Self-lubrication mechanism of chlorine implanted TiN coatings

Different from the conventional physical modifications, significant reduction of wear and friction in severe dry conditions can be accommodated to titanium nitride (TiN) coating via the chlorine ion implantation. High friction coefficient with μ=0.8-1.2 for the as-deposited TiN is reduced to be less than 0.2 at room temperature. Titanium mono-oxide (TiO) and oxides with oxygen deficiency or Magnèli phase with Ti_nO_2n-1, were formed inside the wear track of Cl-implanted TiN coating. Due to the shear deformability of titanium mono-oxide and crystallographic shearing planes in this Magnèli phase, vicinity of the Cl-implanted TiN surface can be elasto-plastically deformed, resulting in reduction of shear stress, wear and friction. Micro-X-ray photoelectron spectroscopy (XPS) measurement as well as high-resolution transparent electron microscopy (HRTEM), were an effective tool to describe local surface reaction taking place inside and outside of the wear track. Oxidation process of TiN during wear is drastically changed at the presence of Cl-atoms on the surface. Cl-atoms diffuse from the inside of TiN to the surface to accelerate the formation of titanium oxides, and to escape out of the system together with oxide debris. Both wear volume and friction coefficient, are preserved to be as low as or lower than diamond like carbon (DLC) coatings. This preferable tribological property comes from self-lubrication mechanism of the Cl-implanted TiN due to significant change of surface reaction by the effect of Cl-atoms.