Comparative Study Of Mechanochemical Wear On Monocrystalline Silicon Surface Under Pure Pressure And Shear

Since the transition state theory has been applied in tribology,there are many controversies about which stress dominates the mechanical chemical reaction.It is of great significance to determine the dominant stress in mechanochemical wear to promote the perfection of mechanochemical wear theory.The wear experiments of monocrystalline silicon substrate under different forces are carried out by means of atomic force microscope.By changing the normal load,cycle number and relative humidity under different force action mode,the wear results under different conditions was obtained,and the mechanism of different stress on the mechanochemical removal of silicon substrate was further analyzed.The main research results are as follows:(1)The mechanism of compressive stress and shear stress in the process of mechanochemical wear of monocrystalline silicon surface material was clarified.The possibility of direct atom removal due to hydrolysis reaction is aggravated by local stress concentration during shearing,and there is no possibility of pressure-induced wear.Therefore,the formation of Si-O-Si bond bridge between interfaces was verified by pressure-induced material removal on the surface of single crystal silicon.It was also proved that shear stress is not a necessary condition for the occurrence of mechanochemical reactions.(2)The reaction kinetic models of mechanochemical wear of monocrystalline silicon surface under pure compressive stress and shear stress were studied.By fitting the relationship between wear rate and contact pressure under different forces using the modified Arrhenius Equation formula and calculating their respective activation volumes,It was found that the reduction of the activation energy of the mechanochemical reaction between silicon and silicon dioxide was more significant under the shear action.(3)The evolution and mechanism of mechanochemical wear of monocrystalline silicon surface under pure compressive stress and shear stress are revealed.Based on first-principles calculations of the surface energy of the initial surface,the actual wear surface and the assumed wear surface by linear fitting,it was found that the mechanochemical removal of the monocrystalline silicon surface will be carried out in the direction of obtaining a lower overall energy structure.(4)The effect of humidity on the surface mechanochemical wear of monocrystalline silicon under pure compressive stress and shear stress was investigated.It was found that the different ways of force action on silicon surface showed different laws with the increase of relative humidity.It was inferred that the water adsorption on silica microspheres had an important influence on the mechanochemical wear.Meanwhile,the movement mode of the probe could aggregate or transfer the adsorbed water between the interfaces.The combined action of the two influenced the condition of adsorbed water film between the interfaces and then affected the friction,adhesion and wear.