XRD investigation of Si-SiC composites with fine SiC microstructure

Si-SiC composite (reaction bonded SiC) with a submicron SiC microstructure (starting SiC particle size: 0.22 mum) was examined by XRD analysis to dete rmine the amount and phase composition of the secondary SiC formed by the r eaction between silicon and carbon during the sintering process. It was fou nd that the secondary SiC has grown onto the original hexagonal alpha -SiC grains as well as into the porosity of the green body. An increase of 3C-Si C was found within the microstructure after infiltration (from 2.6 wt.% bef ore infiltration to 8.8 wt.% after infiltration) whereas the 4H-ploytype co ntent was reduced. This behavior may be explained by the very small origina l SiC grains which acted as seeds for disoriented SiC growth and were assum ed to force the nonepitaxically deposition of secondary SiC. Solid state an d fast transportation processes caused the observed transformation of the S iC. Examinations of the silicon source (infiltrant) after the infiltration procedure showed that most of the carbon was converted to SiC with cubic mo dification (3C stacking sequence). (C) 2001 International Centre for Diffra ction Data.