Effect of Ultrasonic Radiation on the Properties of Laser Melted Ni-based WC Coatings
Based on the high processing efficiency and effective surface modification of laser cladding,ultrasonic radiation has been introduced to support the study of the effect of ultrasonic waves of different amplitudes on the microstructure and mechanical properties of laser cladding Ni-based WC coatings.The work aims to reduce the residual stress of the cladding coating,improve the mechanical properties of the cladding coating and improve the service life of parts to provide technical support.Ni-based WC coating was laser-melted on the surface of Cr12MoV die steel by combining laser cladding technology and ultrasonic radiation technology to eliminate the defects such as cracks and porosity existing in the cladding coating and improve the mechanical properties of molded parts.Firstly,based on the cavitation effect and acoustic flow effect produced by ultrasonic waves in the process of metal solidification,combined with the grain growth law,the effect of different amplitude parameters on the dispersion of WC inside the molten pool,the improvement of the macroscopic morphology of the molten cladding coating,the change of the microscopic structure and the composition of the physical phase was studied and a microscopic study was carried out on the optimization of the mechanical properties and the change of the residual stresses.Secondly,the effect of ultrasonic radiation process on the mechanical properties of Ni-based WC coating was analyzed through comparative experiments on the microhardness and wear resistance of each coating under different amplitude ultrasonic radiation-assisted processes.Finally,the longitudinal residual stress of the cladding coating was measured by X-RAYS diffractometer to investigate the change of the stress of the coating layer by ultrasonic radiation,and the role of ultrasonic radiation mechanism in enhancing the properties of the cladding coating was explained in conjunction with the change of the microstructure.The results showed that the average grain size of the ultrasonic radiation cladding coating with different amplitudes was reduced by 66.47％at most.The microstructure after ultrasonic radiation consisted of columnar and equiaxial crystals,and the coating phases were mainly Ni-Cr-Fe,γ-(Fe,Ni),FeNi3,Cr7C3,W2C and CrB solid solutions.The wear of the applied ultrasonic radiation cladding coating was reduced by 65.17％,95.74％,96.49％,76.67％,and 73.03％,respectively,compared with that of the substrate.The average microhardness of the cladding coating increased by 14.86％,23.20％,28.10％,22.84％,and 16.76％,respectively,compared with that of the substrate.The longitudinal average residual stress of the cladding coating was reduced by 173.0 MPa at amplitude of 14 μm,with a maximum reduction of 95.31％at the bottom of the molten pool.In summary,ultrasonic radiation effectively reduces the formation of residual stresses and cracks in the cladding coating,improves the quality of the cladding coating,and thus increases the service life of the parts.As the amplitude of ultrasonic radiation increases,the surface roughness of the cladding coating decreases,the microhardness and wear resistance increase and then decrease,and the residual stress decreases significantly.It is judged comprehensively that at the amplitude of 14 μm,the coating has the highest grain refinement and the best microhardness and wear resistance.
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