2003 Volume 44 Issue 12 Pages 2701-2710
This paper describes the relation between the interfacial microstructure and the fracture strength of the joints of silicon nitride (Si3N4) and vanadium (V) formed by solid state diffusion bonding. At first, the interfacial microstructure and its evolution process were analyzed in detail. The phase sequence at the interface changes with the bonding time showing five typical stages. In the first stage, a V3Si layer and V2N grains are formed. The V2N grains contact with the V3Si layer at 1473 K and below, while the contact is prohibited at 1498 K and above. The Si3N4/V3Si interface is metastable. In the second stage, a V5Si3N1−X layer appears. In the third stage, V is annihilated. In the fourth stage, the V3Si layer is annihilated and VN grains are formed. In the fifth stage, V2N is annihilated. This evolution process of the interfacial microstructure agrees well with the proposed chemical potential diagram, except the metastable state of the interface. The increase and decrease behavior in the thickness of each reaction product interact with each other. The behavior of the V3Si layer is affected not only by the formation and growth of the V5Si3N1−X layer but also by the formation of a V(Si) zone at the V3Si/V interface. The formation of the V5Si3N1−X layer starts when the spatial gradient of the chemical potential of vanadium in the V3Si layer decreases to a certain value. The fracture strength of the joints changes depending on the bonding temperature and time. The higher bonding temperature leads to the higher maximum fracture strength. The maximum strength at each bonding temperature is achieved when the thickness of the V3Si layer is 2.0 μm. The prolonged bonding time gradually reduces the fracture strength down to 42 MPa.
