Carbon coatings on tools for industrial applications

Abstract

The build-up of intrinsic stress in carbon thin films deposited by vapour deposition is a major cause of delamination. The delamination issue is one of the main reasons preventing the wider application of carbon vapour deposited films. In this thesis, we described a study of single and multilayer thin films of carbon. Under certain deposition conditions, we were able to produce thin films free from delamination. In our preliminary study of carbon films on silicon wafers, two methods of deposition were used: (1) a Filtered Cathodic Vacuum Arc (FCVA) system with both negative DC (up to 3 kV) and negative pulsed bias (15 kV, 20 μs pulse at 300 Hz) and (2) a Radio-Frequency (RF) plasma system with negative pulse bias up to 30kV, 100μs at 60 Hz applied to the substrate. Both single and multilayer structures of carbon films were examined using the Ultra-Micro Indentation System (UMIS), Surface Profilometer (Tencor P10), Raman Spectroscopy, Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). With the aid of SRIM 2003 simulation program, the ion penetration depths into materials were also studied. We found that the carbon ion penetration depth obtained from the experiment was in agreement with the model developed from SRIM 2003 program. The model helped us predict the behaviour of ion penetrating depth between different materials. Based on these results, the optimised film structure with high hardness and elastic modulus were coated on top of Titanium Nitride (TiN) General Purpose Twist (GPT) drill bits. The Rockwell hardness indenter was used to examine films hardness and determine the films adhesion strength. The hardness of the multilayer structures ranges from 50 HRC to 75 HRC while for best adhesion strength the multilayer structure that gives a hardness of 70 HRC was chosen. There were two systems used to deposit the carbon multilayer structures on top of TiN GPT drill bits: (1) the FCVA with rotational substrate holder and (2) the Titanium Gold (TG) with 3 x 3 axes of rotations. The carbon coated TiN GPT drill bits were superior in life performance when tested against the uncoated TiN GPT drill bits. A process has therefore been developed which achieves adherent carbon coatings which is ready to be implemented in industrial cathodic arc deposition equipment. The coatings are promising for cutting tools especially those used with non ferrous metals.