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Author: Eric William Neuman Publisher: ISBN: Category : Borides Languages : en Pages : 259
Book Description
"Research presented in this dissertation focused on the mechanical behavior of ZrB2 based ceramic at elevated temperatures. Flexure strength, fracture toughness, and elastic modulus were measured at temperatures up to 2300°C for three compositions: monolithic ZrB2 (Z); ZrB2 - 30 vol% SiC - 2 vol% B4C (ZS); and ZrB2 - 10 vol% ZrC (ZC). In argon, Z, ZS, and ZC had strengths of 210 (at 2300°C), 260 (at 2200°C), and 295 MPa (at 2300°C), the highest temperatures tested for each composition. Fractography was used extensively to characterize the strength limiting flaws as a function of temperature. Strength of ZS in argon was controlled by the SiC cluster size up to 1800°C, and the formation of B-O-C-N phases that bridged SiC clusters above 2000°C. For ZC, surface flaws introduced during specimen preparation were the source of critical flaws in the material up to 1400°C, sub-critical crack growth of surface flaws between 1600 and 2000°C, and microvoid coalescence above 2000°C. It was also shown that thermal annealing at either 1400, 1500, or 1600°C improves the strength and modulus of ZS at temperatures between 800°C and 1600°C. Heat treatment at 1400°C for 10 hours produced the largest improvement in strength, 430 MPa at 1600°C versus 380 MPa for the as processed material. As a whole, the research pointed to several key microstructural features currently limiting the mechanical properties at the highest temperatures. In particular, removal of unfavorable secondary phases, and improved control over microstructure, should be promising methods to improve the elevated temperature properties of ZrB2 ceramics."--Abstract, page iv.
Author: Eric William Neuman Publisher: ISBN: Category : Borides Languages : en Pages : 259
Book Description
"Research presented in this dissertation focused on the mechanical behavior of ZrB2 based ceramic at elevated temperatures. Flexure strength, fracture toughness, and elastic modulus were measured at temperatures up to 2300°C for three compositions: monolithic ZrB2 (Z); ZrB2 - 30 vol% SiC - 2 vol% B4C (ZS); and ZrB2 - 10 vol% ZrC (ZC). In argon, Z, ZS, and ZC had strengths of 210 (at 2300°C), 260 (at 2200°C), and 295 MPa (at 2300°C), the highest temperatures tested for each composition. Fractography was used extensively to characterize the strength limiting flaws as a function of temperature. Strength of ZS in argon was controlled by the SiC cluster size up to 1800°C, and the formation of B-O-C-N phases that bridged SiC clusters above 2000°C. For ZC, surface flaws introduced during specimen preparation were the source of critical flaws in the material up to 1400°C, sub-critical crack growth of surface flaws between 1600 and 2000°C, and microvoid coalescence above 2000°C. It was also shown that thermal annealing at either 1400, 1500, or 1600°C improves the strength and modulus of ZS at temperatures between 800°C and 1600°C. Heat treatment at 1400°C for 10 hours produced the largest improvement in strength, 430 MPa at 1600°C versus 380 MPa for the as processed material. As a whole, the research pointed to several key microstructural features currently limiting the mechanical properties at the highest temperatures. In particular, removal of unfavorable secondary phases, and improved control over microstructure, should be promising methods to improve the elevated temperature properties of ZrB2 ceramics."--Abstract, page iv.
Author: Sumin Zhu Publisher: ISBN: Category : Ceramic materials Languages : en Pages : 360
Book Description
"The first part of this dissertation was aimed at studying the densification of ZrB2 ceramics by pressureless sintering techniques. Various processes have been applied to coat ZrB2 powders with polymer precursors, which were used to produce C after charring. After sintering at 1900°C, relative density increased of ~70% for uncoated ZrB2 to >99% for ZrB2 coated with at least 1.0 wt% C. Thermodynamic analysis suggested that C reacted with and removed oxide impurities (ZrO2 and B2O3) that were present on the ZrB2 particle surfaces, which promoted densification by minimizing grain coarsening"--Abstract, leaf iv.
Author: William G. Fahrenholtz Publisher: Wiley-American Ceramic Society ISBN: 9781118700785 Category : Technology & Engineering Languages : en Pages : 0
Book Description
The first comprehensive book to focus on ultra-high temperature ceramic materials in more than 20 years Ultra-High Temperature Ceramics are a family of compounds that display an unusual combination of properties, including extremely high melting temperatures (>3000°C), high hardness, and good chemical stability and strength at high temperatures. Typical UHTC materials are the carbides, nitrides, and borides of transition metals, but the Group IV compounds (Ti, Zr, Hf) plus TaC are generally considered to be the main focus of research due to the superior melting temperatures and stable high-melting temperature oxide that forms in situ. Rather than focusing on the latest scientific results, Ultra-High Temperature Ceramics: Materials for Extreme Environment Applications broadly and critically combines the historical aspects and the state-of-the-art on the processing, densification, properties, and performance of boride and carbide ceramics. In reviewing the historic studies and recent progress in the field, Ultra-High Temperature Ceramics: Materials for Extreme Environment Applications provides: Original reviews of research conducted in the 1960s and 70s Content on electronic structure, synthesis, powder processing, densification, property measurement, and characterization of boride and carbide ceramics. Emphasis on materials for hypersonic aerospace applications such as wing leading edges and propulsion components for vehicles traveling faster than Mach 5 Information on materials used in the extreme environments associated with high speed cutting tools and nuclear power generation Contributions are based on presentations by leading research groups at the conference "Ultra-High Temperature Ceramics: Materials for Extreme Environment Applications II" held May 13-19, 2012 in Hernstein, Austria. Bringing together disparate researchers from academia, government, and industry in a singular forum, the meeting cultivated didactic discussions and efforts between bench researchers, designers and engineers in assaying results in a broader context and moving the technology forward toward near- and long-term use. This book is useful for furnace manufacturers, aerospace manufacturers that may be pursuing hypersonic technology, researchers studying any aspect of boride and carbide ceramics, and practitioners of high-temperature structural ceramics.
Author: Matthew Joseph Thompson Publisher: ISBN: Category : Borides Languages : en Pages : 430
Book Description
"The research presented in this dissertation focuses on the processing and thermomechanical properties of ZrB2 based ceramics. The overall goal was to improve the understanding of thermal and mechanical properties based on processing conditions and additives to ZrB2. To achieve this, the relationships between the thermal and mechanical properties were analyzed for ZrB2 ceramics that were densified by different methods, varying amounts of carbon, B4C, or TiB2 additions. Four main areas were investigated in this dissertation. The first showed that decreased processing times, regardless of densification method, improved mechanical strength to >500 MPa. This study also revealed that lower oxygen impurity contents led to less grain coarsening. The second study showed that higher heating rates narrowed the grain size distribution, which resulted in strengths above 600 MPa. However, the decreased processing times led to retention of ZrO2, which decreased the thermal conductivity. The third study revealed that carbon additions interacted with ZrO2 and WC impurities introduced during powder processing to form (Zr,W)C, which led to higher thermal conductivity than ZrB2 with no carbon added. The last area examined the effect of solid solution additions on the electron and phonon contributions to thermal conductivity. The formation of solid solutions decreased thermal conductivity to
Author: Brett Hunter Publisher: ISBN: Category : Languages : en Pages : 100
Book Description
Ultra high temperature ceramics (UHTCs), which typically comprise carbides, nitrides, and borides, are a class of materials associated with high melting temperatures and high hardness. These materials offer a range of mechanical responses, from being very brittle to exhibiting significant plasticity as a function of composition and loading temperature. The purpose of this investigation is to characterize the slip mechanisms in ZrB2, where slip has been inferred but not definitively quantified. This work confirmed prior studies that dense dislocation arrays, with straight dislocation lines, exist under room temperature indents and demonstrates that such networks are highly localized to the load region. For elevated temperature deformation, ZrB2 has been reported to have a drop in flexural strength from 390 MPa at 1200 °C to 110 MPa at 1600 °C. Dynamical electron diffraction and image analysis confirmed basal, pyramidal, and prismatic slip which is rationalized by ZrB2's hexagonal close packed c/a lattice parameter ratio of 1.11, which is less than the ideal ratio of 1.63. The dislocation densities prior to and after this flexural strength drop were 1.3 x 1013 m-2 and 1.0 x 1013 m-2, respectively. This indicates that the reduction in strength was not significantly associated with increased dislocation nucleation but rather stress relaxation.
Author: Ryan Joseph Grohsmeyer Publisher: ISBN: Category : Languages : en Pages : 261
Book Description
"This research had two objectives: characterization of processing-microstructure-mechanical property relationships of conventional ZrB2-MoSi2 ceramics at room temperature (RT) and 1500°C in air, and fabrication of ZrB2-MoSi2 dual composite architectures (DCAs) for use near 1500°C. Elastic moduli, fracture toughness, and flexure strength were measured at RT and 1500°C for 15 ZrB2-MoSi2 ceramics hot pressed using fine, medium, or coarse ZrB2 starting powder with 5-70 vol.% MoSi2, referred to as FX, MX, and CX respectively where X is the nominal MoSi2 content. MoSi2 decomposed during sintering, resulting in microstructures with ZrB2 cores and (Zr[subscript 1-x]Mo[subscript x])B2 shells via surface and grain boundary diffusion. Flexure strength at RT (700-800 MPa for FX, 560-720 MPa for MX, and 440-590 MPa for CX) was controlled by the maximum ZrB2 grain size, and toughness (2.7-3.9 MPa·m[superscript 1/2]) did not trend with MoSi2 content. At 1500°C toughness increased with MoSi2 content and ZrB2 grain size, and strength of FX and MX was controlled by oxidation damage at 1500°C. Strength of CX followed the opposite trend, with C10 exhibiting a strength of ~600 MPa. Four ZrB2-MoSi2 DCAs were fabricated by dispersing granules of selected ZrB2-MoSi2 compositions in matrices of different ZrB2-MoSi2 compositions. Strength limitation at 1500°C by differential oxidation of granules and matrix was resolved by compositional adjustment, but microcracking due to granule-matrix CTE mismatch limited strength to ~140 MPa at RT and ~360 MPa at 1500°C. The granule-matrix interface did not deflect cracks, and the toughness at 1500°C was 6.1-6.9 MPa·m[superscript 1/2], similar to that of conventional ZrB2-MoSi2 ceramics. CTE matching via addition of a third phase and use of a weak granule-matrix interface are recommended areas of focus for future development of high-temperature DCAs"--Abstract, page iv.
Author: Karl Jakus Publisher: Elsevier ISBN: 0080523889 Category : Technology & Engineering Languages : en Pages : 569
Book Description
High Temperature Mechanical Behavior of Ceramic Composites provides an up-to-date comprehensive coverage of the mechanical behavior of ceramic matrix composites at elevated temperatures. Topics include both short-term behavior (strength, fracture toughness and R-curve behavior) and long-term behavior (creep, creep-fatigue, delayed failure and lifetime). Emphasis is on a review of fundamentals and on the mechanics and mechanisms underlying properties. This is the first time that complete information of elevated temperature behavior of ceramic composites has ever been compacted together in a single volume. Of particular importance is that each chapter, written by internationally recognized experts, includes a substantial review component enabling the new material to be put in proper perspective. Shanti Nair is Associate Professor at the Department of Mechanical Engineering at the University of Massachusetts at Amherst. Karl Jakus is Professor at the University of Massachusetts at Amherst.
Author: Eric William Neuman
Author: Eric William Neuman
Author: Dipankar Ghosh
Author: Sumin Zhu
Author: William G. Fahrenholtz
Author: Matthew Joseph Thompson
Author: Stewart M. Lang
Author: Brett Hunter
Author: Ryan Joseph Grohsmeyer
Author: Tatsuki Ohji
Author: Karl Jakus