Diffusion bonding of Si3N4-TiN composite with nickel-based interlayers

The diffusion bonding of a Si3N4-TiN composite with Ni, INVAR (Fe-Ni alloy), and IN600 (Ni-Cr-Fe alloy) interlayers has been investigated between 1100 °C and 1350 °C, under argon or nitrogen atmosphere. For the chosen bonding conditions, the Si3N4 phase of the composite reacts with the interlayer phase, leading to the release of silicon and nitrogen, whereas the TiN phase remains stable. The bonding mechanisms with nickel and INVAR (Ni-Fe alloy) interlayers are rather similar. Released silicon diffuses into the reaction layer and into the interlayer, forming a solid solution, whereas the released nitrogen remains gaseous. The bonding rate depends then on the elimination rate of nitrogen from the reaction interface. The thermal stability of these joints is very high up to 1100 °C. However, the interfacial porosity and the internal stresses created by the high nitrogen pressure are pernicious for the mechanical strength. The bonding mechanism with IN600 (Ni-Fe-Cr alloy) interlayer is rather different. The released nitrogen can form nitrides with interlayer elements (Cr, Al). Released silicon diffuses into the reaction layer and forms silicides. The joint porosity is less significant for the IN600 interlayer, which suggests a good mechanical strength. However, the formation of silicide is pernicious, because of the brittleness of these phases.