TRANSFORMATION BEHAVIOR OF NiTi SHAPE MEMORY ALLOYS TREATED BY THERMOMECHANICAL PROCESSING USING DSC
Authors
Abstract:
Abstract: In the present study the effect of thermomechanical treatment (cold work and annealing) on the transformation behavior of NiTi shape memory alloys was studied. Differential scanning calorimetry was used to determine transformation temperature and its relation to precipitates and defects. Three alloys including Ti-50.3at.% Ni, Ti-50.5at.% Ni (reclamated orthodontic wires) and 50.6at.% Ni alloy were annealed at 673 K and 773 K for 30 and 60 min after 15% cold rolling. It was found that the transformation characteristics of these alloys are sensitive to annealing treatment and composition. The temperature range of transformation is broadened during cold working and after subsequent annealing, the intermediate phase was appeared. The peaks become sharper and close together on each cooling and heating cycle with increasing annealing temperature and time
similar resources
Functionally graded NiTi shape memory alloys
In this study, in order to obtain a functionally graded material, NiTi strips were annealed at 350°C, 450°C and 550°C in a furnace using an assembly that allowed a temperature gradient along them, and their transformation temperatures were studied by Differential Scanning Calorimetry (DSC). Furthermore, the strips were bent at both ends and dipped into a water bath at room temperature which was...
full textOn phase transformation behavior of porous Shape Memory Alloys.
This paper is concerned on the phase transformation mechanism of porous Shape Memory Alloys (SMAs). A unit-cell model is adopted to establish the constitutive relation for porous SMAs, the stress distributions, the phase distributions and the martensitic volume fractions for the model are then derived under both pure hydrostatic stress and uniaxial compression. Further, an example for the uniax...
full textCharacterization of smart MARFOS NiTi shape memory alloys
In the present study, structural characterization of NiTi smart shape memory alloys (SMAs), produced by an alternative powder metallurgy approach named mechanically activated reactive forging (MARFOS), was carried out by means of transmission electron microscopy (TEM), scanning electron microscopy (SEM) and X-ray diffraction (XRD). It was observed that MARFOS materials had a multiphase nanocrys...
full textAtomistic study of nanotwins in NiTi shape memory alloys
Atomistic simulations are performed to study the structure and geometrical limit of nanoscale twins in NiTi shape memory alloys. We analyze compound twins as narrow as 1 nm, involving a few atomic layers. A novel nanotwinned structure is found, forming through the martensitic transformation of sublattices. We predict the temperatures of phase transformation, which are consistent with experiment...
full textGrain size effect on the R-phase transformation of nanocrystalline NiTi shape memory alloys
This study investigated the effect of nanograins size on the R-phase transformation of a nanocrystalline Ti-50.2at%Ni alloy. The nanometric grain size was created by severe cold deformation and low temperature anneal. It was found that in the recrystallized state, nanograin sizes (<100 nm) was effective in suppressing the B2→B19’ martensitic transformation and revealing the B2↔R transformation....
full textA Two Variant Thermomechanical Model for Shape Memory Alloys
Shape Memory Alloys (SMAs) undergo stress and temperature induced reversible diffusionless crystalline phase transformations between a high synmaetry phase (austenite) stable at high tenlperatures and low stresses, and a low symmetry phase (martensite) stable at low temperatures and high stresses. Unusual macroscopic effects arise from these crystallographic changes, chiefly shape memory and su...
full textMy Resources
Journal title
volume 5 issue 4
pages 25- 31
publication date 2008-12
By following a journal you will be notified via email when a new issue of this journal is published.
Hosted on Doprax cloud platform doprax.com
copyright © 2015-2023