Abstract
An experimental study has been made of the influence of simultaneously but independently applied tensile stresses, up to 28 N/mm2, and hydrostatic pressures, up to 14N/mm2, on the creep of copper at 500° C within an internally heated pressure vessel containing argon. The creep rate was reduced by hydrostatic pressure to an extent greater than previously anticipated. This effect was reversible with change in hydrostatic pressure and thus could not simply be related to a reduction in cavitation by pressure, though there was some indication of a link with the retardation of grain-boundary sliding. The results confirmed the substantial increase in creep life and ductility under hydrostatic pressure and provided quantitative information on the corresponding changes in the development of cavitation. The cavities were generally of a crystallographic form and they retained their individual identities to the instant when fracture occurred. This feature assisted in assessing creep damage and factors governing creep life. From experiments involving a change in hydrostatic pressure during creep testing, the results were analysed in a form which leads to a prediction of behaviour when conditions are not constant.
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