Zones free of γ′ precipitate formed adjacent to grain boundaries in the gauge-lengths of specimens of Ni–20 % Cr-base alloys subjected to creep tests or slow-strain-rate tensile tests in the temperature range 750–850°C (1023–1123 K) have been studied. Electron-probe microanalysis did not reveal any significant change in composition between the precipitate-free zones and the grain interior. Consideration of the variation in the stress-dependence of minimum creep rate with temperature and grain size indicates that a diffusion creep mechanism may explain the formation of the precipitate-free zones.
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