EFFECT OF PROCESSING VARIABLES ON INTERFACIAL PROPERTIES OF AN SIC-FIBER-REINFORCED REACTION-BONDED SI3N4 MATRIX COMPOSITE

Fiber/matrix interfacial debonding and frictional sliding stresses wer e evaluated by single-fiber pushout tests on unidirectional continuous silicon-carbide-fiber-reinforced, reaction-bonded silicon nitride mat rix composites. The debonding and maximum pushout loads required to ov ercome interfacial friction were obtained from load-displacement plots of pushout tests. Interfacial debonding and frictional sliding stress es were evaluated for composites with various fiber contents and fiber surface conditions (coated and uncoated), and after matrix densificat ion by hot isostatic pressing (HIPing). For as-fabricated composites, both debonding and frictional sliding stresses decreased with increasi ng fiber content. The HIPed composites, however, exhibited higher inte rfacial debonding and frictional sliding stresses than those of the as -fabricated composites. These results were related to variations in ax ial and transverse residual stresses on fibers in the composites. A sh earlag model developed for a partially debonded composite, including f ull residual stress field, was employed to analyze the nonlinear depen dence of maximum pushout load on embedded fiber length for as-fabricat ed and HIPed composites. Interfacial friction coefficients of 0.1-0.16 fitted the experimental data well. The extremely high debonding stres s observed in uncoated fibers is believed to be due to strong chemical bonding between fiber and matrix.