Ceramic/ceramic and ceramic/steel contacts under lubricated rolling conditions are studied. This work is of interest to ball bearing manufacturers as the use of ceramics in the design of these components has some advantages over traditional bearing-steel materials. Low density and increased stiffness are the mechanical properties which gas-turbine and machine tool manufacturers are most likely to realise. Much research over the past two decades on material structure, quality control and manufacturing techniques has produced a material which can seriously challenge bearing steel in ball-bearing design. This is especially the case for hybrid ball-bearings, ie ceramic balls with steel bearing races which are now used as standard components. The purpose of this study is to examine the rolling contact fatigue failure modes of ceramics. This study concentrates on silicon nitride as this material has most potential for use by industry. The primary reason for studying ceramic balls is because of interest in ball-bearing applications, hence a modified four-ball machine is employed which correctly models ball motions and precisely defines ball load. Experimental and theoretical kinematic analysis of ball motion during modified four ball machine tests is presented. The kinematic analysis reveals that in practice, lower ball tracking exists at high speeds. Test conditions of lubricated contacts under high compressive stress show delamination type failures. Delamination failures are classified in terms of propagation and initiation from scanning electron microscope observations. Residual stresses are measured on delaminated surfaces, which implies plastic deformation of the ceramic. Also, chemical analysis implies that disruption of silicon, nitrogen and oxygen levels may take place on delaminated surfaces. Experiments illustrating various fatigue failure modes using artificially pre-cracked ceramic balls in contact with a steel upper ball are presented.

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During firing, the deformation of ceramic articles under their own weight may be problematic particularly in the sanitary ware industry where articles are large. A model has been developed that predicts the viscoelastic deformation of a range of vitreous china testpieces during the firing process. The model constitutes a novel application of the transmission line modelling technique to viscoelastic deformation. The applicability of the model to the sanitary ware industry is addressed.

Two methods of measuring the dielectric properties of materials - matched termination and coaxial line resonance- have been developed and used to study the properties of two groups of nitrogen ceramics, namely, silicon nitrides and oxynitride glasses. In these methods advantage is taken of the wide frequency range, from 500 MHz up to about 9 GHz, covered by a single apparatus - the General Radio slotted coaxial line. Previous measurements in this Department have indicated the difficulties in the determination of the loss tangent of low to medium loss samples (tan Ỏ ~ 10(^-3) - 10(^-2)). The two methods developed reduced these difficulties. The applicability of these methods was assessed using known materials including the high loss liquids water and chlorobenzene, medium loss solutions of chlorobenzene in cyclohexane and the low loss solids polymethyl methacrylate and polytetrafluoroethylene. The silicon nitride ceramics were in various degrees of nitridation given by the weight gain which ranged from 38% for partially-nitrided to a maximum of 63.2% for the fully-nitrided samples. The dielectric constant at 1 GHz increased from 4.51 for fully-nitrided to about 9.9 for the 38% weight gain samples. The fully-nitrided material has a loss factor of 7.6 x 10(^-3); this increased to 1.85 x l0(^-1)as the weight gain decreased to 38%. These values have been extrapolated to 'zero weight gain' and compared with pure silicon for which the dielectric constant is 11.7 and the loss factor approximately 0.2. The oxynitrides have dielectric constants between 6.5 and 7.5 depending on the cation present and the percentage of nitrogen substituted for oxygen in the glasses. Є' increased in the cation order Mg, Y, Ca and increased with increasing nitrogen substitution in each cation series. The loss factor, however, depends not only on these cation types but also on the other constituents of the glasses. The dielectric constant of both the silicon nitride ceramics and oxynitride glasses fitted the Jonscher universal law of dielectric response (Є' - Є) w(^n-1), where the exponent n - 1 for all the samples. Similarly, the loss factor for these materials showed a frequency dependence Є" w(^n-1), again with n approximately 1. This is a limiting case of dielectric behaviour corresponding to a frequency independent loss where most dipolar processes have been eliminated.

It is known that a newly formed glass container will only possess a very small fraction of its theoretical strength. This suggests that damage occurs on the surface of the glass melt during the forming process due to glass to mould contact and hot glass handling. It might be expected that any damage inflicted on the surface of a glass article during manufacture would heal at the elevated manufacturing temperatures used, however this does not appear to be true. Therefore, the actual mechanism by which glass strength is reduced during forming needs to be fully understood and the work presented in this thesis addresses this problem. Experiments, therefore, have been carried out here which simulate the formation of glass articles using an experimental pressing rig by systematically altering processing parameters such as the mould material, surface fmish of the mould, pressing temperature and atmosphere. Processing parameters that are used industrially for the formation of glass containers were generally reproduced wherever possible in order to investigate the glass-to-mould interaction. The interaction of both a cast iron mould material and carbon-carbon composite materials with a soda-lime-silica glass were examined using the techniques of scanning electron microscopy, x-ray photoelectron spectroscopy and atomic force microscopy in order to determine the type and extent of surface damage formed. The surfaces of the pressed glass samples made were found to contain defects of embedded particles and indented dimples. The embedded particles found were usually due to bulk material transfer from the plunger material used. The texture found on the surface of the pressed glass samples was found to be directly affected by the surface fmish of the plunger. Pressing glass samples using a cast iron plunger at an initial plunger temperature below 450°C resulted in a randomly rippled 'chilled' surface. As the initial temperature of the plunger was increased, the surface texture of the pressed glass became a closer replica of the plunger surface. The use of vacuum assistance to form the glass samples also resulted in the surface of the pressed glass becoming a closer replica of the original plunger surface, even at lower pressing temperatures. The surfaces of the cast iron and carbon-carbon composite plungers appeared to have been affected by the initial plunger temperatures used. As the initial pressing temperature was increased, the amount of oxidation for both material types increased. In the case of the carbon-carbon composite materials investigated, both the matrix and fibres were found to have broken down at the pressing temperatures used. X-ray photoelectron spectroscopy, of the pressed glass surfaces and the plunger materials indicated that sodium ions had migrated from the glass melt to the plunger surface during forming.

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