CHARACTERIZATION OF INTERFACIAL FAILURE IN SIC REINFORCED SI3N4 MATRIX COMPOSITE-MATERIAL BY BOTH FIBER PUSH-OUT TESTING AND AUGER-ELECTRON SPECTROSCOPY

An investigation into the mechanical/chemical properties of the fiber/matrix interface in an SCS-6 SiC reinforced reaction bonded Si3N4 composite is made using a fiber push-out test for determining interfacial shear strength and Auger electron spectroscopy (AES) depth profiling for elemental composition in the interface region. Special emphasis is placed on locating the weak point where interfacial failure occurs. Fiber push-out tests determined the interfacial frictional shear stress to have an average value of 8 MPa and was found to depend only on frictional stresses. AES depth profiles were obtained for composite fracture surfaces as well as pushed-out fibers. For both composite fracture and fiber push-outs, the interfacial failure was determined to occur either between the two C rich coatings that are present on the double-coated SCS-6 SiC fibers or between the inner C rich coating and the SiC fiber. Failure was not observed between the outer C rich coating and the matrix. AES depth profiles indicated that interface failure occurs at points of very abrupt concentration changes. Evidence is presented for substantial mass transport within the fiber coating during composite fabrication. © 1990, American Vacuum Society. All rights reserved.