Strength characterization of yttria-doped hot-pressed silicon nitride

The flexural strength of yttria-doped hot-pressed silicon nitride was determined in 4-point bending as a function of temperature (200 to 14000C) in an air environment. Significantly, high strength (≥ 800 MPa) is maintained from room temperature to 12000C. At 13000C and above, flexural strength decreased considerably due to the softening of the residual glass phase. Flexural stress rupture testing at high temperatures (≥ 12000C) indicated softening of the material and at low temperatures (8000 to 10000C) exhibited a stress enhanced instability. Fractographic evidence to illustrate the importance of microstructures and flaws on strength will be presented