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  • 1
    Electronic Resource
    Electronic Resource
    Improved High-Temperature Strength of Silicon Nitride Toughened with Aligned Whisker Seeds (2005)
    Oxford, UK : Blackwell Science Inc
    Journal of the American Ceramic Society 88 (2005), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The effect of the amount of the sintering additives, i.e., yttria and alumina, on the microstructure and the high-temperature flexural strengths of silicon nitride with and without the aligned whisker seeds was examined. As the amount of the sintering additives was increased, both width and length of the grains were increased. The high-temperature strengths of silicon nitride with and without the aligned seeds were increased and decreased, respectively, according to the increase of the amount of the sintering additives. When both 4.8 wt% yttria and 2.2 wt% alumina were added to silicon nitride with the aligned whisker seeds, the experimental results indicated that it had three times the flexural strength as silicon nitride without the seeds at 1673 K. During the high-temperature flexure testing, observations did not indicate yielding present in the samples with the aligned whisker seeds, while it was present in samples without the whisker seeds. The reinforcing grains growing from the whisker seeds aligned perpendicular to the crack propagation direction acted as effective obstacles to the crack propagation and improved the fracture toughness.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1551-2916.2005.00074.x
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  • 2
    Electronic Resource
    Electronic Resource
    Novel Two-Step Sintering Process to Obtain a Bimodal Microstructure in Silicon Nitride (2002)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 85 (2002), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A two-step sintering process is described in which the first step suppresses densification while allowing the α-to-β phase transformation to proceed, and the second step, at higher temperatures, promotes densification and grain growth. This process allows one to obtain a bimodal microstructure in Si3N4 without using β-Si3N4 seed crystals. A carbothermal reduction process was used in the first step to modify the densification and transformation rates of the compacts consisting of Si3N4, Y2O3, Al2O3, and a carbon mixture. The carbothermal reduction process reduces the oxygen:nitrogen ratio of the Y-Si-Al-O-N glass that forms, which leads to the precipitation of crystalline oxynitride phases, in particular, the apatite phase. Precipitation of the apatite phase reduces the amount of liquid phase and retards the densification process up to 1750°C; however, the α-to-β phase transformation is not hindered. This results in the distribution of large β-nuclei in a porous fine-grained β-Si3N4 matrix. Above 1750°C, liquid formed by the melting of apatite resulted in a rapid increase in densification rates, and the larger β-nuclei also grew rapidly, which promoted the development of a bimodal microstructure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2002.tb00073.x
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  • 3
    Electronic Resource
    Electronic Resource
    Oxidation of Ti(C,N)-Based Ceramics Exposed at 1373 K in Air (2000)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 83 (2000), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Ti(C,N)-based ceramics that contained NbC, TaC, and WC were exposed at 1373 K in air for 10 h to study the effect of these metal carbides on the oxidation resistance. The addition of 10 mol% of NbC and 10 mol% of TaC to Ti(C,N) ceramics improved the oxidation resistance, whereas additions of 10 mol% of WC worsened the oxidation resistance. Weight gain due to the oxidation of Ti(C,N) ceramics with added WC varied in a complicated way, relative to the amount of WC that was involved. There was a competition between weight gain due to the oxidation and weight loss due to the volatile tungsten oxide.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2000.tb01255.x
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  • 4
    Electronic Resource
    Electronic Resource
    Texture in Silicon Nitride Seeded with Silicon Nitride Whiskers of Different Sizes (2003)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 86 (2003), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Silicon nitride ceramics seeded with 3 wt%β-Si3N4 whiskers of two different sizes were prepared by a modified tape casting and gas pressure sintering. The fine whiskers had a higher aspect ratio than the coarse whiskers. Quantitative texture analysis including calculation of the orientation distribution function (ODF) was used for obtaining the degrees of preferred orientation of sintered samples. The maximum multiples of random distribution (mrd) values of samples seeded with the fine and coarse whiskers were large, greater than 15 and 9, respectively. Meanwhile, the mrd value of a sample seeded with fine whiskers was only 9 when it was prepared by conventional tape casting. The microstructures and the XRD data revealed that the well-aligned whiskers grew significantly after sintering and dominated the texture. Differences among the degrees of preferred orientation of the samples were explained using Jeffrey's model on rotation of elliptical particles carried by a viscous fluid.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2003.tb03409.x
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  • 5
    Electronic Resource
    Electronic Resource
    Anisotropy of Silicon Nitride with Aligned Silicon Nitride Whiskers (1999)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 82 (1999), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A model based on anisotropic sintering shrinkage of silicon nitride with aligned silicon nitride whisker seeds was built in order to provide an easy way to obtain information on how the large elongated grains were aligned. The method requires a simple measuring device for the information. XRD analysis showed a good correlation with predictions of the model. Both predictions of the model and experimental results indicated that the fraction of aligned large elongated grains increased as the whisker content increased.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1999.tb01836.x
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  • 6
    Electronic Resource
    Electronic Resource
    Extra-Large Grains in the Silicon Nitride Ceramics Doped with Yttria and Hafnia (1998)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 81 (1998), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Microstructural development of silicon nitride doped with Y2O3 and HfO2 was investigated to determine how extra-large grains develop during gas pressure sintering. Grains as long as 200 µm and a few tens of micrometers wide developed at high temperatures (〉2173 K) in a fine-grained matrix containing a limited amount of liquid which had a poor propensity to spread. A small number of grains could grow quite large before their growth was halted by neighboring grains of comparable size.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1998.tb02560.x
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  • 7
    Electronic Resource
    Electronic Resource
    Indentation Crack Length Anisotropy in Silicon Nitride with Aligned Reinforcing Grains (2000)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 83 (2000), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Vickers indentation was performed on surfaces of silicon nitride with an aligned microstructure in order to study the interaction between cracks and the microstructure. Although there was not much evidence of crack bridging, the transverse radial cracks were very short, resulting in high fracture toughness values. The longitudinal radial cracks tended to propagate along the grain boundary of the reinforcements and were much longer than the transverse cracks. As the sintering temperature increased, the lateral cracks on the casting surface led to spalling and consumed more energy for the crack formation, making the longitudinal cracks shorter. On the surface normal to the alignment direction, there was no spalling and the indentation cracks became longer as the sintering temperature increased.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2000.tb01252.x
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  • 8
    Electronic Resource
    Electronic Resource
    Effect of Carbides on the Microstructure and Properties of Ti(C,N)-Based Ceramics (1999)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 82 (1999), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Ti(C,N)-based ceramics that contained various carbides were prepared via pressureless sintering, to study the effects of the carbides on the microstructure and properties of the ceramics. All the systems showed good densification behavior and formed solid solutions. Impurities introduced from the milling media were sufficient to promote the densification of the ceramics. The grain structures of the systems were a function of carbide crystal structure and their affinity with nitrogen. Microhardness, three-point flexural strength, and fracture toughness of the Ti(C,N)-based ceramics were measured and determined to be 16-18 GPa, 0.7-1.1 GPa, and 3.5-5.5 MPa·m1/2, respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1999.tb02216.x
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  • 9
    Electronic Resource
    Electronic Resource
    Effect of the Sintering Additives on the Microstructure and the Properties of Textured Silicon Nitride (2005)
    s.l. ; Stafa-Zurich, Switzerland
    Key engineering materials Vol. 287 (June 2005), p. 242-246 
    Details
    ISSN: 1013-9826
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Silicon nitride samples without and with 3 wt% of the aligned b-silicon nitride whisker seeds were prepared with 8.2 wt% Er2O3 and 1.9 wt% AlN. After sintering at 2148 K for 4h, the samples exhibited densities higher than 99.5% TD. The microstructures and properties of the samples were compared with those of the samples sintered with 4.8 wt% Y2O3 and 2.2 wt% Al2O3 at 2273 K for4h. For samples without the whiskers, the sample with 4.8 wt% Y2O3 + 2.2 wt% Al2O3 had coarser microstructures than those with with 8.2 wt% Er2O3 + 1.9 wt% AlN. However, the samples with the whisker seeds, the former sample appeared to have only slightly larger grains than the latter sample in spite of the significant difference in the sintering temperatures. For the samples withoutthe whisker seeds, the room temperature flexural strength was higher for the sample with Er2O3 + AlN. However, for the samples with the aligned whisker seeds, the sample with Y2O3 + Al2O3 exhibited higher room temperature flexural strength than that with Er2O3 + AlN although the average grain width of the former sample was larger than that of the latter sample. In case of the high temperature flexural strength at 1673 K, the flexural strengths of the samples with the whisker seeds were higher than double the strengths of the samples without the whisker seeds. Forsamples without the whisker seeds, the sample with Er2O3 + AlN exhibited better mechanical properties than that with Y2O3 + Al2O3. However, for the samples with the aligned whisker seeds, the sample with Y2O3 + Al2O3 exhibited better mechanical properties than those with Er2O3 + AlN. The results were explained in terms of the microstructures of the samples
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/01/49/transtech_doi~10.4028%252Fwww.scientific.net%252FKEM.287.242.pdf
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  • 10
    Electronic Resource
    Electronic Resource
    The Effect of Nitrogen Partial Pressure on Microstructure of Reaction Bonded Silicon Nitride (2007)
    s.l. ; Stafa-Zurich, Switzerland
    Solid state phenomena Vol. 121-123 (Mar. 2007), p. 231-234 
    Details
    ISSN: 1662-9779
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Physics
    Notes: The interaction between gas atmosphere and silicon during reaction bonded siliconnitride(RBSN)process leads to a non-uniform band formation of alpha silicon nitride. The reactionlayer, α -Si3N4, was formed near the surface of the sample in the early stage of RBSN. Reactivenitrogen gas was supplied as static state using computer controlled gas delivery system. Theformation of α -Si3N4 band near the surface of the sample can be explained thermodynamically,based on the nitrogen partial pressure in the gas mixtures
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/02/23/transtech_doi~10.4028%252Fwww.scientific.net%252FSSP.121-123.231.pdf
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