Stable elastocaloric effect under tensile stress of iron-palladium alloy and its in situ X-ray observation

The elastocaloric effect under tensile stress along the [001] direction has been investigated in an Fe-31.2Pd (at.%) alloy, which exhibits a weak first-order martensitic transformation at 230 K from a face-centered cubic structure to a face-centered tetragonal (c/a < 1) structure. A stable temperature variation of 1.9 K was observed at room temperature (∼288 K) up to 10000 cycles of sinusoidal tensile stress (200 MPa). The stress-strain curve shows a macroscopic strain of 1.2% under 200 MPa with a negligible stress hysteresis. The macroscopic strain coincides with the lattice strain obtained by in situ X-ray diffraction. A significant extension of the 200 reflection, perpendicular to the tensile direction, was observed. This peak extension could be the way the specimen realizes a high elastic strain, even under tensile stress.