纳尺度下类金刚石(DLC)薄膜摩擦性能研究

Investigation on the Nano- Friction Properties of Diamond- like Carbon Films

类金刚石薄膜(DLC)作为保护涂层在磁存储系统和微/纳米机电系统(M/NEMS)等方面的应用十分广泛,但其在实际应用中存在着摩擦副的设计问题,本文中采用物理气相沉积(PVD)技术以金属Cr作为过渡层在硅基底上制备类金刚石薄膜,利用原子力显微镜,对类金刚石薄膜的表面特性进行表征,并研究针尖的力学性能对类金刚石薄膜摩擦学性能的影响.结果表明纳尺度下硅针尖和氮化硅针尖测得的摩擦力与法向载荷之间均呈线性关系,这说明针尖材料对类金刚石薄膜的摩擦性能没有影响.Si针尖的SEM图像表明:高载荷下,Si/DLC摩擦副的摩擦系数增加是由于Si针尖的磨损;而类金刚石薄膜的AFM图像表明:Si3N4/DLC摩擦副的摩擦系数增加是由于类金刚石薄膜表面的粗糙峰在高载条件下发生了塑性变形,DMT理论计算验证了我们的实验结果.因此,本研究对于类金刚石薄膜在实际应用中摩擦副的设计具有指导意义.

The diamond- like carbon( DLC) films are widely used as a protective coating layer in the magnetic storage systems and micro / nano- electro mechanical systems. However,the deficiency on the friction pairs' design of the DLC films has limited its practical application. Here,the Cr buffer layer was adopted and deposited on Si substrate to fabricate the DLC films by physical vapor deposition. By using the atomic force microscopy,the surface properties of the DLC films were characterized,and the effects of the mechanical properties of tip materials on the friction properties of the DLC films were also analyzed. Experimental results show that the friction force of the DLC films measured by Si tip and Si3N4 tip increased linearly with the normal force at nanoscale,which was irrelevant to tip materials. From the SEM image of Si tip,it is noted that the increase of the friction coefficient of Si / DLC friction pair was attributed to the wear of Si tip. From the AFM images of the DLC films,it is found that the increase of the friction coefficient of Si3N4/ DLC is led by the plastic deformation of the asperities of the DLC films at high load. Finally,the experiment results are correspondingly matched to the theoretical calculation based on DMT model. Furthermore,this work provides a clue for the design of the friction pairs of the DLC films.