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Title: Solid particle erosion of freestanding CVD diamond
Author: Davies, A.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2002
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The erosion rate of CVD diamond was ascertained using various sized erodents, impacting at different velocities. The relative sizes of the contact area and the size of the grains affected the erosion rate. Since the contact area increased with erodent size and impact velocity, both the sand size exponent and the velocity exponent were dependent upon the size of the grains. This result confirms that the ratio of the contact area to the microstructure is important. CVD diamonds often exhibit small fractures near to grain boundaries. These fractures usually contain graphitic or amorphous carbon that has become trapped during growth. These "micro-features" are discussed in Chapter 4, and the erosion rate of CVD diamond was obtained at regions of different micro-feature densities. The change in erosion rate caused by different micro-feature densities was small, much smaller than that caused by different grain sizes. This was because there were few micro-features, and even fewer that were close enough to the surface to have an affect. They are shown to contribute to fracture progress on the growth side, but have limited effect on the nucleation side. The erosion rate of the nucleation side is dominated by the more numerous grain boundaries. The erosion rate of mechanical grade CVD diamond is experimentally determined to be lower than optical grade CVD diamond. The main difference between the two grades is a higher concentration of dislocations in the mechanical grade. However, the erosion erosion rates of CVD diamonds with very different dislocation densities are shown to be similar. A four-point bend test is used to determine the fracture toughness of mechanical grade CVD diamond, and it is shown that this parameter is higher for the mechanical grade CVD diamond. The low erosion rate of mechanical grade CVD diamond results from higher fracture toughness, but the reason for this is yet to be understood. It is suggested that micro-features may play a significant part in the lower fracture toughness of optical grade CVD diamond. However, Raman spectroscopy has been used to show that non-diamond carbon is present in both grades of CVD diamond.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available