【作者】 戴华；

【导师】 潘春旭； 黄守伦；

【作者基本信息】 武汉理工大学 ， 材料学， 2002， 硕士

【摘要】 激光熔覆是一种新兴的、极有前途的表面改性技术；钴基合金是一种重要的高温材料。利用激光技术在普通金属或合金表面熔覆一层钴基合金能够显著提高材料的高温耐磨、耐蚀性能，在工业生产中越来越多地得到应用。 本工作综合应用扫描电子显微技术、能谱分析技术、显微硬度测试技术对气门密封面激光熔覆钴基合金层的凝固组织特征、成分分布特征、断口特征、显微硬度特征进行了研究，并且将激光熔覆层的各种特征与等离子喷焊层进行比较，为激光熔覆应用于气门密封面修复提供理论依据。试验结果发现激光熔覆层组织比等离子喷焊层细小得多，并且在结合面处组织差异不大，断口分析显示无裂纹存在。这说明如果采用合适的工艺，激光熔覆可以很好地应用于气门密封面的修复。同时通过对激光熔覆凝固组织的研究发现，其在形核生长时会对基体组织有继承性的现象。 残余应力是普遍存在于材料中的一种内应力，如何测定其分布，一直是国内外很多学者关注的问题。显微压入硬度试验是一种实施方便、应用广泛、成本较低的材料性能测试技术。本工作将显微压入硬度试验应用到非均匀组织中残余应力的测定，从理论上推导和研究了非均匀组织中微区残余应力分布与其显微硬度的关系，并利用显微硬度测量技术进行实际测量验证，尝试解决微区残余应力测定的难题。对气门密封面激光熔覆钴基合金层的计算结果显示，显微压入硬度法得到的残余应力分布数据与其它方法测得的激光熔覆层残余应力分布数据具有相同的变化趋势。更多还原

【Abstract】 Laser cladding is a promising method for surface modification of material. Cobalt-based alloy is a kind of important materials used in elevated temperature. Generally, the wear resistant properties of regular metal or alloy surfaces can be improved by cladding a Co - based alloy layer using laser modification. This technique has been widely used in industry.In the present work, the solidification microstructure, elements distributing, fracture characteristic and microhardness characteristic of the hermetic surface of valves was studied by Scanning Electron Microscope (SEM), Energy Disperse Spectroscopy (EDS) and microhardness testing technique. And the difference between laser cladding and plasma spray welding was investigated for giving support for the application of cobalt-based alloy laser cladding on repairing of the hermetic surface of valves. The experiment results show that the size of grain of laser cladding layer is finer than that of the plasma spray-welding layer, and no crack is found at the interface of those two layers from the profile of fracture. Therefore, laser cladding is suitable for repairing of the hermetic surface of valves if using proper processing technics. We also found the microstructure of the laser cladding inherit the growth orientation and pattern of the matrix, and is strongly influenced by that.Residual stress is a internal stress that commonly exists in material, how to measure that is very concerned by many scientists. Microindentation hardness testing is a well known experimental method used for determination of the constitutive properties of conventional materials, which can be used for macroscopic, microscopic and even nanoscopic by nanoindentation developed recent years. In the present research, a new method was developed for measuring the residual stress of the nonhomogeneous material by microindentation hardness testing. The relationship between residual stress and microhardness was studied, and a formula was given at last. That method was used for calculating the residual stress of laser cladding layer of the hermetic surface of valves. There is good agreement between our results and the others quoted from literature.更多还原