On the physical nature of high reversible strain in Fe-Pd single crystals exhibiting lattice softening

Deformation behavior in a Fe-31.2 Pd (at.%) single crystal, which exhibits a second order-like face-centered cubic (fcc)-face-centered tetragonal martensitic transformation at 230 K, is investigated by compressive tests in the [0 0 1]P direction (subscript P represents the parent phase). As a result, a large reversible strain of 6.5% with quite small stress hysteresis is obtained at 240 K under a stress of 250 MPa. The large elastic-like strain is essentially attributed to continuous change in the lattice parameter of a single martensite variant under stress. The yield point appears at 285 MPa, at which the strain is 7.3%, and the residual strain does not recover by heating to 300 K. The main reason for the residual strain is the occurrence of {1 1 1} mechanical twinning. The critical resolved shear stress of a Fe-31.2 Pd (at.%) single crystal is close to the ideal value.