Segregation to fiber/matrix interfaces in Ni < inf> 3 Al IMCs reinforced with single crystal Al < inf> 2 O < inf> 3 fibers

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Previous studies have shown that both precipitation and impurity segregation occur at fiber/matrix interfaces in composites based on NiAl matrices modified by zirconium plus boron and reinforced with Al2O3 fibers. Precipitation reactions involve formation of Zr-rich oxides, and sulfur (a trace impurity) is observed to segregate strongly to the interfaces. In combination, these effects influence the mechanical interaction between the fiber and the matrix. The purpose of this paper is to report observations concerning the segregation and precipitation processes at fiber/matrix interfaces, resulting from several different thermal histories, in a single intermetallic-matrix composite. These results, obtained using Auger electron spectroscopy (AES), indicate that the sulfur segregation present at fiber/matrix interfaces in as-fabricated composites is diminished after annealing in the temperature range between 600°C and 1050°C. The effects of this variation in segregation level on fiber push-out test results are small, but fractographic and AES analyses suggest that sulfur segregation lowers fiber/matrix cohesion. © 1993.

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