An X-Ray Study on the Effect of Hydrostatic Stress on Creep of Polycrystalline Metal at Elevated Temperatures

Abstract

As one of the series of study on the effect of hydrostatic pressure on plastic deformation of polycrystalline metals, in the present paper, the effect of hydrostatic pressure on tensile creep of polycrystalline metals at elevated temperatures was discussed based on the X-ray measurements. In the previous paper by the present authors, the remarkable decrease in creep strain rate of the materials subjected to combined hydrostatic pressure at room temperature was discussed from the viewpoint of continuum mechanics. It was also pointed out that the effect of hydrostatic pressure on tensile creep of metals at elevated temperatures was not fully explained from the extension of creep mechanics of the materials under confining pressure. Therefore, it became necessary to take account of the effect of hydrostatic pressure on the structural change of the metal in the creep process at elevated temperatures.In order to elucidate the structural change in metals creep under hydrostatic pressure at elevated temperatures, in the present study, the experimental measurements of misorientation was performed on the coarse-grained, commercially pure aluminum sheet specimen by using the X-ray back reflection Laue method. It is specially noted that misorientation is a useful measure to study the effect of hydrostatic pressure on creep of metals at elevated temperatures, because it represents not only the density of both edge and screw dislocations but also the grobal imperfection density such as the density of vacancy in plastically deformed metals. It is suggested from the present experimental results that the decrease in the minimum creep rate of the metal under combined hydrostatic pressure at elevated temperatures results mainly from the decrease in jog density which is closely connected to the density of vacancy in the material.