Regulation Of Microstructure And Property Of Laser Cladding By Multi-Dimensional High Frequency Vibration

Laser cladding is the basis for metal additive manufacturing and remanufacturing.However,there are usually defects in the traditional laser cladding,such as porosity,cracks,residual tensile stress and poor reliability.Against the shape-and-performance-control problem,a novel approach on multi-dimensional high-frequency vibration assisted laser cladding technology was proposed in this dissertation.The coating of 316 L stainless steel alloy coating was prepared on the surface of 45 steel using this approach.The relevant theoretical basis,macroscopic morphology,microstructure and properties were studied.The results provided new ideas and ways for the improvement of laser cladding defects and the improvement of performance.In this study,the mechanisms of multi-dimensional high-frequency vibration on laser cladding were explored firstly,and numerical simulations were conducted to analyze the temperature field and flow field of the molten pool.Then,the experimental setup of multidimensional high-frequency vibration assisted laser cladding was built,and the laser process parameters was optimized.Based on the theoretical studies and the platform construction,optical microscope,scanning electron microscope,X-ray diffraction,etc.were used to study the influence mechanism of multi-dimensional high-frequency vibration on the macroscopic morphology and microstructure of laser cladding 316 L coating.And the effects of multidimensional high-frequency vibration on hardness,corrosion resistance and tensile properties of the laser cladding 316 L coating were studied by vickers hardness tester,electrochemical workstation and tensile testing machine.The main conclusions of this dissertation are as follows:(1)The finite element simulation results show that the convection inside the molten pool is accelerated under the action of vibration.Then,the flow rate and the cooling rate is increased,while the temperature gradient is decreased.This effect becomes more significant with multidimensional vibration.(2)Under the action of multi-dimensional high-frequency vibration,the cladding height,the penetration and the wetting angle of the cladding layer gradually decrease,and the cladding width gradually widens.Furthermore,the fusion failure between the overlapped cladding area reduces with multi-dimensional vibration.The grains in the cladding layer are remarkably refined by the vibration,and the width of the top turning dendrites increases.The grain refinement becomes more significant with multi-dimensional vibration.(3)In the 316 L coating treated by multi-dimensional vibration assisted laser cladding,the pores of the cladding layer are significantly reduced.With the three-dimensional highfrequency vibration,the porosity decreases by 95.8%,and the maximum pore size decreases by 65.6%.(4)Under the action of multi-dimensional high-frequency vibration,the micro-hardness,corrosion resistance and the tensile strength have been significantly improved.With the threedimensional high-frequency vibration,the tensile strength of the cladding layer increases by 27.2%,and the elongation after fracture increases by 14.3%.This dissertation aims to meet the rising demands for laser cladding stainless steel in industrial parts including hydraulic columns in coal mine,petroleum pipelines,valves,etc.And using laser cladding stainless steel method to significantly improve its performance and service life.The research results provide an effective way to improve the comprehensive performance of laser cladded coatings,and have significant application value in the repairing and remanufacturing of mining machinery,petrochemical industry,etc.