Inter-martensitic transitions in Ni–Fe–Ga single crystals

Abstract: The strain–temperature response of Ni–Fe–Ga single crystals underscores the role of the inter-martensitic transformation in creating intersecting heating and cooling segments; the separation of these segments occurs due to irreversibilities at high stresses and at high temperatures. An ultra-narrow tensile (1°C) and compressive (<10°C) thermal hysteresis are observed for the A ⇌10M ⇌14M case, accompanied by a small stress hysteresis (<30MPa) in compressive and tensile stress–strain responses. The hysteresis levels increase and the intersecting segments disappear at high stresses and at high temperatures. This paper reports the use of a thermo-mechanical formulation to rationalize the role of inter-martensitic transformations. Plotting the transformation stress as a function of temperature indicates that inter-martensitic transformations enable a very wide pseudoelastic temperature range, as high as 425°C. The measured Clausius–Clapeyron curve slope in compression (2.75MPa°C−1) is eight times the tensile slope (0.36MPa°C−1); the higher slope is attributed to the predominance of A ⇌ L10 at high temperatures. [Copyright &y& Elsevier]