Preparation Of The Graphite/Cu Composite Material By Laser Cladding With Presetting Powder Method

The low strength of pantograph-slide has a strong impact on the development of the high speed railway.The preparation of high-performance pantograph-slide is one of the main focus and the hotspot of current research.Based on the raw material of pure copper powder and squamous graphite.These mixed powers were prepared by high-energy ball milling.The preset piece with thickness of 1mm was obtained by the function of pressure and binder.The graphite/Cu homogeneous composite material was prepared by proceeding a laminated laser cladding on the preset piece.Then,the microstructure of this material is analyzed,hardness,abrasive resistance and electrochemical corrosion resistance were studied.So,the optimum parameter was achieved.Finally,the volume fraction of graphite in every layer was modified to prepare the thickness of the high graphite/copper gradient composites.The research results show that:1.Ball-milling technique is followed as : ball-to-powder weight ratio of 4:1,rotation rate of300r/min,milling time of 8 hours,the carboxymethyl cellulose of 0.6%;2.The optimum parameter for the laser cladding overlap rate is ascertained at 40%,?Z is0.30 mm,the laser power is 1600 W,the scanning speed is 300mm/min.Graphite is uniformly distributed in the graphite/Cu homogeneous composite materials.The size of disperse phase(Fe-rich phase)is small.The maximum hardness of cladding layer is 114.86 HV,the lowest friction coefficient is 0.132.And,it shows a good corrosion resistance.There are three typical forms of graphite in the graphite/Cu homogeneous composite material: flake graphite,vermicular graphite and spheroidal graphite.The composite with spheroidal graphite has an excellent integrated properties.The main wear mechanism of graphite/copper composite materials is the abrasive wear;3.With laser power of 1600 W and scanning speed of 300mm/min,40% of overlap rate,0.30 mm of the Z axis increment,the three different gradient copper/graphite composite was prepared.Functionally gradient material(the gradient factor n=5)has a good mechanical property and conductivity.The maximum hardness is 115.42 HV,IACS% is 79.8%.The prepared graphite/Cu functionally gradient material can be divided into three layers:the bottom layer,the middle layer and the upper layer.In the bottom,it's mainly based on vermicular graphite and biggish spheroidal graphite.In the middle layer,in the proportion of vermicular graphite is decreased.However,the proportion of vermicular graphite is increasedto some extent.In the gradient material,the cladding layer and substrate interface as the baseline,along with the direction of cladding layer,hardness is increased steadily within limits,and it has a maximum value in the middle layer and the upper layer.However,near the upper layer surface,the number of pore is increased,so,the micro hardness has a potential to decreases.