Volume 25, Issue 1 (January 1997)
Ultrasonic Characterization of Interphasial Properties in Sapphire/Haynes 214 Composites
This paper reports ultrasonic measurements of elastic properties of Haynes 214 metal matrix composites reinforced with sapphire fibers. The focus of this work is on the effects of the fibermatrix interphases on the composite moduli. Four groups of samples were prepared using fibers with different coatings (including one with no coating). There are two samples in each group: one subjected to one thermal cycle at 1200°C and the other a failed tensile sample tested in transverse-to-fiber direction. Ultrasonic velocity measurements were performed for different wave propagation directions in two incident planes: parallel and perpendicular to the fibers. The velocity data were used to find the elastic constants of the composite. Due to excess matrix material near the sample surface, a matrix/composite layer/matrix laminate model was used to determine the composite layer moduli. A micromechanical model was developed to estimate the interphasial effective elastic moduli from the composite moduli. The transverse moduli of the composite and the fiber are obtained using an averaging scheme to account for material anisotropy in the transverse plane. It was found that for the thermally cycled samples the interphasial moduli are quite similar among different sample groups. However, for the fractured samples the effective interphasial moduli of one group were extremely low, indicating debonding of the interphases before failure, whereas the interphasial moduli of other groups did not significantly differ from those of the thermally cycled samples.