Friction and wear characteristics of a Ti-containing diamond-like carbon coating with an SRV tester at high contact load and elevated temperature

The friction and wear characteristics of a Ti-containing diamond-like carbon (Ti-DLC) coating have been evaluated with a Schwingungs Reibung und Verschleiss (SRV) tester when reciprocating sliding against a steel ball and a CrN-coated pin at high contact load and elevated temperature under a boundary-lubricated condition. The Ti-DLC coatings exhibit a friction coefficient of 0.06-0.12 and a wear rate of 1.99×10^-10 to 9.5×10^-7 mm³/N m, depending on the counterfaces, load and temperature. The Ti-DLC/ CrN-coated pin pair shows a low friction coefficient than the Ti-DLC/ steel ball pair under the identical wear conditions. Increasing the test temperature reduces the coefficient of friction and, however, clearly increases the wear rate of the Ti-DLC coatings at 20 N. At 50 N and 150 °C, the Ti-DLC coating was removed completely and the wear was applied to the substrate. At below 100 °C, the wear mechanism of the Ti-DLC coatings is dominated by surface polishing effects. At 150 °C, brittle fracture, delamination, partial graphitization, and tribo-chemical reactions are found in the tribo-contact areas. The formation of iron oxides on worn surfaces of the Ti-DLC coatings at 150 °C is attributed to the dissolved oxygen in the oil lubricant and the tribo-chemical reactions. Furthermore, these friction and wear data have been compared quantitatively with pure DLC coatings and multilayered VTiN coatings under the identical wear conditions.