Research On Selective Laser Melting Of Nickel Plating Graphene Reinforced Inconel 625

Graphene has been widely used as a reinforcement phase in composites due to its excellent electrical,thermal and mechanical properties.In this study,graphene was modified by electroless nickel plating to obtain nickel-coated graphene（Ni-GNP）,which was then introduced into spherical Inconel 625 powder by ball milling.Selective laser melting（SLM）was subsequently used to fabricate Inconel 625/Ni-GNP metal matrix composites（MMCs）containing different levels of Ni-GNP（0,0.4 vol%,1.0 vol%）.The effects of Ni-GNP content on the microstructure,mechanical properties,wear properties and corrosion properties of Inconel 625/Ni-GNP composites were investigated.And,the temperature of heat treatment on the microstructure,precipitation phase,mechanical properties and corrosion properties of Inconel 625 alloy were explored.The main findings are as follows:（1）The different pre-treated process on the microstructure and phase of nickel-plated graphene were studied.The pre-treated graphene and untreated graphene were handled by sensitized,activated,and electroless nickel plated.The SEM image showed that the surface of Ni-coated graphene exhibited uniformly loaded of unknown particles by the 2-methylimidazole pretreatment,but the only of unpre-treated graphene had few unknown particles in the surface.XRD showed that the unknown particles were Ni crystals.（2）The addition of Ni-GNP changed the grain orientation in Inconel 625 from<001>and<101>to<111>.After adding 0.4Ni-GNP,the average grain size of Inconel 625 composite decreased from 9.4μm to 8.8μm,its values decreases of 6.4%.Inconel 625/0.4Ni-GNP composite exhibit weaker texture strength and its anisotropy of microstructure decreases.（3）In addition,noticeable grain refinement was observed at the addition of 1.0 vol.%Ni-GNP.The micro-hardness of Inconel 625/Ni-GNP composites increased with increasing Ni-GNP content and registered 348.2 HV_0.2 at the addition of 1.0 vol.%Ni-GNP.However,the Inconel 625/0.4Ni-GNP composite attained the maximum tensile strength（927 MPa）,yield strength（797 MPa）and elastic modulus（227 GPa）.Inconel 625/Ni-GNP composites exhibited lower wear coefficients than Inconel 625 at room temperature.Also,Inconel 625/0.4Ni-GNP composite displayed higher corrosion potential than Inconel 625 and lower corrosion current density than Inconel 625/1.0Ni-GNP composite.The addition of Ni-GNP clearly improves the micro-hardness,tensile strength,yield strength,wear and corrosion properties of Inconel 625principally due to grain refinement,solid-solution strengthening and impediment to dislocation motion.（4）After holding at 870℃for 1h,Inconel 625 and Inconel 625/0.4Ni-GNP composite shows the highest hardness.After holding at 1035℃for 1h,the microstructure of Inconel 625alloy shows the shape of equiaxed grains,with lots of annealed twins,and shows the best corrosion resistance.As special grain boundaries,the twins enhance the order of the grain boundaries,reduce the interfacial energy,and lead to increased corrosion resistance.Meanwhile,the addition of GNP increases the recrystallization temperature of Inconel 625/0.4Ni-GNP composite.Due to smaller grain size and larger residual stress,Inconel 625/0.4Ni-GNP composite can obtain a stable passivation film,thus,the corrosion resistance of the alloy are improved.