Numerical Simulation And Experimental Research On Formation Mechanism Of Laser Texturing Topography

In recent years,Laser Texturing Technology(LTT)is developing rapidly,and is applied to some fields of automobile,architecture,household appliances,military industries.However,studies on the theory and regulations of LTT are still inadequate.Based on the status mentioned above,it is quite essential to conduct numerical simulations of COMSOL Multiphysics and successive experimental investigations.By this way,we can acquire deep understanding on the forming mechanism of LTT and achievements in control of technological parameters.The paper uses numerical simulation and process research to study the forming mechanism and the influence rule of LTT.The main research contents are as follows:(1)Based on the theory of interaction between laser and mental materials,a two-dimensional model used in numerical simulation is established by COMSOL Multiphysics.Next,effects of Marangoni convection value,laser power and pulse width on the formation of laser texturing morphology,temperature field in molten pool,quasi-state fluid flow field and deformation sizes.The simulation results show that:(1)The value of Marangoni convection is the main cause to influence the formation of texturing morphology.When the value is negative,texturing morphology presents a characteristic with crater-shape.By contrast,as the value is positive,it presents spherical cap.(2)Combining with the simulation on crater-shaped morphology,it is confirming that the temperature and flow field in the molten pool will increase with the increase of laser power and pulse width.Besides,the highest temperature in the molten pool appeared at the center of molten pool.And the maximum flow velocity is discovered between the edge and center of pool instead of the area mentioned above.(3)According to the simulation on spherical cap morphology,it is found that spherical cap morphology is changing from dumpy to lanky with the increase of laser power or pulse width.And then we forecast that the convex coronal morphology will evolve to coronal,"M" and crater-shaped texturing morphology along with the increase of laser power or pulse width considering the evaporation and gasification of the material.In addition,the result is testified by experiment on the surface of 45 steel with high S value.(2)High-speed steel tool material is selected as the experimental objective on the formation of LTT according to the simulation investigations.Results are exhibited as follows:(1)Crater-shaped texturing morphology is obtained in the surface of high-speed steel material during experimental process.Besides,the outer diameters,inner diameters and pit depths of the crater-shaped morphology increase with the increase of laser power and pulse width,which are consistent with the results of numerical simulation.By contrast,the height of the protruding is different with the simulation results,which is attributing to recoil pressure caused by evaporation and gasification of the material during process of LTT.(2)There is low related regularity of formation in texturing morphology when oxygen acted as auxiliary gas,which could cause random disturbance on texturing process because of its oxidation and combustion assisting.While molten pool could be well protected when nitrogen is used as auxiliary gas.The outer diameter,inner diameter and depth of texturing morphology are obviously larger than the normalization texturing in the air atmosphere when blow air vertically under 0.1MPa pressure,but the height of the protruding is reduced.The “special” texturing morphology could be obtained in the surface of the high speed steel material with a high side and low side if blowing angle is changed.The maximum height of texturing morphology occurs when the blowing angle is 45 degrees.(3)After metallographic structure observation and micro-hardness testing on texturing area,laser texturing area could be divided into three regions which are the melting zone,heat affected zone and matrix.The metallographic structure of the matrix mainly consists of tempered martensite,alloy carbide and quite small amount of retained austenite.The melting zone is mainly composed of twin martensite and dislocation martensite.Micro-hardness of laser texturing area is obviously higher than matrix.Besides,maximum hardness is 1005.5HV,and its hardness is about 1.24 times than that of matrix.