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Title: Abrasive wear of bulk materials and hard coatings
Author: Allsopp, D. N.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 1999
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Thin coatings and other surface engineering techniques are widely used to improve the friction and wear properties of surfaces. However, current understanding of the behaviour of surfaces is relatively poor. Production methods are therefore to a large extent based upon empiricism. Many well-established materials characterisation tests are inadequate, and so novel techniques for the examination of surface layers have emerged, with the eventual aim of predicting the tribological performance of surfaces. One such technique is the micro-scale abrasive wear test, in which a ball is rotated against a specimen in the presence of a slurry of fine abrasive particles, producing a well-defined crater whose volume may be measured geometrically, allowing the wear coefficient of the specimen to be determined. It has been shown that the existing understanding of test is inadequate; further characterisation of the test has been performed. The effects of various parameters on the mechanism and severity of wear have been identified and explained by adaptation of existing models. Recommendations have been made for the optimisation of the accuracy and reproducibility of the test. The capability of the test to characterise thin coatings has been extended by shallow ball-crater testing which does not penetrate though the coating, thereby eliminating any influence of the substrate wear resistance. A number of different formulations of the wear equation, and a number of data analysis methods have been discussed, with the aim of minimising error. Since many surface coatings are exposed to high temperatures in service, the micro-scale abrasion test and the commonly used scratch test have been adapted for use at elevated temperatures in order to investigate changes in coating properties under these conditions. A new scratch test apparatus was designed and constructed for these tests. The behaviour of various PVD coatings has been investigated by these methods.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available