Engineered surfaces for enhanced performance using thin film coating

Abstract

In the present study, two surface engineering technologies have been used for distinctively different purposes. Whilst nickel/aluminium has been deposited using unbalanced magnetron sputtering for thermal barrier applications, a separate investigation was carried out involving the deposition and characterisation of diamond like carbon (DLC) coating using plasma enhanced chemical vapour deposition (PECVD).
Unbalanced magnetron sputter ion plating at various flow rates, magnetron power and substrates has been used to deposit novel intermetalic NiAI and nitrogen doped NiAI thin films. These have been characterised using surface stylus profilometry, energy dispersive spectroscopy (EDAX), X-Ray diffraction (XRD) and atomic force microscopy (AFM). Scratch tester (CSM) combined with acoustic emission during loading have been utilised in order to compare the coating adhesion. Acoustic emission was used during the indentation process to determine the critical load under which the film begins to crack and/ or break off the substrate. The average thickness of the films was found to be approximately 1 pm. EDAX data revealed that all of the NiAl and nitrogen doped NiAI thin films exhibited near equiatomic NiAI composition with the best results being achieved
using 300 Watt DC power for Ni, and 400 Watt DC power for Al targets respectively. X-Ray diffraction spectra revealed the presence of the 3 NiAI phase. AFM results films on glass samples exhibited a surface roughness of :5 100 nm. The nanoindentor results for coatings on glass substrates displayed hardness and elastic modulus of 7.7 GPa and 100 CPa respectively. The hardest coatings were obtained with 10% of nitrogen. Scratch test results indicated that the best adhesion was achieved at 300 W for Ni, and 400 W for Al targets compared to that of samples with other power values.
DLC and Ti doped DLC films using Titanium Isopropoxide (TIPOT) were deposited at various flow rates, bias voltages and substrates using PECVD. The as-grown film thicknesses were in the thickness range of 90-1 00 nm and were dependent on the TIPOT flow rate. As the flow rate of TIPOT was increased the average roughness was found to decrease in conjunction with the film thickness. The 10/10 ratio obtained from Raman spectra decreased when the bias voltage on the stainless steel substrates was increased. This indicates an increase in the graphitic nature of the film deposited. In addition, SIMS analysis
showed that the Ti peak became much more pronounced at TIPOT flow rates above 25 sccm. On the glass substrates the ID/to ratio increased when the bias voltage was increased indicating a greater degree of diamond like character.
For a different set of experimental conditions, the as-grown films were of the order 200-400nm. When the bias voltage was altered from 100 to 400V the thickness decreased and Raman 'D'1G ratio increased with increasing bias voltage on the glass substrates. However, in contrast, on the stainless steel substrates the 1D110 ratio decreased with bias voltage. For both of the coatings, the contact angle of the films decreased with increasing bias voltages.