Laser welding of thin foil nickel–titanium shape memory alloy
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Nickel titanium
An interest in NiTi alloys with near stoichiometric composition (55 NiTi) has intensified since they were found to exhibit a unique mechanical shape memory effect at the Naval Ordnance Laboratory some twelve years ago (thus refered to as NITINOL alloys). Since then, the microstructural mechanisms associated with the shape memory effect have been investigated and several interesting engineering applications have appeared. The shape memory effect implies that the alloy deformed from an initial shape will spontaneously return to that initial state upon heating. This behavior is reported to be related to a diffusionless shear transformation which takes place between similar but slightly different CsCl type structures.
Nickel titanium
Diffusionless transformation
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Nickel titanium
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While much is known about the shape memory and supereleasticity of equiatomic alloy of Ni and Ti (NiTiNoL), the deformation behavior of Ni-rich NiTi has attracted relatively some attention. The increase in nickel content, however, also hardens the alloy, which can make the alloy difficult to process. A slightly Ni-rich composition of NiTi can be, on the other hand, advantageous in applications where a higher stiffness of NiTi coupled with its shape memory and superelasticity is required e.g. in orthodontic wires, cardiovascular stent or pressure valves. In this study, we investigate the influence of heat treatment on the deformation behavior of superelastic nickel–titanium for biomedical applications. For this, NiTi alloy composed of 56 wt.% (51 at.%) nickel has been investigated after heat treatment within the thermal window of between 400 and 800°C. Heat treatment significantly influenced both the plasticity and the transformation behavior of Ni-rich NiTi. A detailed examination of the microstructural evolution, calorimetric response and tensile test response with respect to the superelasticity allowed us to establish protocols for obtaining nearly ideal superelastic properties in Ni-rich NiTi shape memory alloys. Our findings can enable use of these alloys in e.g. medical devices that require higher stiffness and a larger surface area.
Nickel titanium
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Nickel titanium
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Shape Memory Alloys (SMA) are promising materials for actuator components. This work focuses on the principal aspects underlying the deformation phenomenon known as Two-Way Shape Memory Effect (TWSME). On wire specimens of a near equiatomic NiTi alloy such an effect is achieved by a thermomechanical treatment. Depending on the training parameters and heat treatment conditions, different magnitudes of reversible shape change are obtained. Further experimental work concentrates on the stability of this special effect throughout cyclic application. Again a strong influence of the initial microstructure on the degradation characteristic is observed.
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The NiTi shape memory alloy exhibits a number of remarkable properties, including shape memory, super-elasticity and resistance to fatigue and corrosion. Although Ni as a trace element contributes to the biocompatibility of NiTi alloy enriched with nickel, many experts doubt its safety after a long-time implantation. This paper reviews progress in the study on the biocompatibility of NiTi shape memory alloy and the development of porous NiTi alloy.
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Shape Memory Alloys (SMAs) are one of the most hopeful smart materials, especially, Nickel–Titanium (NiTi or Nitinol). These alloys are great and desirable due to their excellent reliability and behavior among all the commercially available alloys. In addition, strain recovery, (Ni–Ti) is granulated for a wide variety of medical uses because of its favorite properties such as fatigue behavior, corrosion resistance and biocompatibility. This paper explores the creation and the characterization of functionally graded (NiTi) materials. This work demonstrations the impact of Nickel contains changes on the characteristics of NiTi shape memory alloy, in order to obtain the suitable addition of Nickel contain, which gives the optimal balance between hardness, start and finish martensitic point, shape recovery and shape effect of alloys properties. These materials are prepared to obtain suddenly or gradually microstructure or composition differences inside the structure of one piece of material, the specimens made by powder metallurgy process and the influence of every layer of composite by; micro-hardness, transformation temperature DSC and shape effect. The hardness value and shape recovery decrease with increase nickel content. superior shape memory effect (SME) and shape recovery (SR) properties (i.e., 8.747, 10.270 for SMA-FGM1 SMA-FGM2 respectively, and SR is 1.735, 2.977 for SMA-FGM1 SMA-FGM2) respectively.
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