Diffusion bonding of Si 3 N 4 -TiN composite with nickel-based interlayers
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6/28/03
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Diffusion Bonding of Si3N4-TiN Composite with Nickel-Based Interlayers F. DESCHAUX-BEAUME, N. FRETY, and C. COLIN The diffusion bonding of a Si3N4-TiN composite with Ni, INVAR (Fe-Ni alloy), and IN600 (Ni-CrFe 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.
1. brazing with or without reactive elements in a braze alloy; and 2. solid-state bonding, or diffusion-bonding.
perature, and is reserved for low- or medium-temperature applications. On the contrary, the second one can produce refractory bonds, which remain stable up to high temperature. This joining technique needs generally the use of a metallic interlayer, which can interact with the ceramic part during the bonding process. The properties of the joint at high temperature depend on many factors, such as the thermal expansion mismatch between ceramic and interlayer material, or the reactivity of both materials at high temperature. Many previous works have shown the ability of silicon nitride to be joined with refractory metals such as Ni,[6–13] Fe,[14–18] Cr,[18–21] and their alloys[22–27] by diffusion bonding above 1000 °C. On the contrary, titanium nitride is more stable, and no chemical reaction has been observed with metals up to 1400 °C.[14,15,27] Up to now, diffusion bonding of composites combining both phases has not been extensively investigated. The work presented in this article is part of a study concerning the joining of a Si3N4-TiN composite by diffusion bonding using various metals or metallic alloys interlayers, for high-temperature structural applications. This article focuses on the results obtained with nickel and nickel alloy interlayers, according to the bonding conditions. Thanks to scanning electron microscopy, microstructural investigations, and wavelength dispersive spectrometry analyses, the interfacial structu
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