Method for the Determination of Non-Chemical Free Energy Contributions as a Function of the Transformed Fraction at Different Stress Levels in Shape Memory Alloys

Abstract

General equations allowing the determination of the elastic and dissipative energy contributions, as the function of the transformed fraction, , to the martensitic transformation in shape memory alloys are derived. It is shown that the derivatives of these energies by can be calculated from the measured hysteresis loops. It is illustrated, by the example of our previous experimental results obtained on CuAlNi shape memory alloys at different stress levels, , that our evaluation method gives consistent results with those obtained form the DSC measurements. Furthermore, the -and -dependence of the above derivatives as well as their integral values for (0,1) and (1,0) intervals, i.e. the dissipated energy and the elastic energy stored and released during the forward and reverse transformations, are determined as the function of stress.

Hydrogen’s Effect on the Shape Memory Effect of TiNi Alloy Single Crystals

“…In this case, ΔGel increases with an increase in the transformation strain and, accordingly, the volume fraction of В19′ martensite. Using the thermodynamic description of the MT [35][36][37] and the experimental values of the MT temperatures determined from the DSC data, it is possible to calculate the values of the stored elastic energy ΔGel for the forward В2-В19′ MT and the dissipated energy ΔGdis for the reverse B19′-B2 MT in the Ti49.7-Ni50.3 crystals without and with hydrogen:…”

“…The elastic energy for the formation of self-accommodated B19 martensite ∆G el (SAS) is much less than the elastic energy for the formation of oriented B19 martensite ∆G el (Or) [11,12,36,37,43,[46][47][48]. The stresses for the onset of a stress-induced B2-B19 MT at different contributions of ∆G el (SAS) and ∆G el (Or) in the hydrogenated [117]-oriented Ti 49.7 -Ni 50.3 crystals, by analogy with [43], can be written in general form according to [11,36,37,[46][47][48]:…”