Microstructure and Properties of Self‐Reinforced Silicon Nitride

Problems associated with manufacturing Si 3 N 4 /SiC‐whisker composites have been overcome by developing selfreinforced Si 3 N 4 with elongated β‐Si 3 N 4 grains formed in situ from oxynitride glass. This Si 3 N 4 –Y 2 O 3 –MgO–SiO 2 –CaO‐based material has a flexure strength >1000 MPa and fracture toughness >8 MPa·m ½ . The optimum combination of mechanical properties has been obtained with Y 2 O 3 :MgO ratios ranging from 3:1 to 1:2, CaO contents ranging from 0.1 to 0.5 wt%, and Si 3 N 4 contents between 90 and 96 wt%.