Effect Of Equivalent Radius Of Indenter On The Radial Nanofretting Damage Of Monocrystal Silicon And α-CN_X Film

Monocrystal silicon (100) is an important structural material in microelectromechanical system (MEMS). Due to their excellent mechanical properties, amorphous carbon nitride (a-CNx) film and DLC film have been widely used as protective hard coatings in MEMS. Radial nanofretting frequently occurs in MEMS and may affect the reliability of MEMS. Therefore, the research on the radial nanofretting of monocrystal silicon and its coatings can not only enrich the basic knowledge on nanotribology, but also provide valuable suggestions on the nanofretting-resisting design in MEMS.By using a nanoindenter and 2μm spherical indenter, the indentation damage behavior of Si(100) andα-CNx film was studied. Following, the radial nanofretting behaviors of monocrystal silicon and a-CNx film were investigated by using three diamond indenters with various radii. Finally, the effect of sliding velocity on the damage of monocrystal silicon andα-CNx film was investigated by using a nanoscratch tester. The main conclusions can be summarized as following:1. Based on its excellent plasticity, the softα-CNx film can protect the substrate from damages in the radial nanofretting. With the increase in the number of nanofretting cycles, the radial nanofretting damages on Si(100) surface are mainly indentified as the radial cracks and fragments. However, the radial nanofretting damages onα-CNx film are characterized as three stages, namely as the buckling of the film, the initiation and propagation of the ring-like cracks and the radial cracks.2. Compared to the curvature radius, the equivalent radius of indenter plays a more important role on the nanofretting damages of material. As the indentation depth is shallower than the critical depth, the equivalent radius of Berkovich indenter is smaller than that of 2μm and 20μm spherical indenters. As a result, the damages on Si(100) andα-CNx film by Berkovich indenter are more serious than those by the other two indenters. As the indentation depth is deeper than the critical depth, the equivalent radius of 2μm spherical indenter is smallest. Damages under 2μm spherical indenter are the most serious. The contact stiffness of both 2μm spherical indenter and Berkovich indenter increases sharply in the initial nanofretting cycles, which induces an obvious work-hardening process of material. However, no working-hardening process is found during the nanofretting by 20μm spherical indenter. 3. The scratching speed, loading rate and scratching length reveal different effect on the scratch behaviors of monocrystal silicon andα-CNx film. Compared to loading rate and scratching length, scratching speed plays a much more important role on the scratching friction and damages.4. The scratch damages on DLC film experience three stages, namely as elastic deformation, fishbone-cracks and brittle spalling. Under the same applied normal load, the scratch damages on 50 nm DLC film are lighter than that on 20 nm DLC film. With the same thickness, the scratch-resisting prosperities ofα-CNx film are better than that of DLC film.