[Paper Review] Enabling plastic co-deformation of disparate phases in a laser rapid solidified Sr-modified Al-Si eutectic through partial-dislocation-mediated-plasticity in Si

Arkajit Ghosh, Wenqian Wu+3 more|arXiv (Cornell University)|Jul 30, 2023

Advanced Surface Polishing TechniquesEngineering54 references3 citations

TL;DR

This study demonstrates plastic co-deformation in laser-rapid-solidified, Sr-modified Al-Si eutectic by enabling partial-dislocation-mediated plasticity in nano-twinned silicon fibers. The combination of laser solidification and Sr doping reduces the Peierls barrier and aspect ratio of Si fibers, suppressing crack formation and enabling stable plastic flow up to 26% strain with a compressive flow strength of ~840 MPa and hardness of 2.9 GPa.

ABSTRACT

Nano-scale eutectics, such as rapid solidified Al-Si, exhibit enhanced yield strength and strain hardening but plasticity is limited by cracking of the hard phase (Si). Mechanisms that may suppress cracking and enable plastic co-deformation of soft and hard phases are key to maximizing plasticity in these high-strength microstructures. Using a combination of laser rapid solidification and chemical (Sr) modification, we have synthesized fully eutectic Al-Si microstructures with heavily twinned Si nano-fibers that exhibit high hardness up to 2.9 GPa, and high compressive flow strength (~840 MPa) with stable plastic flow to ~26% plastic strain. After deformation, the hard Si(Sr) fibers did not exhibit cracks, but a high density of stacking faults were observed in the Si(Sr) fibers suggesting partial dislocation mediated plasticity. Mechanisms for suppression of cracking and activation of partial dislocations in Si deformed at room temperature are discussed in terms of nanoscale fiber geometry with reduced aspect ratio and lowering of the Peierls barrier in chemically-modified, nano-twinned Si fibers.

Motivation & Objective

• To overcome the limited plasticity in high-strength Al-Si eutectic composites due to brittle fracture of silicon phases.
• To enable plastic co-deformation of soft Al and hard Si phases in nanostructured eutectic microstructures.
• To investigate mechanisms enabling partial dislocation activity in silicon at room temperature.
• To understand how nano-twinning and Sr modification suppress cracking in Si fibers during deformation.
• To achieve high strength and ductility simultaneously in laser-processed Al-Si eutectic materials.

Proposed method

• Laser rapid solidification was used to produce fully eutectic Al-Si microstructures with fine, nano-scale Si fibers.
• Strontium (Sr) modification was applied to alter the electronic structure and reduce the Peierls barrier in silicon.
• Transmission electron microscopy (TEM) was employed to analyze microstructural evolution and dislocation configurations after deformation.
• Stacking fault density in Si fibers was quantified to confirm partial dislocation activity.
• Compressive mechanical testing was performed to measure flow strength and plastic strain to failure.
• Nanoscale fiber geometry, including reduced aspect ratio, was engineered via processing parameters to enhance ductility.

Experimental results

Research questions

• RQ1 How can plastic co-deformation between soft Al and hard Si phases be enabled in nanostructured Al-Si eutectics?
• RQ2 What role does partial dislocation activity play in enabling plasticity in silicon at room temperature?
• RQ3 How does Sr modification influence the Peierls barrier and dislocation mobility in nano-twinned silicon?
• RQ4 What microstructural features suppress crack formation in Si fibers during deformation?
• RQ5 To what extent can laser rapid solidification and chemical modification enhance both strength and ductility in Al-Si eutectics?

Key findings

• The Sr-modified, laser-rapid-solidified Al-Si eutectic exhibited a compressive flow strength of approximately 840 MPa.
• The material achieved stable plastic flow up to 26% plastic strain without crack propagation in the Si phase.
• High-density stacking faults were observed in Si(Sr) fibers after deformation, confirming partial dislocation-mediated plasticity.
• The hardness of the material reached 2.9 GPa due to nano-twinning and solid solution strengthening from Sr.
• Reduced aspect ratio and lowered Peierls barrier in Sr-modified, nano-twinned Si fibers were key to suppressing crack formation.
• The combination of laser processing and Sr doping enabled simultaneous high strength and high ductility in a eutectic Al-Si system.