The Study Of Microstructure And Properties Of Laser Cladding Fe-based Alloy Coating And Numerical Simulation Of Temperature Field And Flow Field

Surface modified materials prepared by laser cladding technology can significantly improve the surface hardness,corrosion resistance and wear resistance of parts,replace expensive alloy,and greatly save the cost.Laser cladding process involves multiple physical field coupling,and it is difficult to obtain the dynamic characteristics of temperature field and flow field in the molten pool by experimental means,and the forming quality cannot be better controlled and optimized.However,the numerical simulation technology has the characteristics of low cost,strong operability,and the calculation results cover a variety of evolution information,which provides an effective way for the research of laser cladding.In this paper,Jmatpro software was used to calculate the material physical property parameters and based on Fluent software,the temperature and flow fields of laser cladding Fe-based alloy coating were studied.A laser cladding model with powder layer as continuum and deformable gas-liquid free interface was established.Under this model,the temperature field distribution,pool morphology,cooling rate variation trend and temperature gradient distribution of the quasi-stable molten pool were investigated,which provided a theoretical basis for the subsequent selection of laser cladding process parameters.At the same time,experimental study was carried out on laser cladding WC reinforced Fe-based composite coating,to explore the variation of microstructure and properties of cladding layer at different depths in the direction of penetration,as well as the influence of different amount of WC on microstructure,hardness,wear resistance and corrosion resistance of the coating.The following conclusions are drawn:(1)The quasi-steady state analysis of the temperature field,molten pool morphology and velocity vector field was carried out under the laser power of 2700 W and scanning speed was5mm/s.It was found that the three situations all reached the quasi-steady state at 2.5 s,the temperature field has a tail,and the molten pool morphology was semi-ellipsoid.The temperature gradient decreases from 6.6×10⁵K/m to 1.6×10⁴K/m and the cooling rate decreases from 1.25×10⁵K/s to 0.9×10⁴K/s from the surface of the molten pool along the depth direction from top to bottom.(2)Comparing the simulation results of different process parameters,it was found that with the increase of power,the temperature field of the peak temperature,the three dimensional size of molten pool and dilution rate increase,when the power was 2900 W,the maximum peak temperature in the center of molten pool was 2830 K;The increase of power enhanced the convection effect of the flow field in the molten pool,and the maximum flow velocity in the molten pool increased from 0.0348 m/s to 0.0737 m/s with the increase of power.With the increase of scanning speed,the temperature peak in the temperature field,the three-dimensional size of the molten pool and the dilution rate decreased,when the scanning speed was 4 mm/s,the maximum peak temperature in the center of the molten pool could be 2900 K.The increase of scanning speed weakened the convection effect of flow field in the molten pool,and the maximum flow velocity in the molten pool decreased from 0.0516 m/s to 0.0294 m/s with the increase of scanning speed.With the powder melting condition and dilution rate as the quantitative standard,The optimal process parameters were power P=2900 W and scanning speed v=5 mm/s.(3)The microstructure and properties of the molten pool at different positions along the depth direction were investigated.It was found that the cladding layer and the matrix had good metallurgical bonding,and the phase composition of the cladding layer at different depths were?-(Fe,Cr),Fe₂C,Fe₂W.The microstructure of sub-surface layer,middle layer and bottom layer were fishbone like dendrite,and there were hard particles around it.With the increase of surface distance,transition layer had cellular crystal.Middle layer had the smallest and most uniform grains and the highest hardness(1057 HV),which was 4.2 times that of the matrix;the bottom layer had the best wear resistance,which wear rate was 0.29 mg/mm²,the best corrosion resistance,which self-corrosion potential was-205.86 m V,and the passivation current in the transition layer was the smallest,which was 0.1865?A·cm^-2,and the corrosion velocity was the slowest.(4)The influence of different WC content on the microstructure and properties of the cladding layer was investigated.It was found that the phases of laser cladding coating with different WC content were mainly composed of Fe₂W,Fe₂C,?-(Fe,Cr),Fe₃W₃C and Cr₇C₃;with the increase of WC mass fraction,the microstructure became finer and finer,and the hardness becomes higher,the wear resistance and corrosion resistance were improved.However,when the WC content was more than 20%,a large number of cracks occur and the surface quality of the cladding layer became worse.When the amount of WC was 20%,the hardness was up to 1283.4HV,which was 5.26 times of the matrix hardness;the lowest wear rate was 0.177 mg/mm²,and the best wear resistance was obtained;the maximum self-corrosion potential was-439.47 m V,and the corrosion resistance was the best;the minimum passivation current density was 24.46?A·cm^-2,and the corrosion rate is the slowest.There are 49 figures,11 tables and 72 references in this paper.