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The utilization of silicon based polymers as a source of amorphous non oxide ceramics obtained upon pyrolytic treatment of them is increasingly gaining attention in research and is currently expanding into the field of commercial products. This work is focused on the near net shaped fabrication mechanical and tribological properties of a polymer derived Si/C/N system. Small sub millimetre thick ceramic test discs and bars were fabricated by casting of polysilazane and/or polycarbosilane precursor mixtures into elastomeric polydimethylsiloxane forms thermal cross linking and subsequent pyrolysis. Additional carbon was introduced on the molecular level using triphenylvinylsilane as the precursor its cross linking with the polymers via hydrosilylation prohibits phase separation of graphite within the amorphous matrix. The characteristic strength of nearly 700. MPa along with stable low friction coefficients in sliding against similar polymer derived ceramics testifies to their potential in micro electro mechanical system applications. © 2012 Elsevier Ltd.

Highly homogeneous Ni–P/SiO2 nanocomposite coatings were prepared by electroless deposition from composite baths containing well dispersed SiO2 nanoparticles. The particle concentration in the coatings increases gradually with the SiO2 concentration in the bath and reaches an observed maximum of 25 vol.% at a bath concentration of 10 g/l. Tribological measurements of the heat treated coatings indicate that while the hardness of the coating is decreased compared to that of the Ni–P coating without particles, an improvement in Pin-on-Disk wear resistance up to a factor of 2 can be achieved. The aspect ratio of the wear track of samples heat treated above 270 °C is found to increase with the concentration of nanoparticles in the coatings. This observation indicates that the nanoparticles also modify the wear behavior of the coatings.

In this work, the ability of ashless anti-wear additives to form protective tribofilms on diamond-like carbon (DLC) and steel surfaces was investigated and compared to the reactions of ZnDTP. Reciprocating sliding tests were performed under mild tribological conditions for steel/steel and DLC/DLC contacts to avoid wearing through the DLC coating. A comparison of the friction behavior of ZnDTP with two ashless additives, a butylated triphenyl phosphorothionate (b-TPPT) and an amine phosphate (AP), indicated that the latter additive behaved in a different manner to the first two. b-TPPT shows the lowest friction coefficient for DLC/DLC contacts whereas the AP give the lowest friction coefficient for steel sliding against steel. AFM and ESEM were performed to analyze the surfaces and showed the build up of tribofilms from ZnDTP and b-TPPT onto both the steel and DLC surfaces. No evidence of such a film formation on DLC was observed when the AP were used.

Increasing use of DLC coatings in oil-lubricated, mechanical systems has led to a great deal of interest in optimising the interactions between lubricant additives and coatings. We have looked at the formation of a tribofilm from ZnDTP on diamond-like carbon (DLC) when sliding in oil against DLC on a polished steel substrate under very low wear conditions. It was found that the tribofilm formed in the absence of iron adhered very weakly to the surface and could be removed by washing in an ultrasonic bath. The wear was too low to be detected with laser profilometry. AFM imaging of the surfaces of steel and DLC after sliding of steel/steel and DLC/DLC showed that the tribofilm formed on DLC had a very different morphology to that formed on steel. EDX was used to demonstrate that the tribofilm contained zinc, sulphur and phosphorus. ToF-SIMS measurements showed that iron was neither present at the DLC surface nor in the tribofilm.

A modified Shell four-ball apparatus was used to determine failure mechanisms and estimate time to failure of hybrid ball bearings using silicon nitride and zirconia balls. The machine was set up to hold a hybrid bearing containing three ceramic balls, instead of the usual 14 in order to increase contact pressure. Five kinds of silicon nitride ceramics, which differed in terms of surface roughness, porosity as well as the amount and chemical composition of additives were investigated. The goal of this study was to establish a quality criterion for silicon nitride for industrial use in hybrid ball bearings. Lifetime and failure mechanisms varied between the five bearings with silicon nitride balls and a dependance was found on the porosity and chemical composition of the materials, whereas surface roughness did not seem to influence their performance.