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

The chemical interaction of a Si3N4 ceramic with pristine and oxidised 100C r6 steel was studied by means of static interaction couple experiments betw een 500 and 1200 degrees C. Si3N4 was not chemically stable in contact with oxidised steel at elevated temperatures, and reacts with the formation of N-2, SiO2 and/or Fe2SiO4 at temperatures at and above 1000 degrees C. At 70 0 and 500 degrees C, Si diffusion into the oxide layer indicated the dissoc iation of the Si3N4 ceramic. Si3N4, also dissociated in contact with pristi ne steel. In the temperature region between 700 and 1100 degrees 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 inte raction. Above 1100 degrees 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. (C) 2000 Elsevier Science S.A. All rights reserved.