在核电站中，流致振动是不可避免的，因此微动磨损普遍存在于核电设备中。其中，蒸汽发生器是核电站的关键设备，且服役于高温高压的严苛环境下，其安全性将直接影响核电站的运行。由于流致振动，蒸汽发生器传热管与其支撑板(或者抗振条)之间产生微动磨损，导致传热管局部磨损甚至破裂，一旦传热管破裂，一回路的辐射物将流入二回路，造成环境污染。本文以蒸汽发生器传热管的微动磨损为研究背景，开展了在空气和水环境中690合金传热管与405不锈钢抗振条的微动磨损试验，并结合数值分析，系统揭示了690合金管的微动磨损行为。本文不仅对探索690合金的微动磨损机制有重要意义，并且也能为核电设备的设计及安全运行提供指导数据。 本文基于高精度液压式微动磨损试验机，通过附加水循环系统，成功实现了高温水环境的微动磨损试验。试验采用管／块接触，运用光学显微镜(OM)、扫描电子显微镜(SEM)、电子能谱仪(EDX)、电子探针(EPMA)、X射线光电子能谱分析(XPS)和三维光学显微镜对磨痕微观形貌及成分等进行分析，对比研究环境、温度和载荷对690合金微动摩擦行为的影响。通过特殊的化学方法去除磨痕表面的磨屑层，获得了较为准确的磨损体积。 本文的主要结论如下： (1)空气环境中690合金传热管的微动磨损性能研究 690合金传热管与405不锈钢抗振条在空气中的试验结果表明，温度与微动磨损行为密切相关。当试验温度较低(室温和90℃)时，主要的磨损机制为磨粒磨损和剥层；当试验温度较高(200℃和285℃)时，磨损机制主要为粘着磨损、剥层和磨粒磨损。试验温度较高时，粘着磨损致使材料转移，在690合金管上形成转移层，转移层减少摩擦副的直接接触，从而使得磨损体积低于较低温度时的磨损体积。 (2)水环境中690合金传热管的微动磨损性能研究 在水环境下，随着温度的增加，剥层现象更加明显，从而磨屑增加，接触面的磨粒磨损增加，最终致使摩擦系数和690合金管的磨损体积增大。由于水担当了润滑剂的作用，因此690合金管在水环境下磨损相较空气环境小，且磨痕表面相对光滑。通过剖面分析，在试验温度为90℃的690合金管上观察到平行于表面的剥层裂纹，未见磨屑层。水不仅起到了润滑的作用，还起到了一定的外力作用，可以将接触区的磨屑排出，减少磨粒磨损。在水环境中，沿着微动方向，轮廓形状大多为“U”型，而在空气中大多为“W”型。 (3)接触温度的计算模型 本文利用MATLAB软件建立了接触模型，从而获得真实的接触区域(即微凸体)；利用ANSYS软件建立热学模型。结果表明，在微动过程中，摩擦系数、频率、位移幅值、正压力、氧化物厚度和材料的流变应力等均对接触温度有影响。自制了一个验证接触温度计算模型的试验装置，试验结果表明：当热源为恒定温度或者温度随时间变化时，在样品上测得的最大温度基本相同：当热源的温度随时间变化时，样品测得的温度在几个循环后就达到稳定；随着两个热源的间距增加，其相互作用减少。 (4)690合金管的磨损预测 研究结果表明，磨屑形态、磨损机制对磨痕轮廓形状有较大的影响；磨损预测是一个非线性过程。以大量轮廓数据作为学习训练和预测样本，通过神经网络技术对微动磨损预测的准确性和可行性进行了分析。结果表明，利用神经网络技术进行微动磨损预测是可行的；学习训练和预测样本越大，其预测值越准确。 关键词：微动磨损；数值模拟；接触温度；神经网络

 Due to flow-induced vibration, fretting became a major problem of components and structures failure in nuclear industry. Steam generator is one of the most critical components in pressurized water reactors (PWRs) and operated in a such aggressive condition, such as high temperature, high pressure and corrosive environment. Surfaces between steam generator tubes and their supports (or anti-vibration bars) are subjected to fretting wear due to flow-induced vibration. Once a wall-penetrating defect occurs in the tube, coolant with radioactive substance will leak into the water steam circuit causing the pollution of the environment. The need for understanding and predicting the fretting wear failure of steam generator tube is driven by the concern of proper design and reliable operation of PWRs, which is of major economic and safety concern. The objectives of this research are to assess the fretting behavior 690 alloy steam generator tubes and 405 stainless steel anti-vibration bars at different normal force conditions and temperature levels both in air and in water. In this dissertation, the fretting wear tests were combined with finite element analysis for better understanding of wear behavior. The experimental investigation was carried out using a specially designed tribometer for tube/plate contact configuration. To achieve elevated temperature in water environment, the fretting wear tester was connected to a water supplying loop system. To distinguish wear mechanisms, the worn surfaces and the morphology of cross-sections of the wear scars were observed through optical microscope (OM), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), electron probe microanalysis (EPMA), X-ray photoelectron spectroscopy (XPS) and 3D optical microscope. Moreover, a particular debris cleaning method was used to remove wear particles of worn 690 alloy tube effectively in order to estimate exact wear volume. The main results are listed as follows: (1)The wear behavior of 690 alloy tubes in air The results indicated that temperature had a great impact on fretting wear behavior and wear mechanisms in air. With increase in temperature, the principal wear mechanisms changed from delamination wear to the combination of delamination and adhesive wear, as demonstrated by the presence of an adhesive transfer layer at 285 ℃, instead of a compacted debris bed at 90 ℃. The adhesive transfer layer seemed to protect the surfaces better due to a reduction in the interaction of the worn surfaces. Finally, higher friction coefficient and wear volume appeared at lower temperature (room temperature-RT to 90 ℃), compared to that associated with higher temperature (200 ℃ and 285 ℃). (2)The wear behavior of 690 alloy tubes in water The friction coefficients and the wear volume increased with the increase of the temperature from RT to 90 ℃ in water. This was attributed to the more distinct delamination, which contributed to material loss, produced more abrasions, and increased the friction and wear damage. Compared with that in air, the worn surfaces in water were smooth, and only a tiny delamination crack was found in the sub-surface of the 90 ℃ fretted tube. Due to lubrication function, the presence of a thin water film likely precluded the metal-metal contact, and resulted in less wear. During the fretting process, water also washed the wear particles away from the contact zone leading to a decrease of abrasion. The main wear mechanisms were delamination and abrasive wear. Consequently, the wear scars commonly showed “U” shape profile along the fretting direction in water, while “W” shape in air. Overall, the damage of specimens in water was slighter than that in air. (3)Contact temperature prediction model A thermal model based on the surface topographies of the real surfaces was developed to predict the contact temperature. Compared to the model based on the uniformly-distributed equal-sized micro contact areas (MCAs), this model showed better ability to capture the contact temperature. Results also showed that, various factors have effect on the maximum temperature rise, e.g. , coefficient of friction, flow stress, amplitude of slip, frequency of oscillation, thickness of oxide layer and normal load. In order to validate this thermal model, a self-designed set-up was established. The results showed that the maximum temperature for both the constant heat source and time-dependent heat source were almost same if the maximum temperature of a time-dependent heat source was equal to the constant temperature. Results also showed that the steady maximum temperature for time-dependent heat source can be reached after several cycles. The interaction with two heaters decreased with the increase of the distance between two heaters for both the constant heat source and time-dependent heat source. (4)Wear prediction of 690 alloy tube The results showed that the wear debris and wear mechanisms have a strong effect on the profiles of wear scars. Wear prediction was a nonlinear problem due to complicated factors during the fretting process. After discussing the fretting behavior of steam generator tubes, an attempt was made to predict wear (wear depth and wear volume) using worn profile through neural network. The results indicated that neural network was a better way for short-term forecast with high accuracy. Moreover, the accuracy of prediction increased with the increasing number of training samples. Key words: Fretting wear; Finite element analysis; Contact temperature; Neural network