Strength measurement and rupture mechanisms of a micron thick nanocrystalline MoS2 coating using AFM based micro-bending tests

Abstract The present study focuses on the measurement of mechanical properties of a 1.1 µm thick nanocrystalline MoS 2 coating deposited by magnetron sputtering with a particular interest in the strength of the coating. Mechanical strength is one of the most important properties to best predict failure of the coating, especially in the case of dry contact lubricated systems in which the coating of interest is often used. An Atomic Force Microscope based micro-bending experiment was developed to measure the rupture strength of MoS 2 micro cantilever-beams directly milled in the coating using a Focused Ion Beam. Rupture strength of the MoS 2 coatings was measured to be 728 ± 88 MPa. Comparisons with nanoindentation were used to validate the micro-bending technique via the statistically indifferent measurement of the Young's modulus: 63.1 ± 5.0 GPa and 64.5 ± 4.0 GPa respectively. In depth study of the fractured beam surface and the microstructure of the coating revealed that the surface roughness and the crystallite size can be directly correlated to the rupture pattern. The crack was additionally shown to propagate within the nanocrystalline network existing in the coating. Parallels with the tribological behavior of the coating are drawn and further confirm the lubrication mechanism described in previous studies.