The study of the tribological properties of TiB2/Cr multilayered coatings over a wide temperature range

Abstract

The TiB2/Cr multilayered coatings were deposited on the 304 stainless steel substrates by a D.C. magnetron sputtering system. The mechanical properties and wide-temperature tribological performances of the coatings were carefully studied using scanning electron micrograph, X-ray diffractometer, Raman spectra, nanoindentation, residual stress tester and scratch tester. The results indicated that the mechanical properties including residual compressive stress, adhesion strength and fracture toughness of TiB2/Cr multilayer coating presented well, which could be attributed to the reason that the Cr interlayer absorbed part of the residual compressive stress through plastic deformation. Meanwhile, the multilayer coatings improved tribological performances because of the formation of lubricated oxides on the wear track in the temperature range of 25 °C–400 °C. The reaction between TiB2 and O2 occurred at high temperatures giving rise to the B2O3, which was a kind of high-temperature lubricant. The lowest friction coefficient of 0.48 ± 0.02 was revealed at 400 °C, whereas the wear rate was (10.1 ± 0.407) × 10−5 mm3/N·m. The upward wear rate for multilayer coatings was mainly due to a severe frictional oxidation reaction on the whole friction surface at high temperatures, making the surface of coating in the dynamic process of oxidation-wear-remove. The main wear mechanism of the coating was considered to be abrasive wear at room temperature, then it transformed into abrasive wear and oxidation wear at high temperature when the coating slid against Si3N4 ball.

Keywords

• Multilayered coatings
• Wide temperature range
• Tribological performances
• Mechanical properties
• Lubricating oxides