Research On Electrohydrodynamic Jet Deposited Soft Coated Tools With Micro-nano Textured Substrate Surfaces

Based on the development and demand of dry cutting tool technology,a new idea of electrohydrodynamic jet deposited soft coated tools with micro-nano textured substrate surfaces is proposed by combining electrohydrodynamic jet deposition(EHDA)and micro-nano textures in order to solve some common problems,such as uncontrollable interfacial structures of coatings-substrates and poor adhesion between coatings and substrates.Compared with the physical vapor deposition(PVD)technology,EHDA has shown many advantages of simple process,high efficiency and low cost,etc.The regular and controllable micro-nano textured surfaces,compared with the smooth surfaces,can improve the specific surface area/surface free energy of the substrates.Also they can increase the adhesion between coatings and substrates.Multi-layers soft coated tools with micro-nano textured substrates surfaces and their fabricating method are invented.The manufacturing technology of electrohydrodynamic jet deposited soft coated tools with micro-nano textured substrate surfaces is obtained through the studies of the mechanisms,equipments and processes of EHDA and laser-induced surface micro-nano textures.The anti-friction and lubrication mechanisms of the electrohydrodynamic jet deposited soft coated tools with micro-nano textured substrate surfaces are revealed through studying their physical properties,friction and wear performance and dry cutting performance.The forming mechanism and scale change law of electrohydrodynamic jet are studied,and the relationship between jet size and slurry physical properties parameters or process parameters is obtained.The numerical simulation model of the forming process of electrohydrodynamic jet is established,and the jet potential/shape change induced by electric field are analyzed.Under the electric field,the free and polarized charges in the droplet will accumulate to the two-phase interfaces,forming a top-down layered potential distribution and a pulling mode.The mechanism of jet scattering atomization and the evolution law of atomized droplets are studied,then the motion equation and motion law of atomized droplets are obtained.In order to meet the requirements of EHDA,a depositing device is designed and developed.A control system is developed,aiming to realize the collaborative control of each functional modules of the device.The EHDA process of home-made WS2 slurry is studied,and the effects of key process parameters(such as voltage,slurry flow rate and needle-substrate distance)on the jet shape and coating quality are studied.The optimal process parameters are voltage of 3.5-4.6 kV,slurry flow rate of 12 ?lmin-1 and needle-substrate distance of 5 mm.Depending on the biological shark skin and nano-texture,the multi-morphology,multi-scale micro-nano textures are designed.Then the textures are fabricated by ns laser and fs laser,and their geometric dimensions are as follows:the width,depth and period of the micro-grooves in the biomimetic shark skin are?10 ?m,?17 ?m and?100?m,respectively.The width,depth and period of the nano-grooves in the nano-texture are?500 nm,?100 nm and?750 nm,respectively.The WS2 coatings and WS2/C coatings are deposited on the micro-nano textured faces,and their physical and mechanical properties are studies.The results show that the WS2/C coatings have higher hardness and plasticity index H/E,the micro-nano texture surfaces does not change the crystal structure of the soft coating but can change the interface bonding morphologies of the soft coatings,the micro-nano texture surfaces increase the surface roughness of deposited coatings and the adhesion between coatings and substrates.The mechanism of micro-nano textured surfaces improving the adhesion between coatings and substrates are as follows:the micro-nano textured surfaces 1)can effectively reduce the interface strain between the substrates and the soft coatings;2)can increase the contact area of the coatings and improve the mechanical meshing force of the substrates;3)have better wettability and free energies;4)can bring about a compressive stress field and dissipate the residual stress of the coatings.The tribological properties of WS2 coatings and WS2/C coatings are studied by sliding against AISI1045 steel balls.Compared with the WS2 coatings,the wear rates of the WS2/C composite coatings are lower and their wear lives are longer,mainly due to the higher hardness,toughness and oxidation resistance.The further reduced wear rates and increased wear lives will be obtained for the deposited coatings deposited on the micro-nano textured surfaces.These results mainly because the micro-nano textured surfaces can improve the adhesion of the coatings,the micro-textures can capture wear debris,store and transfer lubricant,helping to maintain a good lubrication state of the frictional contact surfaces.Compared with the WS2 coatings deposited on the smooth surfaces,the wear rates of the WS2/C(4:1)composite coatings deposited on the micro-nano textured surfaces are reduced by 20%.The dry cutting performances,damage mechanisms and wear-reduction mechanisms of the electrohydrodynamic jet deposited WS2/C(4:1)soft coated tools with micro-nano textured substrate surfaces are studied by dry turning AISI1045 steel.Compared with the traditional tools(PT),the tools with micro-nano textured substrates faces or electrohydrodynamic jet deposited WS2/C(4:1)soft coatings have lower cutting forces,lower cutting temperatures,lower frictional coefficients of tool chip contact surface,improved tool surface wear degree and improved surface quality of workpiece.The tools named WMT-2-N perform best.The tools WMT-2-N are fabricated with 1)micro-nano textures on the rake faces and the micro-grooves in the diamond structure are parallel to the main cutting edge;2)nano-textures on the flank faces and nano-grooves are parallel to the main cutting edge;3)WS2/C(4:1)soft coatings deposited on both rake and flank faces.The mechanisms of soft coatings deposited on the micro-nano textured surfaces improving the dry cutting performance of cutting tools are as follows:the frictional state of the tool-chip contact surfaces is improved by soft coatings;the contact characteristics between tools and chips are improved by micro-nano textures;the bonding strength of soft coatings is improved by micro-nano textures.