Micrometer‐sized refractory metal fibers of Nb were produced by an unconventional method of mechanically reducing arc‐cast ingots of Nb‐Cu in which the original microstructure contains ductile Nb precipitates. During mechanical reduction the precipitates were elongated into fibers, which were extracted by chemically dissolving the Cu matrix. Composite specimens of Nb fibers in a glass matrix were fabricated by dry‐blending a mixture of fibers and powdered glass, then hot‐pressing into disks. Fracture toughness, KIC, was measured using microin‐dentation and three‐point bending methods. The fracture toughness increased with increasing volume fraction of fibers with the greatest improvement noted at 0.10≤vf≤0.20. The values of KIC increased as the interfiber spacing and the fiber diameter decreased. Both the effective fracture surface energy and the fracture strength were enhanced by increasing vf. The small fibers embedded in the brittle matrix showed virtually no evidence of microcracking; Nb fibers and glass matrices also demonstrated good interfacial adhesion. Fractographs suggested that the fibers were very effective in resisting crack propagation. Experimental observations were explained using the concept of crack‐front bowing and fiber bridging.
|Original language||English (US)|
|Number of pages||6|
|Journal||Journal of the American Ceramic Society|
|State||Published - May 1980|