Nitrogen doping of MoS_x thin films sputtered by reactive High Power Impulse Magnetron Sputtering

Incorporating nitrogen into non-stoichiometric molybdenum disulfide (MoS_x) thin films is a promising approach in order to improve the mechanical properties. Nevertheless, the adhesion between the film and the substrate is still challenging and the interaction between the mechanical and the tribological properties is not fully understood yet. Subsequently, reactive High Power Impulse Magnetron Sputtering (HiPIMS) is used to deposit nitrogen doped MoS_x thin films with different nitrogen amounts on 16MnCr5 steel. The interaction between the structural changes, the mechanical properties and the tribological behavior depending on the nitrogen amount is investigated. The results prove that an increasing amount of nitrogen significantly affects the structure and the tribo-mechanical properties of the thin films. X-ray diffraction analysis reveals a transformation from crystalline to amorphous with an increasing amount of nitrogen from (7.1  ±  0.3) at.-% to (19.5  ±  0.5) at.-%. This transformation is related to a suppression of the columnar microstructure as well as an increasing hardness and Young's modulus from (0.14  ±  0.02) GPa, and (5.28  ±  0.32) GPa for the undoped film, to (5.12  ±  0.32) GPa and (92.5  ±  6.2) GPa, for the film with the highest nitrogen amount. The results of the Rockwell indentation tests show that the films with a small amount of nitrogen exhibit an improved adhesion behavior. The wear coefficient can be reduced to a quarter of the value of the undoped MoS_x film, whereas coefficients of friction are at similar level of 0.2 in ambient air. Reactive HiPIMS has proven to be promising to deposit nitrogen doped MoS_x thin films on steel substrates, which reveal improved mechanical properties and an excellent transfer film built-up during the tribo-tests without failures.