Isothermal martensitic transformation in polycrystalline Ni50Mn29Ga21

Kinetic Analysis of the Transformation from 14M Martensite to L21 Austenite in Ni-Fe-Ga Melt Spun Ribbons

“…The relationship between and is evidenced in Figure 9 as a straight line: This yields a much lower average value of 1 − for the transition tempera- This yields a much lower average value of Q(1 − mRT) for the transition temperature range than those from Kissinger's method (one order of magnitude) and predicts an athermal transformation for T ath = 1 mR = 428 ± 8 K, which is coherently above the measured end temperatures (see black triangles in Figure 4, right panel). In this sense, it has been recently proposed that there is not a clear distinction between athermal and isothermal martensitic transformations, with some experimental results indicating an isothermal character for transformations that were previously considered athermal (Cubased [39], Ti-Ni based [40] or Ni-Mn-Ga [41] shape memory alloys). Moreover, it has been reported that the transformation of Ni-Fe-Mn alloys changes from isothermal to athermal under the influence of a magnetic field, while the transformation of binary Fe-Ni alloys changes to isothermal under the application of hydrostatic pressure [42].…”

An interpretation of the kinetics of martensitic transformation in a Ni45Co5Mn36.5In13.5 alloy

“…In fact, in the last couple of decades, the isothermal nature has been revealed in many alloys that were previously considered to exhibit athermal transformations. Typical examples include Cu-based shape memory alloys (SMAs) [2,3], Ti-Ni based SMAs [4][5][6], Ni-Mn-Ga SMA [7] and Fe-based alloys [8].…”

Isothermal B2→B19′ martensitic transformation in Ti40.7Hf9.5Ni44.8Cu5 shape memory alloy

“…This transformation is athermal and the volume fraction of the transformed alloy is controlled by variation in the sample temperature and does not depend on the time hence it could not be realized under isothermal conditions [1]. Nevertheless, it was previously reported that the thermoelastic martensitic transformations were observed at constant temperature in Cu-Zn-Al [2], Cu-Al-Ni [3,4], TiNi-based [5][6][7][8][9][10][11], and Heusler [12][13][14][15][16][17] alloys. It was found that the forward transformation [2][3][4][5][6][7][8][9][10][11][13][14][15][16][17] as well as the reverse transition [6,8,12,14] might occur at a constant temperature.…”

“…Nevertheless, it was previously reported that the thermoelastic martensitic transformations were observed at constant temperature in Cu-Zn-Al [2], Cu-Al-Ni [3,4], TiNi-based [5][6][7][8][9][10][11], and Heusler [12][13][14][15][16][17] alloys. It was found that the forward transformation [2][3][4][5][6][7][8][9][10][11][13][14][15][16][17] as well as the reverse transition [6,8,12,14] might occur at a constant temperature. It was shown that the isothermal martensitic transformation took place during holding at temperatures within the temperature ranges of the martensitic transformation [5,6,8,11,13,14,16] and outside the transformation temperature interval [2,3,7,9,10,12,17].…”

“…This allowed one to draw the conclusion that all thermoelastic martensitic transformations were isothermal. This was subjected to some criticism in [18] because the conclusion about the isothermal nature of the martensitic transformation was based on the variation in the resistivity [2,3,6,[8][9][10][11]16], magnetization [13][14][15]17], acoustic emission [4], or internal friction [5] during isothermal holding. At the same time, these physical properties may vary in the alloys for many other reasons besides the phase transformation, for instance due to martensite variants' reorientation [18].…”