Interfacial Solid State Reactions Of The Si₃N₄/Ni(Fe) And Their Aluminides Systems

The interfacial solid state reactions of the Si3N4/Ni(Fe)and their aluminides systems are the acute problems in using Si3N4 to fabricating for high-temperature structural ceramics,metal matrix composites, and etc. In this paper, studies on the Si3N4/Ni, Si3N4/Fe, Si3N4/Fe3Al and Si3N4/Ni3Al plane-interface reactions were done to reveal the microstructures, phases and elemental distributions of the solid state reaction zones of these couples, and the reaction mechanisms were also investigated. The studies are important theoretially for fabricating Si3N4/Fe3Al and Si3N4/Ni3Al complex components and composites.After the Si3N4/Fe, Si3N4/Fe3Al, Si3N4/Ni and Si3N4/Ni3Al plane-interface couples treated at 1150℃for 10 h in two different atmospheres of Ar and N2, respectively, their reaction zones were all detected using scanning electron microscope(SEM), energy disperse spectroscopy analyzer(EDS) and X-ray diffraction analyzer (XRD). The research work was mainly focused on the morphologies, the microstructures, and the elemental distributions of each reaction zone. Meanwhile, the thermodynamic analyses of the Si3N4/Fe, Si3N4/Fe3Al, Si3N4/Ni and Si3N4/Ni3Al interfacial solid state reactions were also carried out. The main conclusions are described as follow:After heat-treated at 1150℃for 10 h in Ar and N2, the Si3N4/Fe and Si3N4/Ni interface reactions occur and have layer-typical reaction zone. The Si3N4/Fe reaction forms a reaction zone about 120μm thick in Ar atmosphere, and a reaction zone about 40μm thick in N2 atmosphere. The reaction zone is composed of Fe(Si) solid solution, in which a lot of small pores are distributed uniformly. The Si3N4/Ni system forms a reaction zone about 25μm thick in Ar atmosphere, and a reaction zone about 20μm thick in N2 atmosphere. The reaction zone is composed of Ni3Si, in which a lot of small pores are distributed uniformly, too.After heat-treated at 1150℃for 10 h in Ar, the Si3N4/Fe3Al and Si3N4/Ni3Al interfacial reactions are much slown down. The Si3N4/Fe3Al reaction only forms a reaction zone about 3μm thick. The reaction zone is composed of FeAl, Fe(Al,Si) solid solution and Al9FeSi3. The Si3N4/Ni3Al reaction only forms a reaction zone about 2μm thick. The reaction zone is composed of NiAl and Ni3Si. When the couples heat-treated in N2 admosphere, the interdiffusion of Fe and Si in the Si3N4/Fe3Al couple occurs in this process, but it is too week to form a solid reaction zone. In the Si3N4/Fe3Al couple, no interdiffusion of Ni and Si were found.Summarily, the chemical compatibilities of the Si3N4/Fe3Al and Si3N4/Ni3Al systems are much higher than those of the Si3N4/Fe and Si3N4/Ni3Al systems. The primary reason is that the Al element in Fe3Al and Ni3Al decreases the reaction activities of Fe and Ni elements in them, less than these of Fe and Ni elements in pure iron and nickel. As a result, the intensities of the Si3N4/Fe3Al and Si3N4/Ni3Al interfacial reactions remarkably decrease. Moreover, the chemical compatibility of the Si3N4/Ni3Al system is higher than that of the Si3N4/Fe3Al system.As for Si3N4/Fe, Si3N4/Ni, Si3N4/Fe3Al and Si3N4/Ni3Al systems, their reaction intensities in N2 atmosphere are all less than those in Ar atmosphere. It is due to higher N2 partial pressure in N2 atmosphere, which restrains the decomposition of Si3N4, therefore, decreases these interfacial solid state reactions.