SiC/Si3N4 nano/micro-composite - processing, RT and HT mechanical properties

Two SiC/Si3N4 nano/micro composites were prepared from a starting mixture of crystalline α-Si3N4, amorphous SiNC, Y2O3 and/or Al2O3. The composite material for room temperature (RT) application has high strength of 1200 MPa, Weibull modulus of 19 and moderate fracture toughness of 7 MPa m1/2. The composite for high temperature (HT) application, without Al2O3 has RT strength of 710 MPa and is able to keep 60% of its RT strength up to 1300°C. The creep resistance of composite material is approx. 1 order higher compared to relative monolith up to 1400°C

Investigation of the high temperature properties of structural ceramics Final report

The reported project aims at understanding the influence of the composition, microstructure, temperature, environment and loading condition on the high temperature deformation and fracture properties of different structural ceramics based on Si_3N_4 and Al_2O_3. The temperature dependence of Young's modulus of different Si_3N_4 based ceramics was studied using 4-point-bending tests in the temperature range from 25 to 1300 C. The experimental results of the subcritical crack growth in hot pressed Si_3N_4, Si_3N_4+Si_3N_4-whisker, Al_2O_3+SiC-whiskers and in situ reinforced Si_3N_4 systems show that in all cases a very intensive crack growth occurs at the temperature 1200 C, but its velocity for different material systems is different. In the case of the systems Si_3N_4, Si_3N_4+Si_3N_4-whisker, in-situ reinforced Si_3N_4 and Al_2O_3+SiC-whiskers the R-curve behaviour, i.e., the change of the crack growth resistance with rising crack extension at 1200 C was studied using static fatigue testing method. (orig.)Available from TIB Hannover: F95B1349+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEBundesministerium fuer Forschung und Technologie (BMFT), Bonn (Germany)DEGerman