Study On The Electrodeposition Mechanism And Mechanical Properties Of Graphene Reinforced Nickle Matrix Composite

Graphene can significantly improve the strength-toughness of the metal matrix composites due to its high strength,Young’s modulus and a large-surface-area.However,the agglomeration of graphene,low enhancement efficiency and the lack of stability restrict the development and application of graphene/metal composites.In order to improve the enhancement efficiency of graphene reinforced metal matrix composites,we used chemical reduction method to synthesize graphene with high dispersibility and good reducibility,and then using electrodeposition method to prepare graphene/Ni composites with different structures.In this paper,we demonstrate the effects of surfactant,nanoparticle,reduction temperature on the dispersion and reducibility of graphene as well as study the nucleation and growth behaviors of the composites in the electrodeposition process.Meanwhile,the mechanical properties and the strengthening mechanism of graphene/Ni composites were investigated.The main findings are as follows:（1）Graphene can be prepared by adding hydrazine hydrate during the process of chemical reduction.Ni nanoparticles can inhibit the agglomeration of graphene,but the graphene solution is turbid and contains Ni（OH）₂ precipitation.Moreover,the graphene solution added PVP has good dispersibility.Further research shows the graphene synthesized by chemical reduction with hydrazine hydrate and PVP at 80℃has the characteristics of less layers,few oxygen-containing groups.（2）The microstructures of the graphene/Ni composites were analyzed by EBSD.It was found that the addition of graphene will affect the grain size distribution of the nickel matrix.The monolithic nickel shows a long strip shaped microstructure,for which the average is 0.9?m.In contrast,the graphene/Ni composite fabricated by adding 2 ml graphene dispersion in 250 ml plating solution possesses a refined grains microstructure,which exhibits a tendency to transform into a bimodal grain size distribution microstructure with ultrafine grain embedded in coarse grain.When the contents of graphene increased to 4 ml,the Ni crystals grow into uniformly spherical shape with an average size of 0.7?m.The electrochemical behaviors of the electroplating baths are investigated by the cyclic voltammograms and electrochemical impedance spectroscopy.It demonstrated that the graphene nanoflakes can promote the cathode polarization effect,improve the conductivity of the solution,consequently augment the deposition rate of Ni matrix and restrict the growth of the grain and form the graphene/Ni composites with different microstructures.（3）The results of mechanical properties show that graphene enhanced the strength,ductility and strain hardening ability of nickel matrix composites.The graphene/Ni composite fabricated by adding 2 ml graphene dispersion exhibiting the ultimate strength of 870 MPa,elongation of 21%.Therefore,we deduced that that the back stress played a vital role in improving the strength and ductility of the graphene/Ni composites.