Uniaxial Transformation Behavior in Tension and Compression in an Fe-Based Shape Memory Alloy : Transformation Lines and Thermomechanical Hystereses

The uniaxial thermomechanical behavior of a polycrystalline Fe-9%Cr-5%Ni-14%Mn-6%Si (all wt.%) shape memory alloy is investigated for both tensile and compressive stress states. The martensite start stresses measured upon tension and compression loading of austenite depend linearly on temperature, thus forming straight lines in the stress-temperature regime. The lines belonging to tension and compression are not symmetric with respect to zero stress. The austenite start and finish temperatures measured upon heating under external stress, on samples which had previously been strained by inducing martensite, vary linearly with the stress level applied, thus forming the so-called austenite start and finish lines. The temperature difference (retransfornation range) between the austenite start and finish lines increases with increasing amount of previously induced straidmartensite, but the slopes of these lines remain the same. At the minimum amount of previously induced straidmartensite the start and finish lines coincide and are called initial austenite lines. The austenite start and finish lines obtained after previous tensile straining extend to the compression side without change of slope, while the austenite lines obtained after previous compression straining extend to the tensile side without change of slope. The determined tiansformation lines provide a good means to explain the thermomechanical response of the alloy, i.e., the stress-strain-temperature hysteresis loops.