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The Role of Ordering in Martensite Microstructures in Copper Based Shape Memory Alloys

Osman Adiguzel 

Firat University, Department of Physics, Elazig 23169, Turkey


Copper based alloys are widely used as shape memory element in devices. These alloys are metastable in beta phase field and possess simple bcc- structures, austenite structure, at high temperatures. These alloys undergoe the martensitic transition, following two ordering reactions on cooling. This transition, which is the source of shape memory, occurs with shears and shear mechanism on {110}-type planes of parent phase, basal plane for product phase. The product martensite has unusual layered structures   with complicated stacking sequences called as 3R, 9R or 18R martensites depending on the periodicity of layers on the basal plane. Martensitic transitions are  displacive and the product structures  inherit the order in the parent phase. The basal plane is subjected to the hexagonal distortion with martensite formation on which atom sizes have important effect.  In the disordered case, the lattice sites  are occupied randomly, and this distribution makes the basal plane nearly close packed taking the atomic sizes approximately equal. In the ordered case, lattice sites   are occupied regularly by certain atoms which have different atomic sizes, and basal plane deviates from the regular hexagonal arrangement of the atoms due to the atom size differences. Due to this distortion, the knowledge on the interplane distances of the particularly selected diffraction plane pairs reveals the ordering degree of martensite.                                                          In the present contribution, x-ray diffraction and transmission electron microscopy (TEM) studies were carried out on two copper based ternary alloys given different heat treatments. Key Words: Shape memory effect, martensite, atom sizes, and layered structures.



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Presentation: Poster at E-MRS Fall Meeting 2008, Symposium C, by Osman Adiguzel
See On-line Journal of E-MRS Fall Meeting 2008

Submitted: 2008-01-28 15:58
Revised:   2009-06-07 00:48