Study Of Surface Oxidation Mechanism And Material Removal Mechanism In SiCp/Al Chemical Mechanical Polishing

With the rapid development of optical precision instruments,aerospace and automotive manufacturing,silicon carbide particle-reinforced aluminium matrix composites(SiCp/Al)are widely used in these fields due to their many advantages such as high temperature resistance,wear resistance,low coefficient of thermal expansion,high thermal conductivity and high specific modulus.Due to the large difference in hardness between the SiC and Al phases in SiCp/Al,the surfaces obtained using conventional processing methods will have discrete microscopic depression areas of a hundred nanometres in depth,making it impossible to obtain a good quality surface.The chemical mechanical polishing(CMP)technique uses both chemical and mechanical effects to improve the processing efficiency of this material and to obtain a better surface quality,therefore processing SiCp/Al using the CMP technique is one of the solutions to solve its difficult processing problem.The chemical mechanical polishing technique uses chemical means to oxidise the surface of SiCp/Al to produce a surface oxide layer,which is then removed using polished abrasive particles to obtain a high quality surface.This paper focuses on an indepth study of the oxidation mechanism and material removal mechanism of SiCp/Al surfaces.The main research of this paper is as follows.(1)Modeling the oxidation reaction rates of two-phase materials on SiCp/Al surfaces.Based on the two-way diffusion principle and the classical Deal-Grove oxidation model,the oxidation rates of Al and SiC phases in SiCp/Al in the Fenton oxidation system were calculated to investigate the influence of different Fenton reaction types,oxidant concentrations and temperature parameters on the oxidation reaction rates of SiCp/Al surfaces.(2)Study of the oxidation mechanism of SiCp/Al surface.The experiment of SiCp/Al oxidation based on Fenton oxidation system was carried out to determine the rate of oxidation reaction by assessing the thickness of oxidation layer on the surface of SiCp/Al within a certain time,to analyse the effect of oxidation parameters on the concentration of hydroxyl radicals in the Fenton reaction,and to investigate the effect law of Fenton reaction type,oxidant concentration and oxidant temperature on the thickness of SiCp/Al oxidation layer.The surface morphology of SiCp/Al before and after oxidation and the composition of the oxide layer were analysed by SEM and EDS to investigate the effect of oxidant concentration on the degree of oxidation;the breakage and formation of chemical bonds on the surface were analysed by XPS to determine the chemical composition of the oxide layer.(3)Theoretical modelling study of the removal rate of SiCp/Al chemical mechanical polishing.Modelling of SiCp/Al material removal rates considering both chemical and mechanical removal processes.Based on the chemical reaction principle in the oxidation process,an expression for the thickness of the oxide layer is established.On this basis,a model for the depth of the single abrasive grain pressed into the workpiece during mechanical removal and a material removal model are established,taking into account the synergistic effect of chemistry and mechanics.The established pattern of influence of the main chemical and mechanical parameters on the material removal rate was used for the analysis.(4)Experimental study of material removal of SiCp/Al.Chemical-mechanical polishing experiments were carried out to investigate the polishing quality and material removal rate of SiCp/Al under different experimental conditions such as chemical action,mechanical action and synergistic chemical-mechanical action.The influence of parameters such as oxidant concentration,polishing pressure,speed,abrasive grain size and concentration on the surface quality and material removal rate of SiCp/Al is experimentally investigated.The CMP process parameters were optimised to obtain a combination of process parameters that is conducive to both higher material removal rates and better surface quality in the chemical mechanical polishing of SiCp/Al.