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Microstructural Characterization of a Laser Surface Remelted Cu-Based Shape Memory Alloy

Microstructural Characterization of a Laser Surface Remelted Cu-Based Shape Memory Alloy

Cu-based shape memory alloys (SMAs) present some advantages as higher transformation temperatures, lower costs and are easier to process than traditional Ti-based SMAs but they also show some disadvantages as low ductility and higher tendency for intergranular cracking. Several studies have sought for a way to improve the mechanical properties of these alloys and microstructural refinement has been frequently used. It can be obtained by laser remelting treatments. The aim of the present work was to investigate the influence of the laser surface remelting on the microstructure of a Cu-11.85Al-3.2Ni-3Mn (wt%) SMA. Plates were remelted using three different laser scanning speeds, i.e. 100, 300 and 500 mm/s. The remelted regions showed a T-shape morphology with a mean thickness of 52, 29 and 23 µm and an average grain size of 30, 29 and 23µm for plates remelted using scanning speed of 100, 300 and 500 mm/s, respectively. In the plates remelted with 100 and 300 mm/s some pores were found at the root of the keyhole due to the keyhole instability. We find that the instability of keyholes becomes more pronounced for lower scanning speeds. It was not observed any preferential orientation introduced by the laser treatment.
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Laser welding of precipitation strengthened Ni-rich NiTiHf high temperature shape memory alloys: Microstructure and mechanical properties

Laser welding of precipitation strengthened Ni-rich NiTiHf high temperature shape memory alloys: Microstructure and mechanical properties

High temperature shape memory alloys are currently attracting significant attention by the aerospace industry due to the potential use of shape memory and superelastic properties at temperatures above 100 °C. Virtually any advanced engineering material must at some point be joined either to itself, to create complex shaped structures, or to other materials to increase its potential applications. In this work, laser welding of a precipitation strengthened Ni-rich NiTiHf high temperature shape memory alloy is reported for the first time. Starting with a base material aged at 500 °C for 3 hours and air cooled, defect-free joints with a conduction weld mode were obtained. Microstructural characterization, facilitated via microscopy and synchrotron X-ray diffraction, revealed that the fusion zone contained a single-phase martensitic structure at room temperature, compared to a mixture of martensite and H- phase precipitates in the base material. Isothermal loading in both the martensite (at 30 °C) and austenite (at 200°C) phases revealed equivalent strength and near-perfect superelasticity in the welded and un-welded reference material.
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On a nonlinear and chaotic non-ideal vibrating system with shape memory alloy (SMA)

On a nonlinear and chaotic non-ideal vibrating system with shape memory alloy (SMA)

the increase of the temperature between 0.7 ¬ θ ¬ 1 and 1000 < τ < 1266, the angular velocity continually decreases below the resonance region, however the dynamics of the system drastically changes and becomes periodic, which is reflected by the Lyapunov exponent (see Fig. 20), which changes its sign from positive to negative near θ = 0.8. As θ is increased further, the marten- sitic phase transformation happens (martensitic to austenitic) in the interval 1 < θ ¬ 1.26 and 1266 < τ ¬ 1493. In this situation the angular velocity is captured by the resonance region between 1.21 < θ ¬ 1.24 and motion of the system comes back to chaos. In the interval 1.26 < θ ¬ 1.59 with the angular velocity outside the resonance region, the system continues having chaotic be- haviour (a positive Lyapunov exponent exists) and, finally, for 1.6 ¬ θ ¬ 3, the Lyapunov exponent abruptly changes the sign to negative and the behaviour of the system becomes periodic.
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Thermal control of a shape memory alloy for actuation in the Sommerfeld effect of a non-ideal system

Thermal control of a shape memory alloy for actuation in the Sommerfeld effect of a non-ideal system

Nowadays, with the evolution of technology has emerged a growing demand for more lightweight and larger electromechanical systems. These configurations are present in several systems and projects, such as robotic manipulators, portal frame systems and the most diverse structures that are subject to some type of slewing movements (e. g., satellite panels, space antennas, and flexible cranes). However, these more flexible electromechanical structures are susceptible to specific mechanical vibrations phenomena. The union between the mechanical structure and the rotational energy source causes a specific behavior in the system, i.e., an energy exchange between the mechanical system and the rotational/electric system. Because of this specific behavior, this kind of system received a new classification with the name of non-ideal systems (BALTHAZAR et al., 2003, 2004; PICCIRILLO; TUSSET; BALTHAZAR, 2014).
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Investigation of the bainitic reaction in a CuAlNiMnFe shape memory alloy

Investigation of the bainitic reaction in a CuAlNiMnFe shape memory alloy

Slices with ~1.5 mm thickness were spark cut from the rods. The samples were betatized (homogenized) at 1173 K for one hour in an air furnace, then quenched in room temperature water to obtain the γ’ martensitic phase. The quenched samples were then heated to 623 K with 10 K/min in a Netzsch 204 heat flux DSC (Differential Scanning Calorimeter) then subsequently cooled to room temperature with 10 K/min. Ar purge gas was used during the DSC examination. The DSC scans of the first and second heating and cooling runs of alloy B are shown in Fig. 2. The samples were mechanically polished then prepared using ion beam milling for the TEM (Transmission Electron Microscope)
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Effect of Contact Temperature Rise During Sliding on the Wear Resistance of TiNi Shape Memory Alloys

Effect of Contact Temperature Rise During Sliding on the Wear Resistance of TiNi Shape Memory Alloys

sliding tests were carried out using the same Tribometer, a steel pin of mm radius pressed against the TiNi alloy disc specimen under a constant normal load of N and at varying sliding speeds of mm/s, mm/s, mm/s and mm/s so that different contact temperatures could be generated. The contact temperatures for each load and speed combination were calculated using Archard’s flash temperature equations, reproduced in a convenient form in equation . The deformation conditions were determined using the elementary plasticity condition P/ a > (, a being the contact radius. The speed conditions were determined using equation . With these constraints all the test conditions turned out to be high speed elastic. The weight loss of the specimen was again measured using a high precision balance and the plot of experimental wear volume against calculated specimen temperature is shown in Fig. .
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Gas Tungsten Arc Welding of Cu-Al-Mn Shape Memory Alloys

Gas Tungsten Arc Welding of Cu-Al-Mn Shape Memory Alloys

There are no significant differences between the cycling behaviour of the welded and base material specimens. The irrecoverable strain after the first cycle for the base material was around 1.3%. For the welded specimens a slightly higher value for the irrecoverable strain after the first cycle was observed, around 1.5%. The presence of multiple factors can affect the superelastic response of the Cu-Al-Mn alloy. These can include grain size and grain orientation. The slightly larger irrecoverable strain in the welded specimen can be attributed to: the finer grained fusion zone, which has smaller d/D ratio than the base material, which reduces the superelastic recovery upon unloading [20]. In Cu-based shape memory alloys, the recoverable strain depends on the grain size (d) relative to the size of the specimen, for sheet thickness (t) or wire diameter (D), and increases with increasing the relative grain size, defined by the relation d/t or d/D. The superelastic strain increases with increasing d/D, owing to the fact that the free surface grain boundary area also increases, which is equal to the relaxation of the grain constraint [20]. Another reason that can justify the higher irrecoverable strain is related to the presence of α-phase which does not contribute to the superelastic behaviour and to the grain orientation in the fusion zone, which is clearly distinct from the optimized texture of the base material [38].
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VIBRATION CONTROL WITH SHAPE-MEMORY ALLOYS

VIBRATION CONTROL WITH SHAPE-MEMORY ALLOYS

observed the disappearance and reappearance of a martensitic crystal structure by increasing and decreasing the temperature of a CuZn alloy [66]. The thermoelastic properties of the martensitic crystal phase of an AuCd alloy were widely reported by Kurdjumov and Khandros (1949) [86], and Chang and Read (1951) [37]. In the 1960s, Buehler and Wiley discovered the NiTi alloys, while working at the Naval Ordnance Laboratory (NOL). The NOL, now disestablished, was formerly located in White Oak, Maryland and was the site of considerable work that had practi- cal impact upon world technology. As a tribute to their workplace, they named this family of alloys Nitinol [71]. While the potential applications for Nitinol were realized immediately, practical efforts to commercialize the alloy didn’t take place until a decade later. This delay was largely due to the extraordinary difficulty in melting, processing and machining the alloy, technological processes that weren’t really overcome until the 1990s, when finally these practical difficulties began to be resolved [71].
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Characterization techniques of a shape memory nickel titanium alloy

Characterization techniques of a shape memory nickel titanium alloy

the shape memory alloys (SMA) composed by Nickel and Titanium (NiTinol). Two different wire suppliers were studied, starting with metallographic analysis until observe the contours of the grain wires. Differential scanning calorimetry (DSC) test was also performed to obtain phase transformation temperatures of the NiTinol alloys. Finally, after several tensile tests, some results were obtained for stresses, strains, elasticity modules and maximum rupture deformation.

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Impact of Alloy Composition and Thermal Stabilization on Martensitic Phase Transformation Structures in CuAlMn Shape Memory Alloys

Impact of Alloy Composition and Thermal Stabilization on Martensitic Phase Transformation Structures in CuAlMn Shape Memory Alloys

The strain related amplitude depended internal friction (ADIF) was investigated as logarithmic decrement (IF) δ of vibrations free decay in the bending mode at room temperature (293 K). The specimens were clamped into single cantilever bending beam configuration and excited by an electromagnetic excitation to vibrations with the resonant frequency at the maximum strain amplitude of 12E-4. The used damping measurement system is described at detail in 21 .

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Shape Memory Alloy Actuator forBio-medical application

Shape Memory Alloy Actuator forBio-medical application

Forceps which was used in this experiment is Radial Jaw3 manufactured by Boston Scientific. Two linear stages MFA CC Linear Miniature Series made by Newport were used for actuating the two axes. The maximum linear speed attainable by the linear stages was 3mm/s. To measure the forces applied two load cells, MLP10 product of Transducer technology, were used, one with each axis placed coaxially along the axis of applied force. Pig esophagus was used as the tissue sample for performing the biopsy.

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Releasing systems for aerospace industry based upon Shape Memory Alloys: characterization of materials for actuators

Releasing systems for aerospace industry based upon Shape Memory Alloys: characterization of materials for actuators

much lower stiffness until transformation is completed in point K. Reverse transformation has place during unloading, when another critical stress (lower than the prior) is reached at point M. Reverse transformation continues also with a low modulus up to point N, from which elastic unloading continues. SMAs following a superelastic cycle as AJKMNA exhibit high recoverable maximum strains (up to 8%). This capacity provides superelastic slender elements of extraordinary kink resistance capacity [10]. Biocompatible SMAs, as the NiTi based group find an extensive use in medical applications as stents, catheters and orthodontics devices [11, 12]. A novel application has been recently proposed for NiTi superelastic wires. In this case, the reverse transformation load, exerted along an extended displacement range is utilized for the correction of osseous malformations [13, 14]. Non medical applications are related with vibration control of mechanical structures due the dissipative capacity associated with the - hysteresis [15,16]. A last particular behavior, described in Fig 1.c, takes place when a constraint is applied avoiding the austenitic shape of the alloy to be freely recovered upon heating, for example at point P. The alloy reacts generating a load against the constraint. If heating is performed at constant strain, the state of the alloy at temperature T 1 corresponds to point Q. The
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LIGA COM MEMÓRIA DE FORMA - (Shape Memory Alloy – SMA)

LIGA COM MEMÓRIA DE FORMA - (Shape Memory Alloy – SMA)

Shape Memory Alloy (SMA) consists of a group of metallic materials that have the ability to return to a previously defined shape or size when subjected to a suitable thermal cycle. The shape memory effect (EMF) is a unique property, characteristic of some alloys that undergo the martensitic reaction. Form memory alloys exhibit memory that can be triggered by voltage or by temperature change. This article will present concepts about such alloys with regard to their shape memory behavior as well as some of their applications in the most varied sectors of science.
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Correlation Between the Mechanical Cycling Behavior and Microstructure in Laser Welded Joints Using NiTi Memory Shape Alloys

Correlation Between the Mechanical Cycling Behavior and Microstructure in Laser Welded Joints Using NiTi Memory Shape Alloys

Until 1949 the martensitic transformation was established as an irreversible process. However in that year Kurdjumov and Khandros presented the concept of thermoelastic martensitic transformation, which explained the reversible transformation of martensite. Their work was performed in CuZn and CuAl alloys and, some years latter, the thermoelastic martensitic transformation was demonstrated for other alloys such as InTl. Despite the discovery of the reversible martensitic transformation for different alloys, this effect was not utilized until 1963. In that year Buehler and their coworkers discovered the shape memory effect (SME) in NiTi while investigating different materials that could be used for heat shielding. [2] The term “NiTiNOL” is also connoted with NiTi in honor of its discovery at the Naval Ordnance Laboratory (NOL). The discovery of this new alloy triggered active research interest into SMAs. The effects of heat treatment, composition and microstructure were extensively investigated and began to be understood then.
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Gas Tungsten Arc Welding of NiTi Shape Memory Alloy

Gas Tungsten Arc Welding of NiTi Shape Memory Alloy

The properties of SMAs have been successfully implemented in a variety of dental applications. Since the 1970's NiTi orthodontic archwires have been used for being more effective than other alternative materials (Figure 2.17 - a)). Combining NiTi with other materials allows obtaining selective components that are able to control the force applied on each teeth, resulting in a more effective solution. Another dental application for SMAs involves the use of NiTi drills used in root canal surgery, which involves careful drilling within the tooth (Figure 2.17 - b) ). The Nitinol drills can bend to rather large angles, which induce large strains, yet still withstand the high cyclic rotations [1,8].
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Laser Welding of Shape Memory Alloys

Laser Welding of Shape Memory Alloys

Owing to the aforementioned characteristics, this particular alloy has usually a bamboo-like grain structure with a length of at least 1 mm. However, growing such massive grains it was not easy until Omori et al. [30] find out that these alloys can present abnormal grain grown under appropriate processing conditions. When a given material presents abnormal grain growth, selective growth of a few grains occurs by engulfing the neighboring ones. Some of techniques available to activate this phenomena consist on plastic deformation followed by an annealing heat treatment with a temperature gradient or by plastic deformation at high temperatures. However, these methods can only be applied to wires or sheets, in which fracture occurs by slight plastic deformation. For these Cu-Al-Mn alloys a cyclic heat treatment was sufficient to promote the growth of the grain structure. The heat treatment consisted on the following sequence : slow cooling down from the β-phase region (for example at 850 ᵒC) to the biphasic α + β region (for example at 600 ᵒC) and subsequent heating to the β phase region again. This cyclic heat treatment can be performed several times in order to obtain increasingly larger grains.
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Working memory impairment in multiple sclerosis relapsing-remitting patients with episodic memory deficits

Working memory impairment in multiple sclerosis relapsing-remitting patients with episodic memory deficits

If WM alterations, considering its executive and ep- isodic bufer components, were in fact responsible for episodic memory deicits in MS, then episodic memo- ry impairment should be observed only in patients who show WM alterations. his has never been experimental- ly shown. Such a inding would point to the need to study subgroups of MS patients that are homogenous in term of memory impairment so that further steps can be tak- en to determine whether, in what way, and to what ex- tent episodic memory problems result from altered en- coding and/or retrieval processes that involve WM. his, in turn, may help in the development of speciic rehabil- itation practices for these patients.
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Development of paper transistor with memory effect

Development of paper transistor with memory effect

It is of note that the devices’ performances are essentially the same with the exception of NFC+ph5.5. The dielectric’s capacitance per unit area is two orders of magnitude smaller than the rest. This may be due to the Cl - ions left from the HCl treatment, due to these ions’ low mobility; they may remain in the EDL formation zone despite being repelled by the local electric field. This will disturb the device’s ability to accumulate charges in the form of the EDL and thus reduce the membranes capacitance.

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Microstructural characterization and mechanical behavior of NiTi shape memory alloys ultrasonic joints using Cu interlayer

Microstructural characterization and mechanical behavior of NiTi shape memory alloys ultrasonic joints using Cu interlayer

Ultrasonic spot welding (USW) is a rapidly developing non-melting joining method which is widely used in plastic forming, electronics and automotive fields [ 32 , 33 ]. As compared to the fusion welding processes, such as resistance and laser welding, USW can produce high strength joints without metal depletion or reduced extension of the heat affected zone. Such translates into almost no detrimental effects produced on the BM. USW is especially suitable for achieving effective joints of miniature components [ 34 , 35 ], such as metallic foils, wires and plates, which make this process particularly interesting to weld materials with lower weldability. Traditionally, studies have been mainly focused on the joining of light materials for weight reduction in industrial products [ 32 – 35 ]. However, knowledge on the use of USW in NiTi SMAs is currently extremely limited. Thus, carrying out USW on NiTi is a very worthwhile investigation since this technique has great potential for the fabrication of variable electromagnetic switches, radiator fins and other components based on NiTi SMAs.
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