Study On Supercritical Graphene Pulse Composite Electrodeposition Process

Graphene has many excellent properties due to its unique two-dimensional crystal structure.The metal matrix composites have high hardness and wear resistance,which is of great significance in the field of materials.At present,the metal matrix composites were prepared by the method of pressing the graphene nanosheets and the matrix materials,under high temperature condition.The structure and mechanical properties of the composites were affected by the phenomenon that the graphene structure was easily damaged by the mechanical force.Graphene nanosheets were used as the second phase of the composite electrodeposition layer,and the destruction of graphene structure can be avoided,the metal matrix composites prepared by electrodeposition method.In the process of the traditional composite electrodeposition,the second phase was easy to agglomerate,the surface of electric deposition was rough and the hydrogen evolution was serious.In this paper,the high mass transfer and diffusion properties of supercritical CO₂ fluid?SCF-CO₂?were combined with the pulse electrodeposition technique.In order to improve the performance of the composite coating,a new method was developed for the preparation of high performance composite electrodeposition layer by the study of the composite pulse electrodeposition technique.In this paper,the effects of the average current density,duty cycle and frequency on the microstructure and mechanical properties of the composite coatings were studied.The effect of supercritical conditions on the composite electrodeposition was investigated,by compared with the conventional composite coatings prepared under normal temperature and atmospheric pressure.A set of excellent technical processes for preparation of nickel based graphene composite electrodeposition layer were proposed.The main research contents are as follows:1.Technological process of pulse electrodeposition of nickel based composite coating under supercritical state was studied.The influence of various electrical parameters on the microhardness of the composite deposited layer was obtained by orthogonal test:Average >current > density,the best process combination was the average current density 6A·dm-2,frequency 1500 Hz,duty cycle 0.2.2.Based on single factor experiments,the effects of various electrical parameters on the properties of graphene composite coatings were analyzed.?1?Average current density.With the increase of the average current density,the density,microhardness and wear resistance of the composite coatings increased firstly and then decreased.When the average current density was 6A·dm-2,the microstructure of the deposited layer was compact,the content ofgraphene was much,the distribution was uniform,and the microhardness and wear resistance were the highest;?2?Duty cycle.When the duty cycle was 0.25,the composite layer had the best mechanical properties,the grain was small and dense,the amount of graphene was embedded and the distribution was uniform.When the duty cycle was less than 0.25,the microstructure was loose and the surface was free of hydrogen evolution.When the duty cycle was greater than 0.25,the grain size was coarse,and the agglomeration of graphene was uneven;?3?Frequency.When the frequency was 1500 Hz,the composite layer was compact,and the microhardness and wear resistance were the largest.When the frequency was lower than 1500 Hz,the structure was loose,the grains were coarse and the part was off.When the frequency was higher than 1500 Hz,the hydrogen evolution reaction was more serious,the hydrogen evolution hole was increased,and the agglomeration of graphene was serious.3.The optimal technological scheme of pulse electrodeposition of Ni based composite coatings under supercritical condition was studied.Under the condition that the average current density was 6A·dm-2,the duty cycle was 0.25,the frequency was 1500 Hz and the deposition time was 90 min,the mechanical properties of the composite deposited layer were the best.4.Compared to normal atmospheric conditions,SCF-CO₂ conditions for the preparation of nickel based graphene composite electrodeposition layer in the Shi Moxi embedding capacity increased by 1.7 times,more uniform distribution,the particle size of nanometer nickel electrodeposition layer,smooth and compact,the microhardness is increased by 0.67 times,the wear scar area is reduced by 4.68 times,wear resistance substantial increase.The supercritical environment can increase the selectivity of the?200?crystal surface,and decrease the selectivity of?111?and?220?crystal surfaces of the nickel based graphene composite electrodeposition layers.