Effect of grain growth and measurement on fracture toughness of silicon nitride ceramics

摘要

Two kinds of α-Si3N4 powders with differentproperties (high purity and low purity) were pressureless sinteredusing MgAl2O4-ZrO2 as sintering additives. The grain growth wascontrolled by sintering time and temperature. The fracturetoughness was determined using indentation microfracture (IM)and single-edge-precracked-beam (SEPB) methods. A discrepancyof fracture toughness was found between the values obtained bythese two methods, and the SEPB method provided higher fracturetoughness than the IM method. Materials with more largeelongated Si3N4 grains gave higher fracture toughness, R-curvebehavior and larger discrepancy. This is contributed to the effectsof grain bridging, pullout and deflection by the large elongatedSi3N4 grains. Comparing the specimens from two kinds of α-Si3N4 powders with different purity level, both gave high fracturetoughness of over 9MPa·m1/2 by the SEPB method, while the E10samples have a little higher flexural strength.