Study On Pulse-jet Electrodeposition Of Micropit Ni-AlN Bionic Nanocoatings On Metal Surfaces

With the rapid development of modern industry,more and more mechanical equipments operated in the large load,high temperature,high corrosion and other working conditions,which led to a significant increase in the failure rate of mechanical and equipment components.Among them,more than 80%of the failure rate of the components were occurred about the surface failure of metal materials caused by wear and corrosion.Therefore,the surface modification of mechanical parts has become one of the key mechanical engineering problems.Nanocoating is a nanomaterial formed by the second-phase nanoscale particles（such as Si C,AlN,Al₂O₃,etc.）embedded in the base metal.Nanocoating has a large number of second-phase reinforcing particles,and these particles have some excellent properties of their own,making it have certain physical or chemical properties.AlN nanoparticles have the advantages of high hardness,high thermal conductivity and stable performance,making them be well suited as reinforcing phase particles for the deposition of composite coatings on friction sub-surfaces.Pulse-jet electrodeposition is a new technique for depositing coatings,which uses a pulsed power supply instead of conventional direct current to change the static state of the plating solution into a flowing state,which can serve to promote the dispersion of nanoparticles,improve the bond between the coating and the substrate and increase the efficiency of electrodeposition.The rise of bionics has again opened up new research paths for surface modification technology.The intersection of bionics and tribology has promoted the application of friction-reducing,anti-adhesion and anti-wear bionic surfaces in various fields.In this paper,we will transplant and imitate the unique micropit morphology of living organisms,and use the unique friction-reducing properties of the micropit morphology to further optimize the wear resistance of metal material surfaces.The solution to the contact problem and the analytical process are described,using ANSYS Workbench software to model the upper slider moving in a sliding friction state on a smooth surface and micro pits bionic surface,and the effect and friction stress change,wear distribution and temperature field distribution on smooth surface under different parameters and micro pits were also analyzed.The results indicated that the friction stress value of the micro pit was 200μm and the spacing was 300μm,which indicated that the friction coefficient of the bionic surface under the structure parameter was small.Furthermore,the temperature field of the bionic surface of the micropit was low,and the high temperature distribution area was small,which illustrated that the wear reduction effect of the bionic surface was the best.The friction wear test machine was used to test the wear resistance of the micro pits,and the influences of the diameter and spacing on the bionic surface were discussed,and the mechanism of the bionic surface in the sliding friction state was also investigated.During the wear process of the micropited bionic surfaces,the friction surface of the upper and lower parts were worn to a certain extent.The wear process occurs mainly in the stable wear phase of the test piece.In the stable wear stage,the resistance mechanism of the bionic surface was mainly shown the following effects:leveling effect,storage effect,hole resistance reduction effect and pressure reduction effect of the micropited bionic surfaces.The kinetic mechanism of Ni-AlN bionic nanocoatings for pulse-jet electrodeposition was investigated,and the influence of pulse-jet electrodeposition process parameters on the properties of micropit-shaped Ni-AlN nanobionic plating was explored.Then,the process parameters of pulse-jet Ni-AlN nano-coatings were optimized by orthogonal test method,and the best process parameters combination of pulse-jet Ni-AlN was listed as follows:current density 20 A/dm²,AlN nanoparticle concentration 6 g/l,plating injection rate 0.4 m/s,pulse duty cycle 40%and pole spacing 8 mm.Ni-AlN bionic nanocoatings were prepared by direct current electrodeposition,pulse current electrodeposition and pulse-jet electrodeposition,respectively.The influence of different deposition methods and current density on the tissue structure and performance,and the surface morphology,tissue structure,phase composition,wear resistance and corrosion resistance of the coatings were examined.The bionic nanocoating obtained by DC deposition had uneven surfaces,and a large number of AlN nanoparticle particles came together to form larger groups.In addition,the coating surface had deep cracks and depression.However,the micropited Ni-AlN bionic nanocoating prepared by pulse-jet electrodeposition had a smooth and smooth surface,and it had a fine and compact tissue structure.In addition,large numbers of AlN nanoparticles were embedded in Ni-AlN bionic nanocoating.When the current density was 20 A/dm²,the surface of the bionic nanocoating was smooth,the AlN nanoparticles were uniformly dispersed in the coating and the nickel grains was smaller.In this coating,the average particle sizes of the Ni grains and the AlN nanoparticles were 51.5 nm and 39.8 nm,respectively.In addition,the wear resistance and corrosion resistance of the nanocoating were optimal.