Journal of materials research vol:11 issue:5 pages:1265-1276
The chemical interaction between two beta'-O' Si-Al-O-N ceramics and a number of iron-based alloys is studied by means of static interaction couple experiments at 1100 and 1200 degrees C. The onset temperature of reaction of Si3N4 with pure iron was found to be at 1095 degrees C, which is in good agreement with a calculated temperature of 1033 degrees C. During the interaction, silicon and nitrogen from the ceramic dissolve and diffuse into the iron alloy, whereas the remaining aluminum and oxygen form Al2O3 particles. The interaction between ceramic and iron alloy is reaction controlled. In the initial stage of the interaction, the dissociation rate of the ceramic is the rate-controlling step. After the ceramic/metal interface is isolated from the furnace atmosphere, the nitrogen solution rate into the iron alloy becomes rate controlling. The influence of alloying elements on the reactivity could be related to their effect on the nitrogen solubility in the iron alloy. Ni, Si, and C decrease the nitrogen solubility and decrease the reactivity with the sialon ceramic. Cr and Mo have the opposite effect. The thickness of the interaction layer on the ceramic side of the interaction couple was found to be a function of the calculated nitrogen solubility in the iron alloy at 1 atm nitrogen pressure, making it possible to predict the relative chemical reactivity of a number of iron-based alloys with the same sialon ceramic.