Flow stress in submicron BCC iron single crystals: Sample-size-dependent strain-rate sensitivity and rate-dependent size strengthening

Through in situ scanning electron microscope microcompression tests, we demonstrated that the strain-rate sensitivity of bodycentered cubic single crystal iron pillars will be reduced by one order when the pillar size was reduced from 1000 to about 200 nm. In addition, size-strengthening exponent exhibited obvious strain-rate dependence. We propose that the observed behavior is a result of the high stresses required to induce curvature bowout of dislocation arms at small sample or grain sizes, which overwhelms the lattice friction stress contribution and diminishes the role played by the mobility difference between edge and screw dislocations.