Ion implantation into boron suboxide : formation of boron-rich structures and related phenomena

DSpace/Manakin Repository

Show simple item record

dc.contributor.author Machaka, Ronald
dc.date.accessioned 2012-09-25T10:08:40Z
dc.date.available 2012-09-25T10:08:40Z
dc.date.issued 2012-09-25
dc.identifier.uri http://hdl.handle.net/10539/11980
dc.description Ph.D., Faculty of Engineering and the Built Environment, University of the Witwatersand, 2012 en
dc.description.abstract This thesis focuses on the boron suboxide B6O, a boron-rich super-hard ceramic material. With hardness values previously reported between 24 GPa and 45 GPa, B6O is one of the hardest known materials. Although first reports on boron suboxides date back as far as 1909 (Weintraub E., Transactions of the American Electrochemical Society, 16 (1909) 165), it is the B6O-based composites that have attracted considerable interest in recent years due to their enormous technological potential, especially as an alternative to polycrystalline diamond and polycrystalline cubic boron nitride for wear and abrasive applications. Investigations into the properties of B6O itself appear to have been neglected in favour of the improvement of densification and fracture toughness of the composites. The B6O samples used for the work reported in this work was hot-pressed was prepared under an argon environment at 1800 C and 50 MPa for 20 minutes followed metallographical preparation. The density of the hot-pressed compacts measured 2.44 g/cm3. The starting B6O powder material was supplied from the Fraunhofer Institute for Ceramic Technologies and Systems, Dresden. This thesis primarily seeks to generate and report as much practical data for polycrystalline B6O materials prepared by uniaxial hot-pressing as possible from a variety of characterization techniques. Firstly, the Raman spectra of hot-pressed B6O, which was until now poorly understood, was investigated using using a 514.5 nm green Ar+ laser excitation source. Secondly, the fundamental nature of some mechanical properties of hot-pressed B6O were investigated by means of Vickers and Berkovich indentation techniques. New approaches for data analysis, especially the investigations of the nanomechanical properties of hot-pressed B6O by Berkovich nanoindentation, were also suggested. Thirdly, the intrinsic hardness of hot-pressed B6O was investigated by means of a comprehensive inter-model comparison study. Fourthly, a combined experimental and simulation approach for determining mechanical properties of hot-pressed B6O by nanoindentation was also carried out, based on the outcomes of the study, the deformation response of the material under dynamic indentation was investigated at di erent stages using a custom developed finite element model. Finally, based on the preliminary ab initio density functional calculations of the structural properties of B6O conducted by Lowther showing that the presence of a high electronegativity interstitial in the B6O structure could enhance the strength of the bonding in B6O, fluorine ion implantation into B6O were conducted. The e ects to the structural and the nanomechanical properties of radiation damage induced by ion implantation was investigated. The possible formation of novel nanostructures in the ion-irradiated B6O matrix near-surface was also investigated. Results obtained from this study provides a vast amount of practical data for hot-pressed B6O materials as well as a number of novel analysis approaches for the extraction useful properties from the measured raw data. Firstly, using an automated background subtraction method, observable first- and second-order Raman spectra of B6O were obtained. A comparative analysis with previously reported spectra of other -rhombohedral boron-rich ceramic materials demonstrate a good agreement. Results also confirm the existence of highly resolved Raman modes measured at ambient conditions using a green Ar+ excitation source which is contrary to the conventional understanding. Secondly, results from the micro-indentation investigations indicate the measured microhardness exhibits indentation load dependence. A model inter-comparison study of indentation size e ects in the microhardness measurements of hot-pressed B6O is comprehensively discussed. Thirdly, the intrinsic hardness value of 30 GPa was deduced. Fourthly, a quantitative analysis approach was developed to simulate multi-cycling loading load-displacement curves from a single measured load-displacement nanoindentation curve. Based on the results, the nature of the indentation size e ect in the nanoindentation hardness as well as the intrinsic nanomechanical properties of hot-pressed B6O were established. Fifthly, a combined experimental and finite element method simulation approach for determining mechanical properties of hot-pressed B6O by nanoindentation was developed. Based on the outcomes of the combined experimental and simulation studies, the deformation response of the material under dynamic indentation was also investigated at di erent stages using a custom developed finite element model. Finally, results from the structural characterization of the ion implanted B6O material demonstrates the formation of novel nanostructures by means of the ion bombardment of B6O. In addition, the study presented here also seeks to investigate the e ects of the fluorine ion implantation on the near-surface nanomechanical properties of hot-pressed B6O. The principal conclusions that the study provide are both comprehensive practical data for B6O materials prepared by uniaxial hot-pressing. A number of properties, including the Raman spectra, the intrinsic hardness, and the radiation resistance and the e ects of radiation damage are reported in the thesis. en
dc.language.iso en en_US
dc.subject.lcsh boron en_US
dc.subject.lcsh composite materials en_US
dc.subject.lcsh boron composites en_US
dc.subject.lcsh ion implantation en_US
dc.title Ion implantation into boron suboxide : formation of boron-rich structures and related phenomena en
dc.type Thesis en


Files in this item

This item appears in the following Collection(s)

Show simple item record

Search WIReDSpace


Browse

My Account

Statistics