Interpretation of tensile and compressive creep behaviour of two nickel alloys

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Abstract
The tensile and compressive creep behaviour of Nimonic 90 and Nimonic 108 have been studied at 700–900°C and the strain-time curves were found to have similar shapes. At the higher temperatures, both alloys exhibited tertiary creep under compression at strains less than 2 per cent. In Nimonic 108 each stage of the curves coincided for tension and compression, and tertiary deformation was exhibited only at 900°C. For Nimonic 90 tertiary deformation in compression occurred above 700°C and was delayed relative to tension at each temperature. In all cases the primary and secondary stages of deformation coincided. It appears that the more rapid development of tertiary creep in tension is due to the development of cracks and their influence on recovery processes. It is suggested that the structural recovery is mainly through development of zones adjacent to grain boundaries that are denuded of γ′ precipitate.