Bending and Contact Strength of a Si3N4+SiC Micro/Nano Composite

Abstract

Bending and contact strength of a carbon derived in-situ reinforced Si3N4-SiC micro/nanocomposite have been investigated. Four-point bending strength was measured using specimens with different effective volume and Weibull statistical analysis has been used for characterization of the strength values in the form of characteristic strength and Weibull modulus. The characteristic strength values of the investigated composite were σ0 = 675 MPa and σ0 = 832 MPa with the Weibull modulus of 6,4 and 8,6 for the specimens with effective volume 15,9 mm3 and 1,28 mm3 respectively. Contact strength of the investigated material was carried out using sphere on sphere and roller on roller methods and the obtained results are σ0S = 1997 MPa, σ0R = 1242 MPa, and mS = 17,1 mR = 6. Fracture origins in the specimens with effective volume of 15.9 mm3 tested in four-point bending were surface and volume located technological defects with dimensions from 10 μm to 180 μm, mainly in the form of clusters of pores and large SiC grains. Fracture mirror sizes were measured and the mirror constant was calculated. Fracture origins in the specimens with effective volume of 1.28 mm3 tested in four-point bending were surface (subsurface) defects with the same type as for the specimens with a higher effective volume. The fracture during the contact strength test „roller/roller“ has been initiated under the surface of the specimens and during the contact strength test „sphere/sphere“ by creation and growth of the cone cracks to critical size.