Elastic-like deformation and elastocaloric effect of a partly ordered iron-platinum alloy exhibiting a weak first-order martensitic transformation

Abstract

We have studied the temperature dependencies of elastic-like deformation and the elastocaloric effect in an L12-type Fe3Pt alloy with degree of order S = 0.75, which exhibits a weak first-order martensitic transformation (MT) near 85 K (TM). The stress–strain curve under a compressive stress applied in the [0 0 1] direction shows a small stage in the vicinity of TM due to the stress-induced MT. The transformation strain is 0.17% at TM; it decreases linearly as temperature decreases and disappears at 130 K. Thereseems to be a critical point of the MT in the stress–temperature phase diagram at (20 MPa, 130 K). The latent heat of the MT is estimated to be 0.52 J mol−1 from the Clausius–Clapeyron equation. The adiabatic temperature change ΔTadi caused by the latent heat is 0.04 K at 90 K. In contrast, experimentally obtained ΔT is approximately 1 K at 90 K when the applied stress is 100 MPa. The main contribution to ΔT is the temperature dependence of elastic strain caused by softening; the Young’s modulus at 288 K is 55 GPa and it decreases linearly with a slope of 0.28 GPa K−1 as temperature decreases.