Abstract
Beta (β)-Si3N4 powder containing 1mol% equimolar Y2O3-Nd2O3 was gas-pressure-sintered under three combined conditions of temperature, N2 gas pressure and time. Cyclic fatigue testing of these materials was performed using smooth specimens in ambient air. The fatigue crack growth diagram (KI max-da/dN diagram) was calculated from the fatigue lifetime distribution data by using the statistical method proposed by Fett and Munz. These materials had a microstructure of “in-situ composites” as a result of exaggerated grain growth of some β-Si3N4 grains during firing, and showed high fracture toughness. The crack growth rates of the materials were retarded by high fracture toughness. The threshold KI max value of crack growth was recognized in crack growth rate diagrams of these materials. It was deduced that the characteristic fatigue behavior of Si3N4 materials prepared from β-phase powder was due to high fracture toughness caused by in-situ composite microstructure.
