Vanadium nitride and titanium nitride coatings for anti-galling behavior in ironing of aluminum alloy cups

• The 225W–TiN coating exhibits high aluminum adhering resistance.
• The surface roughness has a crucial influence on the galling properties of a coating.
• Surface roughness and metal compatibility are major factors affecting adhering resistance.
• The cups ironed by the 225W–TiN coated die were superior than those from an uncoated die.

The anti-galling behavior of vanadium nitride (VN) and titanium nitride (TiN) coatings were investigated. VN and TiN coatings were deposited on JIS-SKH51 high-speed steel substrates by direct current magnetron sputtering. The coatings were characterized for phase composition using X-ray diffraction (XRD), hardness using nano-indentation and load-to-failure between the coating and substrate using scratch testing. Ring-on-disc testing was conducted to evaluate the tribological properties between AA1050 aluminum alloy ring sliding against SKH51 discs (both uncoated and coated discs) under a lubricating condition. The coated disc samples were cathodic arc TiN, 225W–TiN, 265W–TiN, 225W–VN and 265W–VN. Imaging and chemical analyses of the wear tracks were performed using a scanning electron microscope equipped with energy dispersive X-ray spectroscopy. The chemical analysis results of wear tracks showed that aluminum did not adhere to the 225W–TiN surface as readily as the other coated samples, as evidenced by the lowest amount of aluminum transfer. Results of the transition load for adhesion revealed that all of the coated surfaces improved the adhesive wear resistance i.e., resistance to aluminum adhering on the surface, compared with the uncoated surface. The 225W–TiN coating was further evaluated using an aluminum cup ironing process. The surface quality of the cups was found to be dependent on the Al transfer to the die surface. The cups ironed by the 225W–TiN coated die were superior to the cups obtained from an uncoated die.