Numerical Simulation And Experimental Study Of Laser Texturing Process

Metal surfaces with textured micro-bump have a wide range of applications in the industry.Due to the unique advantages such as designability and controllability,laser texturing technology has attracted the attention of academics and industry.However,as the process of laser texturing is complex and has many factors involved,the formation mechanism of morphology of laser texturing is not fully understood at present,and the research on the size change law of morphology is not sufficient.In view of this,it is necessary to carry out numerical simulation and experimental research on the laser texturing process,and to deeply explore the mechanism of laser texturing,and to master the laser texturing process.This research has important theoretical significance and application value.In this paper,the laser texturing 45 steel material is taken as the research object.The numerical research and experimental research are combined to study the formation process of laser textured morphology,and the formation mechanism of the textured morphology is analyzed.The main contents and conclusions of this research are as follows:1.In the formation mechanism of bump,45 steel is taken as the research object.Using the two-dimensional axisymmetric model to simulate the change of temperature field,fluid flow direction and flow velocity in the molten pool under the action of pulsed laser,so we can study the microscopic mechanism and dynamic process of the formation of the textured morphology.The results show that:(a)The sulfur-containing material which the temperature coefficient of tension is positive has a critical temperature Tc during heating process,and the tension at this temperature will change abruptly.If the temperature of surface exceeds Tc,the temperature coefficient will become negative;(b)During the whole heating process,the region which temperature is below the critical temperature,the tangential stress is negative and the melt flows to the center of the molten pool,while the region which temperature is higher than the critical temperature,the tangential stress is positive and the melt flows toward the edge,this will form two anisotropic circulations on the surface and the convection zero will be formed at the boundary region.For the same kind of circulations,the larger the tangential stress is,the larger the corresponding peak velocity will be;(c)If the surface temperature exceeds the critical temperature,a new circulation will be generated on the surface,and the morphology of the molten pool may change from bump to crater.The larger the new circulation flow rate is,the deeper the depth of crater is;the shape of the cooling process is mainly affected by the normal stress and the surface viscosity;(d)S and other active elements will change the tension distribution on the surface of the molten pool,which is the main reason for the appearance of bump;(e)The heat loss of vaporization will reduce the temperature on the surface of the target,the heat loss of vaporization and the recoil pressure have an influence on the size of the morphologies,but the height of bump is not only reduced by the heat loss of vaporization,but also by the surface tension.2.Through the combination of numerical research and experimental research,the influence law of the size of bump is studied.The results show that:(a)When the power and the pulse width is small,as the power and pulse width increase,the height of the bump increases rapidly,while the width increases linearly.Continue to increase the power and pulse width,the temperature of surface is close to the critical temperature,so the difference of tension in the center of the molten pool is reduced,the increasing speed of the height is slowed down,while the width is still linearly increased;further increasing the pulse width and power,the heat loss and recoil pressure will be generated by material vaporization to slow down the increase of the width of bump.The height of the bump is reduced by the combination of heat loss,recoil pressure and the change of surface tension.The larger the laser parameters are,the more obvious the effect of heat loss and recoil pressure will be.(b)When the power increase,the textured morphologies changes from bump to "W-shaped",and finally evolves into crater.During the evolution,it is crater with a center bump,which decreases with the increase of power.At the same time,the height of edge is gradually increased,and the overall depth is increased.