超硬合金の銀ろう付におけるろう材中のNiとCoの効果

抄録

Ag-based filler metals containing Ni element have been recommended for brazing of cemented carbide because the Ni element is considered to improve the wetting characteristics to the cemented carbide. However, the reason for the improvement is still unknown.
The present study was aimed at clarifying the reason why the Ni element in Ag-based filler metals makes the wetting characteristics improved and the effects of the Ni element on the bending strength of the brazed joints. Ag-Cu-Zn ternary alloys with and without Ni element were produced to investigate the effects of the Ni element. Furthermore, Co element was added into the filler metals to prevent the Co element in the cemented carbide from diffusing into the brazed layer, and the effects of the Co element on the bending strength of the brazed joints were investigated. The obtained results in this study are as follows.
By the Ni element addition into the Ag-based filler metal, α-Cu solid solution phases were formed in the brazed layer along the interface; consequently, the distribution of Ag and Co elements across the interface between the cemented carbide and the α-Cu solid solution phases continuously changed. It seemed that the continuous distribution of Ag and Co elements across the interface caused the wetting characteristics to improve. The Ni element addition expanded the Co-depleted zone of the cemented carbide around the interface and decreased the bending strength of the joint brazed at 750°C. However, when the brazing temperature was set at 850°C, much amounts of Ni element diffused into the Co-depleted zone. As a result, the deterioration of the bending strength of the brazed joint was small. The Co element addition made the Co-depleted zone narrow, resulting in the increase of the bending strength of the brazed joints.