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Title: A study of the interaction of chemical, thermal and mechanical factors in a lubricated sliding contact : thermally-activated wear theory
Author: Kwon, O. K.
Awarding Body: University College of Swansea
Current Institution: Swansea University
Date of Award: 1981
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The friction and wear behaviour in the sliding four-ball contact system has been investigated, using a non-additive base oil, SAE 10, as the test lubricant. Load, speed, and test duration were each varied and the friction behaviour was measured and then related to the flash temperature calculation in the contact. The results of flash temperature calculation indicate that the temperature locally in the contact approaches the melting point of the EN31 steel as the state of the wear in the contact increased markedly in the transition wear region. A controlled micro-etching technique was devised to permit analysis of the sub-surface region. There were clear indications that intense heating had occurred in the sub-surface layers of the worn contact region. Hardness measurements confirmed that the surface hardness increased as a function of the applied load and that embrittlement of the surface layers occurred, notably at the higher loads. The wear particles have been studied using Ferrography in conjunction with the optical and electron microscope, the X-ray probe analyser, and the image analysing system, Quantimet. Important information relating to the wear behaviour was obtained from examination of free metal, oxide, and polymeric particles. From the results of measurement and analysis, a new hypothesis concerning the thermally-activated wear process was proposed in which thermal decomposition of the lubricant is postulated. This activity releases the products of hydrogen and carbon. The former causes embrittlement, and hence, a tendency to fail in a fracture mode, while the latter causes an increase in the hardness of the surface layers. The hypothesis was tested by adding a small quantity of hydrogen scavenger into the test lubricant. By thus nullifying the effect of hydrogen, the friction and wear were reduced and there was about a threefold increase in hardness, with no indication of brittle fracture occurring in the surface. The implications concerning the nature of the wear and the associated controlling mechanisms are discussed.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available