裂纹尺度突变信息实时反馈的喷涂层疲劳磨损失效预警研究

The process of fatigue wear of the sprayed coating shows hidden and sudden. The regularity of the lifetime is also complex. So the prewarning investigation based on on-line response of crack is necessary. Which is important for promoting the service security of sprayed coating. In the present project, the prewarning method is proposed based on on-line information feedback of the crack scale mutant. the acoustic emission (AE) technique is introduced to on-line monitor the damage status. The regularity of the lifetime is investigated.The main contents are listed as follow: (1) AE signal parameters which are fit for characterizing the fracture of sprayed coating are selected. The high-accuracy observations of surface/subsurface microstructures of sprayed coatings are conducted. Then the contact between AE signal and fatigue fracture of sprayed coating is built. (2) The regularity of fatigue crack of sprayed coating under alternate load is investigated based on AE signal and classical mechanics. The dynamic process of initiation and propagation of crack revealed. (3) The prewarning investigation based on on-line signal warning is conducted by using the feature of AE signal response and model of crack dynamic propagation.The effective and reasonable prewarning model is established. And the relevant mechanism is explained. The project shows the intercross and coalescence among the multi-subjects. The achievements of this project will promote the basic theory system of the thermal spray.

面向热喷涂层疲劳磨损过程中的损伤隐蔽性、失效突发性及寿命演变规律复杂等技术难题，开展基于裂纹信息实时反馈的预警等科学问题研究，对于提高喷涂层服役安全性具有重要的科学意义和工程应用价值。本项目提出了基于裂纹尺度突变信息实时反馈的喷涂层疲劳磨损失效预警方法，采用声发射信号反馈喷涂层进行性损伤状态，揭示喷涂层寿命演变规律。主要研究内容包括：（1）探索最佳表征喷涂层疲劳开裂的声发射信号特征参量，辅以TEM/SEM/FIB-SEM等损伤表征技术，揭示声发射信号特征与喷涂层疲劳断裂的映射关系；（2）运用经典力学理论，阐明交变载荷作用下的喷涂层裂纹运动规律，揭示喷涂层裂纹萌生、扩展的动态演变过程，建立裂纹动态扩展预测模型；（3）提出基于实时信号提示的喷涂层疲劳磨损失效预警方法，建立合理高效的预警模型，阐明基于裂纹动态扩展理论的预警机理。本项目体现了多学科的交叉融合，其成果将丰富热喷涂基础理论体系。

针对涂层服役过程中，失效发生的隐蔽性，研究了声发射技术在涂层接触疲劳在线监测中的应用。对比了声发射信号与传统振动、扭矩信号对于涂层疲劳开裂的敏感性，分析了涂层内部疲劳开裂的声发射信号源类型，研究了声发射信号对累积损伤过程的反馈，并进行了基于声发射信号提示的涂层失效预警研究。研究结果表明，声发射信号对于疲劳开裂的敏感性明显优于振动和扭矩信号。研究了表面完整性对涂层接触疲劳行为的影响。分别对结合强度、表面硬度、涂层厚度和表面粗糙度对涂层寿命衰退机制的影响进行了探讨。研究表明，通过制备粘结底层的方法在提高涂层结合强度的同时明显增大了涂层的整体接触疲劳寿命，其主要原因是增强了涂层/基体界面的抗疲劳能力；通过表面渗氮的方法提高涂层硬度的同时在一定程度上降低了涂层的整体寿命，其主要原因是表面硬化后脆性增强使得裂纹敏感度增大，导致渗氮层快速分层失效；通过控制磨削过程增大涂层厚度的同时提高涂层的整体寿命，其主要原因是改善了涂层内部剪切应力的相对分布，使界面处于低应力状态；通过表面精加工的方式降低涂层粗糙度的同时提高了涂层整体寿命，其主要原因是有效避免粗糙接触，减轻了表面磨损。研究结果表明，声发射信号可以准确反馈涂层内部或界面上的疲劳开裂并对累积损伤过程有着明确的反馈，基于声发射信号提示的预警模式，可以较为准确合理的预测即将到来的涂层失效。