Towards hard yet self-lubricious CrAlSiN coatings

• Hard yet self-lubricious CrAlSiVN coatings are developed.
• Incorporating vanadium into CrAlSiN structure refines crystal grains.
• Tribo-oxidized vanadium provides CrAlSiN coatings lubriciousness.

CrAlSiN coatings are of high hardness, excellent wear and oxidation resistance but lack of lubriciousness. Vanadium nitride (VN) is easily oxidized to form vanadium oxides and becomes lubricious under stress. Incorporating VN into CrAlSiN to form CrAlSiVN coating renders both hardness and self-lubrication in dry machining. This study investigates the effect of vanadium content on hard yet self-lubricious coating’s mechanical and tribological properties. The coatings are deposited on cemented tungsten carbide and Si wafer (1 0 0) substrates in an in-line magnetron sputtering system. Grazing incidence X-ray diffractometer, scanning electron microscopy, transmission electron microscopy, electron probe micro-analyzer, X-ray photoelectron spectroscopy and energy dispersive X-ray spectroscopy are employed to characterize the microstructures and chemistry. Nanoindentation and ball-on-disc tribo-tester are used in characterization of the mechanical and tribological properties. The coatings demonstrate lubriciousness of coefficient of friction with tungsten carbide from 0.55 down to 0.39 with acceptable loss of hardness (from ∼35 GPa down to ∼30 GPa).