Transformation-mismatch plasticity in sub-millimeter iron wires

Wires of 99.5% pure iron with 406 and 508 μm diameter were subjected to a uniaxial tensile stress while being thermally cycled about the α–γ allotropic transformation temperature. The strain increments per cycle are proportional to the applied stress in the range 1–22 MPa, indicating that transformation-mismatch plasticity is the dominant deformation mechanism. The strain increments for the wires have the same magnitude as those reported for bulk iron samples, thus, indicating that the internal mismatch strains responsible for this deformation mechanism are undiminished in the wires, despite their high surface-to-volume ratio. Very high average strain rates (up to 3 × 10−3 s−1) were achieved through resistive heating and convective/radiative cooling of the thinnest wires.