MECHANICAL INTERROGATION OF INTERFACES IN MONOFILAMENT MODEL COMPOSITES OF CONTINUOUS SIC FIBER ALUMINUM MATRIX

The interfacial region between continuous SiC fiber and aluminum alloy matrix, in monofilament metal matrix composites (MMC), has been characterized. The study utilized two SiC fibers, produced by Textron (SCS-2) and Sigma (SIGMA) and two aluminum alloys: Al1100 and Al6061. Characterization methods employed included: optical and electron microscopy (i.e. SEM and EPMA), mechanical testing of as-received and heat treated single fiber samples and monitoring of acoustic emission (AE) during tensile tests. In addition, interfacial shear strength (ISS) was experimentally determined by two different techniques, indentation and fragmentation. Indentation tests were carried out in the temperature range of 0-320-degrees-C. Results indicate that load is transferred from the matrix to the fiber, primarily by frictional stresses. The friction between fiber and matrix during loading of composite stems residual compressive thermal stresses, which result from the temperature differential between consolidation and testing temperatures, and the difference between the thermal expansion coefficients of the fiber and matrix. Consolidation had no effect on fiber strength and no reaction zones formed. Exposure for 700 h at 600-degrees-C had no significant effect on ISS. Fiber fractures were accompanied by intense AE. The breaks produced a small piece between adjacent larger fragments, and gave rise to characteristic AE with distinct waveforms for the two different fibers (SIGMA and SCS-2).