Axial distribution improvements of DLC film on the inner surface of a long stainless steel tube

The internal surface of a stainless steel AISI 304 tube, 200 cm in length and 10 cm in diameter, was coated with diamond-like carbon (DLC) using the Plasma Enhanced Chemical Vapor Deposition (PECVD) technique, using two group of experiments for the entry and exit of the gas flow to determine the effect of their position on the quality and thickness of the DLC film. First, the temperature rise along the tube surface was measured during the argon and acetylene plasma phase. Secondly, the PECVD experiments were analyzed to evaluate the coating for all arrangements used. Thus, the tube temperature, the film thickness, the structural changes and the friction coefficient were measured, using optical microscopy, an infrared Thermometer, a Raman Spectrometer and a pin-on-flat tribometer, respectively. Our measurements revealed DLC films with symmetrical and asymmetrical distributions along the tube. Raman and tribological characterization shown that the lowest I(D)/I(G) ratio and lowest friction coefficient were in the regions with thickest DLC films. The study indicates that DLC films may be grown by PECVD inside of long tubes that exhibit excellent thickness and friction characteristics when entry/exit points for the gas flow are placed at both ends of the tube. (AU)