Tribological behavior of sputtered boron carbide coatings and the influence of processing gas

Boron carbide thin coatings were deposited on silicon wafers by DC magnetron sputtering using a B4C target with Ar as processing gas. Various amounts of methane gas (CH4) were added in the deposition process to better understand their influence on tribological properties of the coatings. Reciprocating wear tests employing an oscillating friction wear tester were performed to investigate the tribological behaviors of the coatings in ambient environment. The chemical characteristics of the coatings and worn surfaces were studied using X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). It revealed that CH4 addition to Ar processing gas strongly affected the tribological properties of sputtered boron carbide coating. The coefficient of friction was reduced approximately from 0.4 to 0.1, and wear resistance was considerably improved by increasing the ratio of CH4 gas component from 0 to 1.2 vol.%. By adding an optimal amount of CH4 (∼1.2 vol.%) in the deposition process the boron carbide coating exhibited the lowest friction and highest wear resistance.