Silicon nitride composites reaction-bonded

SiC FIBER-REINFORCED REACTION-BONDED SILICON NITRIDE COMPOSITES... 

FIGURE 1. Fabrication steps for SiC fiber reinforced reaction-bonded silicon nitride composites. 

Bhatt, R.T., Phillips, R.E. (1990), Thermal effects on the mechanical properties of SiC fibre reinforced reaction-bonded silicon nitride matrix composites , J. Mater. Sci., 25, 3401-3407. 

The thermodynamics of the above-elucidated SiC/C and SijN Si composites are determined by the decomposition of silicon carbide and silicon nitride, respectively, into their elements. The chemistry of ternary Si-C-N composites is more complex. If producing Si-C-N ceramics for applications at elevated temperature, reactions between carbon and silicon nitride have to be considered. Figure 18.2, which exhibits a ternary phase diagram valid up to 1484°C (1 bar N2) displays the situation. The only stable crystalline phases under these conditions are silicon carbide and silicon nitride. Ceramics with compositions in the three-phase field SiC/Si3N4/N are unknown (this is a consequence of the thermal instability of C-N bonds). Although composites within the three-phase field SiC/Si3N4/Si are thermodynamically stable even above 1500°C, such materials are rare. The reasons are difficulties in the synthesis of the required precursors and silicon melting above 1414°C. The latter aspect is of relevance, since liquid silicon dramatically worsens the mechanical properties of the derived ceramics. 

J.W. Lucek, G.A. Rossetti, Jr., and S.D. Haitline, Stability of Continuous Si-C (-0) Reinforcing Elements in Reaction-Bonded Silicon Nitride Process Environments, pp. 27-38 in Metal Matrix, Carbon, and Ceramic Matrix Composites 1985, NASA CP-2406, Edited by J.D. Buckley, NASA, Washington, B.C., 1985. 

R.T. Bhatt and ILE. Phillips, Laminate Behavior for SiC Fiber-Reinforced Reaction-Bonded Silicon Nitride Matrix Composites, J. Comp. Techn. Res. 12, p. 13, 1990. 

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