Sintering and Morphology of Porous Structure in NiTi Shape Memory Alloys for Biomedical Applications

2012 ◽  
Vol 570 ◽  
pp. 87-95 ◽  
Author(s):  
Irfan Haider Abidi ◽  
Fazal Ahmad Khalid
Keyword(s):  
Elastic Modulus ◽  
Shape Memory Alloys ◽  
Porous Structure ◽  
Shape Memory ◽  
Shape Memory Effect ◽  
Memory Effect ◽  
Biomedical Implants ◽  
Recoverable Strain ◽  
Porous Niti ◽  
Niti Shape Memory Alloys

The combination of attractive properties of porous NiTi shape memory alloys like high recoverable strain due to superelasticity and shape memory effect, good corrosion resistance, improved biocompatibilty, low density and stiffness along with its porous structure similar to that of bone make them best materials for biomedical implants. In current study porous NiTi SMAs have been fabricated successfully by space holder technique via pressureless sintering using NaCl powder as a spacer. Various volume fractions of NaCl powders have been involved to study their effect on the pore characteristics as well as on mechanical properties of foam. Porous NiTi with average porosity in the range of 44.3%-63.5% have been fabricated having average pore size 419µm which were very appropriate for various biomedical implants. Porous NiTi SMAs exhibited superelasticity at room temperature and shape memory effect was also determined. Maximum recoverable strain of 6.79% was demonstrated by the porous NiTi alloy with 44.3% porosity and it was diminishing with increasing porosity. Compression strength and elastic modulus have shown a decreasing trend with increasing porosity content. Elastic modulus of porous NiTi extends from 1.38 to 5.42GPa depending upon the pore volume which was very much comparable to that of various kinds of bones.

scholarly journals Biomedical Porous Shape Memory Alloys for Hard-Tissue Replacement Materials

Materials ◽  
2018 ◽  
Vol 11 (9) ◽  
pp. 1716 ◽  
Author(s):  
Bin Yuan ◽  
Min Zhu ◽  
Chi Yuen Chung
Keyword(s):  
Elastic Modulus ◽  
Shape Memory Alloys ◽  
Porous Structure ◽  
Shape Memory ◽  
Biological Properties ◽  
Preparation Technique ◽  
Hard Tissue ◽  
Porous Niti ◽  
Tissue Replacement ◽  
Structure Relationship

Porous shape memory alloys (SMAs), including NiTi and Ni-free Ti-based alloys, are unusual materials for hard-tissue replacements because of their unique superelasticity (SE), good biocompatibility, and low elastic modulus. However, the Ni ion releasing for porous NiTi SMAs in physiological conditions and relatively low SE for porous Ni-free SMAs have delayed their clinic applications as implantable materials. The present article reviews recent research progresses on porous NiTi and Ni-free SMAs for hard-tissue replacements, focusing on two specific topics: (i) synthesis of porous SMAs with optimal porous structure, microstructure, mechanical, and biological properties; and, (ii) surface modifications that are designed to create bio-inert or bio-active surfaces with low Ni releasing and high biocompatibility for porous NiTi SMAs. With the advances of preparation technique, the porous SMAs can be tailored to satisfied porous structure with porosity ranging from 30% to 85% and different pore sizes. In addition, they can exhibit an elastic modulus of 0.4–15 GPa and SE of more than 2.5%, as well as good cell and tissue biocompatibility. As a result, porous SMAs had already been used in maxillofacial repairing, teeth root replacement, and cervical and lumbar vertebral implantation. Based on current research progresses, possible future directions are discussed for “property-pore structure” relationship and surface modification investigations, which could lead to optimized porous biomedical SMAs. We believe that porous SMAs with optimal porous structure and a bioactive surface layer are the most competitive candidate for short-term and long-term hard-tissue replacement materials.

Indentation-induced two-way shape memory surfaces

2009 ◽  
Vol 24 (3) ◽  
pp. 823-830 ◽  
Author(s):  
Xueling Fei ◽  
Yijun Zhang ◽  
David S. Grummon ◽  
Yang-Tse Cheng
Keyword(s):  
Shape Memory Alloys ◽  
Shape Memory ◽  
Shape Memory Effect ◽  
Memory Effect ◽  
Deformation Zone ◽  
Plastic Strains ◽  
Spherical Case ◽  
Indent Depth ◽  
Niti Shape Memory Alloys ◽  
Made In

A method is described for the creation of surfaces with cyclically reversible topographical form. Using spherical and cylindrical indenters applied to NiTi shape-memory alloys, an indentation-planarization technique is shown to result in a two-way shape memory effect that can drive flat-to-wavy surface transitions on changing temperature. First, it is shown that deep spherical indents, made in martensitic NiTi, exhibit pronounced two-way cyclic depth changes. After planarization, these two-way cyclic depth changes are converted to reversible surface protrusions, or “exdents.” Both indent depth changes and cyclic exdent amplitudes can be related to the existence of a subsurface deformation zone in which indentation has resulted in plastic strains beyond that which can be accomplished by martensite detwinning reactions. Cylindrical indentation leads to two-way displacements that are about twice as large as that for the spherical case. This is shown to be due to the larger deformation zone under cylindrical indents, as measured by incremental grinding experiments.

From Dual-Shape/Temperature Memory Effect to Triple-Shape Memory Effect in NiTi Shape Memory Alloys

2012 ◽  
Vol 78 ◽  
pp. 1-6 ◽  
Author(s):  
Cheng Tang ◽  
Wei Min Huang ◽  
Chang Chun Wang
Keyword(s):  
Shape Memory Alloys ◽  
Shape Memory ◽  
Shape Memory Effect ◽  
Memory Effect ◽  
Sample Length ◽  
Step Motion ◽  
Temperature Memory Effect ◽  
Triple Shape Memory ◽  
Niti Shape Memory Alloys ◽  
Temperature Strain

Triple-shape memory effect (SME), i.e., to recover the original shape through one intermediate shape upon heating, has been demonstrated as an intrinsic feature of thermo-responsive shape memory polymers (SMPs) after being uniformly programmed, but seemingly has yet been achieved in shape memory alloys (SMAs). In this paper, we study two programming approaches, in which the deformation is uniform throughout the whole sample length without involving any permanent change in material properties at all, to realize the triple-SME in NiTi SMAs. We show that the triple-SME can be tailored to meet the temperature/strain requirements. With this technique, now we are able to achieve step-by-step motion control in SMAs.

Thermomechanical Forming of NiTi Shape Memory Alloy Wire

2014 ◽  
Vol 939 ◽  
pp. 430-436 ◽  
Author(s):  
Kuang Jau Fann ◽  
Hau Chi Hsu
Keyword(s):  
Shape Memory Alloy ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Shape Memory Effect ◽  
Memory Effect ◽  
Niti Shape Memory Alloy ◽  
Processing Temperature ◽  
Shape Memory Alloy Wire ◽  
Alloy Wire ◽  
Niti Shape Memory Alloys

Because of their smart characteristics with shape memory effect and superelasticity, NiTi shape memory alloys used in sensors and actuators are regarded as an emerging applied material with high added value by their additional biomedical compatibility for medical devices and implants. It is meaningful to pay more attention to study the production technique of NiTi shape memory alloys. For this reason, this article is aimed to investigate the results of a NiTi shape memory alloy wire in thermomechanical forming process regarding the processing temperature and duration. Thereafter a NiTi shape memory alloy wire of 0.63 mm in diameter is formed in a furnace at 450°C, 500°C, 550°C, and 600°C, respectively, by a semi cylindrical punch of 32 mm in diameter, then held together with the die set in the furnace for 10, 30, and 50 minutes long, respectively, and then quenched in the water. All of the formed wires have shape memory effect. That is, the wires returned their formed geometry once they were straightened below martensite transformation finishing temperature about room temperature and heated again above austenite transformation finishing temperature about 70°C. These thermomechanical forming processes were also investigated by commercial finite element software DEFORM. Both analytical and experimental results showed that the formed wires could not have the geometry precision as wanted because of stress relaxation found in process, which depends on the process temperature and the treatment duration. As a result, the lower the temperature and the shorter the duration is, the larger the springback is. That means that the higher the treatment temperature is and the longer the holding time is, the better the precision of the formed part is.

On the impact of lattice parameter accuracy of atomistic simulations on the microstructure of Ni-Ti shape memory alloys

2021 ◽  
Author(s):  
Lorenzo La Rosa ◽  
Francesco Maresca
Keyword(s):  
Molecular Dynamics ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Shape Memory Effect ◽  
Memory Effect ◽  
Lattice Parameter ◽  
Lattice Parameters ◽  
Atomistic Simulations ◽  
Interatomic Potentials ◽  
The Impact

Abstract Ni-Ti is a key shape memory alloy (SMA) system for applications, being cheap and having good mechanical properties. Recently, atomistic simulations of Ni-Ti SMAs have been used with the purpose of revealing the nano-scale mechanisms that control superelasticity and the shape memory effect, which is crucial to guide alloying or processing strategies to improve materials performance. These atomistic simulations are based on molecular dynamics modelling that relies on (empirical) interatomic potentials. These simulations must reproduce accurately the mechanism of martensitic transformation and the microstructure that it originates, since this controls both superelasticity and the shape memory effect. As demonstrated by the energy minimization theory of martensitic transformations [Ball, James (1987) Archive for Rational Mechanics and Analysis, 100:13], the microstructure of martensite depends on the lattice parameters of the austenite and the martensite phases. Here, we compute the bounds of possible microstructural variations based on the experimental variations/uncertainties in the lattice parameter measurements. We show that both density functional theory and molecular dynamics lattice parameters are typically outside the experimental range, and that seemingly small deviations from this range induce large deviations from the experimental bounds of the microstructural predictions, with notable cases where unphysical microstructures are predicted to form. Therefore, our work points to a strategy for benchmarking and selecting interatomic potentials for atomistic modelling of shape memory alloys, which is crucial to modelling the development of martensitic microstructures and their impact on the shape memory effect.

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