Damage Resistance of In Situ Reinforced Silicon Nitride

Abstract

ABSTRACTThe room temperature fracture behavior for in situ reinforced (ISR) silicon nitride is correlated to its microstructure and R-curve behavior. The relation of strength to fracture origin suggests that stable growth of the intrinsic flaw precedes catastrophic fracture. Grainbridging that generates a rising bridging stress behind the crack-tip has been proposed as the cause for stable crack growth, which in turn reduces the strength dependency on initial flaw size. As a result of strong bridging by the acicular β-Si3N4 grains, ISR Si3N4 is characterized for high Weibull modulus. At elevated temperatures, the material's tensile creep rupture behavior follows the Monkman-Grant type plot. A tensile creep rate of -10−9s−1 at 1260°C/250 MPa, 1300°C/180 MPa, and 1350°C/90 MPa has been recorded. This relatively strong creep resistance is related to the sliding-resistance of the acicular grains and the properties of the amorphous film between the grains in ISR Si3N4.