Electrical resistance of non-oxide ceramic matrix composites: Health monitoring and design considerations

Abstract

For Ceramic Matrix Composites (CMCs) with an electrically conductive matrix, direct current potential drop techniques have the potential to detect composite state such as conductive constituent content (e.g., Si in melt-infiltrated composites) or local defects such as delamination or porosity. In our study, we aimed to evaluate effectiveness of Electrical Resistance (ER) as a NDE method for different 2D woven SiC-based Melt-infiltrated composites, each exhibiting varying degrees and types of processing defects. We conducted three types of ER measurements: a. Bulk Resistivity b. Through-thickness c. Axial, along the axial length of dogbone specimens in the gauge section. Microstructural analysis was performed to correlate observations with microstructure. The bulk resistivity of the specimens in our study exhibited a linear correlation with the infiltrated Si in the matrix, even with different percentage and type of porosities present, allowing us to comment on Si-content of coupon size specimens. For Through-thickness measurements, absolute values of the measured potential represent Si-content, but it was not sensitive to porosity due to processing defects. In some cases, the local flow of current for axial type measurements is affected by and able to locate the local and distinct type porosity. Resistance was sensitive for regions of poor Si-infiltration i.e., “dry-slurry” type defects as well as for isolated larger rounded pores. It was very sensitive to local surface porosity but not as sensitive for cases where porosity was homogenously present throughout the specimen. Such one-sided axial measurements suit optimally for cases when only one side of the manufactured specimen or fabricated component is easy to access, or the porosity present is one-sided. The results confirm the potential of ER as a valuable tool for assessing the properties and integrity of Si/SiC CMCs in particular and should be applicable to CMCs where the matrix is conductive than the fibers. The technique offers insights into both material composition and the presence of specific types of defects.