【作者】 胡小平；

【导师】 黄之初； 张厚安；

【作者基本信息】 武汉理工大学 ， 机械制造及其自动化， 2010， 博士

【摘要】 对陶瓷材料高温摩擦磨损性能的研究是摩擦学领域中的热点方向之一。可是,陶瓷材料对于复杂精密零件的难加工性和低力学可靠性,严重阻碍了其在高效动力机械等工程领域中的应用。金属间化合物二硅化钼(MoSi2)是一种极有吸引力的高温结构材料,它具有硬度高、弹性模量高、高温抗氧化性极好、在1400℃下强度基本不降低和可用电火花进行加工等特点。因此,MoSi2材料有望成为高温等特殊工况下选用的新型耐磨材料,广泛应用于航空、航天、武器装备、交通运输及高效动力机械等领域。本文采用自蔓延高温合成技术制备了MoSi2及0.8wt.%La2O3-MoSi2复合材料,分别以氧化铝、碳化硅和氮化硅为对摩件,研究不同的环境温度(700-1100℃)、载荷(10-50N)和滑动速度(0.084-0.252m/s)对MoSi2材料高温摩擦磨损行为的影响,探讨了其磨损机制；并建立了基于人工神经网络的MoSi2材料的高温磨损率预测模型。同时也考察了MoSi2涂层的高温摩擦学特性及其磨损机制。本文主要研究结果如下：1.随环境温度、载荷和滑动速度的增加,MoSi2/SiC和MoSi2/Si3N4两种摩擦副的摩擦因数呈下降的趋势,MoSi2的磨损率均逐渐减小；而MoSi2/Al2O3配对副的摩擦因数呈先上升后下降的趋势,MoSi2的磨损率随温度的增加先增加后减小,随载荷和滑动速度的增加,其磨损率逐渐下降。比较三种配对副材料,与SiC对摩时,MoSi2/SiC配对副的摩擦因数最小且MoSi2磨损率最小,因此,SiC是MoSi2一种合适的高温配对副材料。2. MoSi2材料在高温磨损过程中,氧化磨损始终存在。随着载荷的增大,MoSi2的磨损机制还表现为粘着、研磨、疲劳断裂；随着温度的升高,MoSi2的磨损机制主要表现为粘着、研磨和疲劳断裂等形式；滑动速度的增加使MoSi2的磨损机制从磨粒擦伤为主转化为以粘着和研磨为主。3.稀土La203的加入提高了MoSi2基复合材料的高温抗磨性,归因于其强韧化作用。稀土-MoSi2复合材料的磨损机制除氧化磨损之外,随载荷的增大,还表现为粘着磨损、研磨和疲劳磨损；随着温度的增加,表现为以粘着磨损为主逐渐向研磨和粘着磨损转变；随滑动速度的增大,表现为粘着磨损、研磨和磨粒擦伤。4.比较了K403合金及硅化钼涂层的高温摩擦学性能。结果表明,与氧化铝1100℃对摩时,硅化钼涂层明显提高了材料的高温抗磨性,30Vol.%ZrO2-MoSi2涂层效果更加显著。镍基合金的高温磨损机制为氧化磨损和疲劳断裂。硅化钼涂层能有效地防止镍基合金的高温氧化,涂层材料的磨损机制表现为氧化磨损、粘着磨损和脆性断裂。5.在对人工神经网络和BP神经网络分析的基础上,着重讨论和研究了具有学习率自适应和附加二次动量项的BP网络预测模型的建立,并给出了网络的训练过程。结果表明：利用改进的BP神经网络对温度、载荷以及转速等条件综合作用下的二硅化钼磨损率的预测具有较高的预测精度和实用价值,可以满足综合条件下的二硅化钼磨损率的预测需要。更多还原

【Abstract】 Friction and wear properties research of ceramic materials at high temperature is a hotspot of tribology. However, ceramics is difficult to be made into complex precision component and has low mechanical reliability, which hinders its application in the engineering areas. Intermetallic compound MoSi2 has better performance such as high hardness, high elasticity modulus, high thermal conductivity and electricity conductivity, superior oxidation resistance and electrical discharge machining. MoSi2 will be expected to use as a new type of wear resistant material under high temperature circumstance.In this paper, MoSi2 and 0.8wt.%La2O3-MoSi2 composites were prepared by self-propagating high-temperature synthesis(SHS) and vacuum sintered. Alumina, Silicon carbide and silicon nitride were used as friction disc, while MoSi2 and MoSi2-based composites as pin. The effects of temperatures (700～1100℃), loads(10～50N), sliding velocity(0.084-0.252m/s) on its frictional and wear properties were investigated by using XP-5 type high temperature friction and wear Tester. The wear mechanisms were also studied. A network forecasting model for wear rate is built with artificial neural network technology. The friction and wear properties of MoSi2 coatings were also studied. The results are shown as follows:1. With the ambient temperature, load and sliding speed increasing, the friction factor of MoSi2/SiC and MoSi2/Si3N4 gradually reduced, and the wear rate also reduced. However, the friction factors of MoSi2/Al2O3 increase first and then decline. With the ambient temperature increasing, the wear rate of MoSi2 increases first and then decline. With the load and sliding speed increasing, the wear rate of MoSi2 gradually reduces. In the three pairs, the friction factor of MoSi2/SiC is the smallest and the ware rate is also the smallest. From the perspective of couples, SiC ceramic is more suitable couples for MoSi2 material at high temperatures.2. The oxidation wear of MoSi2 materials always exists during the wear process. With the load increasing, the main wear mechanisms of MoSi2 are adhesion wear, grinding and fatigue fracture. With temperature increasing, the main wear mechanisms of MoSi2 are adhesion wear, grinding and fatigue fracture.With Sliding velocity increasing, the wear mechanisms of MoSi2 change from scratches abrasive to adhesive and grinding.3. The wear resistance of MoSi2 is improved by adding La2O3 into MoSi2 substrate due to the strengthening and toughening. The oxidation wear of rare-MoSi2 materials always exists during the wear process. With the load increasing, the main wear mechanisms of rare-MoSi2 materials are adhesion wear, grinding and fatigue fracture. With temperature increasing, the main wear mechanisms of rare-MoSi2 materials change from adhesion abrasion to grinding and adhesion wear. With sliding velocity increasing, the wear mechanisms of rare-MoSi2 materials are adhesion wear, grinding and grind scratch.4. The friction and wear properties of the K403 alloy and MoSi2 coating at 1100℃were compared. The results show that the wear resistance of K403 alloy is improved after coated the MoSi2 coating and the wear resistance effect is more obvious after coated 30Vol.%ZrO2-MoSi2. The wear mechanisms of Nickel-based alloys are oxidation wear and fatigue fracture. The oxidation of K403 alloy was prevented after coated MoSi2 coating. The wear mechanics of MoSi2 coating are oxidation, adhesion wear, and fatigue fracture.5. Based on the artificial neural network and BP neural network analysis, the adaptive learning rate and additional secondary momentum BP neural networks prediction model were studied. The network training process was also given. Network prediction and the actual testing results show that the improved BP neural network has higher prediction accuracy. Network prediction can meet the predicting need of molybdenum disilicide under the complex conditions.更多还原