Thick DLC films deposited by PECVD on the internal surface of cylindrical substrates

Abstract

A new and exciting technique for performing DLC deposition on the inside of cylindrical substrates, in particular pipes, will be described. Using the hollow cathode effect (HCE), a high density plasma can be generated within such cylindrical substrates by using Plasma Enhanced Chemical Vapor Deposition (PECVD). As the pipe itself is the vacuum chamber, such high density plasmas can be maintained by using asymmetric bipolar direct current (DC) pulsed power. Very high deposition rates can thus be achieved of the order of 1 μm/min. The coating thickness can be tailored for a specific application and is typically from 5–70 μm. A hydrocarbon precursor (C 2H 2) is used to deposit thick DLC films which are inert and have a high corrosion resistance. Adhesion to the metallic substrate is improved by adding silicon to the DLC layer. These films also have excellent erosion and wear resistant properties and the process can be optimized depending on what film properties are most vital for whatever application the coating is required for. Corrosion and wear resistance are also improved by having a pure DLC layer on top of the deposited structure. The actual process and deposition system will be described in detail as well as how the technology works and how such high density plasmas can be maintained for various lengths and diameters of pipe. Testing of such novel DLC films was done by various techniques and results will be shown of hardness, adhesion, layer thickness, wear and corrosion resistance. A vast number of applications can greatly benefit from this novel process, on both a large and small scale. Examples of such applications would be industrial piping, offshore drilling, chemical delivery systems, gun barrels and medical devices.