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Thesis (M.S.)--University of Texas at El Paso, 2009. / Title from title screen. Vita. CD-ROM. Includes bibliographical references. Also available online.

The compressive creep behaviour of a high purity silicon nitride ceramic with and without the addition of Ba was studied at 1400°C. Two distinct creep stages were observed during high temperature deformation of these materials. The stress exponents for creep of the two materials indicate that they have different creep mechanisms during the second stage of creep. Cavitation during creep was determined by measuring the density change before and after creep using a water­-displacement method. The Ba doped material exhibited an obvious density decrease, indicating cavitation during creep, whereas the undoped material exhibited no cavitation. This is consistent with TEM observations. The microstructure of the materials, especially the amorphous grain-boundary phase was investigated for both as-sintered and crept specimans by means of transmission electron microscopy (TEM). Statistical analysis of a number of grain-­boundary films indicates that the film thickness is confined to a narrow range (standard deviation less than 0.15 nm) in the as-sintered materials. The average film thickness depends on film chemistry, increasing from 1.0 nm to 1.4 nm when Ba is added. The standard deviation of the film thickness of a given material after creep, however, is considerably larger than before (0.30 nm ~ 0.59 nm). This suggests that the grain-boundary glass phase is redistributed during creep. Viscous flow of the glass phase is proposed as die mechanism responsible for the first stage of creep. The data are compared with a model for viscous creep, yielding good correlation. / Thesis / Master of Engineering (ME)

<p>Spark Plasma Sintering (SPS) is a promising rapid consolidation technique that allows a better understanding and manipulating of sintering kinetics and therefore makes it possible to obtain Si₃N₄-based ceramics with tailored microstructures, consisting of grains with either equiaxed or elongated morphology.</p><p> The presence of an extra liquid phase is necessary for forming tough interlocking microstructures in Yb/Y-stabilised α-sialon by HP. The liquid is introduced by a new method, namely by increasing the O/N ratio in the general formula RE_xSi_12-(3x+n)Al_3x+nO_nN_16-n while keeping the cation ratios of RE, Si and Al constant. </p><p>Monophasic α-sialon ceramics with tailored microstructures, consisting of either fine equiaxed or elongated grains, have been obtained by using SPS, whether or not such an extra liquid phase is involved. The three processes, namely densification, phase transformation and grain growth, which usually occur simultaneously during conventional HP consolidation of Si₃N₄-based ceramics, have been precisely followed and separately investigated in the SPS process.</p><p>The enhanced densification is attributed to the non-equilibrium nature of the liquid phase formed during heating. The dominating mechanism during densification is the enhanced grain boundary sliding accompanied by diffusion- and/or reaction-controlled processes. The rapid grain growth is ascribed to a <i>dynamic ripening</i> mechanism based on the formation of a liquid phase that is grossly out of equilibrium, which in turn generates an extra chemical driving force for mass transfer. Monophasic α-sialon ceramics with interlocking microstructures exhibit improved damage tolerance. Y/Yb- stabilised monophasic α-sialon ceramics containing approximately 3 vol% liquid with refined interlocking microstructures have excellent thermal-shock resistance, comparable to the best β-sialon ceramics with 20 vol% additional liquid phase prepared by HP. </p><p>The obtained sialon ceramics with fine-grained microstructure show formidably improved <i>superplasticity</i> in the presence of an electric field. The compressive strain rate reaches the order of 10^-2 s^-1 at temperatures above 1500oC, that is, two orders of magnitude higher than that has been realised so far by any other conventional approaches. The high deformation rate recorded in this work opens up possibilities for making ceramic components with complex shapes through super-plastic forming. </p>

Spark Plasma Sintering (SPS) is a promising rapid consolidation technique that allows a better understanding and manipulating of sintering kinetics and therefore makes it possible to obtain Si3N4-based ceramics with tailored microstructures, consisting of grains with either equiaxed or elongated morphology. The presence of an extra liquid phase is necessary for forming tough interlocking microstructures in Yb/Y-stabilised α-sialon by HP. The liquid is introduced by a new method, namely by increasing the O/N ratio in the general formula RExSi12-(3x+n)Al3x+nOnN16-n while keeping the cation ratios of RE, Si and Al constant. Monophasic α-sialon ceramics with tailored microstructures, consisting of either fine equiaxed or elongated grains, have been obtained by using SPS, whether or not such an extra liquid phase is involved. The three processes, namely densification, phase transformation and grain growth, which usually occur simultaneously during conventional HP consolidation of Si3N4-based ceramics, have been precisely followed and separately investigated in the SPS process. The enhanced densification is attributed to the non-equilibrium nature of the liquid phase formed during heating. The dominating mechanism during densification is the enhanced grain boundary sliding accompanied by diffusion- and/or reaction-controlled processes. The rapid grain growth is ascribed to a dynamic ripening mechanism based on the formation of a liquid phase that is grossly out of equilibrium, which in turn generates an extra chemical driving force for mass transfer. Monophasic α-sialon ceramics with interlocking microstructures exhibit improved damage tolerance. Y/Yb- stabilised monophasic α-sialon ceramics containing approximately 3 vol% liquid with refined interlocking microstructures have excellent thermal-shock resistance, comparable to the best β-sialon ceramics with 20 vol% additional liquid phase prepared by HP. The obtained sialon ceramics with fine-grained microstructure show formidably improved superplasticity in the presence of an electric field. The compressive strain rate reaches the order of 10-2 s-1 at temperatures above 1500oC, that is, two orders of magnitude higher than that has been realised so far by any other conventional approaches. The high deformation rate recorded in this work opens up possibilities for making ceramic components with complex shapes through super-plastic forming.

No description available.

The diploma work is focused on the ceramic tool materials and its effective use. The introductory part of the work contains the detail characteristic of the ceramic tool materials from the point of view of their dividing, physic-mechanical propertis, production methods and marking. The main part of the work is focused to judging of the ceramic portion at the production assortment of the top World producers of tool materials and to evaluation of cutting ability of the particular materials of these producers. The detail analysis of recommended cutting conditions, which is aimed to an effective use of the ceramic materials, had been worked up for this purpose. The technical economic analysis confirms, that the present effective aplications of ceramic are limited only for specific cases of machining cast irons, steels and alloys.

Thesis dealing with cutting ceramics and its efficient use. Introduction describes the general characteristics of the cutting of ceramics, its history and development and production of various kinds. This section describes the mechanical and physical properties with potential application in machining. The se-cond part is an overview of cutting-frame in the range of selected world leaders. Ano-ther section focuses on general assessment of the power of cutting tools and other ma-terials comparison. The fourth part, is comparing the working conditions of producers and tools intended for cutting.

Master’s thesis are concerned with the cutting ceramic materials and its ef-fective usage. The first part of the thesis is focused on the general properties of the cutting ceramics, its history, development, production and description of the various types. This part includes as well a description of the mechanic-physical properties and the potential of the usage for machining. The second part of the work solves the general evaluation of the cutting power. The main issue in the next part is the identification of cutting ceramics range and the selection accor-ding to main world producers. The fourth part deals with the assessments and the comparison of the working conditions for different types of the machined ma-terials. The technical economic assessment shows the potentials in the total pro-duction costs reduction.

Thesis dealing with cutting ceramics and its efficient use. Introduction describes the general characteristics of the cutting of ceramics, its history and development and production of various kinds. This section describes the mechanical and physical properties with potential application in machining. The se-cond part is an overview of cutting-frame in the range of selected world leaders. Ano-ther section focuses on general assessment of the power of cutting tools and other ma-terials comparison. The fourth part, is comparing the working conditions of producers and tools intended for cutting.