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

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.