  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.
