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

摘要

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.