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Experiments on Nanostructured Carbon for Wear Resistant Coating Applications

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Abstract:
Exploiting the exceptional mechanical properties of nanostructured carbon for improving wear and erosion resistance of various surfaces is the main objective of the research presented in this thesis. In the first part, carbon nanofibers were investigated for their potential to toughen ceramic based coatings. In the second part, nanocrystalline diamond was investigated as a potential coating on tools for dry machining applications. Multiwalled carbon nanotubes (MWCNTs) and carbon nanofibers (CNFs) infiltrated with silicon nitride, using dichlorosilane and ammonia, to fabricate composite coatings. Fracture surfaces of these dense composites show that nanotubes pull out substantially more than nanofibers, which was attributed to the flexible structure and unique deformation mechanisms of nanotubes. MWCNT reinforced coatings were also nano-indented to evaluate their toughness, with the aid of detailed FEM analysis. It was estimated that nanotubes can contribute more than 10 MPa-m1/2 to the toughness by bridging of cracks, an increase of more than an order of magnitude over the silicon nitride matrix. Nanocrystalline diamond (NCD) holds significant promise as a low-friction, wear resistant coating. Microwave plasma of Ar/H2(2-10%)/CH4 (1%) was used to grow NCD on a Si substrates. Pin-on-disc testing of these films revealed that the coefficient of friction (COF) values started as high as 0.7, but then dropped to relatively low saturation values of 0.1 as the pin revolutions increased. This friction response was correlated with wear of the diamond surface and explained by systematic AFM topography analysis of the as grown surface and the worn surface. The decrease in COF was attributed to the decreasing frictional shear stresses with increasing contact spot size, based on Hurtado and Kim's theory. Furthermore, Raman spectroscopy of these coatings indicated that grain boundary chemistry has a substantial impact on the friction response of NCD in sliding contact with 319 Al alloys and also with Si3N4 ceramics.
Notes:
Thesis (Ph.D.) -- Brown University (2009)

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Citation

Kothari, Abhishek K., "Experiments on Nanostructured Carbon for Wear Resistant Coating Applications" (2009). Materials Science Engineering Theses and Dissertations, Engineering Theses and Dissertations. Brown Digital Repository. Brown University Library. https://doi.org/10.7301/Z0902264

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