al体系的嵌入原子势，运用分子动力学方法在不同载荷及不同变形温度、不同应变速率下进行分子动力学模拟。在拉/压循环载荷下，其循环前期均为界面位错破坏过程，而在循环后期疲劳饱和阶段，室温下镍基高温合金变形机制为扩展位错在两相之间往复运动，而在温度高于500 K时，其变形机制会转变为扩展位错在Ni相内往复运动。项目的实施将为航空发动机服役寿命预测提供科学的理论基础。