Microstructure characterization and process-structure correlations in SiC/ BN/SiC minicomposites

This article presents a methodology to characterize coating uniformity and defects and to establish processstructure correlations in SiC/BN/SiC minicomposites. Finely polished cross-sections of minicomposites are imaged via scanning electron microscopy. Image analysis is used to measure coating thickness, fiber locations, fiber contacts, and other microstructural metrics. Correlations between coating characteristics and fiber locations and local volume fractions are examined. A meso-scale diffusion/reaction model examines effects of distance from the tow boundary on coating uniformity. Key findings include: (i) Closed clusters of contacting fibers, produced by tow twisting, severely impede coating deposition and cause large coating variations. (ii) Away from fiber contacts, coating uniformity correlates with distance to the tow boundary and local fiber volume fraction. Uniformity decreases as deposition proceeds. (iii) The diffusion/reaction model shows that spatial variations in coating uniformity are governed by a Thiele modulus which depends on deposition temperature and tow porosity. Comparisons to experiments suggest the methodology can provide insights into process-structure linkages and potentially guide process improvements.