The Formation Mechanism of Reaction-Phases and its Regulation on a Solid-State Bonding Silicon-Nitride Ceramics to Metals

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The summary of the results of this research is shhown below.In the case bonded under low pressure, there is a slight time lag in the formation of reaction layrs, but there is no influence on the structure itself of reaction layres. There is a little difference in the structure of reaction layrs for different silicon-nitride ceramics bonded at abobu 1403K.The fracture bending strength of Si_3N_4/SUS304 couple bonded with the insert Cr-plated 2.0-3.5mum in thick showed the maxmum of 440MPa at room temperature. At early stage of the heating to bond at less than 1423K,Ni-Cr solid-solution at Ni side, Cr_2N at the interface of Ni and Cr-plating layr and Ni-Cr-Si ternary alloy at near the bonding interface were formed respectively. Thereafter, Cr_2N transforms to CrN and the mixed phase with CrN, (Cr_3Si) and Ni- (Si) alloy were formed at bonding interface. The thickness of this mixed phase depend on the thickness of Cr-plating. After disappearance of Cr as a plating layr as a result of the formation of reaction layrs, Ni-Cr-Si ternary eutectic alloy of low melting temperature is formde by the another reaction with diffused Ni through the mixed phases to Si_3N_4, so that this alloy phase fuses and Si_3N_4 are aggressively attacked and CrN phases already formed aer decomposde. On the bonding at 1473K,the close condensed CrN phases including little Ni- (Si) alloy are formed at bonding interface, so that the formation of fused phases are suppressed. A similar close condensed CrN phases can form by using a previously annealed Cr-plating Ni sheet as a insert. As a result of this research, it was found that there is a possibility of higher grade heat-resisting bonding using a insert with dual layr plating of Ni and Cr on Mo plate.