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Creep of whisker-reinforced ceramics

Description: The results of high-temperature creep of various ceramic composites will be reviewed. In particular, creep results for Al{sub 2}O{sub 3} and Si{sub 3}N{sub 4} matrices reinforced with SiC whiskers will be emphasized. For a given temperature, stress and grain size, the creep rate of the Al{sub 2}O{sub 3} composite is usually lower than that of the ceramic matrix. In general, creep at low stresses occurs by grain boundary sliding accommodated by diffusion, whereas higher stresses lead to damage a… more
Date: January 1, 1991
Creator: Routbort, J.L; Goretta, K.C. (Argonne National Lab., IL (United States)); Dominguez-Rodriguez, A. & de Arellano-Lopez, A.R. (Seville Univ. (Spain))
Partner: UNT Libraries Government Documents Department
open access

Enhanced use of clips at the Los Alamos National Laboratory

Description: Early efforts in producing Expert Systems for engineering applications used a limited subset of CLIPS features. We discuss implementation details of previous Expert Systems and the current Expert System used for training operators in the control of the Isotope Separation System. 4 refs., 8 figs.
Date: January 1, 1991
Creator: Duerre, K. H.; Parkinson, W. J. & Osowski, J. J.
Partner: UNT Libraries Government Documents Department
open access

Application of artificial intelligence control to the vapor-liquid-solid silicon carbide whisker process

Description: Silicon carbide whiskers have excellent mechanical and chemical properties, making them very desirable as a reinforcement for structural ceramic and other composite materials. Los Alamos has developed a laboratory-scale batch process for producing very high quality SiC whiskers by the vapor-liquid-solid (VLS) method which is an active candidate for technology transfer involving significant scale-up. The process, however, involves quite complex chemical/physical and parametric relationships and … more
Date: January 1, 1989
Creator: Shalek, P.D. & Parkinson, W.J.
Partner: UNT Libraries Government Documents Department
open access

Development of the VLS process for SiC whisker growth

Description: Our whisker work involves preparation of whisker samples, whisker characterization, and process scaleup. Sample whiskers are used for composite preparation and for whisker characterization work, while modelling of the production process is itself proving useful. The approach to scaleup recognizes the importance of a full understanding of the process variables. Hence our work in this area is proceeding with studies of the chemistry of the process gases and investigation of the growth mechanism.
Date: January 1, 1984
Creator: Hurley, G. F.
Partner: UNT Libraries Government Documents Department
open access

Nondestructive evaluation development for process control

Description: A joint project between Garrett Ceramic Components (GCC) of Allied Signal Aerospace Corporation and Argonne National Laboratory (ANL) is ongoing to evaluate nondestructive characterization (NDC) methods to detect and measure process-induced variations in ceramic materials. The process methods of current focus on slip-casting and injection molding and the NDC methods being evaluated are microfocus X-ray computed tomography (XCT) and nuclear magnetic resonance computed tomography (MRCT). As part … more
Date: January 1, 1991
Creator: Ellingson, W.A.; Holloway, D.L.; Sivers, E.A. (Argonne National Lab., IL (United States)); Ling, J. (Chinese Academy of Science, Shanghai SH (China). Inst. for Ceramics); Pollinger, J.P. & Yeh, H.C. (Allied-Signal Aerospace Co., Torrance, CA (United States). Garrett Ceramic Components Div.)
Partner: UNT Libraries Government Documents Department
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Intergranular and interphase boundaries in ceramics

Description: Interfaces are of great importance in both electronic and structural ceramics. The microstructure and microchemistry of interfaces can be studied by transmission electron microscopy, both high resolution and analytical. Examples are taken from both intergranular and interphase boundaries in ceramics. The former include low angle, twin and 90/degree/ boundaries in YBa/sub 2/Cu/sub 3/O/sub 7/ superconductors. Interphase boundaries include epitactic layers of YBa/sub 2/Cu/sub 3/O/sub 7/on SrTiO/su… more
Date: January 1, 1989
Creator: Mitchell, T.E.; Roy, T. & Unal, O.
Partner: UNT Libraries Government Documents Department
open access

Microwave sintering of alumina-SiC composites at 2. 45 and 60 GHz

Description: Composites of alumina-10 vol % silicon carbide whiskers were sintered to 70% of theoretical density using both 2.45 and 60 GHz microwave radiation. Further densification was inhibited by formation of a constrained network of whiskers. Alumina-10 vol % silicon carbide platelet composites were sintered to 94% of theoretical density with 2.45 GHz microwaves in less than 20 minutes. 4 refs., 11 figs.
Date: January 1, 1988
Creator: Katz, J. D.; Blake, R. D. & Petrovic, J. J.
Partner: UNT Libraries Government Documents Department
open access

Performance of commercial and research grade SiC whiskers in a borosilicate glass matrix

Description: Dry blending of the whiskers and glass powder yielded composites of satisfactory, but not optimum, homogeneity. The whiskers inhibited composite densification, but this could be remedied by modifying the hot-pressing conditions. All types of whiskers produced improvements in the flexural strength of the composites, with the highest value achieved with the smallest diameter whiskers. The composites displayed a 4- to 5-fold increase in fracture toughness compared to that displayed by the unreinfo… more
Date: January 1, 1986
Creator: Gac, F. D.; Petrovic, J. J.; Milewski, J. V. & Shalek, P. D.
Partner: UNT Libraries Government Documents Department
open access

Analysis of ceramic composites by 3D microtomography

Description: In the first part we describe the use of 3D X-ray microtomography for the analysis of density distributions inside and between cold pressed green state whisker reinforced Si{sub 3}N{sub 4}/Si{sub 3}N{sub 4} bending test specimens. The differences between a changing content of whisker volumes (0 to 35%) show a sharp density reduction between 10 and 15%. This agrees with previous research which shows that maximum density is achieved between 10 and 15% whisker loadings. Since density is directly r… more
Date: January 1, 1991
Creator: Luethi, T. (EMPA, Duebendorf (Switzerland)) & Ellingson, W.A. (Argonne National Lab., IL (United States))
Partner: UNT Libraries Government Documents Department
open access

Microstructure and properties of alumina-whisker-reinforced tetragonal zirconia polycrystal matrix composites

Description: With the increasing demand of today's technology, there is a growing need for high temperature materials with improved fracture toughness. Whisker-reinforced ceramic composites are materials with potentially high fracture toughness. Many whisker-matrix systems are possible, but the choices for toughened composites are limited by such considerations as chemical compatibility and thermal expansion mismatch. In view of the high fracture toughness of tetragonal zirconia polycrystals (TZP) matrix, m… more
Date: January 1, 1991
Creator: Roberts, J.M.; Singh, J.P. (Argonne National Lab., IL (USA)) & Scattergood, R.O. (North Carolina State Univ., Raleigh, NC (USA). Dept. of Materials Science and Engineering)
Partner: UNT Libraries Government Documents Department
open access

Application of neutron diffraction technology to the determination of residual strain in engineering composites

Description: Knowledge of fabrication induced residual stresses in the fiber and matrix of advanced engineering composites is important as these stresses can greatly influence the mechanical properties of these composites. In this paper, the application of neutron diffraction technology to the determination of thermal residual strains in the constituents of composites (from which stresses can be calculated) is discussed. Experimental determination of temperature dependent strain in the fiber and matrix of t… more
Date: January 1, 1992
Creator: Kupperman, D. S.
Partner: UNT Libraries Government Documents Department
open access

Reinforced ceramics employing discontinuous phases

Description: The fracture toughness of ceramics can be improved by the incorporation of a variety of discontinuous reinforcing phases and microstructures. Observations of crack paths in these systems indicate that these reinforcing phases bridge the crack tip wake region. Recent developments in micromechanics toughening models applicable to such systems are discussed and compared with experimental observations. Because material parameters and microstructural characteristics are considered, the crack bridgin… more
Date: January 1, 1990
Creator: Becher, P.F.
Partner: UNT Libraries Government Documents Department
open access

Thermally induced micromechanical stresses in ceramic/ceramic composites

Description: The internal micromechanical stresses which develop in ceramic-ceramic composites as a consequence of temperature changes and thermoelastic property differences between the reinforcing and matrix phases are addressed by the Eshelby method. Results for two whisker reinforced ceramic matrix composites and for quartz particles in porcelain are discussed. It is concluded that the stresses which develop in the second phase reinforcing inclusions are quite substantial (GPa-levels) and may be highly a… more
Date: November 1, 1992
Creator: Li, Zhuang (Argonne National Lab., IL (United States)) & Bradt, R.C. (Nevada Univ., Reno, NV (United States). Mackay School of Mines)
Partner: UNT Libraries Government Documents Department
open access

Whisker growth: a new mechanism for helium blistering of surfaces in complex radiation environments

Description: Implantation of helium concurrent with the generation of large numbers of displaced atoms in surface layers of materials exposed to /sup 252/Cf ..cap alpha..-particles and fission fragments produces a unique form of low temperature surface blistering. The purpose of this paper is to formulate a basis for the whisker-growth mechanism for helium blistering as an aid to the specification of conditions under which the mechanism might apply.
Date: January 1, 1978
Creator: McDonell, W.R.
Partner: UNT Libraries Government Documents Department
open access

Theoretical and experimental analysis of the toughening behavior of whisker reinforcement in ceramic matrix composites

Description: Analytical solutions are presented describing the experimentally verified toughening of whisker reinforced ceramics. Clear insights are provided into the interrelationships of whiskers, matrices, and interfaces in the case of strong interfaces with minimized whisker pullout.
Date: January 1, 1988
Creator: Becher, P. F.; Hsueh, C. H.; Angelini, P. & Tiegs, T. N.
Partner: UNT Libraries Government Documents Department
open access

Effect of whisker surface treatments and processing conditions on the SiC/Al sub 2 O sub 3 interface

Description: Various electron microscopy techniques have been used to evaluate the microstructural and interfacial characteristics of silicon carbide whisker-reinforced alumina composites. The effects of subjecting whiskers to oxidizing and reducing treatments prior to composite fabrication were examined. Whisker/matrix interfaces in which carbon coatings were applied to whiskers prior to specimen fabrication were also examined. Physical and thermodynamic arguments can be used to explain why it is difficult… more
Date: January 1, 1990
Creator: Alexander, K.B.; Angelini, P. & Becher, P.F.
Partner: UNT Libraries Government Documents Department
open access

Tensile testing of SiC whiskers

Description: The room temperature tensile mechanical properties of SiC whiskers have been examined using a micro-tensile-test apparatus. SiC whiskers exhibit an average tensile strength of 8.4 GPa for a 5 mm tested length, and an average elastic modulus of 581 GPa. These results indicate that SiC whiskers possess significant potential as short-fiber reinforcement elements in ceramic matrix composites.
Date: January 1, 1984
Creator: Petrovic, J. J.
Partner: UNT Libraries Government Documents Department
open access

Whisker reinforced structural ceramics: Progress in the VLS growth and use of long silicon carbide whiskers. [Vapor-liquid-solid]

Description: A VLS (vapor-liquid-solid) whisker growth process, optimized for the production of short (approx.10 mm lengths) SiC whiskers, was modified to produce greater than or equal to 25 mm long whiskers. In conjunction with this modification, a plan was developed for incorporating an artificial-intelligence system to enhance the whisker growth process. An oriented whisker ribbon was produced from the long whiskers, as a step toward the development of a staple whisker yarn.
Date: January 1, 1987
Creator: Gac, F.D.; Shalek, P.D.; Parkinson, W.J.; Edwards, C. & Price, J.B.
Partner: UNT Libraries Government Documents Department
open access

Fabrication of SiC whiskers and composites

Description: The Los Alamos Structural Ceramics Program is a multi-faceted program with an overall objective of producing superior strength and fracture toughness in ceramic bodies for load bearing applications. One phase of the program is pursuing the development of silicon carbide whiskers which are used to prepare ceramic matrix composites. The purpose of this work is to investigate strengthening and toughening mechanisms in ceramic composites. In the following we describe some elements of the whisker de… more
Date: January 1, 1984
Creator: Hurley, G. F.; Shalek, P. D.; Gac, F. D. & Petrovic, J. J.
Partner: UNT Libraries Government Documents Department
open access

Application of neutron diffraction technology to the determination of residual strain in engineering composites

Description: Knowledge of fabrication induced residual stresses in the fiber and matrix of advanced engineering composites is important as these stresses can greatly influence the mechanical properties of these composites. In this paper, the application of neutron diffraction technology to the determination of thermal residual strains in the constituents of composites (from which stresses can be calculated) is discussed. Experimental determination of temperature dependent strain in the fiber and matrix of t… more
Date: December 1, 1992
Creator: Kupperman, D. S.
Partner: UNT Libraries Government Documents Department
open access

Recovery of crystallinity in ground calcite

Description: Recovery processes by thermal treatment and recrystallization are examined in a calcite specimen severely disordered by ball milling. As the annealing temperature is increased, restructuring in the bulk lags behind the recovery of crystalline perfection in the surface regions. Surface reordering is significant at temperatures as low as 150 to 175/sup 0/C and is rapidly completed at 400/sup 0/C. Annealing at 600/sup 0/C is required for removal of all lattice strain. Before loss of surface can oc… more
Date: January 1, 1976
Creator: Gammage, R. B. & Glasson, D. R.
Partner: UNT Libraries Government Documents Department
open access

EVALUATION OF LOCAL STRAIN EVOLUTION FROM METALLIC WHISKER FORMATION

Description: Evolution of local strain on electrodeposited tin films upon aging has been monitored by digital image correlation (DIC) for the first time. Maps of principal strains adjacent to whisker locations were constructed via comparing pre- and post-growth scanning electron microscopy (SEM) images. Results showed that the magnitude of the strain gradient plays an important role in whisker growth. DIC visualized the dynamic growth process in which the alteration of strain field has been identified to ca… more
Date: May 11, 2011
Creator: Hoffman, E. & Lam, P.
Partner: UNT Libraries Government Documents Department
open access

Nondestructive evaluation development for process control

Description: A joint project between Garrett Ceramic Components (GCC) of Allied Signal Aerospace Corporation and Argonne National Laboratory (ANL) is ongoing to evaluate nondestructive characterization (NDC) methods to detect and measure process-induced variations in ceramic materials. The process methods of current focus on slip-casting and injection molding and the NDC methods being evaluated are microfocus X-ray computed tomography (XCT) and nuclear magnetic resonance computed tomography (MRCT). As part … more
Date: December 31, 1991
Creator: Ellingson, W. A.; Holloway, D. L.; Sivers, E. A.; Ling, J.; Pollinger, J. P. & Yeh, H. C.
Partner: UNT Libraries Government Documents Department
open access

Properties of whisker-reinforced ceramics

Description: The paper summarizes studies of SiC whisker-reinforced alumina composites their properties and the influence of composition and microstructure. Both steady-state toughness and R-curve response increase with whisker content and diameter. Room temperature flexure strength of aluminas with different grain sizes also increases with whisker content. Resistance to slow crack growth under both monotonic and cyclic loading is improved by whisker reinforcement compared to alumina and other ceramics. The… more
Date: September 1, 1994
Creator: Becher, P. F.; Hsueh, C. H.; Lin, H. T.; Alexander, K. B.; Tiegs, T. N.; Warwick, W. H. et al.
Partner: UNT Libraries Government Documents Department
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