Improvement on uniformity of diamond-like carbon coatings inside metal tubes using high power pulse supply

Hollow cathode plasma-enhanced chemical vapor deposition (HC-PECVD) technique with high power pulse supply was employed to deposit multi-layer diamond-like carbon (DLC) coatings on the inner surface of 304 stainless steel (SS304) tubes. Pulse width of high power pulse supply was varied from 2 to 20 μs with constant frequency, negative bias voltage, and power to investigate the effects on the uniformity, microstructure, mechanical properties, and tribological performance of the deposited coatings. The results implying the uniformity of DLC coatings inside SS304 tubes can be improved significantly using the high power pulse supply. At the low pulse width, the uniformity of DLC coatings is outstanding along the axis direction of tube. At the high pulse width, the uniformity of DLC coatings became poor along the axis direction of tube as the plasma density and deposition rate are high; however, the mechanical properties and tribological performance are superior. Besides, the ion bombardment effect and the heating effect appear the competition relationship inside SS304 tubes with the increase of pulse width.