Abstract
AbstractA nickel aluminide with the composition Ni-23.5 Al-O.5 Hf-O.2 B (at. %) was creep-tested in tension at constant load (initial stress 250 MPa, temperature 1033 K). The creep rate reaches a minimum at a strain of approximately 0.3%. Its increase at larger strains is partly caused by grain boundary cavitation. Cavity size distributions corresponding to different creep times and strains were determined metallographically and evaluated in order to obtain the cavity growth rate as a function of cavity size. Contrary to a newly developed model for crack-like diffusive growth the cavity tip velocity increases with cavity size. This discrepancy is attributed to cavity coalescence. Sintering at elevated temperatures (1473 K) reduces the diameter and increases the thickness of the disc-shaped cavities. Sintering of such cavities might be exploited to measure surface diffusivities.
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