Phenomenological Equations for Predicting plus Two-Phase Region of Fe-Mn-Si-Cr-Ni Shape Memory Alloys

Three methods, i.e., optical metallographic method, differential scanning calorimeter (DSC), and thermal expansion, were evaluated to measure /+ boundary temperature (T/+) and +/ boundary temperature (T+/) of Fe-Mn-Si-based shape memory alloys. The optical metallographic method is most suitable and selected to determine the T/+ and T+/ temperatures of Fe-(14 to 25)Mn-(4.0 to 6.5)Si-(7 to 12)Cr-(2.0 to 8.5)Ni-(0.006 to 0.140)C alloys. Based on the above experimental data, the following phenomenological equations for predicting the T/+ and T+/ temperatures of Fe-Mn-Si-Cr-Ni-C shape memory alloys were established by nonlinear regression: T/+ (degrees C)=1762.83+18.46Mn-0.38Mn(2)-250.30Si+19.71Si(2)+28.66Cr-3.20Cr(2)-6.50Ni+1.69Ni(2)+289.44C; T+/ (degrees C)=2758.13-6.24Mn+0.22Mn(2)-387.82Si+32.60Si(2)-59.50Cr+2.25Cr(2)+16.75Ni-1.61Ni(2)+345.84C; chemical symbols represent weight percent of Mn, Si, Cr, Ni, and C elements. The two phenomenological equations provide a basis of composition design for the fabrication of training-free processed Fe-Mn-Si-based alloys utilizing phase transformation.