ULTRASONIC CHARACTERIZATION OF INTERPHASIAL PROPERTIES IN SAPPHIRE HAYNES-214 COMPOSITES/

This paper reports ultrasonic measurements of elastic properties of Ha ynes 214 metal matrix composites reinforced with sapphire fibers. The focus of this work is on the effects of the fiber-matrix interphases o n the composite moduli. Four groups of samples were prepared using fib ers with different coatings (including one with no coating). There are two samples in each group: one subjected to one thermal cycle at 1200 degrees C and the other a failed tensile sample tested in transverse- to-fiber direction. Ultrasonic velocity measurements were performed fo r different wave propagation directions in two incident planes: parall el and perpendicular to the fibers. The velocity data were used to fin d the elastic constants of the composite. Due to excess matrix materia l near the sample surface, a matrix/composite layer/matrix laminate mo del was used to determine the composite layer moduli. A micromechanica l model was developed to estimate the interphasial effective elastic m oduli from the composite moduli. The transverse moduli of the composit e 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 am ong different sample groups. However, for the fractured samples the ef fective interphasial moduli of one group were extremely low, indicatin g debonding of the interphases before failure, whereas the interphasia l moduli of other groups did not significantly differ from those of th e thermally cycled samples.