Wear mechanism maps for TiN-coated high speed steel

Abstract

Dry sliding wear experiments were conducted on PVD TiN-coated high speed steel (HSS) discs over a range of contact loads (5-200 N (0.25-10 MPa nominal contact pressure)) and sliding speeds (0.25-2.5 m s -1 ) against HSS pins using a pin-on-disc test configuration. Friction heating effects were monitored by recording bulk pin surface temperatures and correlated with wear rates and mechanisms for 3 μm thick TiN coatings. Steady state wear rate, wear mechanism and bulk temperature data were summarized on load versus sliding speed axes in the form of wear and bulk surface (T b ) temperature maps. Four TiN wear regimes were identified: (i) tribochemical polishing and rapid removal of the TiN by oxidation of TiN at loads below 10 N and sliding speeds below 0.5 m s -1 ; (it) mild wear of TiN coating asperities at loads below approximately 100 N and where T b remained below approximately 150 C; (iii) mild wear of TiN coating asperities at high sliding speeds and loads where severe wear, softening and transfer of the opposing HSS pin occurred at a critical T b of approximately 300°C, thereby minimising coating damage; (iv) rapid wear of TiN at T b between 150 and 200°C where sliding speeds remained below approximately 1.68 m s - 1 and loads were above 100 N.