Genjiro Mima1 and Toshihiro Oka2
1Faculty of Engineering, Osaka University, Osaka
Grain-boundary sliding and zone shear during a constant rate heating under various constant shear stresses of 10,000 g/sq. cm to 40.000 g/sq. cm were measured in high-purity aluminium bicrystals (99.999%) with a boundary misorientation angle of 26 deg. The amount of grain-boundary sliding increased with increase of the shear stress up to 20,000 g/sq. cm, but when the stress increased to 30,000 g/sq. cm or 40,000 g/sq. cm, the amount of grain-boundary sliding became smaller than that for the shear stress of 20,000 g/sq. cm. A plot of the logarithm of the amount of the grain-boundary sliding per deg. cent. versus the reciprocal of the absolute temperature was found to lie on a series of a straight line over the lower temperature range. This relationship was discucced by the relation between the amount of grain-boundary sliding per deg. cent. and the rate of grain-boundary sliding, derived by the present authers. The activation energy thus obtained was 10,510 cal/mol for the test conducted in vacuum. According to the microscopic observation, grain-boundary sliding was found together with zone shear, but not vice versa.
In a microscopic observation on the specimen heated up to 300°C under the constant shear stress of 30,000 g/sq. cm, a polygonized structure was found within a band region adjacent to the grain-boundary. Voids formation due to grain-boundary siliding was observed in a common grain-boundary, and their number were dependent upon the amount of sliding. These voids obstructed the grain-boundary migration in the grain-boundary sliding process.
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