多场超声协同评价与主动调控激光熔覆层应力损伤机理研究

The problem of engineering equipment service failure caused by damage of its key component could be solved by preparing good performance laser cladding coating on surface of key component, while service performance assurance of laser cladding coating was still not solved. The research for evaluating and controlling stress and fatigue damage was an effective method for service performance assurance of laser cladding coating, but lots of problems were still needed to be solved. Therefore, the ultrasonic method was used in this research, behavior of ultrasonic wave responding to microstructure of laser cladding coating was discussed, corresponding analysis method and theory for ultrasonic wave was proposed, ultrasonic wave characteristic parameter used to characterize stress and fatigue damage of laser cladding coating was extracted, relationship between ultrasonic wave characteristic parameter and stress, fatigue damage was determined respectively, influence mechanism of inhomogeneous and discontinuous microstructure of laser cladding coating on stress and fatigue damage evaluation with ultrasonic wave was revealed, modified model for stress and fatigue damage evaluation under complex influence factors was also built. The controlling mechanism of stress and fatigue damage of laser cladding coating with ultrasonic vibration treatment and ultrasonic impact treatment was analyzed respectively, then coordinated controlling technology with ultrasonic vibration and ultrasonic impact was cleared, its coordinated controlling mechanism was also clarified. Finally, the integrated approach for evaluating and controlling stress and fatigue damage of laser cladding coating with multi-field ultrasonic was determined. This study was not only as technical support for service performance assurance of laser cladding coating, but also important for service safety prediction and service life improvement of engineering equipment.

在关键零部件表面制备高性能激光熔覆层是解决关键零部件损伤导致工程装备整体失效问题的有效手段，然而激光熔覆层服役性能的保障仍未得到良好解决。对激光熔覆层应力与疲劳损伤进行评价和调控是解决这一问题的可行方法，但当前研究仍存在诸多问题。鉴于此，本项目基于超声技术，通过激光熔覆层超声波信号分析方法与理论的研究，探讨激光熔覆层应力与疲劳损伤超声波特征参量的提取方法，构建超声波特征参量与应力及疲劳损伤间的映射关联，揭示不均匀/不连续组织结构对超声波评价应力与疲劳损伤的影响机制，构筑多因素耦合影响超声波评价应力与疲劳损伤的数值模型；探究超声振动/冲击协同调控激光熔覆层应力与疲劳损伤的方法，明确其关键技术，揭示其调控机理；最终实现激光熔覆层应力与疲劳损伤的一体化超声评价与调控，这不仅为激光熔覆层服役性能保障提供技术支撑，而且对实现工程装备服役安全性预测及寿命延长具有重要意义。

激光熔覆技术是机械装备表面修复技术之一，但激光熔覆层的应力损伤一直影响激光熔覆修复产品服役安全的重要因素，然而当前仍缺乏有效解决这一问题的手段，因而积极探索可实现激光熔覆层应力损伤评价和调控的技术就迫在眉睫。因具有无损、快速及可实现在线操作等优点，功率超声和超声波评价技术为这一问题的解决创造了可行性。鉴于此，本研究通过探究激光熔覆层超声波信号的分析方法和理论，明确了可表征激光熔覆层应力损伤的超声波特征参量提取方法，揭示了超声波评价激光熔覆层应力损伤的机理，进而澄清了多场超声协同评价与调控激光熔覆层应力损伤的科学本质。研究结果表明：激光熔覆层的各向异性组织及由超声振动/冲击诱导其发生形变、枝晶破碎等是影响激光熔覆层超声波信噪比的主要原因，以morlet小波为母小波，6层分解，采用软阈值对激光熔覆层超声波进行降噪处理即可满足本研究对其信噪比的要求；通过数值分析方法构建了不同信噪比的超声波信号，明确了互相关步长影响超声波特征参量（用于定量表征激光熔覆层应力损伤）的规律，认为1周期为最佳互相关步长；借助力学实验，建立了超声波特征参量与应力、疲劳循环周次间的关联，明确了缺陷、初始应力状态对超声波评价应力的影响机理，提出了其修正方法。分析认为，激光熔覆层的不均匀弹塑性变形、熔覆层内部位错滑移和塞积以及缺陷的应力集中效应是决定上述结果的关键；随超声冲击覆盖率和超声振动幅值增大，激光熔覆层组织呈明显梯度变化，且激光熔覆层的超声波特征参量也随之变大，但后续呈无规律变化，这为超声振动/冲击调控激光熔覆层应力损伤提供了支撑。分析认为，超声冲击的机械作用和超声振动的空化效果是导致这一结果的重要原因。本项目从材料学、声学、力学等角度出发，揭示了多场超声协同评价与调控激光熔覆层应力损伤的机理，这不仅为激光熔覆技术在机械装备表面修复领域的应用提供支撑，更为实现机械装备的延寿具有重要意义。