Simulation And Experimental Study Of Femtosecond Laser Cladding Zr-BN Ceramic Powder Coating

A large number of metal parts in industrial production often face the problem of fatigue failure due to long-term centrifugal load,thermal stress and corrosion and other harsh environment.In recent years,with the rapid development of laser micro-machining technology,laser cladding technology is widely used to strengthen the surface of the substrate and improve the comprehensive performance of the surface.Cladding powder system has been advanced from single alloy powder to composite powder,which provides more choices for improving the properties of coating.In this context femtosecond laser was used as a heat source to cladding Zr-BN composite ceramic powder on the substrate of superalloy GH742.The following research contents were carried out:Based on the thermal analysis theory of laser cladding,the dynamic heat source,heat transfer model and elastic-plastic total strain matrix were proposed.The thermoelastic basic equation and its solution method consistent with the characteristics of femtosecond laser cladding were constructed.The femtosecond laser micromachining system was designed,and the construction of femtosecond laser optical path and the attenuation control of laser beam were completed.A machining platform combining two-dimensional linear displacement table and three-dimensional manual focusing displacement table was constructed.A focus adjustment scheme combining real-time machining and reference table is designed.The key parameters of femtosecond laser such as powder density,molar mass and spot diameter were measured.A mathematical model based on the thermodynamic coupling algorithm was established,and the transient temperature field,stress field and thermal cycle distribution at the cladding point in the interaction between laser and matrix were analyzed,and the process parameters needed for the material to reach the appropriate molten pool temperature were obtained.The fluid dynamics model of liquid phase sintering tank was established and the evolution process of coating was simulated.The formation process of molten channel was studied,the evolution mechanism of molten pool and the flow law of liquid phase sintering pool were analyzed.A single factor experiment was designed to analyze the influence of laser parameters on the coating morphology,predict the possible defects of coating forming,and obtain the optimal combination of parameters required for the coating surface smoothness.According to the numerical simulation results,a multi-parameter experiment of Zr-BN composite ceramic powder cladding was carried out,and the macroscopic morphology of the cladding layer was measured.The results show that the laser scanning speed and laser spacing have great influence on the morphology of the cladding layer.EDS and XPS test results show that the microstructure of cladding layer is columnar crystal with obvious directivity,and scanning speed affects the number of crystals and element content in cladding layer.Using the same process parameters combination experiments to validate the simulation results,by cladding layer surface roughness and micro cladding powder particle size,the main elements,elements form chemical bonds,etc.The experimental results,demonstrates the laser power,scanning speed,spot diameter and main process parameters such as laser scanning spacing between matching,a matching parameters can reduce the forming defects or failure,Finally,the cladding layer with fine grain and uniform structure is obtained,which can effectively improve the processing efficiency.