Abstract
Composites of 1 to 20 vol % sapphire whiskers contained in a nickel matrix were produced by roll-bonding and by hot-pressing. The composites were examined using transmission electron microscopy, X-ray and electron diffraction, optical microscopy and mass spectrographic analysis. Composites were annealed in vacuum (1.3×10−3 N m−2), in low-pressure air (13.3 N m−2) and in dried hydrogen (101.3 N m−2) in the temperature range 1100 to 1400° C for times up to 3800 h. Whiskers in situ and the whisker/matrix interface were observed by transmission electron microscopy; matrix dislocations were associated with whiskers and were stable after annealing at 1400° C. Whiskers extracted from annealed composites showed significant morphological changes. These were attributed to: (i) ovulation from the tips of whiskers by interfacial diffusion, (ii) waisting from surface undulations, (iii) Ostwald ripening and (iv) constant-volume shape changes.
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Stapley, A.J., Beevers, C.J. The stability of sapphire whiskers in nickel at elevated temperatures. J Mater Sci 8, 1287–1295 (1973). https://doi.org/10.1007/BF00549344
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DOI: https://doi.org/10.1007/BF00549344