Deposition and characterisation of (Ti,Zr) based hard compound and multi-layer PVD films.

Industrial recognition of the importance of optimising engineering component performance has recently led to a significant increase in the use of surface coating technologies. An important process for the production of such coatings is Physical Vapour Deposition (PVD) which has proved to be a consistent, reliable and improving technique for industry. In the area of advanced wear resistant coatings however, fundamental research to improve deposition efficiency and enhance coating performance has been required. This thesis describes research investigating the following three areas: A series of experiments was carried out to study the design, metallurgy and performance of TiZr, ZrMo and TiMo segmented targets for use in steered cathodic arc evaporation and unbalanced magnetron sputter PVD techniques. A hot isostatic pressing technique was used to manufacture a range of prototype targets by diffusion bonding of appropriate metallic segments to controllable depths. In steered arc evaporation trials, a deleterious evaporation phenomenon occurred at segment interfaces when the cathode spot traversed from high vapour pressure to low vapour pressure materials. Analysis of the spot motion has led to the proposal of a simple model. Reactive unbalanced magnetron sputtering trials successfully produced a range of TiZrN, TiMoN and ZrMoN coatings of compositions in good agreement with Monte-Carlo simulation predictions. However, preferential poisoning of the high reactivity metal segments on TiMo and ZrMo targets was found to occur during high N[2] partial pressure processes. A comparative study of unbalanced magnetron sputtering, steered arc evaporation and the hybrid arc-bond sputter technique has been made during deposition trials on the ternary TiZrN hard coating system. Examination of the influence of two process parameters, substrate bias voltage and nitrogen partial pressure, on the mechanical and physical properties of TiZrN coatings is also reported. Stoichiometric TiZrN films were generally found to exhibit a single phase, face centred cubic structure with lattice parameters which followed Vegard's law. Alteration of the elemental composition of the alloy could be achieved by altering the power to individual magnetron cathodes or varying the current of the arc discharge during co-deposition. Solid solution strengthening mechanisms produced high hardness values (2500-3600H[k]) which maximised as the alloy composition approached Ti[0.6]Zr[0.4]. Further studies have been undertaken where Al was partially substituted for Zr within the lattice to enhance oxidation resistance properties and a range of fully adherent TiAlZrN quaternary films on high speed steel substrates were produced. The development of an original technique for industrial scale fabrication of a range of hard, low period (<150A) multi-layer PVD thin films is outlined and the effects of substrate rotation velocity, type of rotation (1-fold or 3-fold) and deposition rate have been investigated. The high level of lattice mis-match and substantial differences in dislocation line energy and shear modulus has given rise to TiAlN-ZrN films exhibiting Knoop micro-hardness in excess of 4000H[k]. Bulk and micro-analysis techniques have indicated a reproducible lamella coating structure can be formed, with accurate control of the layer period. Excellent levels of coating adhesion were implemented by a metal ion etch substrate pre-treatment and the deposition of a sputtered base layer and films exhibited relatively low surface roughness and high density. A coating strategy, based upon the reactivity of the individual target materials and the characteristics of arc evaporated and magnetron sputtered vapour fluxes, has been determined which provides high flexibility in the coating elemental composition. The investigations clearly indicate that the multi-layer coating methods utilised allow the deposition of 3rd generation films without a productivity loss in comparison to 1st generation and 2nd generation hard coatings.