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Factors Influencing the Residual Stresses in Layered Silicon Nitride-Based Composites
Abstract In the field of Si3N4 ceramics/ceramic composites quite promising achievements were reached in the last decades. The room temperature strength > 1 GPa, fracture toughness > 10 MP a.m1/2 and Weibull modulus > 40 are reported [1–5]. These excellent properties of Si3N4 based ceramics/ceramic composites were achieved by deeper understanding of the basic phenomena taking part during processing. Based on knowledge of phase transformation, grain growth, densification, glassy phase formation and crystallisation, role of its chemistry, etc., ceramic materials with tailored microstructure and outstanding properties are produced. This approach requires more sophisticated processing and application of high purity starting powders because of known sensitivity to defects either in the form of agglomerates or local changes in chemistry. Presence of large and sharp defects (size several times larger than the largest grain in the microstructure) causes an abrupt decrease in strength to only a fraction of the actual potential of the material. In our previous work it was reported that decreasing the maximum defect size from approx. 80 μm to the size of the largest grain (20 – 30 μm) caused an increase of bending strength in β-Si3N4 whisker reinforced Si3N4 ceramics from 512 MPa to 930 MPa [6]. By removing the free carbon precipitates from the Si3N4-SiC micro/nano composite the bending strength is increased from 630 MPa to 1.2 GPa [7]. Only the “defect free” ceramics/ceramic composites are those perspective materials for structural applications which are usually reported as candidates for the technologies of the next millennium. The production of this kind of materials puts extreme requirements on each processing step and their cost becomes unacceptable.
Factors Influencing the Residual Stresses in Layered Silicon Nitride-Based Composites
Abstract In the field of Si3N4 ceramics/ceramic composites quite promising achievements were reached in the last decades. The room temperature strength > 1 GPa, fracture toughness > 10 MP a.m1/2 and Weibull modulus > 40 are reported [1–5]. These excellent properties of Si3N4 based ceramics/ceramic composites were achieved by deeper understanding of the basic phenomena taking part during processing. Based on knowledge of phase transformation, grain growth, densification, glassy phase formation and crystallisation, role of its chemistry, etc., ceramic materials with tailored microstructure and outstanding properties are produced. This approach requires more sophisticated processing and application of high purity starting powders because of known sensitivity to defects either in the form of agglomerates or local changes in chemistry. Presence of large and sharp defects (size several times larger than the largest grain in the microstructure) causes an abrupt decrease in strength to only a fraction of the actual potential of the material. In our previous work it was reported that decreasing the maximum defect size from approx. 80 μm to the size of the largest grain (20 – 30 μm) caused an increase of bending strength in β-Si3N4 whisker reinforced Si3N4 ceramics from 512 MPa to 930 MPa [6]. By removing the free carbon precipitates from the Si3N4-SiC micro/nano composite the bending strength is increased from 630 MPa to 1.2 GPa [7]. Only the “defect free” ceramics/ceramic composites are those perspective materials for structural applications which are usually reported as candidates for the technologies of the next millennium. The production of this kind of materials puts extreme requirements on each processing step and their cost becomes unacceptable.
Factors Influencing the Residual Stresses in Layered Silicon Nitride-Based Composites
Šajgalík, P. (author) / Lencčéš, Z. (author) / Dusza, J. (author)
1997-01-01
9 pages
Article/Chapter (Book)
Electronic Resource
English
Residual Stress , Fracture Toughness , Thermal Expansion Coefficient , Layered Composite , Weibull Modulus Engineering , Industrial and Production Engineering , Materials Science, general , Ceramics, Glass, Composites, Natural Methods , Characterization and Evaluation of Materials , Inorganic Chemistry
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