Three-dimensional observation of ductile fracture process by deflection contrast imaging in cast Al-7%Si alloys

Synchrotron X-ray microtomography has been utilized for the in-situ observation of ductile fracture in cast Al-7%Si alloys exposed at a high temperature for 0-10⁶ s. A high resolution experimental configuration and deflection contrast imaging technique have enabled the reconstruction of silicon particle images with an isotropic voxel with a 0.474 μm edge. The variations in particle shape, size and spatial distribution at the high temperature are readily observed, along with the existence and growth of high-density micro-pores. Three-dimensional image analysis is applied and its feasibility is confirmed. It is clarified that in the case of an as-cast material void nucleation and growth have been observed as has been reported for the general ductile fracture of metallic materials. When it is exposure at the high temperature for a long time, however, ductile fracture is found to be attributable mainly to the growth of pre-existing micro-pores and not the nucleation of new voids at silicon particles. Since such tendency has been also confirmed for other materials, more detailed analysis might be expected in a near future in order to understand actual ductile fracture process in practical materials.