Martensitic transformations and the shape memory effect in Ti-Zr-Nb-Al high-temperature shape memory alloys

2017 ◽  
Vol 679 ◽  
pp. 14-19 ◽  
Author(s):  
Fei Zhang ◽  
Zhiguo Yu ◽  
Chengyang Xiong ◽  
Wentao Qu ◽  
Bifei Yuan ◽  
...  
Keyword(s):  
High Temperature ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Shape Memory Effect ◽  
Memory Effect ◽  
Martensitic Transformations

Unexpected Constrained Twin Hierarchy in Equiatomic Ru-Based High Temperature Shape Memory Alloy Martensite

2013 ◽  
Vol 738-739 ◽  
pp. 195-199 ◽  
Author(s):  
Philippe Vermaut ◽  
Anna Manzoni ◽  
Anne Denquin ◽  
Frédéric Prima ◽  
Richard Portier
Keyword(s):  
High Temperature ◽  
Martensitic Transformation ◽  
Shape Memory Alloy ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Shape Memory Effect ◽  
Memory Effect ◽  
Martensitic Transformations ◽  
Single Transition

Among the different systems for high temperature shape memory alloys (SMA’s), equiatomic RuNb and RuTa alloys demonstrate both shape memory effect (SME) and MT temperatures above 800°C. Equiatomic compounds undergo two successive martensitic transformations, β (B2) → β’ (tetragonal) → β’’ (monoclinic), whereas out of stoechiometry alloys exhibit a single transition from cubic to tetragonal. In the case of two successive martensitic transformations, we expect to have a finer microstructure of the second martensite because it is supposed to develop inside the smallest twin elements of the former one. In equiatomic Ru-based alloys, if the first martensitic transformation is “normal”, the second one gives different unexpected microstructures with, for instance, twins with a thickness which is larger than the smallest spacing between twin variants of the first martensite. In fact, the reason for this unexpected hierarchy of the twins size is that the second martensitic transformation takes place in special conditions: geometrically, elastically and crystallographically constrained.

The Role of Twinned and Detwinned Structures on Memory Behaviour of Shape Memory Alloys

2015 ◽  
Vol 1105 ◽  
pp. 78-82 ◽  
Author(s):  
Osman Adiguzel
Keyword(s):  
High Temperature ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Shape Memory Effect ◽  
Memory Effect ◽  
Parent Phase ◽  
Martensitic Transformations ◽  
Phase Region ◽  
Finish Temperature ◽  
Β Phase

Shape memory alloys have a peculiar property to return to a previously defined shape or dimension when they are subjected to variation of temperature. Shape memory effect is facilitated by martensitic transformation governed by changes in the crystalline structure of the material. Martensitic transformations are first order lattice-distorting phase transformations and occur with the cooperative movement of atoms by means of lattice invariant shears in the materials on cooling from high temperature parent phase region. The material cycles between the deformed and original shapes on cooling and heating in reversible shape memory effect. Thermal induced martensite occurs as twinned martensite, and the twinned martensite structures turn into detwinned structures by deforming the material in the martensitic condition. Deformation of shape memory alloys in martensitic state proceeds through a martensite variant reorientation. The deformed material recovers the original shape on first heating over the austenite finish temperature in reversible and irreversible shape memory cases. Meanwhile, the parent phase structure returns to the twinned structure in irreversible shape memory effect on cooling below to martensite finish temperature and to the detwinned structure in reversible shape memory effect. Therefore, the twinning and detwinning processes have great importance in the shape memory behaviour of the materials. Copper based alloys exhibit this property in metastable β-phase region, which has bcc-based structures at high temperature parent phase field, and these structures martensitically turn into layered complex structures with lattice twinning following two ordered reactions on cooling.

Microstructure and Shape Memory Effect of Cu-Al-Be-Mn Quaternary Shape Memory Alloys

2015 ◽  
Vol 813-814 ◽  
pp. 213-217 ◽  
Author(s):  
A.G. Shivasiddaramaiah ◽  
Singh Prashant ◽  
S.Y. Manjunath ◽  
U.S. Mallikarjun
Keyword(s):  
High Temperature ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Shape Memory Effect ◽  
Memory Effect ◽  
Induction Furnace ◽  
Beta Phase ◽  
Optical Microscope ◽  
Ingot Metallurgy ◽  
Step Quenching

Copper based shape memory alloys are the alloys prepared with the combination of 66-88 wt% of copper, 10-14 wt% of aluminum, 0.3-0.6 wt% of beryllium and 0.1-0.4 wt% of manganese in the induction furnace through ingot metallurgy. The prepared SMAs is subjected to homogenization, it was observed that the samples exhibits Beta phase at high temperature and shape memory effect after going through step quenching to a low temperature. Microstructure and Shape memory effect was studied with the help of optical microscope and bend test respectively. It was seen that with increase in wt % of manganese the shape memory effect also increases.

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