Joining strength characteristics of large silicon nitride block joined without using any insert material

Large silicon nitride blocks were joined without using any insert material; further the microstructure of the joint region, and joining strength and its Weibull distribution of the joined block were investigated. Commercially available silicon nitride blocks sintered with Y2O3 and Al2O3 were used as the parent material; and the blocks were joined at 1800°C for 4 h under a nitrogen gas pressure of 0.9 MPa and a mechanical pressure of 11 MPa. The equiaxed and/or elongated silicon nitride grains of the parent silicon nitrides seemed to directly bond to each other; moreover, the joint interface was not clearly distinguishable from the parent silicon nitride region. The joined silicon nitride block had a room-temperature flexural strength of 622 MPa. The high-temperature strength of this block at 1000°C was decreased to 426 MPa, in spite of the absence of a joint layer. Further, the joined silicon nitride block had a Weibull modulus comparable to that of the parent silicon nitride.