| Utilizing laser cladding technology to prepare special coating in the surface of gray cast iron parts can significantly improve the surface performance of parts.The bonding state of the laser cladding coating is a main aspect affecting the bond strength,and then it can influence the application of laser cladding coating.Most of the existing research focus on the surface features of laser cladding coating,but there is little research about its bonding state.As the middle part between the laser cladding coating and the gray cast iron substrate,bonding area is tend to initiate and extend cracks in the process of gray cast iron parts service,and then it led to the cladding coating failure.The research work in this dissertation aims at microstructure features and some macro mechanical properties of bonding area of laser cladding coating.The influence law of microscopic composition and microstructure defects and shear strength of bonding area to its bonding state is analyzed profoundly.The main research contents are as follows.Based on theory of heat transfer and the mechanism of laser thermo effect,using the nonlinear thermal-mechanical indirect coupling method,a numerical model of laser cladding coating is established to analyze the changing of temperature field and stress field of bonding area in the process of laser cladding.According to the result of temperature field and stress field,the mechanism of microstructure changes and micro crack and residual stress is analyzed.Laser cladding process is carried out to verify the simulation results of the mechanism of microstructure changes and micro crack of bonding area,and determine the microstructure of bonding area.The influence mechanism of microstructure strength by each phase organization is analyzed to conclude the microcosmic influence mechanism of bonding area of laser cladding coating,and parameterized the microcosm influence factors.The existing coating bond strength testing method for the applicability of the laser cladding coating is analyzed,and appropriate bond strength testing methods according to the characteristics of laser cladding coating is selected and improved.The stress field of laser cladding coating under bond strength testing methods is analyzed to improve the structure of laser cladding coating specimens,and conclude the microcosmic influence mechanism of bonding strength.The design and manufacture of laser cladding coating bond strength measurement of experimental fixture is researched.According to the results of stress field simulation of the bonding strength measuring fixture in the process of testing,the heat treatment process is determined.Laser cladding coating bond strength experiment is carried to explore the orders of magnitude of the bond strength of laser cladding coating,concluded that the influence mechanism of the bonding state of laser cladding coating by the micro and macro mechanical properties. |
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