超声冲击复合电火花表面强化技术及机理研究

发布时间：2018-04-22 18:03

本文选题：超声冲击处理 + 电火花沉积　；参考：《天津大学》2015年博士论文

【摘要】：表面强化处理是提高材料表面及疲劳性能的重要手段,但采用传统单一表面强化处理技术难以在显著提高材料表面性能的同时改善其疲劳性能,基于此本文基于超声冲击和电火花表面加工,提出了新型超声冲击复合电火花表面强化处理(UIET)技术。在设计研制专用UIET设备基础上,通过大量工艺试验在金属材料表面制备了存在残余压缩应力场的涂层。通过分析UIET过程中的撞击信号和电流信号,揭示了其基本原理;利用SEM、EDS、XRD、XPS等手段表征了涂层的组织构成,进一步分析了其形成机理;研究了各工艺参数对涂层的影响,并测试了涂层的表面性能以及使用性能。以Ti-6Al-4V为基体系统研究了UIET过程及涂层形成机制,结果表明:UIET过程稳定可持续,涂层是由基体元素、电极元素及被电火花电离的气体或液体元素发生合金化反应而形成的新相。涂层由于其快速凝固过程且受到冲击球的撞击,增加了形核率,在撞击和挤压作用下最终形成细小的颗粒。以45号钢为基体,YG6硬质合金为冲击球的工艺研究结果表明,UIET过程中冲击球的稳态温度和撞击能量是影响涂层质量的主要因素。采用优化后的UIET工艺在45号钢表面制备出了厚度均匀且存在残余压缩应力场的涂层,涂层下方为难以被腐蚀的白层。UIET后材料表面硬度由于涂层的存在得到显著提高,涂层下方白层的硬度也由于晶粒细化得到了明显提高。UIET后材料表面残余应力为-1786MPa。UIET表面由于涂层的存在及其与基体的冶金结合,摩擦磨损性能和腐蚀性能得到显著提高,在中低应力水平下的疲劳性能也有明显提升。疲劳性能的改善机制主要为UIET过程中电火花对材料表面的重熔作用消除了可能存在的叠形缺陷,并且UIET制备的涂层在疲劳过程中可减少材料表层残余压缩应力的释放,以对疲劳裂纹的萌生和扩展起到延缓作用。
[Abstract]:Surface strengthening treatment is an important means to improve the surface and fatigue properties of materials. However, it is difficult to improve the fatigue properties of the materials by using the traditional single surface strengthening treatment technology while improving the surface properties of the materials. Based on ultrasonic impact and EDM, a new type of EDM surface strengthening technology is proposed in this paper. Based on the design and development of special UIET equipment, a coating with residual compressive stress field was prepared on the surface of metal material through a large number of technological tests. By analyzing the impact signal and current signal in the process of UIET, the basic principle is revealed, the microstructure of the coating is characterized by means of UIET, and the mechanism of the coating formation is further analyzed, and the influence of various process parameters on the coating is studied. The surface properties and application properties of the coatings were also tested. The UIET process and coating formation mechanism were systematically studied by using Ti-6Al-4V as substrate. The results show that the UIET process is stable and sustainable. The coating is a new phase formed by alloying reaction of matrix element, electrode element and gas or liquid element ionization by electric spark. Due to its rapid solidification process and the impact of the impact ball, the coating increased the nucleation rate, and finally formed fine particles under the impact and extrusion action. The process of using 45 steel as substrate and YG6 cemented carbide as impact ball shows that the steady state temperature and impact energy of the impact ball are the main factors affecting the coating quality during UIET process. Using the optimized UIET process, a uniform thickness coating with residual compressive stress field was prepared on 45 steel surface. The hardness of the coating was improved because of the existence of the coating, which was hard to corrode under the white layer. The hardness of the white layer under the coating is also improved obviously because of the grain refinement. The surface residual stress of the material is -1786 MPa.UIET after grain refinement. Because of the existence of the coating and its metallurgical bonding with the substrate, the friction and wear properties and the corrosion resistance of the white layer are greatly improved. The fatigue properties at low and medium stress levels are also significantly improved. The improvement mechanism of fatigue performance is that the remelting of EDM on the surface of the material in the process of UIET eliminates the possible stacking defects, and the coating prepared by UIET can reduce the release of residual compressive stress in the surface of the material during fatigue. In order to delay the initiation and propagation of fatigue cracks.
【学位授予单位】：天津大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TG668

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