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Comparison of short and longer term loading on the creep behaviour of alumina-silicon carbide whisker composites

Description: The incorporation of SiC whiskers into alumina ceramics has resulted in several improved room temperature properties of the composite such as fracture toughness, strength, erosion resistance and fatigue. The creep resistance has also been generally observed to increase with the addition of whiskers. However, significant scatter in measured secondary creep rates still exist, depending on the material and the test conditions that were utilized. The objective of this investigation was to compare two separate creep tests performed in compression using a SiC{sub w}/Al{sub 2}O{sub 3} material obtained from the same process batch. The differences in creep behavior between the tests could thus be ascribed to the difference in creep conditions solely. In one case the creep behavior was studied under short term loading (<3 h) conditions in air, while longer term loading (<100 h) conditions in argon were applied in the other case. The creep results and the microstructure of the samples were compared and related to each other, and to previous results in the literature.
Date: November 1, 1992
Creator: Swan, H.; Arellano-Lopez, A.R. de; Dominguez-Rodriguez, A.; Routbort, J.L. & Swain, M.V.
Partner: UNT Libraries Government Documents Department

Superplasticity and joining of zirconia-based ceramics

Description: Steady-state creep and joining of alumina/zirconia composites containing alumina volume fractions of 20, 60, and 85% have been investigated between 1,250 and 1,350 C. Superplasticity of these compounds is controlled by grain-boundary sliding and the creep rate is a function of alumina volume fraction, not grain size. Using the principles of superplasticity, pieces of the composite have been joined by applying the stress required to achieve 5 to 10% strain to form a strong interface at temperatures as low as 1,200 C.
Date: December 10, 1999
Creator: Dominguez-Rodriguez, A.; Gutierrez-Mora, F.; Jimenez-Melendo, M.; Chaim, R. & Routbort, J. L.
Partner: UNT Libraries Government Documents Department

Deformation of an alumina-zirconia-silicon carbide-whisker reinforced composite

Description: Alumina-zirconia composites (MERC) with the addition of 0 and 28 vol % of silicon carbide whiskers have been deformed under compression at constant rate at 1450C, in air. Mechanical results are compared with the behavior of a commercial alumina (ARCO) with analogous proportions of silicon carbide-whiskers (0 and 30 vol %), under the same testing conditions. Flow stresses are typically higher for ARCO materials than for MERC materials. The addition of SiC whiskers increases flow stresses in ARCO composites, and decreases them for MERC samples. Microstructural observations confirm that the change in flow stress is the result of the presence of a glass phase in the MERC samples.
Date: April 1, 1993
Creator: Calderon-Moreno, J. M.; DeArellano-Lopez, A. R.; Dominguez-Rodriguez, A.; Routbort, J. L. & Leasky, T.
Partner: UNT Libraries Government Documents Department

High-temperature deformation of ZrO{sub 2}-Al{sub 2}O{sub 3}/SiC whisker composites fabricated by two techniques

Description: ZrO{sub 2} {minus} Al{sub 2}0{sub 3}/SiC whisker-reinforced composites, with whisker volume fractions of 0 to 28%, fabricated both by powder and precursor processing, have been deformed at temperatures of 1300--1500 C under constant compression rates of 1.7 {times} 10{sup {minus}5} to 6.8 {times} 10{sup {minus}5} s{sup {minus}1}. Above 1400 C, a stress at which the work-hardening rate became zero could be measured and correlated with whisker content. On the other hand, at 1300 C all samples broke within the elastic.regime. At 1350 C, increased whisker content appeared to inhibit fracture, so plastic behavior was obtained for samples containing 28% SiC. In the range of temperatures and compression rates, noted above, stress exponents were determined and tentatively correlated with microstructural features and their evolution during plastic deformation.
Date: March 1, 1995
Creator: Calderon Moreno, J.M.; DeArellano-Lopez, A.R.; Dominguez-Rodriguez, A. & Routbort, J.L.
Partner: UNT Libraries Government Documents Department

Diffusion-controlled creep in mixed-conducting oxides

Description: Steady-state creep rate of the mixed conducting oxides La{sub 1-x}Sr{sub x}MnO{sub 3} (x=0.1, 0.15, 0.25) and La{sub 0.7}Ca{sub 0.3}MnO{sub 3} has been investigated between 1150 and 1300 C. Creep parameters and TEM indicate that deformation is controlled by lattice diffusion of one of the cations. Dependence of creep rate on Sr concentration, combined with a point-defect model, confirms this hypothesis; however the oxygen partial pressure dependence of creep (from 10{sup -1} to 2x10{sup 4} Pa) cannot be accounted for within the framework of a simple point-defect model.
Date: June 1, 1996
Creator: Routbort, J.L.; Goretta, K.C.; Cook, R.E.; Wolfenstine, J.; Armstrong, T.R.; Clauss, C. et al.
Partner: UNT Libraries Government Documents Department

Plastic deformation of alumina reinforced with SiC whiskers

Description: Addition of small amounts of stiff reinforcement (SiC whiskers) to a polycrystalline AL{sub 2}O{sub 3} matrix partially inhibits grain boundary sliding because of an increase in threshold stress. When the concentration of whiskers is high enough, a pure diffusional mechanism takes over the control of plastic deformation of the composites. For higher whisker loadings, the materials creep properties depend on a microstructural feature different from the nominal grain size. A tentative correlation of this effective microstructural parameter with the spacing between the whiskers was established through a model.
Date: June 1, 1993
Creator: DeArellano-Lopez, A.R.; Dominguez-Rodriguez, A.; Goretta, K.C. & Routbort, J.L.
Partner: UNT Libraries Government Documents Department

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 accumulation processes which are manifested by triple point cavitation and cracking. The quasi-steady-state creep rates depend on grain size, whisker concentration, and the amount of glass phase present between the boundary of the whisker and the matrix. Unless all of the parameters are known, including the fabrication and loading histories, comparisons between various studies that used samples prepared in different ways are difficult. 44 refs., 7 figs., 2 tabs.
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

Influence of fabrication on mechanical properties of SiC-whisker-reinforced alumina

Description: Samples of SiC-whisker-reinforced Al{sub 2}O{sub 3} composites obtained from three different sources have been crept in compression at 1400{degrees}C using both constant load (CL) and constant strain rate (CSR). Macroscopic results indicate some difference in behavior due to fabrication. TEM is used to support this hypothesis. 10 refs., 3 figs.
Date: October 1, 1991
Creator: DeArellano-Lopez, A.R.; Dominguez-Rodriguez, A. (Seville Univ. (Spain). Dept. Materia Condensada); Goretta, K.C. & Routbort, J.L. (Argonne National Lab., IL (United States))
Partner: UNT Libraries Government Documents Department

High-temperature mechanical properties of SiC whisker reinforced Al sub 2 O sub 3 composites

Description: High-temperature constant strain rate compressive tests have been performed on Al{sub 2}O{sub 3} reinforced with different concentrations of SiC whiskers. The samples were obtained from three sources, but contained whiskers from the same source. The temperature range was from 1300 to 1500{degree}C and experiments were conducted in air and argon. Strain rates varied from 3 {times} 10{sup {minus}8} to 5 {times} 10{sup {minus}5} s{sup {minus}1} with stresses between 3 and 500 MPa. Stress exponents were fond to vary between 1 and 5 and depended on microstructure, whisker concentration and stress, indicating a change in the mechanism controlling plastic deformation. Change from diffusional creep to a damage accumulation mechanism was supported by TEM observations on samples as-received and deformed both in the n = 1 regime and in the n = 5 regime. Degradation of SiC whiskers occurred when testing in air. 12 refs., 1 tab., 7 figs.
Date: January 1, 1990
Creator: DeArellano-Lopez, A.R.; Dominguez-Rodriguez, A. (Seville Univ. (Spain). Dept. Materia Condensada); Goretta, K.C. & Routbort, J.L. (Argonne National Lab., IL (USA))
Partner: UNT Libraries Government Documents Department

Deformation of high-temperature superconductors

Description: Of the many families of high-temperature superconductors, only the properties of those discovered prior to 1989 - Y-Ba-Cu-O, Tl-Ba(Sr)-Ca-Cu-O, and Bi(Pb)-Sr-Ca-Cu-O - have been studied extensively. Deformation tests have been performed on YBa{sub 2}Cu{sub 3}O{sub x} (Y-123), YBa{sub 2}Cu{sub 4}O{sub x} (Y-124), TlBa{sub 2}Ca{sub 2}Cu{sub 3}O{sub x} (Bi-2223). The tests have revealed that plasticity is generally limited in these compounds and that the rate-controlling diffusional kinetics for creep are very slow. Nevertheless, hot forming has proved to be quite successful for fabrication of bulk high-temperature superconductors, so long as deformation rates are low or large hydrostatic stresses are applied. Steady-state creep data have proved to be useful in designing optimal heat treatments for superconductors and in support of more-fundamental diffusion experiments. The high-temperature superconductors are highly complex oxides, and it is a challenge to understand their deformation responses. In this paper, results of interest and operant creep mechanisms will be reviewed.
Date: August 1, 1994
Creator: Goretta, K. C.; Routbort, J. L.; Miller, D. J.; Chen, N.; Dominguez-Rodriguez, A.; Jimenez-Melendo, M. et al.
Partner: UNT Libraries Government Documents Department