Research On The Fabrication Of Functional Surface Structure By Selective Laser Melting Of Copper Nanoparticles

With the rapid development of surface engineering technology and novel materials,surface functional structure manufacturing has become more and more important in the field of interdisciplinary research in recent decades.Fabrication the surface textures according to the designed requirements is an significant development trend of surface functional structure manufacturing.Additive manufacturing technology possessing high flexibility,small batch,low cost and simple principle,which combines digital design,advanced materials and fabrication,has become a hotspot in the field of advanced manufacturing.Different from macro surface structure,surface structure with nano-scale material can further the surface properties and endow them with special effects.In this work,the method of selective laser melting(SLM)of ink-printed(IP)copper(Cu)nanoparticles(NPs)in air ambient was proposed.The method of SLM-IP Cu NPs is based on the"bottom-up"principle of fabricating structure layer by layer realizing the properties of flexibility,high efficiency,high stability,multi-scale and composite surface function structure manufacturability.Under the protection of alcohol and organic polymer,the method of SLM-IP Cu NPs uses a laser beam to sinter the specific area which could fabricate metallic structure in the air environment.Cu nanoparticles,PVP and alcohol were selected according to the relationship between alcohol,metal oxide and polyvinylpyrrolidone(PVP).The mechanism among Cu nanoparticles,PVP and alcohol was analyzed by DSC/TG.A thermal-fluid-solid coupling mathematical model was established by using the energy,momentum and mass conservation equation according to the Cu nanoparticles melting principle.The process of material melting and combining were simulated based on the model.Considering the natural convection,interfacial tension and marangoni effect,the effects of solvent boiling on the dispersion and the effects of gravity and surface tension on the melting process of particles were analyzed.The laser distribution in the nanoparticle solvent was established by Monte Carlo method.The SLM-IP Cu NPs continuous model was also established on the basis of the energy of the phase change,conservation of mass a nd mass flow equivalence principle.The evolution of the contour formation by SLM-IP Cu NPs was simulated based on the continuous model which was validated by experiment.The coating model of slot-die was established based on the flow characteristics of copper nanoparticle dispersion and wetting characteristics with the substrate.The SLM-IP Cu NPs experimental setup was developed.The single track processing experiments were conducted based on the device and the processing parameter window was proposed.Plateau--Rayleigh flow instability criterion was applied to analyze the cause of single track balling effect.The influence of scanning line space and hatch method on the height of monolayer were analyzed.On the basis of the single-layer processing paramters,the double layer processing paramters was also obtained.Hydrophobic/superhydrophobic surface functional structures and friction-reducing surface microtextures with micro/nano hierachical structures were fabricated by SLM-IP Cu NPs.The static contact angle model of grid structures with nanoparticles was established.Maximum of 160°contace angle can be reached fabricated by the method of SLM-IP Cu NPs.Based on the quasi-state Reynolds equation,the influence of area ratio and geometrical structure of different microtexture on hydrodynamic pressure was analyzed.The lubrication state and friction-reducing properties of the micro-texture were studied by friction test.The experimental results show that the convex surface microtexture manufactured by SLM-IP Cu NPs can realize hydrodynamic lubrication.The squared ring surface texture(square ratio S_p=0.28 and internal diameter characteristic size to microtexture unit size ratio r_i/r_l=0.6)fabricated by SLM-IP Cu NPs can realize the friction coefficient of under the speed of 0.6m/s and load of 28kPa in the lubrication oil of 4050.Moreover,both the surface texture and the material property contribute to the friction reduction under the speead of 890mm/s and load of 140GPa.