高温超高周微动疲劳激光熔覆表面强化效应研究

Fretting fatigue is the mainly reason of the failure of the power components in aviation, aerospace, energy applications. In the proposed project, the laser cladding effect on very high cycle fretting fatigue and the fracture mechanism is investigated. Based on the optimization of laser cladding process, the fatigue strength of the alloy GH4169 is tested in 600℃ and 800℃ respectively in very high cycle fatigue (VHCF) regime with fretting friction on the improved ultrasonic fretting fatigue machine. By using the analysis methods, such as white light interferometer, electron scanning electron microscope, electron backscatter diffraction, transmission electron microscope and infrared camera, the wear morphology, microstructure and damage characteristics of laser cladding layer of the tested specimen are well studied. The laser cladding’s influence on the crack initiation and propagation is explored through the above ways. In order to predict the strength and life of the fretting fatigue in VHCF, the micro mechanics theory in contact and fatigue calculation and non-linear cumulative damage model are used to evaluate the local wear damage, local micro plastic deformation and fatigue damage. The optimization of laser cladding and multi-scale model for fretting fatigue in VHCF regime could be applied to the analysis model, design method in VHCF with fretting friction cases for power components in high temperature.

微动疲劳是航空、航天、能源等工业领域动力装备零部件失效的重要原因。本课题研究激光熔覆对高温环境下镍基合金的长寿命微动疲劳强化机理。在优化激光熔覆处理工艺的基础上，改进高温超高周微动疲劳试验系统，试验激光熔覆层对镍基高温合金GH4169在600℃和800℃的抗微动疲劳强度。采用白光干涉仪、电子扫描电镜、电子背散射衍射、透射电子显微镜、红外摄像仪等研究微动疲劳激光熔覆层的磨损形貌、微观结构变化及损伤特点，分析高温激光熔覆层超高周微动疲劳裂纹萌生位置特点和扩展规律。采用微观力学的接触和疲劳弹塑性计算模型和非线性累积损伤理论，多尺度分析微动磨损、疲劳微观变形和疲劳损伤，估计高温下激光熔覆强化后的微动疲劳强度和寿命。本课题的激光熔覆工艺的优化结果和高温微动疲劳试验及多尺度分析模型将为动力设备高温微动部件长寿命提供设计方法和试验数据参考。

镍基高温合金广泛应用于涡轮转子叶片、导叶支架等航空发动机关键部件中，承受高温、疲劳及微动载荷作用。激光熔覆（Laser Cladding）技术可改善材料和结构表面力学性能，提高其耐久性和可靠性。本课题选取镍基高温合金(Nimonic80A和GH4169)作为激光熔覆基体材料，选取抗高温磨损粉料（Stellite X-40和In625+WC）作为激光熔覆材料，开展激光熔覆表面处理及工艺参数的优化。基于光学显微镜（OM）、电子背散射衍射（EBSD）等设备对熔覆层的微观结构特征进行了分析。改进了高温超高周微动疲劳实验方法，设计了超高周微动疲劳试件并开展了高温600℃和800℃的实验工作，获取了不同熔覆材料在600℃和800℃条件下的微动疲劳强度。采用扫描电镜（SEM）、共聚焦显微镜（CLSM）、透射电子显微镜（TEM）等设备分析了微动接触表面磨损特性及超高周疲劳断裂特征，获得了磨损机理与裂纹萌生机理。采用晶体塑性有限元（CPFEM）计算方法并基于EBSD表征结果，考虑晶粒实际形状、大小、取向等信息建立了CPFEM微观计算模型，完成了微动接触应力分析与局部疲劳不可逆塑性变形分析。引入累积塑性应变作为疲劳指示因子（FIP），采用临界平面的多轴疲劳控制参数，用于评估疲劳损伤积累和预测微动疲劳寿命。本课题的研究结果可为高温合金材料的表面改性提供参考，开发的高温微动超高周疲劳损伤和寿命估计方法可为航空发动机涡轮部件高温微动疲劳设计提供参考。