【作者】 王兴国；

【导师】 姚曼； 徐久军；

【作者基本信息】 大连理工大学 ， 材料加工工程， 2010， 博士

【摘要】 耐磨涂层能够显著提高缸套耐磨性、抗蚀性以及延长使用寿命。随着耐磨涂层在缸套上的广泛应用,如何检测与评价涂层性能,预测涂层的寿命成为制约涂层技术进一步应用的关键性问题。传统涂层性能的检测方法主要集中在外观上,而局部力学性能(如硬度、界面结合强度等)测试一般都是破坏性的,影响了现役设备的正常运转和使用。另外,涂层及界面缺陷大多数随机地分布在内壁表面上,目前还没有一种成熟的评价方法和准则使缺陷被完全检测出来。所以如何基于非破坏性的检测方法,评价涂层特性、界面缺陷以及涂层能够承受的临界载荷等综合性能是本文所要研究的重点问题。本文以平面涂层和缸套内壁曲面涂层为研究对象,提出基于超声波和声发射技术检测涂层及界面特性、涂层在外加载荷条件下的损伤模式等耐磨涂层的综合性能。首先,利用超声波回波信号,建立了基于频率谱法检测涂层物理性能的两种数学模型；然后利用检测数学模型获得了超声波特征值,针对橡胶涂层和等离子涂层建立了超声特征值与涂层特性及界面粘结质量的关系；最后,研究涂层在径向膨胀模拟载荷作用下的损伤模式,通过对涂层损伤过程中声发射参数及声发射信号的识别,基于小波能量理论,建立了声发射特征参量与涂层不同损伤模式的关系。以仿真涂层为研究对象,利用超声波在基体和涂层中传播过程中产生的回波信号,建立了评价涂层特性参量的传递函数法和时间延迟谱法,获得了超声波在涂层介质中的传播速度、涂层密度、衰减系数以及表征涂层界面特性的反射系数等参量。基于橡胶涂层的超声波检测表明,衰减系数随着频率的增大而变大,其原因是超声波在橡胶涂层中传播时,介质的吸收、散射以及声束扩散使能量逐渐变小。对两种不同传感器提取的时域信号进行解析可知,中心频率为1MHz传感器获得的传递函数和时间延迟谱曲线在频率为2.2-2.4MHz之间均产生“锯齿形”的畸变；中心频率为1.5MHz传感器获得的传递函数和时间延迟谱曲线相对比较平滑,无畸变点。通过对不同粘接程度的橡胶涂层界面超声波检测结果表明：由完好界面获得的反射系数最小,弱粘结界面的次之,脱粘界面的最大。对于粘结完好界面,声能反射与透射的大小与基体和涂层物理特性相关；而对于弱结合界面和脱粘界面,声能的反射、透射的大小除了与基体和涂层物理特性有关外,还取决于界面的粘结情况。随着等离子喷涂涂层孔隙率的增加反射系数有增大趋势；声波在涂层中传播的速度有减小趋势。因此,反射系数反映了涂层及界面特性,可以作为评价涂层界面的特征参量。基于超声频谱检测涂层特性的研究结果,针对缸套内壁涂层界面设计了一套超声波C扫描检测成像系统,该系统集机械传动装置、计算机控制与超声检测技术于一体,实现了系统的整体性,提高了系统机电控制的自动化程度及检测速度。采用水浸超声C型扫描方法,利用超声波时间延迟谱检测原理,通过对时域信号的分析,计算出反射系数。利用反射系数来绘制表征缸套内壁涂层界面质量的C扫描图像。开发出一套模拟缸套耐磨涂层损伤的加载装置。该装置通过与声发射检测设备的集成,模拟涂层在外加载荷条件下的损伤过程,同时提取了声发射参数及声发射信号。镀铬涂层的声发射检测结果表明：声发射参数如计数、能量、撞击等参数随着外加载荷的增大而增大；另外,基于声发射的涂层损伤模式识别技术,运用小波分解理论对声发射信号进行分析,发现涂层正常摩擦与涂层损伤的能量信号有较大区别,涂层正常摩擦的能量信号主要集中在低频,而涂层损伤的能量信号主要集中在中、高频。该模拟系统具有检测装置小、检测迅速、精确度高等优点。采用超声C扫描技术,在外加模拟载荷为54MPa,对厚度分别为80μm、130μm及180μm镀铬涂层界面进行扫描,结果表明：随着涂层厚度的增大,缺陷数量随之增大,原因是随涂层厚度增大,涂层的内聚强度和界面的结合强度减小。通过声发射检测涂层缺陷位置与超声C扫描的对比分析可知,两种检测方法都能够对涂层的缺陷进行定位和识别,后者更加精确。更多还原

【Abstract】 The wear-resistant coating applied to the cylinder liner can improve wear, corrosion resistance and prolong service life. With the wide application of the wear-resistant coating in the cylinder liner, it is a key that how to test and evaluate coating performance, predict coating life, which restricts the further development of the coating technology. The traditional methods for testing coating performance focus on appearance, while testing for the local mechanical properties such as hardness, bonding strength are generally destructive, which has an effect on normal running of the active device. In addition, most of defects exist in the coating and interface at random, there are still not any mature evaluation methods and criteria to test such defects completely. Therefore this paper focuses on evaluating comprehensive performance of coating such as the physical properties, defects and the critical load based on non-destructive testing.Taking a planar coating and a cylinder wall coating as the research objects, the method based on ultrasonic technology and acoustic emission technology is proposed for testing comprehensive properties of wear resistant coatings including the properties of the coating and interface, damage mode under applied loading. Fist of all, two mathematical models are established for evaluating the physical properties of coating based on frequency spectrum of ultrasonic echo. Next, based on detection mathematical model ultrasonic eigenvalue can be obtained. The relationship between ultrasonic eigenvalue and the coating properties and interface quality are built for the rubber coating and plasma spraying coating respectively. Finally, the coating damage mode is investigated under the simulative loading exerted by the self-designing radial expansion device. The relationship between the characteristic parameters of acoustic emission and different damage mode of the coating is established through recognizing acoustic emission parameters and signals according to wavelet energy theory.Taking simulative coating as the research object, models of the time delay spectrum and transfer function for evaluating character parameters of the coating are established by ultrasonic echo propagating in the coating and the substrate, from which the parameters relative to the coating such as ultrasonic propagation velocity, coating density, attenuation coefficient and reflection coefficient are obtained. Ultrasonic testing results for the rubber coating show that the attenuation coefficient increases with the increase of frequency. During ultrasonic propagating in the rubber coating acoustic beam diffusion, scattering, and media absorption leading to sound pressure diminishes. According to analyze time delay spectrum and transfer function obtained by two different sensors, the sawtooth distortion appears in frequency 2.2-2.4MHz by sensor of center frequency 1 MHz, the smoothing appears by sensor of center frequency 1.5 MHz.Ultrasonic testing results for the rubber coating with different bonding interfaces show that as regards to the reflection coefficient for the different bonding interface, the perfect interface is the lowest and weak interface is in the second place, and debonding interface is the highest. This is mainly because that for the perfect interface the reflection and transmission of the ultrasonic energy relate to physical properties of the substrate and the coating. While for the weak or debonding interface the reflection and transmission of the ultrasonic energy depend on not only physical properties of the coating and substrate, but the interfacial bonding. In addition, the reflection coefficient increase and sound velocity decrease with the increase of the porosity of the plasma spraying coating. Thereby, the reflection coefficient can be used to evaluate the coating character and reflect its quality. An ultrasonic C scan imaging system is designed for testing the cylinder wall coating interface based on ultrasonic spectrum evaluating the coating characteristics results which consists of the mechanical gearing, computer control and ultrasonic technology, and improves the automation of electromechanical control and testing speed. According to ultrasonic time delay spectrum theory the reflection coefficient can be obtained using time domain signal collected by ultrasonic immersion C scanning system. The reflection coefficient is employed to plot C scan image, which is able to characterize the bonding quality of the cylinder wall coating.A loading device is developed for simulating the damage of cylinder liner wear-resistant coating. The loading device which assembles acoustic emission equipment simulates damage process of the coating under the applied load and collects acoustic emission parameters and signal simultaneously. Acoustic emission testing results shows that for the coating with chromium plating process acoustic emission parameters such as counts, energy, and impact increase with the applied load increasing. In addition, based on acoustic emission recognition technology of the coating damage mode, there exits greater difference between the energy signals of the normal friction and coating damage through wavelet theory that is employed to analyze acoustic emission signal. The energy signal for normal friction mainly concentrates on the low frequency, energy signal of coating damage concentrates on the medium and high frequency. The simulation device is small, and has rapid detection, high accuracy.Under the simulative applied load of 54MPa the scanning test by the ultrasonic C scan system for chromium plating coating with thickness of 80μm,130μm and 180μm, respectively were conducted. The results show that the number of defects increases with the coating thickness increasing, it is because that cohesive strength and interface bonding strength for the thin coating is higher than those for thick coating. Comparing between acoustic emission and ultrasonic C scanning, it is concluded that both methods can be employed to locate and identify defects in the coating, the later is more accurate.更多还原