Search

Massive technological developments can produce material functionality with a wide variety to meet various needs such as flexibility and smart devices, one of which is shape memory alloy (SMA) material. SMA is a smart material that is unique in remembering its original shape even though it has undergone load deformation above the elastic limit due to temperature or load stimulation. Ni-Ti-based is one of the well-established SMA materials, compared to Cu-based and Fe based. Shape memory alloy made from iron, also known as shape memory steel, is widely used in various applications due to various advantages over NiTi. In its development, Iron-Based SMA was applied to various fields, including civil engineering, mechanical engineering, and biomedical. The use of Fe as an alternative material in the application of shape memory alloys has advantages such as low processing costs and the availability of abundant raw materials. Fe-based SMA properties such as ductility, magneticity, strength, biocompatibility, and bioactivity are used in various biomedical applications, including cardiovascular stents and bone prostheses. Other advantages found in Fe-based SMA are weld-ability, ductility, elastoplastic damping and strain hardening due to deformation induction ɣ to ɛ martensitic transformation. However, there is still lack of research that discusses the use of Fe-based SMA in biomedical applications. Some of the reasons are instability, impracticability and poor thermo-mechanic performance, which results in a low percentage of shape recovery. This is an opportunity to encourage research and development in optimizing Fe as an alternative shape memory material. This review will provide an overview of the development of Fe-based SMA materials, especially in the biomedical field. In addition, discussions related to challenges and opportunities will also be described based on the research results that have been carried out to date. [ABSTRACT FROM AUTHOR]

Due to their biocompatibility, superelasticity, and corrosion resistance, binary and ternary NiTi (NiTiNOL) shape memory alloys (SMAs) are at the forefront of materials research for biomedical applications. The first half of the study reviews the biocompatibility and uses of NiTi SMAs. Traditional machining techniques have difficulty dealing with binary and ternary NiTi SMAs. The second half of the research discusses the literature review of unconventional SMA machining techniques from laser beam to wire electrical discharge machining (Wire EDM). Significant output responses, such as surface roughness and material removal rate, are also investigated as a function of numerous non-traditional machining process input factors. The conclusion outlines the few areas of research that remain to be done on the subject of NiTiNOL SMAs' machinability. [ABSTRACT FROM AUTHOR]

Porous Nickel-Titanium (NiTi) alloy has been developed especially in the biomedical sector due to its shape memory ability and its mechanical properties which is comparable to human bones. However, NiTi alloy carries the risk of Nickel (Ni) ions leaching when implanted in the human body making it less favourable for biomedical use forlong term. Therefore, the goal of this research is to passivate the porous NiTi by oxidizing the surface via annealing treatment. Initially, the porous NiTi alloy was fabricated via powder metallurgy technique with addition of Calcium Hydride (CaH2) as a pore forming agent. Here, the degree of porosity was measured and the pore morphology, phase identification and transformation behavior were characterized by Scanning Electron Microscope (SEM), X-Ray Diffractometer (XRD), and Differential Scanning Calorimeter (DSC), respectively. Then, the surface treatment was performed by varying annealing temperatures where the oxide layer formation was characterized by using SEM and Energy Dispersive Spectrometer (EDS). The result shows that the sample's porosity increased by up to 42% from its theoretical density, demonstrating that the weight percentage of the pore-forming agent has a significant effect on theporosity of the NiTi alloy. For surface treatment, at higher annealing temperature i.e. 500°C, it produced a thicker oxide layer of TiO2 as compared to samples annealed at 300°C and 400°C. This indicates that the annealing temperature highly affects the formation of oxide layers on the surface. This oxide layer adheres well to the NiTi alloysurface and is expected to prevent the Ni ion from releasing, thus making this porous NiTi biocompatible metal. [ABSTRACT FROM AUTHOR]

This study emphasizes on Shape memory alloys (SMA) essentially NiTinol, which is extensively used in development of composites in the form of a reinforcement either as a fiber or particulate which help in improving the mechanical properties, providing it the dynamism due to the presence of uniqueness in the property of shape memory upon change in temperature. SMA is super elastic and have the ability to recover. NiTinol is used as an alternative to many traditional smart structures used in bulk, it is also used to embed in the development of an actuator, morphing of blades with embedded strips, in carbon fiber reinforced polymer composites, MMC's and many more applications to improve the properties of the composite. The study focuses on the SMA, NiTinol in specific, its properties, fabrication techniques and its phases. Due to excellent mechanical properties, there are numerous applications in various sectors and domains where they are actively being used in Structural Design, in medical fields and also in Space research domain as well. Hence this comprehensive study gives an innate understanding of shape memory alloys and its properties, their phases and fabrication techniques with their applications which imbibes various unique properties to the composites. [ABSTRACT FROM AUTHOR]

This manuscript covenant by means of the random natural rate of recurrence analysis of hybrid composite plate by employing the finite element (FE) based numerical approach. Shape memory alloy (Nitinol) in the form of rods will be inserted in glass epoxy composite plates to obtain the hybrid composites. An algorithm is resultant for vagueness quantification of accepted frequencies of the hybrid composite owing to uncertain disparity in the substance properties. This deterministic finite element code is verified with the preceding copy. The effects of degree of randomness and specific volume on the first three natural frequencies will be determined. Monte Carlo simulation will be coupled with finite element code to conduct the random analysis. The outcome demonstrates the key in parameters painstaking in the current learning have momentous possessions on the randomness of initial three accepted frequencies of plank hybrid composite plates. [ABSTRACT FROM AUTHOR]

Smart material alloys are researched and used in various applications due to their superelastic, mechanical properties, and shape memory effects. The smart material used in this project is a Nickel-Titanium (Nitinol) alloy. In this study, research is conducted to use Nitinol as a pair of coiled muscles for the flexion and extension - actuation processes and also to check their biocompatibility. The unique arrangement of nitinol springs actuators enables the robotic hand to curl and uncurl its fingers, to hold something. It has a design power requirement of a minimum of 14 watts. The shape setting of nitinol wire of 0.4mm dia to form springs was carried out by firmly constraining it on a mandrel and then performing heat treatment. A series arrangement of nitinol springs along the forearm is implemented into a hand model after deliberation of different designs. Its activation is done using a joule heating approach. Finally, the performance characteristics of these nitinol spring actuators would be compared with the traditional robotic actuators and conclude this study. [ABSTRACT FROM AUTHOR]

This work aims to evaluate the force-deflection behavior of NiTi shape memory alloy archwire towards the effect of friction in orthodontic leveling. A universal bending jig setup was developed to perform three-point bending, two-bracket bending, and three-bracket bending tests at room temperature (27°C). The three-point bending setup follows the ISO 15841 standard and is then modified to compensate for the setup of bracket bending tests. Two different wire sizes were used; 0.014-in and 0.016-in NiTi round archwire, and 0.016-in × 0.022-in and 0.018-in × 0.025-in NiTi rectangular archwire, coupled with 0.022-in stainless steel brackets. The polytetrafluoroethylene (PTFE) bracket is resembling a frictionless bracket used as a control experiment. The force-deflection behavior of the NiTi archwire mounted on the PTFE bracket/support showed a flat plateau of force at stress-induced martensitic phase transformation (SIMT) at activation and deactivation stages, in all bending configurations. However, the use of the stainless-steel bracket/support causes a positive and negative gradient in the activation and deactivation of the force. The force gradient is, even more, steeper in the three-bracket configuration compared to the two-bracket configuration. On the other hand, the sliding friction is determined at the bending point while the binding friction is determined at the bending point. The frictions that have occurred vary depending on the size and shape of the wire. The presence of friction increased the force required to deflect the orthodontic wire to the prescribed deflection distance. The negative gradient of the force plateau during wire deactivation may prevent the deflected wire from being fully recovered. [ABSTRACT FROM AUTHOR]

This work is focused on a TPMS primitive unit cell, modeled with NiTi as a base material and subjected to cyclic loading. Its functional fatigue behavior is analyzed via an FEM model, and the appropriate post-processing of the data. Full periodic boundary conditions are applied onto each of the cell's faces, to simulate an infinitely-large structure. The loading and unloading surfaces, from the first unloading onwards, depend on the accumulation of the martensite phase, due to a residual stress field. This effect, functional fatigue, is taken into account to derive loading and unloading surfaces via double interpolation. This double interpolation is done from the information of calibration cases. Then, it is validated with a different loading path. This facilitates the prediction of the functional cyclic behavior of primitive TPMS cells made of NiTi. [ABSTRACT FROM AUTHOR]

The regime of heat treatment (annealing at 1448 K, 8 h with quenching in water), which leads to the appearance of thermal-induced martensitic transformation in [001]-oriented Ni42Fe19Ga27Co12 (at.%) single crystals was experimentally established. The large regions of γ-phase in size of 50−500 µm and volume fraction of∼20–25% were precipitated during annealing. The γ-phase leads to a decrease in the content of iron and cobalt and an increase in the content of gallium in the matrix; reduction of stresses for oriented martensite formation in stress-assisted thermal cycles by 4 times (from 200 to 50 MPa); broadening of thermal hysteresis in stress-assisted thermal cycles and stress hysteresis in loading/unloading cycles; a shift of superelasticity temperature range to higher temperatures. [ABSTRACT FROM AUTHOR]

This investigation comprises a study of the influence of the silicon on the morphology, topographical parameters, and deformation behavior of the Ti-N-Nb and Ti-Ni-Nb-Si surface alloys (SAs) formed on the NiTi-substrate by the electron-beam synthesis. It was shown that addition of Si10 (at. %) to the chemical composition of sputtered film during electron-beam synthesis of SAs leads to smoothing of the surface microrelief with the average roughness parameter R a I N T ≈ 0.211 μm , that ∼1.7 times lower than compared to its value in SA without silicon ( R a I N T ≈ 0.355 μm). The presence of silicon in SA leads to a high value of the yield strength (σy≈3.3 GPa), values of which monotonically decrease from the surface to the values of NiTi-initial. Evaluation of the deformation behavior showed, that in surface layers of synthesized SAs, due to an increase of plasticity, there was a decrease in superelasticity by no more than ∼5%. This result shows that the presence of SAs on the surface of NiTi-substrate will not lead to a significant decrease of the superelastic properties of NiTi-substrate. [ABSTRACT FROM AUTHOR]

The responses of two models of heterogeneous medium to impact loading are compared, namely, the direct numerical simulation model and the additive mixture model. Verification of Ni and Ti material parameters in the simulation of spall in a homogeneous barrier is performed. The calculated free surface velocity for homogeneous plates corresponds to the experimental data with an accuracy of at least 10%. A simulation of the impact loading process of plates made of Nitinol based on mathematical models of heterogeneous materials has been performed. The additive mixture model more accurately reproduces the free surface velocity profiles than direct numerical simulations. Nevertheless, the deviation of numerical simulation results from experimental data does not exceed 10% for both models. A comparison of the results of the models' responses to impact loading has shown that it is acceptable to use both models in problems considering alloys as heterogeneous media. [ABSTRACT FROM AUTHOR]

The study of the structure of the melted metal at the boundary of the explosion-welded composite titanium VT1-0 - Cr20Ni80 nichrome was carried out. It has been established that areas of chemical microheterogeneity are formed at the interlayer boundary in the form of local inclusions of melted metal of the NiTi(Cr) composition and continuous interlayers based on nonequilibrium solid solutions (Ti, Ni, Cr). The calculated cooling rates of the melted metal showed the possibility of the formation of non-equilibrium phases and amorphous structures characterized by the absence of a long-range order in the arrangement of atoms. [ABSTRACT FROM AUTHOR]

Recently, near-equiatomic TiNi alloy has been recognized as a successful alternative to replace traditional of next generation Ti alloy for biomaterial applications. This is owing to its distinctive shape memory effect in addition to lower young modulus. Ti alloy is known for many years as crucial alloy in aerospace applications, which is utilized for the airframe and the engine parts. This is rationalized to reduce fuel consumption due to lower density for the alloy. However, aerospace materials still suffer from inadequate fretting wear, corrosion and stress corrosion cracking. It has been reported that the tribology behavior of NiTi alloy is better than many conventional alloys. Consequently, this study has been emerged to evaluate the progress in developing NiTi alloy. [ABSTRACT FROM AUTHOR]

Clothing for protection against critical low temperatures is constantly being improved. Modern materials and alloys with shape memory are used for its production. This article presents a method of incorporation of such materials into textile structures. The peculiarity of these alloys is shape memory as a result of training in a different temperature range taking into account the influence of various impurities. The purpose of this article is to develop and evaluate a methodology for shape memory training of functional parts for use in clothing at negative temperatures. In the course of the research, the current conditions for training materials with shape memory that differ in the boundary temperatures, the number of training cycles and the ways of forming the thermal conditions were investigated, The object of this article is thin metal- coated threads (wires) based on the binary alloy of nickel and titanium - Nitinol (NiTi). The geometric parameters of the thread (thin wire) are justified by the geometric parameters of the textile structure, which is specially designed to determine the diameter of threads set at 0.5 mm (based on the mean thickness of materials for winter protective clothing). A thermomechanical training technique was developed. It takes into account the chemical composition of the NiTi-based functional alloy, loading mode, rest mode, number of training cycles, fixation of the desired shape (using a steel mandrel) for set temperature conditions (that are assured by an autonomous refrigerated container and thermostat). Two phase shapes of a thin part were studied - a straight shape and an angular bend shape (for an angle of 2 degrees). It has been established that the developed method of thermomechanical training, including 200 cycles of training and temperature interval from +200C to -180C allowed achieving the form memory effect for trained parts with its direct and reverse response to the change of set temperatures. The obtained result makes it possible to embed the prepared thin metal threads (wires) into the textile structure to control the shape of the volume and overall thermal insulation of the functional clothing for protection against the cold. [ABSTRACT FROM AUTHOR]

Fibers are utilized in a variety of ways to reinforce cement products (such as concrete). The behavior of shape memory alloys SMA nanofiber reinforced cement effect is the subject of this research. The shape memory alloy used in this investigation is NiTi. Cement is slump tested, is put to the test for seven days. SMA nanofibers are added to the cement mix at a constant rate of 4% wt. SAM micro powder and SAM microfiber reinforced cement are also made,mechanical parameters such as compressive strength and and bending strength are examined for 7 days. Results are compared to SMA nanofiber reinforced cement. cement reinforced with 4% nitinal PVA nanofibers improved Compressive strength to 47 MPa comparer with 18, MPa for standard cement-sand, while decrees deflection to 0.048mm compare with 0.11,0.249 and 0.26 for standard cement-sand, nitinol to cement and microfiber /standered cement sample respectively. [ABSTRACT FROM AUTHOR]

Shape memory alloys exhibit interesting phenomena termed as shape memory effect, which occurs at a specific composition for a class of materials when alloyed together. In current work, we consider Nickel and Titanium (nitinol) which exhibits this interesting phenomena at near equiatomic composition. In a quest to develop a structure-property correlation, it is expected that among other parameters, defects in the materials also contribute towards the properties of material developed. As a result, stacking fault energy is one such defect which decides the properties of materials. The current work estimates the staking fault energy of nitinol based alloy system from second nearest neighbor embedded atomic model using molecular dynamics simulation that allows to establish a structure-property correlation. [ABSTRACT FROM AUTHOR]

The paper presents the results of studying the effect of thermal cycling modes of TN-1 alloys on thermocyclic creep and related irreversible deformation. It is shown that non-isothermal creep of these materials is maximal at thermocycling through martensitic transitions interval during free state cooling and heating under load. [ABSTRACT FROM AUTHOR]

The paper presents the analysis of the research data on the investigation of the local deformation behavior and mechanical properties of the surface layers of NiTi alloy depend on the shape of the indenter's tip (Vickers and Berkovich). Investigations of the mechanical properties (microhardness HOP, Young's modulus EOP, parameter of plasticity δh, and shape recovery ratio η) of the surface layers of NiTi alloy were held by the method of instrumented indentation test. The analysis of the experimental data shows, that at a maximum load Pmax from ∼5 up to ∼300 mN, the deformation behavior of the surface layers of the initial NiTi samples under instrumented sharp indentation with tips of different shapes are similar at a surface layer of ∼1 µm thickness. It means that, regardless of the shape of the indenter's tip, almost identical stress and strain states are created in the indentation zone and adjacent areas. [ABSTRACT FROM AUTHOR]

Nitinol shape memory alloy (SMA) exhibits distinctive characteristics like biocompatibility, shape memory effect, Pseudoelasticity, high resistance to oxidation, superior functional stability. Owing to these superior properties, Nitinol SMA becomes favourable choice for automotive, actuators, biomedical applications, aerospace industries and micro-electromechanical systems (MEMSs). The traditional machining techniques for Nitinol SMA imposes multiple difficulties owing to its characteristics like high toughness, lower strain hardening effect, increased ductility, and improved chemical reactivity. Wire-Electric Discharge Machining (WEDM) through powder-mixed dielectric is one such technique which is mostly suitable for difficult-to-cut materials. In current study, pulse-on-time (Ton), pulse-off-time (Toff), current, nano-graphene powder concentration were designated as machining parameters while SR as response variable for the WEDM of nitinol SMA. Design of experiments (DOE) was employed to create the experimental matrix with total of 27 experiments to be performed. Analysis of variance (ANOVA) was employed to study the statistical analysis of the obtained results. Influence of machining variables on SR response has been investigated by using main effect plots. 3D surface plots were incorporated to understand the simultaneous effect of two variables on SR. Best parameter combinations for obtaining the lowest SR value was determined from the analysis. Authors believes that present work will be useful in the area of powder-mixed machining of Nitinol SMA. [ABSTRACT FROM AUTHOR]

In this paper we establish, on the basis of calorimetric measurements by direct reaction, new values of enthalpies of formation of the ternary intermetallic compounds (Ni3Ti(Al), NiTi(Al) and NiTi2(Al)) of ternary phases based on the system Ni–Ti at 1073 K. Precisely, we determine the variation of the enthalpies of formation of ternary compounds with the substitution of Aluminium atoms by Titanium at Nickel constant concentration. Then structures, compositions and limits of solubility of these ternary phases were investigated by X-ray powder diffraction (XRD) and electron probe microanalysis (EPMA). This last technique was also used to determine the limits between Ni3Ti(Al), NiTi(Al) and NiTi2(Al) solid phases in the isothermal section of the Al-Ni-Ti diagram at 1073 K. Our experimental results are compared with literature data and with predicted values based on semi–empirical and theoretical models. [ABSTRACT FROM AUTHOR]

Nowadays with an abundance of wire alloys to choose for orthodontic treatment, dentists must be wise to select an appropriate wire for the treatment while considering its biological effects on the patient. This review will discuss the possible genotoxic effects of NiTi alloy (Nitinol) orthodontic wires caused by metal ion release. Essentially, the release of metal ions promotes ROS production and induces oxidative stress, which will potentially oxidize nucleotide bases and could cause mutations. Even though the release of metal ions cannot be fully avoided, attempts could be made to minimize its effects on the human body. Clinicians should be aware of the patient's relevant status (such as hypersensitivity) and get updated on newer wire alternatives to optimize the patient's treatment while avoiding undesirable biological effects. [ABSTRACT FROM AUTHOR]

In this work, the thermomechanical stability of heterophase [001]-oriented Ti–51.5 at % Ni single crystals was investigated. Experiments include a high-temperature and high-stress martensite ageing and also loading/unloading cycling at superelasticity (SE) during forward and reverse B2-B19′ martensitic transformations (MT). It was found that Ti–51.5 at % Ni single crystals containing large Ti3Ni4 particles (d ∼ 600 nm after ageing at 850 K for 1 h) is not resistant to stress-assisted martensite ageing and cycling. Stress-assisted martensite ageing at 423 K, 1.7–2 GPa, for 2–4 h leads to the deformation of large Ti3Ni4 particles, the appearance of dislocations at the particle-matrix boundaries, an increase in MT temperatures (by 10 K), and a strong diffusion of the MT (the intervals of forward and reverse MT Δ 1 σ and Δ 2 σ increase in 2 times). During loading/unloading cycling at 423 K and 1.0–2.0 GPa single crystals with large particles were destroyed after 20–25 cycles. It is possible to increase the thermomechanical stability due to the additional precipitation of nanosized Ti3Ni4 particles (d<30 nm by ageing at 673 K, 1 h), which appear in the B2 matrix between large particles. In such crystals with a bimodal structure no changes in the microstructure and functional properties were observed after stress-assisted martensite ageing and loading/unloading cycling. [ABSTRACT FROM AUTHOR]

A study was carried out of the effect of crystal structure on the two-way shape memory effect (TWSME) and its cyclic stability using ferromagnetic single crystals of the Co49Ni21Ga30 alloy (at %), oriented along the [001]-direction, after quenching (T = 1423 K, 0.5 h) and stress-free ageing (T = 623 K for 3 h). The TWSME in [001]-oriented single crystals of the Co49Ni21Ga30 alloy was manifested after training of samples during implementation of B2-L10 martensitic transformation (MT) in the cooling/heating cycle, with constant external stress |σext|. The value of the TWSME was found to depend on the structure of the crystals and the level of applied stress during training. The maximum TWSME value (εTWSME = –4.3(±0.2)%) was achieved after training at |σext| = 125 MPa in single-phase crystals and was equal to lattice deformation ε0 in MT for [001]-oriented single crystals under compression. Ageing lead to a decrease in the TWSME value compared with the single-phase state in three times. In [001]-oriented single crystals with γ′-phase particles, the value of TWSME εTWSME, the temperature hysteresis ΔTTWSME, and the start temperature of the forward MT Ms remained unchanged for 500 cycles, and in quenched crystals, up to 150 cycles. [ABSTRACT FROM AUTHOR]

The development and implementation of organ-preserving treatment methods in patients of reproductive age is the priority trend in modern oncology. The results of using high-tech methods developed at Tomsk Cancer Research Institute were discussed. The technique of forming the obturator apparatus of the uterus using the superelastic nitinol mesh implant was presented, and high efficacy of this implant in terms of pregnancy outcome was shown. The reproductive results and recommended methods of assisted reproductive technologies for this category of patients were analyzed. In conclusion, recommendations for the application of high-tech methods for radical trachelectomy, as well as guidelines for follow-up care and delivery in patients with cervical cancer after radical trachelectomy were given. [ABSTRACT FROM AUTHOR]

The present investigation aims at studying the mechanical properties like microstructure, grain refinement shape memory effect and martensite transformation behavior of Cu-Al-Ni Shape Memory Alloys and it has been studied thorough EDAX, Optical Microscopy (OM) and Differential scanning Calorimetry (DSC). From the investigation it is found that shape memory effect of the Cu-Al-Ni alloys is able to display at a specific composition of about 12-14 wt.%for aluminum and 3-5 wt.% for nickel. Bend test is used to study the properties of shape memory alloys.Various mechanical tests were carried out on the specimen which shows maximum shape memory effect. It is observed that the composition of Cu(81.8) Al(13.7) Ni(4.5) shows the best shape memory effect and it is calculated to be 95.66 (%). It is found that alloys show better hardness property as well. [ABSTRACT FROM AUTHOR]

Shape Memory Alloys (SMAs) are a peculiar class of materials able to recover their initial shape by a phase solid transformation thermally activated. The research activity is focused on the characterization of corrosion behavior of Cu-Zn-Al SMA. Potentio-dynamic anodic polarization tests and electronic microscopy (SEM-EDS) observations of corroded surfaces have been carried out in order to analyze corrosion resistance to different chemical environments. [ABSTRACT FROM AUTHOR]

This paper reports investigation results of microstructure transformation and shape memory property in Cu- 22Zn-7Al (wt%) shape memory alloy in the heat treatment process with the variable of various quench mediums. The alloy was made by the melting process of Cu ingot, yellow brass, and Al ingot. Molten metal was poured and solidified in a permanent mold. Then, solid Cu-22Zn- 7Al alloy was heat treated by homogenizing and stress relief annealing. Martensite of the alloy was formed by heating Cu-22Zn- 7Al in Beta phase temperature then continued by cooling in air, oil, water, and brine. Each cooling medium has a different effect on cooling rate. Chemical composition, microstructure, non- equilibrium transformation temperature, hardness, and shape memory properties were investigated in detail. The result shows that the martensite phase increases by enhancement of cooling rate. Alloy quenched by brine not only performs the best quality of martensite but also exhibits the highest shape memory recovery. [ABSTRACT FROM AUTHOR]

Cu-Al-Mn ternary shape memory alloys (SMAs) obtained through ingot metallurgy process by using induction furnace. Specimens prepared by varying percentage of aluminium (10-15wt. %) and manganese (2-10wt.%). Application of these SMAs requires it to be fabricated to required shape. Machinability of SMAs has not been investigated to shape the alloy. In the present work machining characteristics of Cu-Al-Mn ternary shape memory alloys are investigated by WEDM machining process. The effect of input parameters like Current (I), Diameter of the wire (D) and Wire Speed (S) on Material Removal Rate (MRR) in WEDM of Cu-Al-Mn ternary shape memory alloys was studied. The WEDM specimens and cross section of ternary alloys were analyzed using Scanning Electron Microscope. The obtained results indicated that, the MRR increases with increase in wire speed and diameter of the wire. A SEM image indicates the surface morphology of the machined surface. [ABSTRACT FROM AUTHOR]

Modifications achieved by laser irradiation on titanium-base alloys were studied to promote their surface properties in addition to the ion release behavior. Laser pulses was use for three different types of Ti-base alloys; commercial pure Ti alloy, Titanium-Tantalum alloys, and Nickel-Titanium alloys. The alloys were manufactured by using powder technology then the Nd: YAG laser pulses were used. The characterizations of samples have been done which includes; microstructure observation, XRD, surface roughness (AFM), and ion release analysis. The microstructure observation show that the use of Nd: YAG laser pulses was effective method to provide energy focused on one spot especially at the surface which produce complex microstructures and roughening the surfaces to increase effective surface area. XRD showed the sintering process under controlled atmosphere produced samples with complete sintering reaction. AFM results show the same response to the laser irradiation and the slight differences in the roughness values was observed. From the results of ion release analysis it was found that the release of Ti ion rise in first three days and after that released of Ti ions begin to stabilize after the laser pulses. The appearance of a slight differences in the amount of titanium ions that released from the samples for each group was due to the influence of the surface activation process that have been employed as a primary treatment which effect on the stability and thickness of the titanium oxide. [ABSTRACT FROM AUTHOR]

The materials which perform the desired reactions are received from external influences such as temperature, pressure and magnetic field are called smart materials. Shape memory alloys, which are smart materials, show shape memory effect by solid-state phase transformation. With these properties, they are separated from the classical material groups. However, environmental factors affect the structure of shape memory alloys as like all materials. Furthermore, materials can age by temperatures shift, moisture, radiation, high strains, stress, etc. So that s the major reason of the materials deterioration rate increase. The purpose of using material will be lost day by day andtake them it a useless application. Therefore, in our study, the effect of the pressure applied to NiTi based shape memory alloy at different waiting periods and different applied pressures on phase transformation temperatures were investigated. [ABSTRACT FROM AUTHOR]

Hot isostatic press (HIP) is an advanced kind of powder metallurgy production technique which prevents vaporization loss of alloying elements with low melting points during melting. In this work, ternary Cu-Zn-Al shape memory alloys (SMAs) withnew chemical compositions were fabricated by using hot isostatic pressing technique, then the obtained alloys were homogenized at 900 °C and quenched in iced-brine water to surpass the formation of hypo-eutectoid precipitations and lead to the formation of β’1 martensite phase in the alloy. Then the small specimens of the alloy were undergone through thermal and structural measurements. The thermograms obtained from differential thermal analysis measurements of the alloy by DTA instrument demonstrated the characteristic hysteresis curves and peaks of martensitic phase transformations which indicated the shape memory effect (SME) property exists in the alloy. The start and finish temperatures of phase transitions and some other thermodynamical parameters were determined by using the data of these thermal measurements. The structural XRD analysis made in room conditions showed the patterns of martensitic structures. The average crystallite size of the alloys were computed by using XRD data. The valence electron concentration (VEC) value of the alloys were also calculated, since it is a pre-conditional and hypothetical sign of having SME property. Furthermore, the effect of HIP production technique on these new Cu-Zn-Al SMAs was discussed. [ABSTRACT FROM AUTHOR]

In today’s technology, the useful materials attract more attention for sustainable of energy sources. Shape memory alloys (SMAs) are one of these useful materials due to their unique properties as pseudoelasticity and shape recovery property. SMAs can be classified as Cu-based (Cu-Zn, Cu-Al and Cu-Sn), Iron-based and NiTi. The copper-based system is the most useful because of easy fabrication and low cost production. In these systems, there are two main phases; martensite low symmetric temperature phase and austenite the high temperature phase. So the SMA got certain characteristic temperature that each phase starts and ends from high temperature to low temperature. There are many applications of these alloys as aerospace, medical, automobile, petroleum industry, sensors, actuators, etc. The characteristic transformation temperatures, the thermodynamic parameters and structural features of shape memory alloys (SMAs) are sensitive to variations in alloy composition, so in this study, we searched the effect of additive elements on the characteristic transformation temperatures, thermodynamic parameters and structure of Cu-Al based SMAs. In this context, Cu–12.9Al–22.73Be-0.37Mn (at%) alloy and Cu–18.73Al–21.06Be–0.13Mn (at%) alloy were studied here as structural and thermodynamical. Upon thermal analyses, they were classified as HTSMA since the martensitic transformation temperatures for both alloy became above 100 °C. Also the martensite phases were detected in both alloys by XRD measurements at room temperature. [ABSTRACT FROM AUTHOR]

Copper based alloys are preferred because of their excellent electrical and thermal energy transmission, corrosion resistance, lattice structure and being a much more economical alternative instead of NiTi shape memory alloys. In this study, thermal and structural properties of Cu-based shape memory alloy were investigated. The characteristic austenite and martensite transformation temperatures were determined by Differential Scanning Calorimetry (DSC). Structural properties were investigated by X-Rays analysis (XRD) and the results obtained were concluded to be in parallel with the literature. [ABSTRACT FROM AUTHOR]

The paper investigates the effect of isothermal (T=295 K, above Af) mechanical cycling by bending to a strain of 4.5% and 20.2% on the development of reversible inelastic deformation manifested as the shape memory and superelasticity effects (SE and SME, correspondingly) in binary alloy Ti49.3Ni50.7 (at.%). It is found that the increment of plastic strain and chnges of SE and SME are expressed brightly after seven cycles and absent practically at the increase of number cycles to 11 (independently of the value of total strain εt in cycles). The cycling with εt=4.5% leads to the weak accumulation of plastic strain (∼1%) and, correspondingly, to the decrease of SE from 4/5% to ∼3.5% (SME ≤ 0.2%). It is shown that the increase of εt to 20.2% leads to increases of SE to ∼6.2% and SME to ∼4.8% at the first bending cicle. The sharp decrease of SME (to ∼0.5%) is observed under subsequent mechanical cycling due to development of plastic strain. At the same time, SE becomes stable on high level (∼6.5%). The possible reasons of similar changes of SE and SME are discussed. [ABSTRACT FROM AUTHOR]

The effect of ageing under high stress (666-1072 MPa) at 423 K on the stability of the shape memory effect and the superelasticity in single-phase and heterophase [001]-oriented Ni50.6Ti49.4 single crystals was studied. It was shown that single crystals, containing dispersed Ti3Ni4 particles (after stress-free ageing at 823 K for 1 hour (h) and 573 K for 1.5 h particles size was 400 nm and < 10 nm, respectively), are more stable to stress-assisted ageing at 423 K than single-phase quenched crystals (annealed at 1253 K for 1 h followed by water quenching). In heterophase crystals, stress-assisted ageing practically does not affect the stress-induced martensitic transformations and the parameters of the shape memory effect and superelasticity, irrespective of the particle size. In single-phase quenched crystals, stress-assisted ageing leads to a decrease in the transformation temperatures by 20 K, an increase in thermal hysteresis, an increase in the critical stress for martensite formation by 110-150 MPa and an increase in the austenite yield strength by 70 MPa. [ABSTRACT FROM AUTHOR]

We investigate the effect of heat treatments of nanocristalline Ni-rich NiTi alloy on the precipitation of Ti3Ni4 phase in the alloys grain/subgrain structure after annealing at 300°C and at 400°C, as well as on martensitic transformations and inelastic behavior. It is shown that the increase in Ti3Ni4 precipitate size and change in their distribution in the substrucrure is accompanied by a shift of martensitic transformation temperatures, leading to the occurrence of the R-phase, and ensuring change of mechanical responses from pseudoelastic to shape memory. [ABSTRACT FROM AUTHOR]

The impact of the pulse number at low-energy High-Current Pulsed Electron Beam (HCPEB) treatment at constant energy density ES upon the deformation behavior of TiNi alloy, its inelastic properties and fracture pattern under quasistatic uniaxial tension are described. It is shown that inelastic properties of the TiNi alloy can be kept at the initial level whereas ductility and ultimate strength can be increased when the following parameters of low-energy high-current pulsed electron beam treatment are used: pulse duration τ = 2−2.5 μs, maximum electron energy 25 keV, energy density ES = 3.8 ± 0.7 J/cm2 as well as the pulsed irradiation mode and optimal number of irradiation HCPEB pulses (n) are taken. The HCPEB modification of the TiNi surface layer results in the increase of martensite yield plateau length, which is 15-30 % larger than one in the unirradiated TiNi samples. The strength properties decrease of the HCPEB-modified TiNi alloy at n = 15 due to the formation of a columnar structure in the matrix B2-phase. After the HCPEB treatment at n = 5 these parameters are varied due to the change of the chemical composition, namely, the nickel depletion of the B2- phase in the surface layer. The mentioned variation of the chemical composition of the matrix B2-phase is responsible for the increase in the temperature of the martensite transformations. [ABSTRACT FROM AUTHOR]

The paper presents analysis of the research data on investigation of physical-mechanical properties of NiTi alloy after microsecond low-energy high-current pulsed electron beam treatment depending on the number of pulses of electron beam. Investigation of physical-mechanical properties (Young’s modulus EIT, dynamic hardness HIT, plasticity characteristic δН, and shape recovery ratio η) of NiTi surface before and after electron beam treatment was held by method of instrumented nanoindentation test. As a result electron beam modification of the surface of NiTi alloy leads to a change in the strength and plasticity characteristics in depth from the irradiation surface. The hardening of the surface layer reaches a depth of up to ∼500 nm at n = 5 (HIT ≈ 60 GPa), and up to ∼1000 nm at n=15 (HIT ≈ 100 GPa). At a depth of more than ∼1500 nm, the value of parameter of shape recovery ratio η decreased by ∼5–10%, which is due to the hardening of the modified surface layers of NiTi alloy. [ABSTRACT FROM AUTHOR]

The properties of TiNi-based alloys are very sensitive to alloy composition, heat treatment, type and amount of impurities, particularly hydrogen atoms. The influence of isochoric annealing temperatures on the structural-phase thermal stability and the temperatures of martensitic transformations of electrolytic-hydrogenated samples of Ti49,1Ni50,9 (at %) alloy with nanocrystalline structure is studied in this paper. It is shown that at annealing temperatures above 473K, hydrogen is desorbed from the samples and precipitates enriched with nickel atoms are formed. In this case, the temperatures of martensite transformations increase. [ABSTRACT FROM AUTHOR]

In this study the effect of high-energy mechanical activation of Ti-Ni powder on the hydrogen interaction has been investigated. High-energy mechanical activation was carried out in a planetary ball mill with an acceleration of 60g. The initial powder has a mixture of phases TiNi (B2) and (B19′), Ti2Ni, TiNi3. The lattice parameters of these phases correspond to literature data. It has been shown that after high-energy mechanical activation a quasi-amorphous phase was formed in a powder. The content of crystalline phases decreases from 100% up to 45%, while the content of the quasi-amorphous phase increases accordingly. It was shown that lattice parameters of phases slightly change for 0.3– 0.5%. The width of all peaks doesn’t significantly changes during the first 10 s of mechanical treatment, but a longer processing time leads to its increase which corresponds to an increase of the defect density. It has been shown that lattice parameters of the TiNi and TiNi3 almost does not change after hydrogenation of studied powders, while the lattice parameter of Ti2Ni increases by 2.5% after hydrogenation; this means that the main interaction of hydrogen in the Ti-Ni system occurs with the Ti2Ni phase. It has been shown that lattice parameters of Ti2Ni-based phase corresponds to the hydrides Ti2NiH0.5 and Ti2NiH0.8 after 30 and 300 s of mechanical activation. It has been obtained that the time of hydrogenation of 90 min is a critical time after which one can observe changing of lattice parameter of studied powders after treatment. The lattice parameter corresponds to the Ti2NiH0.5 hydride after 180 min of hydrogenation. A possible reason may be oxide films formed on the surface during mechanical activation treatments, which broke at long-time hydrogenation. [ABSTRACT FROM AUTHOR]

Ni-Mn based Heusler shape memory alloys are type of smart materials which possesses both ferromagnetic and shape memory properties. Due to multifunctional properties these materials have increased significant interest for the applications in actuators, sensing devices and magnetic refrigeration. The aim of this work was to synthesize and structural study of Ni-Mn-Sn and Ni-Mn-Al alloys which have recently emerged as Gallium-free shape memory alloys. Two alloys Ni48Mn26Sn26 and Ni51Mn26Al23 (at %) were synthesized using vacuum arc remelting technique under an argon gas atmosphere to improve homogeneity of the alloys. The structural studies of the prepared alloys were conducted and compared using X-ray Diffraction (XRD) and scanning electron microscope (SEM) coupled with Energy -dispersive X-ray spectroscopy (EDX). The results revealed that an average crystallite size of Ni-Mn-Al was smaller than Ni-Mn-Sn alloy. The morphology showed an average particle size of 5-6 μm and 0.6-0.7 μm for Ni-Mn-Sn and Ni-Mn-Al alloys respectively. Magnetic behavior studied by Vibrating sample magnetometer (VSM) showed soft magnetic behavior of the alloys. The synthesized alloys have exhibited and confirmed closely matching stoichiometric composition of Heusler shape memory alloys (X2YZ) with no contamination. [ABSTRACT FROM AUTHOR]

Additive manufacturing (AM) processes involving the use of an electric arc, laser or electron beams and a deposited material in the form of a wire are efficient methods enabling the making of elements having complicated shapes and which are made of expensive technical alloys, e.g. stainless steels, nickel or titanium alloys. The demand for fast prototyping results from the development of new technologies in the automotive, aviation and machine-building industries. Generally speaking, AM offers numerous advantages. At the core of these are reduced production and material costs, reduced development and lead times, and improved performance. However, not all of the current AM processes are equally suited to provide all of these advantages. Compared to the powder and wire systems some aspects can be underlined. During the powder deposition process a certain amount of powders cannot be caught by the melt pool. The powders are blown to the surrounding environment, which causes potential hazard to the operators and environment. Compare to powder feeding, wire feeding method has higher material usage efficiency. Almost all the materials fed into the melt pool during the process are used to form the deposit. In the paper the advantages of AM methods are presented. The main focus of the work was to presented the results of AM process with wire of stainless steel. The evaluation of the microstructure and the mechanical properties of AM parts, manufactured by arc, laser beam and electron beam processes, are presented. The analysis revealed that the properties of the deposited parts are not worse than that properties guaranteed by producer of filler material. Thus the fast AM technologies involving the use of a wire and an arc or a laser and an electron beams as the source of energy should gain recognition among entrepreneurs intended to implement innovative solutions in their companies. [ABSTRACT FROM AUTHOR]

Dry sliding of copper, nickel, titanium and a nitinol alloy (NiTi) against a steel counterbody is carried out under the influence of high-density electric current. It is shown that the surface layer of these metals undergoes phase transformation and forms a tribolayer. It is noted that the high strength of the tribolayer corresponds to high contact electrical conductivity and to low wear intensity. The tribolayer of a nitinol alloy has a weak connection with the basic material. This factor, as well as low thermal conductivity and the presence of a superstructure of the nitinol alloy, leads to its rapid deterioration. [ABSTRACT FROM AUTHOR]

The paper presents the results of studies of inelastic strains (shape memory effect (SME) and superelasticity (SE)) and plastic deformation developed under torsion in specimens of TiNi-based alloys with Ni content of 50.2 and 50.8 at. %, characterized by the initial B19' structure of the martensite phase. It was shown that both SME (10–14%) and SE (5–6%) had been observed in plastically deformed samples of these alloys. The factors determining SE development in specimens of TiNi-based alloys with B19 martensite structure during deformation are discussed. [ABSTRACT FROM AUTHOR]

Endovascular prothetics is a frequent procedure in the case of arterial sclerotic disease of the arterial bed of different disposition. The following factors are necessary for the correct performance of the implant: biological intertness and reendothelization of the internal surface of the implanted stent. In the absence of bio-inertness of the constituents of the stent, these components can have a general toxic effect on the patient’s body. Incomplete re-endothelization of the inner surface of the stent may cause the formation of intra-stents thrombi (late thrombosis occurring more than 30 days after percutaneous intervention). The presence of such thrombi can dramatically worsen the quality of life of the patient (a life threatening complication). The paper demonstrates that the Ni-Ti stents with the surface modified with silicon ions have higher speed of re-endothelization process than in the case of commercial stents use. [ABSTRACT FROM AUTHOR]

Grain structure and substructure of a nanocrystalline Ti–50.9 at. % Ni alloy was investigated using the transmission electron microscopy. The regularities of recovery and recrystallization processes of the alloy structure after annealing at 500°C are revealed. It is shown that the subgrain structure inhibits recrystallization due to the presence of Ti3Ni4 coherent particles at the subgrain boundaries. The coalescence of subgrains is a main mechanism of recrystallization in a substructure. A relationship between recovery and recrystallization and the dissolution and coagulation of Ti3Ni4 particles was found. [ABSTRACT FROM AUTHOR]

Among the macroscopic characteristics of solids, elastic properties play a crucial role in the analysis of the loss in the phase transition stability of the crystal lattice of materials. For shear-type transitions, such as martensitic transformations in metals and alloys, the study of the elastic parameters of crystal structures: elastic moduli and constants, Poisson’s ratio, etc., is of particular significance. In this study obtained the central sections of the surfaces of Young’s modulus and shear surfaces, as well as the Poisson’s ratio of TiFe and TiNi intermetallide crystals, both stable and under martensitic transformations. The extremes of the elastic properties and the maximum-to-minimum ratio are determined. The effective values of the elastic moduli and Poisson’s ratio are calculated based on the data on elastic constants and the compliance coefficients of materials. [ABSTRACT FROM AUTHOR]

This paper presents a model of surface modification of nickel titanium specimen by electron beam. Chemical reactions were taken into account in the framework of a simple kinetic scheme and the difference in diffusion coefficients in nickel titanium volume and its boundary. The dynamics of formation of the reaction product with increasing temperature and diffusion of silicon into the specimen was investigated. Non-uniform phase formation, which leads to a complication of the heterogeneous structure of the titanium nickelide surface, was demonstrated. [ABSTRACT FROM AUTHOR]

The regularities of localization of transformation deformation during tensile loading on macro- and mesoscale levels for Ti–50.8 at. % Ni samples with different texture (a load axis along and transverse to the axis of the extruded rod) are examined. The speckle photography method for image processing is used. The samples demonstrate the superelastic behavior and stability of the mechanical hysteresis regardless of the texture. At the same time, it is shown that the initiation and the propagation of martensite front, as well as the front structure are determined by the texture of the NiTi samples. The texture affects the features of deformation curves: stresses and strains of the beginning of stress plateau region, the slope and length of the plateau, strain to failure. It is found transverse specimens show a higher localization of deformation at meso- and macroscale levels. As a result, the transverse—samples fail at lower strain as compared to the longitudinal specimens. [ABSTRACT FROM AUTHOR]

The problem of elastic waves reflection on the free surface moving with the constant velocity is considered. The reflection coefficients as well as the reflection angles of longitudinal and transverse waves and the frequency relations of primary and secondary waves allow us to study the dynamic deformations on the boundary. Functional relations for various deformation modes and rotation on the free surface depending on the incidence angle and the polarization of primary wave, the velocity of interface moving and the elastic properties of body have been obtained and analyzed. These results can be used to define the deformation changes caused by the free surface moving as the frequency shifts which determine Doppler effect. [ABSTRACT FROM AUTHOR]