Influence of mechanical pressure and temperature on the chemical interaction between steel and silicon nitride ceramics

The chemical interaction between a Si3N4 ceramic, with Al2O3 and MgO sinter ing additives, and DIN 100Cr6 steel was studied by means of static interact ion couple experiments between 500 and 1200 degrees C. At 500 degrees C, th e ceramic was chemically stable in contact with the steel. In the temperatu re range between 700 and 1100 degrees C, the silicon nitride dissociated in contact with the steel. The Si dissolved and diffused into the steel, wher eas a nitrogen pressure built up in the micropores at the interface, limiti ng and inhibiting the reaction rate. The strength of the obtained interfaci al bond was too low to withstand the residual stresses formed during coolin g, and therefore, the interaction couples fell apart during cooling. Above 1100 degrees C, the nitrogen also dissolved and diffused into the steel, en hancing the overall rate of interaction. A strong interface was formed, res ulting in a well-defined interaction layer on the ceramic side of the inter action couple. The mechanical pressures on the interaction couples were adj usted to study the influence of plastic deformation of the steel on the che mical interaction. Higher contact pressures resulted in more homogeneous an d uniform interaction layers. The reactivity of plastically and elastically deforming steel, however, was found to be the same.