Distribution of plates׳ sizes tell the thermal history in a simulated martensitic-like phase transition

Abstract

A phenomenological 2D model, simulating the martensitic transformation, is built upon existing experimental observations that the size of the formed plates -in direct transformation-decreases as the temperature is lowered; then they transform back in reversed order. As such, if a reverse transformation is incomplete ("arrested"), the subsequent direct one will show anomalously large number of big size plates-old plus newly formed-but consequentially a depletion of intermediate sizes, due to geometrical constraints, phenomenon that generates thermal memory.

Magnetic and Magnetostrictive Properties of Ni50Mn20Ga27Cu3 Rapidly Quenched Ribbons

“…When cooling without an applied magnetic field, can be seen a continuous contraction passing through the MT ( Figure 4 b). The martensite variants can accommodate the strain to minimize the elastic energy and keep the shape of the ribbons (see [ 36 ] for a model based on different plates sizes).…”

“…When cooling without an applied magnetic field, can be seen a continuous contraction passing through the MT (Figure 4b). The martensite variants can accommodate the strain to minimize the elastic energy and keep the shape of the ribbons (see [36] for a model based on different plates sizes). accommodate the strain to minimize the elastic energy and keep the shape of the ribbons (see [36] for a model based on different plates sizes).…”

“…The martensite variants can accommodate the strain to minimize the elastic energy and keep the shape of the ribbons (see [36] for a model based on different plates sizes). accommodate the strain to minimize the elastic energy and keep the shape of the ribbons (see [36] for a model based on different plates sizes). In Ni-Mn-Ga alloys, the magnetoelastic coupling is described by a negative magnetostriction constant (see, e.g., [32]) and can be correlated with the appearance of an easy-magnetization direction along the short c-axis accompanied by the large uniaxial magnetic anisotropy [33].…”

Thermal memory fading by heating to a lower temperature: Experimental data on polycrystalline NiFeGa ribbons and 2D statistical model predictions

“…Finally, if the second arrest is performed at T 4 = 70.5 o C the dip at T 1 drastically reduces after a single procedure and completely vanishes after three arrests at T 4 , showing that the memory fading effect is stronger if the second arrest temperature is closer to the first one. In the following, we give the predictions of a 2D phenomenological model, first proposed in [8]. The model assumes that the austenite-martensite phase transition takes place by successive formation of finite size squareshaped plates, which nucleate randomly in the untransformed area.…”

“…[1][2][3][4][5][6][7]). Unlike the shape memory effect, the thermal memory effect (TME) in SMA is less understood, proposed scenarios including the redistribution of accumulated stress [2][3][4], or geometrical constrictions effects [8]. Within a brief definition, TME means that if the martensite-austenite transformation is stopped before completion (or "arrested", at a temperature T A ), then after the sample is cooled back into the martensite state, if one performs one final, complete martensite-austenite transformation, a specific dip will appear in the calorimetric signal at a temperature close to T A , proving that the alloy has temperature memory.…”