| Al,Mg,Ti and their alloys,which are ideal materials to realize the lightweight design of products,have attracted high attention.They were treated by microarc oxidation,and the MAO ceramic films with high hardness and high wear resistance were prepared on the surface of them.However,the MAO films had poor antifriction performance,which seriously affects the tribological properties of materials.Therefore,it is of great significance to improve the antifriction performance of MAO films.Micropores(abbreviation,film holes)on MAO films can be used as the storage units of antifriction materials.In this paper,the formation mechanism of film holes was researched in order to controlling size,structure and porosity of film holes,hardness of MAO films,increasing the storage capacity of antifriction materials in film holes,and the adhesion strength of antifriction materials with MAO films.MAO antifriction composite films with appropriate hardness,strong adhesion strength and excellent antifriction performance were prepared by adjusting size,structure and porosity of film holes.In order to controlling effectively the size,structure and porosity of film holes,the formation mechanism of film holes was researched.The formation process of film holes was divided into three stages,the formation of plasma source in MAO films,the growth and development of plasma,and formation of film holes through the eruption and flowing of plasma.The conduction mechanism of MAO insulation films in the initial stage of films holes formation was researched.It was believed that the field electron emission was the reason for the conduction of the MAO insulation films.The formation mechanism of plasma source was analyzed.The growth and development mechanism of plasma in the early stages of film holes formation was researched.The formation mechanism of charged particles in plasma was analyzed.The action mechanism of the coulomb scattering effect between same charges on the formation of film holes was analyzed.The electric field force formed by outside strengthening electric field and the magnetic field force excited by electric field were analyzed.The separation mechanism of outside strengthening electric field on the point charges was researched.This separation mechanism effectively promoted the action mechanism of coulomb scattering effect between point charges on the formation of film holes.The action mechanism of the magneticpinch effect of the magnetic field on the formation of film holes was researched.The action mechanism of plasma oscillation on formation of film holes was analyzed.The heat transfer mechanism during film holes formation was analyzed.The phenomenon of phase change and energy dissipation during film holes formation were analyzed.The growth and development model of plasma was established.The formation mechanism of film holes was researched.The film holes were formed by eruption and flowing of plasma.The source of eruption and flowing of plasma was the presence of thermal pressure.Analyzed the formation mechanism of thermal pressure.The dissipation ways of thermal pressure during the formation of film holes were analyzed,and the dissipation mathematical model of thermal pressure was established.The flow patterns and flow characteristics of plasma were researched.Plasma flow was turbulence flow.The turbulence flow strengthening mechanism of plasma was researched.The physical model of MAO film holes formation was established.The factors influencing the formation of micro-arc oxide film holes were analyzed,including the influence of electric parameters,electrolyte and doped particles on the formation of film holes.Based on the formation mechanism of MAO film holes,the film holes were regulated.The MAO treatment of substrate materials was carried out by adjusting the electric paramters of MAO and adding nano-particles additives to the electrolyte,respectively,and the structure,size and porosity of film holes.The effects of electrical parameters and nanoparticles on the size,structure and porosity of film holes,and surface roughness,thickness and phase composition of MAO films were researched.The results showed that the regulation of size,structure and porosity of film holes can be achieved by adjusting MAO process.After the formation of MAO films,the antifriction materials were deposited in film holes by dip coating process,and MAO antifriction composite films were prepared by two-step method.The effects of size,structure and porosity of film holes on the adhesion strength between MAO films and substrate materials,and on the adhesion strength between antifriction materials and MAO films were researched.The results showed that the adhesion strength between antifriction and MAO films can be adjusted by the regulation of size,structure and porosity of film holes.The antifriction performance of MAO antifriction composite films was researched.The friction coefficient,morphologies of wear tracks and wear rates of MAO films and MAO antifriction composite films were compared and analyzed.The wear mechanism of MAO antifriction composite films was analyzed.It results showed that MAO antifriction composite films showed excellent tribological properties.In this paper,a new process,which improved the antifriction performance of MAO films and the adhesion strength between antifriction materials and MAO films by controlling the size,structure and porosity of film holes on the surface of MAO films was proposed. |
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