Abstract: A nanoindenter is adopted to study the radial nanofretting behaviors of diamond indenters of different curvature radii on the monocrystal silicon surface and the damage characteristic. It is found that compared to the tip nominal curvature radius, the equivalent curvature radius of indenter at a certain identation depth plays a much more important role in the nanofretting damage of material. Under a peak indentation load of 50 mN, no obvious damage is observed on Si<100> after 200 nanofretting cycles by 20 μm spherical indenter. Even with a relatively smaller curvature radius, 150 nm Berkovich indenter induces the weaker nanofretting damage than 2 μm spherical indenter on Si<100>. Analysis indicates that the equivalent half cone angle of Berkovich indenter is 70.32°，which is much larger than that of 2 μm spherical indenter, 42.50°. As the indentation depth is larger than 300 nm, the equivalent curvature radius of Berkovich indenter is larger than that of 2 μm spherical indenter. As a result, the contact area of Berkovich indenter will be larger and nanofretting damage will be weaker. The results also indicate that the contact stiffness of both 2 μm spherical indenter and Berkovich indenter increases sharply in the initial nanofretting cycles, which induces an obvious work-hardening process of material. However, no work-hardening process is found during the nanofretting by 20 μm spherical indenter.

Key words: Curvature radius of indenter, Monocrystal silicon, Nanofretting, Nanotribology, Radial nanofretting, exhaust hood, flow guide, quadratic regression orthogonal experimental, static pressure recovery coefficient, steam turbine