Thermodynamic considerations of " solid state engines" based on thermoelastic martensitic transformations and the shape memory effect

Au-50%Cu (at. %) alloy presents the shape memory effect (SME), which is dependent of the solid state transformation that happens during heating, after the introduction of an internal stress in the quenched state. The solid state phase transformation temperatures were determined by means of Differential Thermal Analysis (DTA), both in heating and cooling cycles. With the obtained DTA results, a sequence of high temperature X-ray diffraction (XRD) experiments were made, in order to confirm the presence of the solid state phase transformations and to determine their stable crystal structure and lattice parameters. These XRD results were compared with those obtained from the literature. The displacements of the lattice parameters were determined, for each equilibrium phase, for measurements at room temperature and at high temperature. The characteristics of the quenched samples were also studied in order to determine the phase transformations that are responsible for the shape memory effect in this alloy.

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Defects and Diffusion in a Prototype of Shape Memory Alloys: β2' Au-Cd Alloys

Defect and Diffusion Forum ◽

10.4028/www.scientific.net/ddf.283-286.139 ◽

2009 ◽

Vol 283-286 ◽

pp. 139-148

Author(s):

Devendra Gupta ◽

David S. Lieberman

Keyword(s):

Shape Memory ◽

Shape Memory Effect ◽

Memory Effect ◽

Thermal History ◽

Alloy Composition ◽

Martensitic Transformations ◽

Contributing Factors ◽

Diffusion Mechanisms ◽

And Diffusion ◽

Nanometer Regime

The Au-Cd alloys continue to be important vehicles of research for the shape memory effect involving martensitic transformations and related phenomena.They transform to a variety of martensitic structures depending on the alloy composition and thermal history. Additionally, the Au-rich alloys display rubber like behavior involving thermo-elastic memory. Defects and diffusion play important roles in determining these properties. Defects and diffusion mechanisms in the Au- 47.5 - 50.5 at.% Cd alloys are examined. Diffusion in the nanometer regime and the states of defects are found to be important contributing factors to determine the shape memory effect, the variable martensitic transformations and the rubber like behavior, which are discussed in details.

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Extreme shape memory effect during martensitic transformations with a nanoinvariant habit plane

Russian Metallurgy (Metally) ◽

10.1134/s0036029515050110 ◽

2015 ◽

Vol 2015 (5) ◽

pp. 407-411

Author(s):

S. V. Khachin ◽

A. A. Il’in ◽

V. N. Khachin

Keyword(s):

Shape Memory ◽

Habit Plane ◽

Shape Memory Effect ◽

Memory Effect ◽

Martensitic Transformations

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Martensitic Transformation and Microstructural Characteristics in Copper Based Shape Memory Alloys

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.510-511.105 ◽

2012 ◽

Vol 510-511 ◽

pp. 105-110 ◽

Cited By ~ 9

Author(s):

Osman Adiguzel

Keyword(s):

Martensitic Transformation ◽

Shape Memory ◽

Shape Memory Effect ◽

Memory Effect ◽

Martensitic Transformations ◽

Microstructural Characteristics ◽

Shape Memory Property ◽

Martensite Variant ◽

Cooperative Movement ◽

Β Phase

Martensitic transformations are first order solid state phase transitions and occur in the materials on cooling from high temperature. Shape memory effect is an unusual property exhibited by certain alloy systems, and based on martensitic transformation. The shape memory property is characterized by the recoverability of previously defined shape or dimension when they are subjected to variation of temperature. The shape memory effect is facilitated by martensitic transformation, and shape memory properties are intimately related to the microstructures of the materials. Martensitic transformations occur as martensite variant with the cooperative movement of atoms on {110}β - type plane of austenite matrix. Martensitic transformations have diffusionless character, and the atomic movement is confined to interatomic lengths in the materials. The basic factors which govern the martensitic transformation are Bain distortion and homogeneous shears. Copper based alloys exhibit this property in metastable β-phase field.

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