A thesis submitted to the Faculty of engineering. University of Witwatersrand.
Johannesburg, in fulfilment of the requirements for the Degree of Doctor of Philosophy
Pretoria, 1995 / This thesis describes a study of the friction and wear characteristics of a range of oxide and
silicon-based ceramics sliding against AlSI 440C stainless steel, as well as various sliding
combinations of two types of De Beers polycrystalline diamond (PCD), namely Syndite and
Syndax, To facilitate the former work, a high-speed reciprocating sliding test machine with
computerized data acquisition and control was developed.
It was confirmed that under water-lubricated sliding, the oxide ceramics (alumina, PSZ, 3YTZP,
and Ce-TZP) showed higher friction coefficients and Weal' rates than the silicon-based
ceramics (Sialon and silicon nitride). This was related to different levels of adhesion and the
formation of metallic transfer films. For the zirconia ceramics, increased transformation
toughening was associated with increased surface fracture damage and metallic film formation.
In general, the metallic transfer films were beneficial, protecting the underlying ceramic and
dominating the friction and wear behaviour. The superior performance of the silicon-based
ceramics was related to the formation of lubricious tribofilms containing silicon oxides and
hydroxides.
Experiments with synthetic mine water as lubricant demonstrated that the presence of
significant amounts of chloride and sulphate in the water generally reduced friction and wear.
This was tentatively explained in terms of reduced adhesion and the promotion of iron oxide
and hydroxide formation. It is suggested that the influence of sulphate may be more
important in thi'3 regard than that of chloride.
The tribological behaviour of self-mated Syndite PCD sliding couples is dominated by the
formation of Co-rich trlbofilms, which nrc associated with increased friction coefficients and
reduced load carrying capacity (LCC). Syndax, which employs silicon as the binder phase,
shows lower friction coefficients anti higher LCe under both dry and water-lubricated sliding
conditions. Mixed Syndax/Syndite couples show superior performance to self-mated Synditc
tinder dry sliding conditions, but 110 improvements in the presence of water. The former
effect is related to the preferential removal of Co 11'0111 the Syndite surface to the Syndax / GR 2017
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/21731 |
| Date | January 2017 |
| Creators | Damn, Oliver Frank Rudolf August |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | Online resource (229 leaves), application/pdf |
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