Martensitic Transformation Cycling and the Phenomenon of Two-Way Shape Memory Training

1983 ◽  
Vol 21 ◽  
Author(s):  
J. Perkins
Keyword(s):  
Martensitic Transformation ◽  
Shape Memory ◽  
Martensite Plate ◽  
Parent Phase ◽  
Memory Training ◽  
Al Alloy ◽  
Microscopic Studies ◽  
Thermoelastic Transformation ◽  
Number Of Cycles ◽  
Physical Features

ABSTRACTThe character and mechanism of two-way shape memory (TWSM) “training” has been investigated in a Cu-Zn-Al alloy by means of detailed thermomechanical evaluation and TEM observations. The progressive effects of training on the TWSM behaviour, as well as an accompanying substructural evolution, have been established. The results indicate a relationship between the substructural effects of cyclic thermoelastic martensitic transformation and the ability to exhibit TWSM. Microscopic studies reveal that as the number of cycles of thermoelastic transformation under stress increases, specific physical features develop in the parent phase submicrostructure. These take the form of dislocation structures which evolve into “vestigial” martensite markinqs. These in turn assist in the nucleation and growth of a preferred martensite plate arrangement on cooling which is similar to that induced under stress during the training cycles.

Thermal cycling effects in high temperature Cu–Al–Ni–Mn–B shape memory alloys

1997 ◽  
Vol 12 (9) ◽  
pp. 2288-2297 ◽  
Author(s):  
J. Font ◽  
J. Muntasell ◽  
J. Pons ◽  
E. Cesari
Keyword(s):  
High Temperature ◽  
Martensitic Transformation ◽  
Shape Memory Alloys ◽  
Thermal Cycling ◽  
Shape Memory ◽  
Parent Phase ◽  
Aluminum Boride ◽  
Transformation Temperatures ◽  
Dsc Measurements ◽  
Number Of Cycles

The effects of thermal cycling through the martensitic transformation have been studied in three Cu–Al–Ni–Mn–B high temperature shape memory alloys. An increase of the martensitic transformation temperatures with the number of cycles (up to ∼7 K after 60 cycles) has been generally observed by DSC measurements. The microstructure of these alloys is rather complicated, with the presence of big manganese or aluminum boride particles and small boron precipitates, as well as the formation of dislocations during thermal cycling. By means of aging experiments, it has been shown that the evolution of transformation temperatures during cycling is mainly due to the step-by-step aging in parent phase accompanying the thermal cycling, and that the dislocations formed during cycling have only a very small effect, at least up to 60 cycles.

Effect of L21 Ordering on the Martensitic and Intermartensitic Transformations in a Ni-Mn-Ga Shape Memory Alloy

2007 ◽  
Vol 130 ◽  
pp. 127-134
Author(s):  
Concepcio Seguí ◽  
Jaume Pons ◽  
Eduard Cesari
Keyword(s):  
Martensitic Transformation ◽  
Shape Memory Alloy ◽  
Single Crystal ◽  
Shape Memory ◽  
Parent Phase ◽  
Heat Treatments ◽  
Free Energies ◽  
Transformation Temperatures ◽  
Reverse Martensitic Transformation ◽  
Order Degree

The present work analyses the influence of austenite ordering on a single crystal Ni-Mn- Ga alloy which displays, on cooling, a sequence of martensitic (MT) and intermartensitic (IMT) transformations. The MT and IMT show distinct behaviour after ageing in austenite: while the MT temperatures are not affected by the performed heat treatments, the IMT shifts toward lower temperatures after quenching from increasing temperatures, progressive recovery occurring upon ageing in parent phase. Such evolution can be related to changes in the L21 order degree, in the sense that ordering favours the occurrence of the intermartensitic transformation, while it does not affect noticeably the forward and reverse martensitic transformation temperatures. The closeness of the free energies of the different martensite structures allows to explain this behaviour.

Martensitic Transformation and Shape Memory Effect of Ni53.25Mn21.75Ga25 Ferromagnetic Shape Memory Alloy

2012 ◽  
Vol 476-478 ◽  
pp. 1504-1507
Author(s):  
Hai Bo Wang ◽  
Shang Shen Feng ◽  
Pei Yang Cai ◽  
Yan Qiu Huo
Keyword(s):  
Magnetic Field ◽  
Martensitic Transformation ◽  
Shape Memory ◽  
Shape Memory Effect ◽  
Memory Effect ◽  
Parent Phase ◽  
Transformation Strain ◽  
Scanning Calorimetry ◽  
Reversible Transformation ◽  
Ferromagnetic Shape Memory

The martensitic transformation, crystalline structure, microstructure and shape memory effect of the Ni53.25Mn21.75Ga25 (at.%) alloy are investigated by means of Differential Scanning Calorimetry (DSC), X-ray diffraction (XRD), Transmission Electron Microscope (TEM) and the standard metal strain gauge technique. The XRD results showed that the Ni53.25Mn21.75Ga25 alloy is composed of cubic parent phase at room temperature. TEM observation proved that the typical twin martensite is tetragonal structure and tweed-like contrast which is typical image for the parent phase. A large reversible transformation strain, about 0.54%, is obtained in this undeformed polycrystalline alloy due to martensitic transformation and its reverse transformation. This transformation strain is also increased to 0.65% by the external magnetic field. It is believed that the effect of the magnetic field on the preferential orientation of martensitic variants increases the transformation strain.

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.

TRANSFORMATION BEHAVIOR AND SHAPE MEMORY EFFECT OF A CoAl ALLOY

2009 ◽  
Vol 23 (06n07) ◽  
pp. 1931-1936 ◽  
Author(s):  
FENG CHEN ◽  
BING TIAN ◽  
YUXIANG TONG ◽  
YUFENG ZHENG
Keyword(s):  
Martensitic Transformation ◽  
Shape Memory ◽  
Shape Memory Effect ◽  
Memory Effect ◽  
Strain Curve ◽  
Bending Test ◽  
Al Alloy ◽  
Sem Images ◽  
Β Phase ◽  
Fcc Phase

This paper investigates the microstructure, martensitic transformation and shape memory effect of Co -16 Al alloy. The optical micrographs of Co -16 at .% Al alloy quenched from 1200°C show that the ε martensite occurs at room temperature, while some remaining γ phase can also be observed. This microstructure analysis can be supported by XRD pattern. It is shown that the alloy undergoes a martensitic reverse transformation at about 220°C during heating. However, no transformation from the fcc phase to hcp phase is detected by DSC measurement upon cooling. It is thought that the precipitation of β phase by aging at high temperature may suppress the martensitic transformation. The tension strain is 12% and the fracture strength is above 800MPa. No obvious yield deformation is observed from the stress-strain curve. SEM images exhibits many dimples on the fracture surface, which means the fracture mechanism is ductile rupture. Bending test show that only 25% deformation can be recovered due to shape memory effect when the pre-strain is 5%.

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