Analysis of wear mechanisms in low-friction AlMgB14-TiB2 coatings

Recent developments in coating science and technology offer new opportunities to enhance the energy-efficiency and performance of industrial machinery such as hydraulic fluid pumps and motors. The lubricated friction and wear characteristics of two wear-resistant coatings, diamond-like carbon and a nanocomposite material based on AlMgB14-50 vol.% TiB2, were compared in pin-on-disk tribotests using Mobil DTE-24™ oil as the lubricant. In each case, the pins were fixed 9.53 mm diameter spheres of AISI 52100 steel, the load was 10 N, and the speed 0.5 m/s in all tests. Average steady-state friction coefficient values of 0.10 and 0.08 were measured for the DLC and nanocomposite, respectively. The coatings and their 52100 steel counterfaces were analyzed after the tests by X-ray photoelectron and Auger spectroscopy for evidence of material transfer or tribo-chemical reactions. The low-friction behavior of the boride nanocomposite coating is due to the formation of lubricative boric acid, B(OH)3. In contrast, the low-friction behavior of the DLC coating is related to the relatively low dielectric constant of the oil-based lubricant, leading to desorption of surface hydrogen from the coating.