Chemical reactivity of silicon nitride with steel and oxidised steel between 500 and 1200°C

The chemical interaction of a Si3N4 ceramic with pristine and oxidised 100Cr6 steel was studied by means of static interaction couple experiments between 500 and 1200°C. Si3N4 was not chemically stable in contact with oxidised steel at elevated temperatures, and reacts with the formation of N2, SiO2 and/or Fe2SiO4 at temperatures at and above 1000°C. At 700 and 500°C, Si diffusion into the oxide layer indicated the dissociation of the Si3N4 ceramic. Si3N4 also dissociated in contact with pristine steel. In the temperature region between 700 and 1100°C, the Si dissolves and diffuses into the steel whereas a nitrogen pressure is built-up in the voids of the metal–ceramic interface, limiting the degree of interaction. Above 1100°C, the nitrogen dissolves and diffuses into the steel as well, enhancing the reactivity and resulting in the formation of a strong metal–ceramic interface.