Thermodynamics of martensite formation in Fe–Mn–Al–Ni shape memory alloys

2021 ◽  
Vol 192 ◽  
pp. 26-31 ◽  
Author(s):  
Alexander Walnsch ◽  
Mario J. Kriegel ◽  
Mykhaylo Motylenko ◽  
Grzegorz Korpala ◽  
Ulrich Prahl ◽  
...  
Keyword(s):  
Shape Memory Alloys ◽  
Shape Memory ◽  
Martensite Formation

scholarly journals Influence of Structural Defects on the Properties of Metamagnetic Shape Memory Alloys

Metals ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 1131
Author(s):  
J. I. Pérez-Landazábal ◽  
V. Sánchez-Alarcos ◽  
V. Recarte ◽  
O. A. Lambri ◽  
F. G. Bonifacich ◽  
...  
Keyword(s):  
Martensitic Transformation ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Entropy Change ◽  
High Energy ◽  
Milling Process ◽  
Structural Defects ◽  
Internal Stresses ◽  
Spin Glass Behavior ◽  
Deformed State

The production of μ-particles of Metamagnetic Shape Memory Alloys by crushing and subsequent ball milling process has been analyzed. The high energy involved in the milling process induces large internal stresses and high density of defects with a strong influence on the martensitic transformation; the interphase creation and its movement during the martensitic transformation produces frictional contributions to the entropy change (exothermic process) both during forward and reverse transformation. The frictional contribution increases with the milling time as a consequence of the interaction between defects and interphases. The influence of the frictional terms on the magnetocaloric effect has been evidenced. Besides, the presence of antiphase boundaries linked to superdislocations helps to understand the spin-glass behavior at low temperatures in martensite. Finally, the particles in the deformed state were introduced in a photosensitive polymer. The mechanical damping associated to the Martensitic Transformation (MT) of the particles is clearly distinguished in the produced composite, which could be interesting for the development of magnetically-tunable mechanical dampers.

Self-Accommodating Nature of Martensite Formation in Shape Memory Alloys

2014 ◽  
Vol 213 ◽  
pp. 114-118
Author(s):  
Osman Adiguzel
Keyword(s):  
Martensitic Transformation ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Parent Phase ◽  
Alloy System ◽  
Phase Region ◽  
Martensite Formation ◽  
Martensite Variant ◽  
Β Phase ◽  
Phase Condition

Shape memory effect is a peculiar property exhibited by certain alloy system. This behavior is facilitated by martensitic transformation, and shape memory properties are intimately related to the microstructures of alloys; in particular, the morphology and orientation relationship between the various martensite variants. Martensitic transformation occurs in thermal manner, on cooling the materials from high temperature parent phase region. Thermal induced martensite called self-accommodated martensite or multivariant martensite occurs as multivariant martensite in self-accommodating manner and consists of lattice twins. Shape memory alloys are deformed in low temperature martensitic phase condition, and deformation proceeds through a martensite variant reorientation. Copper based alloys exhibit this property in metastable β - phase region.

Thermo-mechanical effects caused by martensite formation in powder metallurgy FeMnSiCrNi shape memory alloys

2018 ◽  
Vol 61 (4) ◽  
pp. 348-356 ◽  
Author(s):  
Bogdan Pricop ◽  
Elena Mihalache ◽  
George Stoian ◽  
Firuța Borza ◽  
Burak Özkal ◽  
...  
Keyword(s):  
Powder Metallurgy ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Martensite Formation ◽  
Mechanical Effects

scholarly journals Coherent Precipitates as a Condition for Ultra-Low Fatigue in Cu-Rich Ti53.7Ni24.7Cu21.6 Shape Memory Alloys

2021 ◽  
Author(s):  
L. Bumke ◽  
N. Wolff ◽  
C. Chluba ◽  
T. Dankwort ◽  
L. Kienle ◽  
...  
Keyword(s):  
Grain Size ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Internal Stresses ◽  
Cyclic Stability ◽  
Partial Loss ◽  
Functional Fatigue ◽  
Transformation Temperatures ◽  
Different Temperatures ◽  
B2 Phase

AbstractSputtered Ti–rich TiNiCu alloys are known to show excellent cyclic stability. Reversibility is mostly influenced by grain size, crystallographic compatibility and precipitates. Isolating their impact on cyclic stability is difficult. Ti2Cu precipitates for instance are believed to enhance reversibility by showing a dual epitaxy with the B2 and B19 lattice. Their influence on the functional fatigue, if they partly lose the coherency is still unknown. In this study, sputtered Ti53.7Ni24.7Cu21.6 films have been annealed at different temperatures leading to a similar compatibility (λ2 ~ 0.99), grain size and thermal cyclic stability. Films annealed at 550 °C exhibit a superior superelastic fatigue resistance but with reduced transformation temperatures and enthalpies. TEM investigations suggest the formation of Guinier–Preston (GP) zone-like plate precipitates and point towards a coherency relation of the B2 phase and finely distributed Ti2Cu precipitates (~ 60 nm). Films annealed at 700 °C result in the growth of Ti2Cu precipitates (~ 280 nm) with an irregular distribution and a partial loss of their coherency. Thus, GP zones are assumed to cause the reduction of transformation temperatures and enthalpies due to increased internal stresses, whereas the coherency relation of both, Ti2Cu and GP zones, help to increase the superelastic stability, well beyond 107 cycles.

scholarly journals Influence of the Texture and Strain on the Behaviour of Ni53.6Mn27.1Ga19.3 and Ni54.2Mn29.4Ga16.4 Shape Memory Alloys

2013 ◽  
Vol 2013 ◽  
pp. 1-8
Author(s):  
Alexandra Rudajevova ◽  
Jiří Pospíšil
Keyword(s):  
Shape Memory Alloys ◽  
Shape Memory ◽  
Longitudinal Axis ◽  
Internal Stresses ◽  
Sample Treatment ◽  
Round Cross Section ◽  
Columnar Grains ◽  
Shape Memory Effects ◽  
Round Cross ◽  
Martensitic Variants

Polycrystalline samples of Ni53.6Mn27.1Ga19.3 and Ni54.2Mn29.4Ga16.4 shape memory alloys were investigated using dilatometry. The longitudinal axes of the samples were perpendicular to the columnar grains. Both alloys showed positive shape memory effects. The martensitic phase transformation occurred without hysteresis in both alloys with transformation temperatures of 174°C for the Ni53.6Mn27.1Ga19.3 alloy and 253°C for the Ni54.2Mn29.4Ga16.4 alloy. The dilatation characteristics for both alloys were determined in three perpendicular directions. The strain associated with the internal stress at the interface between the two martensitic structures and the two grains affected the dilatation characteristics in the y and z directions (perpendicular to the longitudinal axis of the sample). The microstructure was determined for all the directions investigated. To investigate the mechanical history, a round cross-section of the Ni54.2Mn29.4Ga16.4 sample was machined using a milling machine along the longitudinal axis so that both sides of the sample were symmetrical. This sample treatment changed the dilatation characteristics of the martensite and austenite. The study and analysis of the dilatation characteristics of the thermal cycle showed the relaxation of internal stresses and the reorientation of the martensitic variants.

A Free Energy Model for the Inner Loop Behavior of Pseudoelastic Shape Memory Alloys

2005 ◽  
Vol 881 ◽  
Author(s):  
Olaf Heintze ◽  
Stefan Seelecke
Keyword(s):  
Free Energy ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Energy Model ◽  
Polycrystalline Materials ◽  
Internal Stresses ◽  
Control Programs ◽  
Rate Dependent ◽  
Numerical Effort ◽  
Free Energy Model

AbstractThe paper presents a free energy model for the pseudoelastic behavior of shape memory alloys. It is based on a stochastic homogenization process, which uses distributions in energy barriers and internal stresses to represent effects typically encountered in polycrystalline materials. This concept leads to a realistic desription of the rate-dependent inner loop behavior, but is characterized by rather long computation times. This is prohibitive in regard to a potential implementation into other numerical codes, such as finite element or optimal control programs or a Matlab/Simulink environment. For this purpose a parameterization method is introduced, which is derived from the concept of a representative single crystal. The approach preserves the desirable properties of the original formulation, at the same time reducing the numerical effort significantly. Finally, we show that the method can reproduce the experimentally observed behavior accurately over a large range of strain rates including the minor loop behavior.

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