Abstract
In this paper, the fracture strength in low-temperature flux bonding (below 1000°C) of sintered alumina is determined in terms of bonding conditions such as temperature, time, pressure and grain size of flux, and is discussed in the basis of the linear fracture mechanics concept.The fracture stress was measured on bonded specimens by a four-point bending test. The fracture stress increased with increasing bonding pressure and decreasing grain size of flux. As for the bonding temperature and time, peaks in the stress appeared at about 750°C and 60 min, respectively. The fracture stress was also closely related to the size of the residual pores observed by microscope on the fracture surface of the bonding flux layer, which in turn depended on bonding conditions. The maximum fracture strength which attained in the bonding conditions employed was approximately 80% of the strength of solid.Based on the linear fracture mechanics concept, the fracture strength in bonding was interpreted by regarding the residual pores as an equivalent circular crack type defect. It was found that the fracture stress is proportional to 1/√a, where a is the equivalent crack size, so that the predominant factor affecting fracture strength is the residual pore size in the bonding flux layer.
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