Plastic deformation induced microstructure transition in nano-fibrous Al-Si eutectics

Indentation plastic zone of Al-20 wt% Si laser rapid solidified (LRS) alloy with nanoscale, fibrous, fully eutectic microstructure is characterized using a combination of atomic force microscopy (AFM), scanning electron microscopy (SEM) and scanning/transmission electron microscopy (S/TEM). In contrast to cracking around the indents in the as-cast Al-Si alloy, the LRS nano-fibrous eutectic microstructure demonstrated higher strength, strain-hardening, and uniformly distributed plasticity around indents with no cracks. A transition in morphology from long nano-fibrous Si to short nano-fibrous Si is observed underneath the indent in LRS eutectics. The mechanism for this morphological evolution with increasing plastic strain is postulated to involve three stages of the deformation process: First, the formation of closelyspaced dislocation arrays in the nano-channels of Al matrix confined by Si fibers. Second, fiber segmentation when the stress field of the dislocation array exceeds the critical stress for fracture in Si nanofibers. Third, recovery of dislocation substructures and sub-grain formation in Al leading to a rotation of fractured Si segments. The final microstructure consisted of short Si nano-fibers along triple junctions of the subgrains in Al. The implication of this unusual microstructure evolution with increasing plastic strain on the plastic co-deformation in high-strength LRS nano-eutectic microstructures was discussed in this report. (c) 2022 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).