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Ph.D.

Physical vapour deposition (PVD) techniques used for the application of advanced surface engineering materials have been developed over many years, but only in about the last 10 years has the unbalanced magnetron sputtering (UBMS) PVD technique been developed and emerged as one of the most promising techniques for depositing reliable and high quality films used in industrial production. Hard coatings have been studied for many years for the purpose of improving the performance of various tools, mechanical parts, and engineering components. The most studied binary hard coatings (such as stoichiometric titanium nitrides and titanium carbides) and the ternary hard coating (such as titanium carbonitride) have been developed for wear resistance for many years. Although many investigations have been made into the production of coatings with stoichiometric phases, it is both scientifically and commercially interesting to investigate the production and reproducibility of the pure titanium sub-nitride Ti2N films. The first results in chapter 5 describe work carried out to investigate the effect of nitrogen and carbon concentration within the films and was a prelude to the main activity of the development of Ti2N films using commercial conditions. The work for Ti2N was carried out without substrate rotation in the UBMS coating process. The static deposition processes were studied to give a better understanding of the effect of partial pressures on the compositions of the Ti-N films. The phase development as a function of the composition of the films was investigated. The main contribution during this procedure was to achieve a suitable range of nitrogen partial pressure by which the films containing pure Ti2N phase were produced using a UBMS deposition technique. The nitrogen content of the film was very sensitive to variation in nitrogen partial pressure and the nitrogen concentration influenced the phases developed in the films. The reproducibility of the pure Ti2N phase was also discussed in this initial work. A series of extensive experiments were conducted to investigate the formation of Ti2N phase in the UBMS deposition processes using one to three fold rotations. The nitrogen partial pressure of the deposition process was basically determined from the results of the initial work. The effect of substrate rotation on the film composition during processing was studied. In general the film deposited using substrate rotation consisted of different composition using the same chamber condition in one process in which the nitrogen content of the coating increased from one fold rotation to three fold rotation. The film containing dominant eTi2N phase could be produced on a sample using three fold rotation in a process whilst the multiphase compositions (aTiN0.3 + eTi2N) were developed on the sample using the one and two fold rotations in the same process. Characteristics of the eTi2N films and the films containing multiphase compositions were investigated using transmission electron microscopy (TEM), scanning electron microscopy (SEM), glow discharge optical emission spectrometer (GDOES), X-ray diffraction (XRD), and a variety of mechanical testing instruments. The eTi2N films have very smooth surface, very dense and fine columnar structure, relatively high hardness, and excellent adhesion with the substrate. The drilling tests using coated high speed steel drills compared the coatings containing eTi2N phase with those containing a single TiN phase and showed excellent wear resistant results.6.

A study and comparison of two commercially available and competitive physical vapour deposition techniques has been made. Titanium nitride (the most widely used hard and decorative coating) has been deposited by both steered arc and the new Arc Bond Sputter (ABS) magnetron technique under a range of deposition conditions. The coatings have subsequently been analysed by a variety of methods and the results reported here. The steered arc technique has been identified as the better technique for everyday ease of use in producing mononitride and monocarbide coatings with good batch uniformity and reproducibility in terms of composition and microstructure. However, for versatility the ABS magnetron technique allows the possibility to vary multiple parameters and hence change coating properties at will, albeit with some difficulty to maintain stable and reproducible operation. In this respect, plasma uniformity is discussed and problems with water vapour contamination and gas flow regulation are highlighted and possible solutions suggested. The coating-substrate interface region is considered, and the merits of metallic interlayers and arc etching are compared. An interlayer achieves good adhesion only at an optimum thickness as confirmed in this work. The good adhesion afforded by the arc etch phase of both processes is addressed and the ion-surface interactions modelled using commercially available computer software. The improvement in adhesion on high speed steel is explained by sputtering of the substrate matrix leaving hard carbide particles standing proud of the surface. When deposition takes place, the carbides mechanically key the coating to the substrate surface, and also possibly act as physical blocks to interfacial crack propagation. A theoretical contribution to the explanation of preferred crystallographic orientation during coating deposition is proposed derived from experimental results, surface physics and semiconductor growth theory. This attempts to explain the flexibility of sputtering techniques to produce a wide range of orientations, and the reasons why arc evaporation almost always produces {111} orientated coatings. Finally, a consideration of a comparatively new analytical technique (Glow Discharge Optical Emission Spectroscopy) to the application of PVD coatings evaluation is addressed. The speed and versatility of this technique makes it strategically important in the future research, development and quality control of thin film production.

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