Tribological behavior of micro-indented 100Cr6 steel surfaces in dry contact conditions

Abstract

The aim of the present work is to investigate the tribological behaviour in dry conditions of a 100Cr6 steel, whose surface was textured using microindentation techniques. Specifically, dimples were created on the surface of a sphere using an automatic Microhardness tester equipped with a Vickers indenter, setting a load of 0.5N. Friction tests were performed at different speeds considering surfaces with two different Void Ratios (VRs). Both textured and untextured spherical surfaces were tested using a ball-on-disc tribometer. In addition, the effect of dimple size was evaluated by producing Vickers indented surfaces at a load of 5N per each indentation, while keeping the VR values unchanged and testing the frictional properties of such surfaces at a fixed speed of 4.18 mm/s. Textured surfaces were also characterized, before and after the tribological tests, in terms of surface microgeometry and nanohardness, using a light microscope, a scanning electron microscope, an atomic force microscope, a contact profilometer and a nano-indenter. Notably, compared to the untextured samples, the microindented samples exhibited a much lower Coefficient of Friction (COF), with a friction reduction compared to the untextured case ranging from 45–65%, depending on the VR values. We noted that the adoption of large dimples allows the reduction of the COF, already at smaller VR value but, in such a case, the presence of bulges at the edge of the dimple worsens the wear resistance of the counter-surface. The local measurement of strength by nanoindentations allowed to clarify that the friction reduction is determined by the work hardening effect produced by the microindentation texturing. The proposed approach can be applied using specific tools to effectively and selectively affect the friction behaviour of components, during its use or its production (for example in stamping operations).