In Situ Observations of Tensile and Compressive Deformations in Semi Solid Metallic Alloys Using Time-resolved X-ray Imaging

摘要

Synchrotron X-ray radiography was used to study tensile and compressive deformations of semi solid Al-Cu and/or Fe-C alloys. In the case of tensile deformation of globular Al-Cu sample at similar to 60% solid, relatively high strain regions were formed even at mean strain of 0.005. The normal strain rate at the regions was 10 times as high as mean normal strain rate (3.45x10(-3) s(-1)). At mean strain of 0.04, tensile deformation was localized in the high strain region, resulting in the formation of internal cracking in the plane normal to the tensile axis. On the other hand, in the case of compressive deformations of globular Al-Cu sample at similar to 55% solid and polygonal Fe-C sample at similar to 73% solid, shear bands with decreased solid fraction were formed at the domains tilted by approximately 45 degrees with respect to compressive plane. Rearrangement of solid particles including translation and rotation caused the shear induced dilation at the shear domains. Shear strain was localized at the shear domain with decreased solid fraction. Deformation of the polygonal solid particle of Fe-C sample caused a force to transmit over a longer distance than for the globular Al-Cu sample. Shear fracture finally occurred due to inadequate liquid flow into the expanding spaces between solid particles caused by shear-induced dilation. The solid/solid interaction including impingement between solid particles and rearrangement has significant role in the compressive deformation. These observations demonstrated that the mechanism of cracking formations induced by compressive deformation was totally different from that in the tensile deformation.