This thesis contains the results of a study focused on cubic carbide and carbonitride grain growth retardation in hardmetals. Large additions of VC, or VC and TiC, or (W,V)C were made to the WC-Co hardmetal, which was then sintered in vacuum or nitrogen. The effectiveness of Ti as the grain growth inhibitor, and the influence of nitrogen sintering on grain coarsening were investigated using transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffractrometry (XRD) and atom probe field ion microscope (APFIM). Analysis of vacuum-sintered WC-VC-Co revealed that the cubic carbide grains have a core-rim structure. Ti was found to be a core-rim inhibitor in vacuum-sintered WCVC- TiC-Co. The average cubic carbide grain size distribution for the vacuumsintered materials was narrowed in the Ti-containing hardmetal. The nitrogen-sintered WC-VC-TiC-Co consisted of two phases of cubic carbonitride, one with high Ti-content and the other with high (W,V)-content. The surface region of the nitrogen-sintered WC-VC-TiC-Co was covered with a cubic carbonitride phase. Similar phenomena was observed in nitrogen-sintered WC-VC-Co where two types of carbonitrides were found, those with high V-content and the others with low Vcontent. A gradient zone, consisting of fine WC grains in a Co-rich binder and free from cubic carbonitride grains, was created in the surface region. The nitrogensintered materials consisted of a narrow grain size distribution. The use of (W,V)C as a starting powder affected the mechanical properties of the material with the WC-(W,V)C-Co material being the hardest of those produced in this study. Addition of (W,V)C powder to WC-Co was shown to be the most effective way to limit the cubic carbide grain size during sintering and produce a hard material. The cubic carbide grain size in the material produced this way was the smallest of all studied.

Thesis (Ph. D.)--University of Sydney, 2002. / Title from title screen (viewed Apr. 24, 2008). Submitted in fulfilment of the requirements for the degree of Doctor of Philosophy to the School of Physics, Faculty of Science. Degree awarded 2002; thesis submitted 2001. Includes bibliographical references. Also available in print.

BaBibliography: pages 88-92. / A variety of ceramic and ultrahard materials have been subjected to both solid particle and cavitation erosion. The materials tested include three grain sizes of alumina, stabilised zirconias, sialon, cubic boron nitride and polycrystalline diamond, and these have a range of microstructural, physical and mechanical properties. The damage modes are described for the two types of erosion and the results are critically discussed. It has been shown that different properties and microstructural features control the respective types of erosion. Hardness is the critical property which controls material loss during solid particle erosion. Cavitation erosion in contrast is less sensitive to hardness, but is extremely defect sensitive and preferentially attacks weak or damaged regions on the target. Grain size and shape, and th.e properties of the grain boundary or intergranular phase exert a strong influence on both types of erosion. It has in addition been concluded, that a propensity for a stress induced phase transformation, such as that exhibited by stabilised zirconia, will benefit the resistance of a ceramic to erosion. Ultrahard materials generally outperform the structural ceramics that were tested. While it was not possible to ascertain the effects of grain size conclusively, a large extent of intergrowth between the crystallites during manufacture appears to be beneficial to erosion resistance.

A series of boron suboxide films with hardness higher than 40 GPa was prepared and characterized. The correlation between OB ratio and mechanical properties, both hardness and elastic modulus were analyzed. Our studies on beta r-B, B2O3, surface oxidation of betar-B, and B6O illustrate that an XPS peak shift can be caused by a change in chemical state and bonding configuration. The shifts of B 1s peaks provide some good evidence to substantiate this conventional wisdom of XPS. We have applied this concept to enrich our XPS studies of boron and BxO y, and indeed found an intriguing variety of surface and interfacial physical conditions of those samples. / In our study, three boron nitride (BN) samples, the c-BN, h-BN and a-BN were prepared to serve as the standard specimens. And also, a series of thick BN films with different cubic phase content were prepared using a dual-ion beam assisted deposition (DIBAD) system. A quantitative method to measure the various phases content in BN film by the deconvolution of the energy loss features of N 1s signal was established. The feasibility of this method was proved by comparing the results with the results from FT-IR. To our understanding, this method has never been reported. / Many mechanical applications constantly demand superhard materials. Commonly a material is qualified as "superhard" when its microhardness exceeds 40 GPa. Therefore, great efforts have been made to search for other materials with high hardness in the past several decades. In the design of superhard materials, boron is a peculiar element/constituent. c-BN that possesses the zinc-blende structure shows numerous highly desirable mechanical properties, especially the high hardness and chemical inertness. Boron often exhibits three-center two-electron bonds in addition to the common two-center two-electron bonds. This overall bonding configuration must be very effective as shown by the high hardness of solid boron at 35 GPa. When impurities with more valence electrons than boron are added to pure boron, the overall mechanical strength can be further enhanced. By incorporation of oxygen, a family of hard boron suboxide compounds is thereby formed such as B6O. / Zheng Bin. / "August 2005." / Adviser: Chan Man Chor. / Source: Dissertation Abstracts International, Volume: 67-11, Section: B, page: 6427. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2005. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts in English and Chinese. / School code: 1307.

Ab initio plane wave based density functional calculations within the generalised gradient approximation (GGA) have been carried out on a wide range of phases and stoichiometries for the platinum-titanium (Pt-Ti) and iridium-titanium (Ir-Ti) alloy systems, using the Vienna Ab Initio Simulation Package (VASP) with projector augmented wave (PAW) potentials. For all of the phases in this work, the equilibrium structures were found by performing a full relaxation of the atoms. There were 20 di erent phases considered for varying atomic percentage compositions for each alloy system. Energy-volume calculations and heats of formations were used to determined the equilibrium structures at each atomice percentage composition and to determine if there were high temperature phases at that composition. The elastic constants and elastic moduli are calculated and the electronic structure and density of states (DOS) were considered to understand the hardness and stability properties of the alloys. For the Pt-Ti system, the low and high temperature phases at di erent compositions agreed with previously published results in the literature. Intermediate phases at 50% were also determined, in agreement with previous results. Alloying Pt with Ti resulted in a decrease in the bulk modulus, i.e. not adding strength to the metal. However, the shear modulus increased for most of the alloys compared to bulk Pt and it was found that in general, alloying may increase the resistance to shear. PtTi alloys were found to be ductile in nature, as with both constituent metals in their bulk form. In the Ir-Ti system, bulk Ir was found to have the highest bulk, shear and Young's modulus with each of these values decreasing with increasing percentage Ti in the alloy. IrTi alloys with 66.7% Ir composition or higher were found to be brittle in nature, similar in behaviour to bulk Ir; alloys with a higher percentage concentration of Ti were found to be ductile. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2011.

No description available.

Thesis (Ph.D.) -- McMaster University, 1998. / Includes bibliographical references (leaves 187-195). Also available via World Wide Web.

Thesis (Ph. D.)--Ohio State University, 2007. / Title from first page of PDF file. Includes bibliographical references (p. 201-215).

The study of factors governing cutting tool performance and life is driven by manufacturers’ need to increase economic efficiency in their production facilities. Tooling and process optimization represent an ongoing opportunity for realizing substantial improvements, thus manufacturers continue to focus on promoting design and development of cutting tools and surface treatment technology relevant to machining. The central goal of cutting tool technology is to increase productivity while simultaneously reducing cost and meeting the quality targets of the machined parts. This thesis considers a nano-tribological approach to explain some of the past performance improvements in cutting tools used in dry machining applications and to look for opportunities to make further improvements in this field. The approach considers tribofilms, which are often described as tribo-oxides composed of either the base cutting tool material or freshly cut workpiece material transferred to the tool that have formed on the friction surface through interaction with the environment (air or cutting fluids) and a tribo-oxidation process. In general, the formation of tribofilms plays an important role in friction and wear behaviour by offering thermal protection and/or in-situ lubrication, which is especially important during dry machining of hard workpiece materials. The formation of various tribofilms on cutting tools have been reported through: 1) cutting tools with surface modification and further tribo-oxidation during the cutting process; 2) mass transfer from freshly cut workpiece material due to tool/chip contact in machining; and 3) interaction between the cutting tool surface and the cutting environment. This dissertation presents a novel method to control the formation of tribofilms on the cutting tool surface during machining of hard materials such as Inconel DA 718 and hardened steels (AISI T1 and AISI D2), with coated and uncoated tools. In particular, the frictional conditions experienced by the cutting tool during the initial period of cutting (the running-in stage) are shown to strongly influence whether or not beneficial processes related to adaptability will trigger. Employing a more aggressive cutting speed during the running-in stage noticeably enhances the generation of protective/lubricious tribo-ceramic films on the friction surface. When the cutting speed is subsequently reduced, the accelerated formation of beneficial tribofilms previously initiated is not fully removed and therefore the rate of tool wear is considerably less than if the tool is run at the lower cutting speed for its entire life. In addition, preliminary results are presented regarding tribofilms formation under the influence of the cutting environment, specifically the nature of the cooling medium used, which demonstrates an entirely different avenue to explore in terms of fine-tuning of tribofilms generation. The overall objective of this dissertation is to highlight different approaches to control the tribofilms formed on the cutting tool surface in order to benefit the machining process and to improve cutting tool life, material remove rate and the machined surface quality. Additionally, little work has been found demonstrating the formation of tribofilms on the tool surface through mass transfer from the workpiece material or through interaction with the cooling medium. Thus a secondary objective of this work is to demonstrate the formation of tribofilms through these different means and to investigate the effect of cutting parameters on their formation. / Thesis / Doctor of Philosophy (PhD)

Tez (Doktora) - Süleyman Demirel Üniversitesi, Fen Bilimleri Enstitüsü, Makina Mühendisliği Anabilim Dalı, 2009. / Kaynakça var.