Strength and creep resistance of hot pressed silicon nitride (HPSN) reinforced by silicon carbide platelets

The effect of strengthening of a HPSN doped with 5 w/o Y2 O3 and 2 w/o Al2 O3 by a Si C platelet dispersion was studied. For that, the strength and creep resistance of samples containing a volume fraction of 20 vol% of Si C platelets in the size range from 32 to 50 μm was measured. The fracture strength at room temperature was considerably reduced by platelet addition, i.e from 900 MPa to 510 MPa, and it could be shown that this reduction is caused by an increased flaw size, the platelets acting as critical flaws. The creep rate of the reinforced material was clearly reduced as compared to that of HPSN without platelets and exhibited a stronger stress dependence. Thus, the reduction in the creep rate due the platelet reinforcement was most pronounced in the range of small stresses where it reached a factor of 3, whereas at higher stresses the creep rate approached that of the pure HPSN. (author)