Yield of polygonized aluminum single crystals

Abstract

Large single crystal segments of aluminum were produced by strain anneal, deformed in tension, and sectioned to produce tensile specimens with axes parallel to the original tensile axis and with other orientations. The specimens were annealed to produce a polygonized substructure. Their critical shear stress in tension was determined. The critical shear stress was shown to be the sum of a substructure independent stress and a stress proportional to the square root of the average primary subboundary misorientation over the average primary subboundary spacing. Comparison of the critical shear stress of specimens cut from the same parent crystal with varying tensile axes demonstrated that the significant subboundary spacing is that between primary subboundaries along the active slip plane of the specimen. The tests also showed that average subboundary misorientation is significant because it represents the average spacing of dislocations in the subboundaries. The results, interpreted in terms of current substructure strengthening theories, indicate that slip is propagated across primary subboundaries by the activation of dislocation sources in the subboundaries.