Shape Memory Alloy Samples Research Articles

Stable superelasticity with large recoverable strain in NiTi alloy via additive manufacturing

We report a stable superelasticity with large recoverable strain in Ni51·2Ti48.8 (at.%) shape memory alloy (SMA) via additive manufacturing of laser powder bed fusion (LPBF). Microstructure analysis indicates that the LPBFed SMA samples have a non-homogeneous microstructure of two different grain zones, i.e., the coarse columnar one and the fine cellular one. Specifically, the coarse columnar grain zone accounts for a predominated content as high as ∼79 vol% and has a relatively low dislocation density. In contrast, the fine cellular one has a low content of ∼21 vol% yet a high dislocation density. Especially, all LPBFed non-homogeneous SMA samples exhibit a strong (100) texture with high intensities of 40.2–56.1, accompanied by homogeneous coherent Ti4Ni2Ox nanoprecipitates. Constant-stress cyclic compression shows that the LPBFed sample with 79 vol% coarse columnar grain zone and 52.8 (100) texture presents stable superelasticity with large recoverable strains, 5.71 % from 15 to 30 cycles at high loading of 1200 MPa. Such a large recoverable strain herein is superior to those in NiTi SMAs fabricated by various methods. Basically, the stable superelasticity is attributed to the strong (100) texture against plastic deformation and the pinning effect of the homogeneous coherent Ti4Ni2Ox nanoprecipitates on dislocation motion during cyclic loading. Meanwhile, the large recoverable strain originates from the high ability to accommodate new dislocation in the high content columnar grain zone. This work can provide significant insights into design of high-performance NiTi SMAs and further accelerate their engineering application by additive manufacturing.

Effect of tantalum ion implantation on deformation behavior and fracture of TiNi SMA. Part I. quasi-static tension

The effect of high dose implantation of Ta+ ions (Dion = 5′1016 cm−2) into samples from a TiNi shape memory alloy (SMA) on patterns of deformation and fracture mechanisms under quasi-static uniaxial tensile loads was studied. Using X-ray diffractometry, transmission electron microscopy, and scanning electron microscopy, it was shown that ion implantation resulted in amorphization of the surface layer with a thickness of ∼100 nm due to the formation of a chemical composition of approximately Ti36Ni41Ta23 (at.%), thermodynamically corresponding to the highest glass forming ability in the Ti–Ni–Ta system. In the implanted surface layer, both the microstructure and crystal structure defects subsystem were modified at a depth of ∼5 mm. Using the digital image correlation (DIC) method, the dynamics of changes in the integral and local (εyy longitudinal, εxy shear and εxx transverse) strain components were investigated in the tensile tests of both as-received and implanted TiNi SMA samples. On the basis of the obtained results, both integral and local stress–strain diagrams were plotted. In all studied cases, the main contribution to strain accumulation was made by the εyy and εxx strains, which differed significantly for the as-received and implanted TiNi SMA samples. It was concluded that the positive effect of ion implantation was manifested in loading ranges close to the martensitic yield stress (at strain range of 1–6%), despite a noticeable decrease in the ultimate tensile strength and plasticity of the implanted TiNi samples.

Coexistence of five domains at single propagating interface in single-crystal Ni[sbnd]Mn[sbnd]Ga shape memory alloy

Coexistence of both austenite and martensite during phase transformation is a common feature of all Shape Memory Alloys (SMAs). The martensite has different variants featuring characteristic deformations rotationally linked to each other due to the symmetries of the austenite parent phase, and the martensite variants can form twins with different mean characteristic deformations. Multiple-domain microstructures (consisting of austenite, martensite twins and individual martensite variants) evolve collectively within an SMA sample during the phase transformation, contributing thus to the material's macroscopic response (e.g., its global deformation). Particularly, the multiple domains can exist at the diffuse austenite-martensite interface nucleating and propagating in a single crystal in certain conditions. This implies an energy barrier for this interfacial structure, influencing the interface kinetics and the driving force (energy dissipation) of the phase transformation. In this paper, we report an experimentally observed interface consisting of five domains (austenite, one martensite variant and three twins) in a Ni–Mn–Ga single-crystal initially consisting of one martensite variant and subjected to a uniaxial thermal gradient. The compatibility analysis (performed from the characteristic strains of the three martensite variants having approximately a tetragonal symmetry) reveals that the five-domain interface is not a perfectly compatible pattern like the basic habit plane (consisting of only one twin compatible with austenite). However, its level of non-compatibility is similar to that of the quite common X-interface (four-domain coexistence) which is observed in many SMAs. Further, the significant effects of the thermal loading path and the material initial state (the initial martensite variant) on the domain pattern formation are demonstrated and analyzed. The experimental observation and the theoretical analysis of the domain patterns can provide hints to better understand diffuse interface kinetics and phase transformation hysteresis.

Fe-Mn-Al-Ni Shape Memory Alloy Additively Manufactured via Laser Powder Bed Fusion

Fe-Mn-Al-Ni is an Fe-based shape memory alloy (SMA) featuring higher stability and low temperature dependency of superelasticity stress over a wide range of temperatures. Additive manufacturing (AM) is a promising technique for fabricating Fe-SMA with enhanced properties, which can eliminate the limitations associated with conventional fabrication and allow for the manufacture of complicated shapes with only a single-step fabrication. The current work investigates the densification behavior and fabrication window of an Fe-Mn-Al-Ni SMA using laser powder bed fusion (LPBF). Experimental optimization was performed to identify the optimum processing window parameters in terms of laser power and scanning speed to fabricate Fe-Mn-Al-Ni SMA samples. Laser remelting was also employed to improve the characteristics of Fe-Mn-Al-Ni-fabricated samples. Characterization and testing techniques were carried out to assess the densification behavior of Fe-Mn-Al-Ni to study surface roughness, density, porosity, and hardness. The findings indicated that using a laser power range of 175–200 W combined with a scanning speed of 800 mm/s within the defined processing window parameters can minimize the defects with the material and lead to decreased surface roughness, lower porosity, and higher densification.

Enhancing the Mechanical Properties of Cu-Al-Ni Shape Memory Alloys Locally Reinforced by Alumina through the Powder Bed Fusion Process.

A classical problem with Cu-based shape memory alloys (SMAs) is brittle fracture at triple junctions. This alloy possesses a martensite structure at room temperature and usually comprises elongated variants. Previous studies have shown that introducing reinforcement into the matrix can refine grains and break martensite variants. Grain refinement diminishes brittle fracture at triple junctions, whereas breaking the martensite variants can negatively affect the shape memory effect (SME), owing to martensite stabilization. Furthermore, the additive element may coarsen the grains under certain circumstances if the material has a lower thermal conductivity than the matrix, even when a small amount is distributed in the composite. Powder bed fusion is a favorable approach that allows the creation of intricate structures. In this study, Cu-Al-Ni SMA samples were locally reinforced with alumina (Al2O3), which has excellent biocompatibility and inherent hardness. The reinforcement layer was composed of 0.3 and 0.9 wt% Al2O3 mixed with a Cu-Al-Ni matrix, deposited around the neutral plane within the built parts. Two different thicknesses of the deposited layers were investigated, revealing that the failure mode during compression was strongly influenced by the thickness and reinforcement content. The optimized failure mode led to an increase in fracture strain, and therefore, a better SME of the sample, which was locally reinforced by 0.3 wt% alumina under a thicker reinforcement layer.

Enhancing elastocaloric effect of NiTi alloy by concentration-gradient engineering

By formulating the martensite transformation start temperature (Ms) of NiTi shape memory alloys (SMAs) as a function of Ni concentration, a Ni-concentration dependent phase field model is newly proposed in this work. Then, based on correspondent phase field simulations, the elastocaloric effects (eCEs) of the NiTi SMA samples with different Ni-concentration gradients and various aspect ratios are investigated and discussed. The simulated results show that the martensite transformation start stress of NiTi SMAs in the sample with a Ni-concentration gradient along the tensile direction progressively increases during the tensile loading, leading to a step-by-step martensite transformation; hence the suppression of microscopic instability results in a small stress-strain hysteresis loop in the process of tensile-unloading and a tremendous improvement in the coefficient of performance of material (COPmat) if addressing the eCE of the sample. When the aspect ratio of the sample is relatively small (e.g., 1:1), the microscopic instability can be suppressed due to the strong boundary constraint, indicating that reducing the aspect ratio is an efficient way to obtain a small stress-strain hysteresis loop and improve the COPmat of NiTi SMA samples. Moreover, for the sample with a Ni-concentration gradient, when its aspect ratio is relatively large, its eCE is mainly determined by the Ni-concentration gradient; while, when the aspect ratio becomes relatively small, the eCE of the sample is strongly dependent on both the Ni-concentration gradient and the aspect ratio. It implies that the NiTi SMA sample with both a small Ni-concentration gradient and a small aspect ratio and that with both a large Ni-concentration gradient and a large aspect ratio demonstrate the optimal eCE. In other words, a pioneering approach, i.e., concentration-gradient engineering, can be put forward to enhance the eCE of NiTi SMAs based on the detailed phase field simulations. The new findings in this work provide available guidance for improving the eCE of NiTi SMAs and open a novel way for developing advanced SMA-based elastocaloric materials.

Evolution of Structure and Properties of Nickel-Enriched NiTi Shape Memory Alloy Subjected to Bi-Axial Deformation.

The effect of a promising method of performing a thermomechanical treatment which provides the nanocrystalline structure formation in bulk NiTi shape memory alloy samples and a corresponding improvement to their properties was studied in the present work. The bi-axial severe plastic deformation of Ti-50.7at.%Ni alloy was carried out on the MaxStrain module of the Gleeble system at 350 and 330 °C with accumulated true strains of e = 6.6-9.5. The obtained structure and its mechanical and functional properties and martensitic transformations were studied using DSC, X-ray diffractometry, and TEM. A nanocrystalline structure with a grain/subgrain size of below 80 nm was formed in bulk nickel-enriched NiTi alloy after the MaxStrain deformation at 330 °C with e = 9.5. The application of MaxStrain leads to the formation of a nanocrystalline structure that is characterized by the appearance of a nano-sized grains and subgrains with equiaxed and elongated shapes and a high free dislocation density. After the MaxStrain deformation at 330 °C with e = 9.5 was performed, the completely nanocrystalline structure with the grain/subgrain size of below 80 nm was formed in bulk nickel-enriched NiTi alloy for the first time. The resulting structure provides a total recoverable strain of 12%, which exceeds the highest values that have been reported for bulk nickel-enriched NiTi samples.

Effect of volume energy density on selective laser melting NiTi shape memory alloys: microstructural evolution, mechanical and functional properties

Equi-atomic NiTi shape memory alloy (SMA) samples were manufactured by selective laser melting (SLM) with different laser volume energy densities via synchronously varying laser power and scanning speed. The processing quality, phase transformation, and microstructural evolution were investigated to explore the mechanisms that are responsible for mechanical and functional properties. The results showed scattered micro-sized spherical gaseous defects inside the deposit. One-stage phase transformation occurred without intermediate R-phase transition, and the temperature of both endothermic and exothermic peaks was lower than that of the ingot. The microstructure initially grew along the building direction, but displayed different crystal orientations between coarse columnar grains and refined irregular sub-grains. The micro-hardness mapping revealed that homogenous anti-indentation properties were acquired independent of location variations. While the anisotropic behavior in tensile properties occurred due to the passive effect of columnar B2 austenitic grains, a synergistic effect of strength and plasticity was acquired primarily due to the combined effect of sub-grain refinement strengthening and transformation-induced plasticity. The pre-deformed NiTi samples recovered to their original shape when heated above its critical phase transition point. This work demonstrated that the crack-free NiTi SMA with exceptional comprehensive performances could be fabricated by SLM through the control of energy density.

Effect of a constant laser energy density on the evolution of microstructure and mechanical properties of NiTi shape memory alloy fabricated by laser powder bed fusion

As the key parameter in the laser powder bed fusion (L-PBF), the laser energy density can directly determine the comprehensive quality of NiTi shape memory alloys (SMAs). However, the specific role of laser parameters under the energy density value is rarely discussed. In this work, the effect of specific laser power and scanning speed variation on the properties of NiTi alloy under the same energy density (62.5 J/mm3) was studied. Results show that the phase transformation temperatures decrease as the Ni content was increasing with the simultaneous increases in laser power and scanning speed. Under the influence of Ni content, the SMA samples with low phase transformation temperatures were fully austenite at room temperature. In the cyclic compression test at Af + 15 °C, the sample built under the lowest laser power and scanning speed showed the best superelasticity effect. Higher scanning speed resulted in a stronger <100>//BD texture, and the increase of laser power produced a deeper molten pool, which remelted the solidified part at the bottom and further enhanced the <100>//BD texture. The TEM characterization shows that more Ni4Ti3 precipitates with larger sizes are obtained in the sample with the lowest laser power and scanning speed. The finite element analysis shows the lowest peak temperature in the molten pool under the lowest laser power and scanning speed, which can promote the precipitation of Ni4Ti3 particles. The promoted formation of Ni4Ti3 precipitates enhanced the austenite stability and further enhanced the superelasticity of NiTi alloy fabricated at the lowest laser power. The present work shows that the specific laser parameter under the constant energy density value can further improve the comprehensive performance of L-PBF NiTi SMAs.

Experimental investigation of the pseudoelastic behavior on zirconium modified Cu–Al–Be shape memory alloys for seismic applications

This paper examines the effect of 0.05–0.3 wt.% of zirconium-doping on microstructure, transformation temperatures, tensile properties, and pseudoelastic behavior of the parent -phase Cu87.93–Al11.5–Be0.57 shape memory alloys (SMAs). Results reveal that alloying zirconium in the evaluated SMA samples exhibits an excellent grain refinement up to 0.15 wt.%. Further, higher additions of Zr ⩾ 0.2 wt.% lowers the grain refinement efficiency due to precipitates agglomeration. Larger the size and volume fraction of Al3Zr precipitates led to higher transformation temperatures. Tensile properties were improved with Zr-doping, resulting enhancements in the maximum tensile strength and ductility with the addition of 0.15 wt.% Zr. The alloy with 0.05 wt.% of Zr-dope showed a good pseudoelastic strain recovery of deformation strain and then lowered by retaining large residual strain, indicating deterioration in the pseudoelasticity of SMAs.

THERMAL PARAMETERS AND STRUCTURAL INVESTIGATIONS OF Cu-BASED SHAPE MEMORY ALLOYS IRRADIATED WITH Co-60

Gamma radiation is a type of radiation that can change the structural properties of materials. Many physical and structural properties of metals and alloys change due to defects in their crystal structures in response to irradiation. Shape memory alloys (SMAs) are functional materials and are used in mechanical devices for monitoring nuclear facilities. In this study, copper-based SMAs were used. Copper-based SMAs are very sensitive to alloying elements and small changes in element percentages. Cu-11.6Al-0.42Be, Cu-11.8Al-0.47Be, Cu-13Al-4Ni, and Cu-13.5Al-4Ni (wt%) SMA samples were irradiated with a fixed radiation dose of 50 kGy. The effect of irradiation on the thermodynamic parameters and structural properties of copper-based SMAs was investigated. The effects of irradiation on thermodynamic parameters were determined by differential scanning calorimetry (DSC). Structural examinations were made by X-ray diffraction (XRD) and optical microscope observations. Microhardness measurements were taken. The results obtained for Cu-based SMAs were evaluated both as homogeneous and irradiated samples and according to alloying elements.

Microstructural and Cavitation Erosion Behavior of the CuAlNi Shape Memory Alloy

Microstructural and cavitation erosion testing was carried out on Cu-12.8Al-4.1Ni (wt. %) shape memory alloy (SMA) samples produced by continuous casting followed by heat treatment consisting of solution annealing at 885 °C for 60 min and, later, water quenching. Cavitation resistance testing was applied using a standard ultrasonic vibratory cavitation set up with stationary specimen. Surface changes during the cavitation were monitored by metallographic analysis using an optical microscope (OM), atomic force microscope (AFM), and scanning electron microscope (SEM) as well as by weight measurements. The results revealed a martensite microstructure after both casting and quenching. Microhardness value was higher after water quenching than in the as-cast state. After 420 min of cavitation exposure, a negligible mass loss was noticed for both samples. Based on the obtained results, both samples showed excellent cavitation resistance. Mass loss and morphological analysis of the formed pits indicated better cavitation resistance for the as-cast state (L).

Influence of the Nb Content on the Microstructure and Phase Transformation Properties of NiTiNb Shape Memory Alloys

NiTi shape memory alloys (SMAs), as smart materials, are broadly used in medical implants and appliances despite the presence of toxic Ni. In this study, NiTiNb alloys were produced using the substitution of biocompatible Nb instead of Ni. The arc-melting method was utilized to make five SMA samples comprising Ni(29−x)Ti50Nb(21+x) (x = 0, 1, 2, 3, and 4); then, the phase transformation temperatures, microstructures, crystal structures, and chemical compositions were investigated by DSC, optical microscopy, XRD, and EDX measurements, respectively. The DSC results showed that the samples had a wide hysteresis with the B19′↔B2 phase transformation and martensite start temperatures below room temperature, which makes them suitable for superelastic implants. The presence of dissolved Nb in the matrix of the alloys was the main reason for the widening of temperature hysteresis. When the XRD and SEM results were examined, the β-rich, B2, B19′, and Ti2Ni phases were observed in all samples. Additionally, the main constituent in the dendritic microstructures was Nb.

Hot workability of FeMnSiCrNi shape memory alloy based on processing map and martensitic transformation

Hot workability of Fe66Mn15Si5Cr9Ni5 (wt.%) shape memory alloy (SMA) with γ austenite and ε martensite at room temperature was investigated by establishing processing map and simultaneously considering martensitic transformation. All the FeMnSiCrNi samples subjected to hot deformation are composed of ε martensite and γ austenite. Furthermore, the higher temperature results in the larger fraction of ε martensite, whereas the higher strain rate leads to the smaller fraction of ε martensite. Simultaneously, the higher temperature or the lower strain rate leads to the larger grain size. In addition, dislocations, stacking faults and austenite twins appear in the deformed samples. According to processing map, the optimal hot processing parameters for the FeMnSiCrNi SMA is determined as the temperature range of 850–925 °C at the strain rate below 0.0008 s−1 and the temperature range of 925–1000 °C at the strain rate range of 0.001–0.03 s−1. Furthermore, the existence of ε martensite in the deformed FeMnSiCrNi samples has an adverse effect on shape memory effect of FeMnSiCrNi SMA. In addition, dynamic recrystallization (DRX) and subsequent martensitic transformation weaken the textures of the grains with γ austenite phase in the deformed FeMnSiCrNi SMA samples. Therefore, it is necessary to prevent FeMnSiCrNi SMA from being subjected to hot workability in the case of too high temperatures or too low strain rates.

Heat treatment and quenching media effects on the thermodynamical, thermoelastical and structural characteristics of a new Cu-based quaternary shape memory alloy

In this study, Cu-based shape memory alloy (a smart material) with a new quaternary Cu-22.78Al-2.59Fe-2.44Mn (at%) composition was produced by arc melting and the samples cut from this cast-ingot alloy were homogenized at 900 °C for 1 h and quenched in traditional iced-brine water. Then except keeping one as the reference the others were all heat-treated (aged) at 200 °C for 1 h and then quenched/cooled in several different media. To find out the effects of the aging and varied quenching/cooling media types on the characteristic martensitic transformation temperatures, thermodynamical parameters and structural properties of this CuAlFeMn shape memory alloy (SMA) the thermal and X-ray measurements were carried out. The differential scanning calorimetry (DSC) and differential thermal analysis (DTA) measurements were made at different heating/cooling rates for all of the different types of the alloy samples. Thermal results showed that the characteristic forward martensite to austenite and backward phase transitions occurred at varied temperatures in between 44 and 176 °C and the different samples had different characteristic transformation temperatures and hysteresis due to the different quenching media effects. All of the samples exhibited high temperature shape memory alloy (HTSMA) behavior since all of their austenite start temperatures came up over 100 °C. The highest average austenite phase finish temperature belonged to the sample quenched in boiling water and the lowest belonged to the sample quenched in liquid nitrogen. The least amount of transformation entalphy and entropy change values were found for the aged sample quenched in liquid nitrogen which is the fastest coolant medium among others and caused the neatest martensite and interface formations and this was also understood from this sample having the lowest Gibbs free energy difference (ΔG). The X-ray analyses of the CuAlFeMn SMA samples showed the formations of β1′(M18R) and γ1′(2H) in the alloy and a main peak plane change occurred by aging. Besides this, there has been an adverse magnitude ranking correspondency found between average crystallite size and entropy change values of the aged samples. The analyses showed that the characteristic thermodynamical, thermoelastical and structural parameters of the CuAlFeMn high temperature shape memory alloy are strongly affected from the conditions of composition, aging temperature and quenching/coolant medium type used and the different combinations of those conditions can lead to their own distinctive genuine consequences.

Prediction of grain scale plasticity of NiTi shape memory alloy based on crystal plasticity finite element method

Abstract Grain scale plasticity of NiTi shape memory alloy (SMA) during uniaxial compression deformation at 400 °C was investigated through two-dimensional crystal plasticity finite element simulation and corresponding analysis based on the obtained orientation data. Stress and strain distributions of the deformed NiTi SMA samples confirm that there exhibits a heterogeneous plastic deformation at grain scale. Statistically stored dislocation (SSD) density and geometrically necessary dislocation (GND) density were further used in order to illuminate the microstructure evolution during uniaxial compression. SSD is responsible for sustaining plastic deformation and it increases along with the increase of plastic strain. GND plays an important role in accommodating compatible deformation between individual grains and thus it is correlated with the misorientation between neighboring grains, namely, a high GND density corresponds to large misorientation between grains and a low GND density corresponds to small misorientation between grains.

Process optimization, microstructures and mechanical properties of a Cu-based shape memory alloy fabricated by selective laser melting

The Cu-13.5Al-4Ni-0.5Ti copper-based shape memory alloys (SMAs) were fabricated by selective laser melting (SLM). The parameters were optimized to obtain almost fully dense copper-based SMAs samples. The phases and microstructures were characterized and the tensile properties at room temperature and 200 °C were evaluated. The XRD results showed that only the β1′ phase could be detected in the Cu-based SMAs, which was attributed to the extremely short solidification time for the precipitation of α and γ2 phases during SLM process. The grains were well refined and the average grain size was approximate 43 μm, which was much smaller than that of the cast copper-based SMAs. The X-phase (Cu2TiAl) is observed, which is granular and size 20–50 nm. The Cu-13.5Al-4Ni-0.5Ti copper-based SMAs fabricated by SLM exhibited excellent mechanical properties at room temperature, which was higher than that of the cast copper-based SMAs. This is attributed to two aspects: (1) grain refinement, (2) suppress of brittle γ2 phase. Remarkably, the tensile test results at 200 °C showed both higher strength and elongation, which is attributed to the bcc structure of the parent phase and the stress-induced martensitic transformation at 200 °C. Meanwhile, the difference of microstructures and properties between SLM-fabricated Cu-based SMAs and casting Cu-based SMAs were analyzed and discussed in detail.

Three-dimensional in situ characterization of phase transformation induced austenite grain refinement in nickel-titanium

Near-field and far-field high-energy diffraction microscopy and microcomputed tomography X-ray techniques were used to study a bulk single crystal nickel‑titanium shape memory alloy sample subjected to thermal cycling under a constant applied load. Three-dimensional in situ reconstructions of the austenite microstructure are presented, including the structure and distribution of emergent grain boundaries. After 1 cycle, the subgrain structure is significantly refined, and heterogeneous Σ3 and Σ9 grain boundaries emerge. The low volume and uneven dispersion of the emergent Σ boundaries across the volume show why previous transmission electron microscopy investigations of Σ grain boundary formation were inconsistent.

S-N curve fatigue study and the stress-strain properties on the refurbish NITI SMA for reinforcing bar in concrete

The earthquake load in structures is assumed as a low-cycle loading type load in structures that may cause low-cycle fatigue in earthquake resisting structures. Hence, this paper is to highlight and compare the fatigue properties of refurbish pseudoelastic shape memory alloy (SMA) and structural steel for used as seismic reinforcement features in concrete structures. This experiment study on the stress (S) against the number of cycles to failure (N) known as an S-N curve were conducted using INSTRON 8801 Servo hydraulic Fatigue Testing System with 3Hz of loading frequency with the stress varies between 0.9Fyield and 1.45Fyield for 8 SMA samples and 2 steel samples with stress varies of 0.64Fyield and 1.15Fyield. Two type of SMA samples were used including three 12.7mm SMA samples with Af-25, 6 SMA samples with Af-6.3 with 12 mm diameter respectively. As a result, the structural steel were observed could with stand approximately 93710 cycles before failure if loaded up to its yield stress, while SMA of diameter 12.7mm can withstand until 19040.75 cycles. Type 1 of refurbish SMA rebar that were reused shows a much better behaviour against fatigue than structural steel rebar and is more reliable in seismic periodic loads. However, for second type refurbish and reused of SMA shows the vice versa and can only sustain maximum 23674.25 cycles.

Ion polishing as a method of imaging the magnetic structures in CoNiGa monocrystal

Abstract Magnetic domain structure of magnetic shape memory alloy was observed using backscattered electron detector in scanning electron microscope and using Fresnel imaging in transmission electron microscope. The sample subjected to additional ion polishing allowed observation of the contrast associated with the magnetic structure of the material under conditions that exclude the use of Foucault or Fresnel transmission electron microscopy imaging. The additional research conducted using atomic force microscopy showed a significant relationship between the method of preparation and the magnetic shape memory alloy sample surface.