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Title: Deformation of hard materials
Author: Giuliani, F. E.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2006
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Initial work has concentrated on studying the deformation processes in bulk single crystal samples. The hardness was measured by nanoindentation allowing plastic to flow to be studied without the complicating effects of cracking. To test a much greater range of flow stresses, a high temperature nanoindentation system was developed and tested. The flow patterns beneath the indents were studied by transmission electron microscopy with electron transparent sections through the indents, produced using focussed ion beam techniques. Observations of the deformation below indents formed at room temperature into CaAs show that deformation is dominated by twinning while at 300°C dislocation is dominant. Furthermore, there are also significant changes in the flow patterns between the two temperatures: at 300°C the material displaced by the indenter flows around the indenter to form pile up on the surface, which is similar to observations of flow pattens in metals, whilst at room temperature no pile up is observed, suggesting that all the displacedmaterial is accommodated below the indenter. The studies of multilayer systems were carried out on AIN / CrN and TiB2 / metal thin films. In the AIN / CrN system, an increase in hardness and moulus was measured in the multilayers. This has been correlated with changes in film structure and deformation behaviour. In the TiB2 / metal systems the deformation patterns were highly dependant on the ability of the metal layers to flow laterally. Furthermore, the measured properties are lower than might be expected. However, this was attributed to the highly porous structure of the coatings.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available