【作者】 朴钟宇；

【导师】 徐滨士； 王海斗；

【作者基本信息】 燕山大学 ， 机械设计及理论， 2010， 博士

【摘要】 再制造是废旧机电产品高技术修复改造的产业化,是符合我国实现节能减排,建设两型社会的指导方针的有效举措。随着我国经济增长模式的良性转变,再制造产业进入了高速发展的快车道,从事再制造的企业日益增多,再制造概念深入人心。再制造领域中的诸多基础性科学问题引人关注,尤其是再制造产品的质量评估问题是影响其社会接纳度的关键问题,需大力关注。等离子喷涂是一种常用的再制造工程技术,经等离子喷涂再制造后再制造产品的寿命评估实际上可以简化为对表面涂层的寿命评估。本文研究了等离子喷涂层的接触疲劳失效机理和寿命评估。通过等离子喷涂制备表面Fe基涂层,通过正交设计的方法对喷涂参数进行优化,选择喷涂距离、喷涂电压和喷涂电流为正交因子,以涂层的显微硬度和孔隙率作为评价的指标,最终得到了较优的喷涂参数,制备了结构致密、结合良好的等离子喷涂层。采用点接触式滚动接触疲劳实验机开展涂层接触疲劳实验,通过两参数Weibull分布评估涂层寿命。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N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N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。研究了负载条件对涂层接触疲劳行为的影响。分别对接触应力、转速对涂层寿命衰退机制的影响进行了探讨。研究表明,增大接触应力和转速均显著降低了涂层的整体寿命,增大接触应力后涂层内部和界面上强烈的剪切应力是涂层短期分层失效的主因,增大转速后单位时间内涂层承受的交变应力的频次增多,累积损伤进程加快,局部甚至可能出现应力叠加,因此寿命较短。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,同时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。研制了基于表面压入法的喷涂层结合强度检测设备。探讨了表面压入法与声发射技术联合使用评估喷涂层结合强度的原理和可行性,设计和制造了便携式的压入设备样机,并开展了验证实验。有限元分析表明,表面交变压入可以引起较大的界面剪切应力。压入过程信号分析表明,声发射信号能量参数的突变可以作为评价涂层结合强度的特征参量。涂层的微观分析表明,表面交变压入可以有效诱发涂层界面裂纹,同时对涂层内部和基体无明显损伤。更多还原

【Abstract】 Remanufacturing is industrialization of maintain of waste electromechanical products using high and new technologies. At the same time, remanufacturing is also an effective approach for economizing energy, decreasing discharge and establishing amphitypy society. As rising mode of economy of homeland benign transformation, remanufacturing domain fleetly develops. More and more corporations engaging remanufacturing appear. More and more people are approval with the concept of remanufacturing. Many scientific problems about remanufacturing are dramatic. The problem of quality evaluation of remanufacturing product need be specially focused. Plasma spraying is a useful technology for remanufacturing. The life evaluation of remanufacturing product by using plasma spraying can be actually predigested to the life evaluation of surface plasma sprayed coating.Mechnism and method of rolling contact fatigue (RCF) life evaluation of plasma sprayed coating are investigated in the present paper. Fe-based coatings were depositted by plasma spraying technology. Optimization of spraying parameters was conducted by orthogonal design. Spraying distance, spraying volitage and spraying current were selected as orthogonal factors. The micro-hardness and porosity of the coating were used as evaluation criterions. Optimizational spraying parameters were obtained. The optimizational coatings own density microstructrue and high bond strength. A ball on disk RCF tester was introduced to conduct the RCF experiments of the coatings. Two-parameter Weibull distribution was used to evaluate the coating life.The influence of surface integrity on RCF behavior of coating was investigated. The influence of bond strength, surface hardness, coating thickness and surface roughness on RCF behavior of coating were investigated, respectively. Experimental results showed that deposition of undercoating not only increases the bond strength, but also improve the holistic RCF life. The reason is the increase of fatigue resistance of the coating/substrate interface. Nitridation of the coating surface increase the surface hardness, but decrese the holistic RCF life. After nitridation, the brittleness of coating was obviously improved, as a result, the crack sensitiveness increased. So the nitriding layers always sloughed in a short time. The increase of coating thickness by controlling the grinding process can improve the holistic RCF life. The relative distribution of shear stress within the coating is charged by increasing thickness, and the interface bears lesser stress. The decrease of surface roughness by using surface finishing machining can improve the holistic RCF life. The surfaec abrasion is alleviated for smooth coating.The influence of loading condition on RCF behavior of coating was investigated. The influence of contact stress and rotational speed on RCF behavior of coating were investigated, respectively. Experimental results showed that the increase of contact stress and rotational speed both obviously decrease the holistic RCF life. The intensive shear stresses within the coating or on the interface are the main drivers for coating delamination in a short time. The coating bears time after time altering shear stress in unit time when rotational speed is more rapid. The accumulate damage process charges quick. The nestification of stress may appear. As a result, the holistic RCF life reduces.Application of acoustic emission (AE) technology in on-line monitor of RCF process of coating was investigated. The comparison of sensibility of AE signal, acceleration signal and torque signal on coating fatigue fracture was conducted. The origin modes of AE signals within the coating were analyzed. The response of AE signal on accumulate damage process was addressed. The prewarning of coating failure based on AE signals was investigated. Experimental results showd that AE signal is more sensitive for coating fracture than acceleration signal and torque signal. At the same time, AE sensor can accurately capture the fatigue fracture within the coaitng. AE signal can also r feedback the accumulate damage process of the coating during RCF experiment. The prewarning mode based on AE signal can effectively predict the coming coating failure.Evaluation technology of bond strength of sprayed coating based on surface altering indentation was investigated. The mechnism and feasibility of surface altering indentation were discussed. The model machine of indentation device were designed and fabricated. The certification experiments were conducted. Experimental results showed that energe parameter of AE signal can be used as feature parameter to evaluate the bond strength of coating. The observations of the coating released that the surface altering indentation can effectively induce the interface crack, but no damages in the coating interior and substrate.更多还原