NiTi Research Articles

Mechanical behavior of Ni/Ti bilayer-based shape memory alloys: Endorsement via atomistic simulations

To gain a structural and thermodynamic understanding along with the interpretation of atomic diffusion in a Ni/Ti bilayer, detailed first-principles simulations using density functional theory (DFT) and molecular dynamics (MD) simulations have been carried out. The interface energies and electronic structure of the Ni/Ti bilayer have been calculated using DFT. The MD simulations of interface atomic diffusion in the Ni/Ti bilayer were performed at 773 K for different annealing times to investigate the formation of Ni–Ti alloy. The simulated results indicate that Ni atoms predominantly diffuse into the Ti side. The radial distribution functions (RDFs) have been plotted to understand the nature of bonding that exists between the Ni and Ti atoms in the bilayer. The shape of the RDFs reveals information about the extent to which Ni and Ti atoms mix together. Classical MD simulations have been used to simulate the deformation behavior of the material under tension and to investigate the effects of annealing time on the mechanical properties of the materials.

Cyclic fatigue and Structural Analysis of Three Rotary Nickel Titanium Files

Cyclic fatigue and Structural Analysis of Three Rotary Nickel Titanium Files

Heating of metallic orthodontic devices during anti-aging treatment with vacuum and electromagnetic fields: In vitro study.

The physical appearance of an individual plays a primary role as it influences the opinion of the viewer. For this reason, orthodontic therapy to improve perceived aesthetics is in high demand among patients. This factor, combined with the increase in the number of non-invasive facial aesthetic treatments, has led to the need to understand potential risk factors in the application of medical devices to the perioral skin in patients with fixed orthodontic appliances. The aim of this study was to evaluate in vitro heating of the orthodontic bracket following electromagnetic fields and negative pressure (V-EMF) used as an anti-aging treatment. Two different types of titanium alloy wires, one made of "beta-Titanium" alloy and the other "Ni-Ti" (DW Lingual Systems GmbH-Bad Essen-Germany) were used. The orthodontic wires and brackets mounted on a resin mouth were covered with porcine muscle tissue, then subjected to anti-aging therapy with a Bi-one LifeTouchTherapy medical device (Expo Italia Srl-Florence-Italy) which generates a combination of vacuum and electromagnetic fields (V-EMF) already adopted for antiaging therapy. During administration of the therapy, the orthodontic brackets and porcine tissue were thermally monitored using a Wavetek Materman TMD90 thermal probe (Willtek Communications GmbH-Germany). In total 20 orthodontic mouths were used, 10 with Beta Titanium wires and 10 with Nickel Titanium wires. A temperature increase of about 1°C was recorded in each group. The outcome of the present research shows that the absolute temperatures measured on orthodontic appliances, which, despite having a slightly different curve, both show an increase in temperature of 1.1°C at the end of the session, thus falling well within the safety range of 2°C as specified by the standard CENELEC EN 45502-1. Therefore, V-EMF therapy can be considered safe for the entire dental system and for metal prostheses, which tend to heat up at most as much as biological tissue (+0.9°C/1.1°C vs. 1.1°C/1.1°C). In conclusion, anti-aging therapy with V-EMF causes a thermal increase on orthodontic brackets that is not harmful to pulp health.

Thermomechanical response and elastocaloric effect of shape memory alloy wires

Refrigeration technologies based on the elastocaloric effect of shape memory alloys (SMAs) have attracted much interest in recent years. To seek for schemes that can improve the temperature span and efficiency of elastocaloric devices, this work explores more practical loading conditions (between adiabatic and isothermal) of SMAs. To account for the smoothness of the martensite phase transformation of SMAs, a general polynomial form of hardening-like function is adopted in the phenomenological multi-physics coupling framework. The modeling framework is further calibrated by measurements of the thermomechanical responses of pre-trained Ni–Ti wires. Due to the hardening-like function, the martensitic volume fraction cannot be explicitly expressed. Accordingly, a new numerical scheme is also presented in this work. Moreover, an empirical function of the maximum transformation strain is proposed based on the experimental observation, which improves the capability of the model to capture experimental data. This work aims to provide a paradigm from material characterization to theoretical modeling and numerical simulation, and then to elastocaloric cooling performance analysis of SMAs.

Effect of Elastomeric Module Degradation and Ligation Methods on Kinetic Friction between NiTi or Stainless Steel Wires and Stainless Steel Brackets.

Objectives: The reduction of resistance to sliding between the archwire and bracket promotes more seamless tooth movement, leading to a faster and improved orthodontic treatment experience. This research aimed to examine how the degradation of elastomeric modules, different ligation methods, bracket-wire angle, and wire type (nickel titanium, NiTi or stainless-steel, SS) impact the kinetic friction resulting from the interaction between NiTi or SS archwires and SS brackets. Materials and Methods: The current in vitro study was conducted on nine groups, including NiTi and SS archwires with three types of ligations (O-ring, figure of 8, and SS wire ligature) and two bracket-wire angles (0˚ and 10˚). The kinetic friction in each group was measured using a Universal Testing Machine at four time intervals: baseline, day one, week one, and week four. Repeated measures ANOVA, Mauchly test of sphericity followed by the Greenhouse-Geisser test, and relevant post hoc tests were used for statistical analysis (P<0.05). Results: The authors found a decrease in kinetic friction in all types of ligations, which confirmed the effect of time on the degradation of ligation modules. The kinetic friction of figure of 8 ligations was higher than both O-ring and SS wire ligations. No difference was observed between O-ring and SS wire ligations. Furthermore, the bracket-wire angle did not affect friction. Conclusion: The authors suggest that the use of figure of 8 ligations in NiTi and SS wires should be limited due to their high friction and replaced with other types of ligations, if possible.

Dually boosting the performance of photovoltaic module via integrating elastocaloric cooler

Photovoltaic module (PVM) only can utilize visible and ultra-violet parts of solar spectrum, constrained by the Shockley-Queisser limit. To fully use solar spectrum, in this study, solar selective absorber (SSA) and elastocaloric cooler (ECC) are gradually hybridized with PVM to form a new hybrid system for the first time. The performance metrics of PVM, ECC, and hybrid system, taking into account various irreversible effects, are mathematically derived. The hybrid system achieves approximately a 63% enhancement in both energy efficiency and power output density compared to a standalone PVM, outperforming other similar PVM-based hybrid systems. Exhaustive parametric studies show that increasing the operating temperature, solar irradiance, diode ideality factor, length ratio or section area ratio can enhance the hybrid system performance. The optimal combination of refrigerant and actuator materials are, respectively, Ni–Ti and Cu–Zn–Al alloys. Furthermore, a case study conducted to forecast practical performance under southeast China's weather conditions reveals that the hybrid system attains significant annual maximum energy efficiency and power output density, reaching 29.3% and 54.66 W m−2, respectively. The findings from this study provide valuable insights and recommendations for the optimum design and operation for such a hybrid system.

Evaluation of Thermomechanical Properties in a 2D Rotational Elastocaloric Prototype: A Numerical Study for Enhanced Energy Efficiency

So far, much of the research on the caloric effect has focused on the magnetocaloric effect, which was the first investigated chronologically, in the field of room temperature for about 40 years. Subsequently and especially in the last decade, scientific research has focused on the development of solid-state technologies other than the magnetocaloric one, including the one of interest for this work: elastocaloric technology. This work is part of the “SUSSTAINEBLE” project of the Department of Industrial Engineering at the University Federico II of Naples, aimed at developing the first Italian prototype of an elastocaloric device for environmental conditioning. The prototype is currently in the experimental development phase and its design and construction are dynamically accompanied by a two-dimensional numerical model that fully reproduces its thermo-fluid dynamic operation. The rotary-type prototype consists of 600 Nickel Titanium wires subjected to loading and unloading phases controlled by a properly programmed optical encoder. The thermo-fluidic medium that regulates heat transfer is air. The aim is to characterize the operation of the elastocaloric device using numerical analysis software in order to optimize its geometric, operational, and environmental parameters, to maximize its energy performance in terms of temperature difference, useful thermal power, and coefficient of performance.

Comprehensive Characterization of Blue Wire NiTi File Failure: A Comparative Analysis of Cyclic Fatigue and Torsional Resistance Properties

This study compared the fatigue resistance and elemental composition of two blue heat-treated nickel–titanium (NiTi) files used in root canal preparation as follows: Tia Tornado Blue (TTB) and Race Evo (RE) file systems. For cyclic fatigue testing, the two systems were tested where each file was rotated inside an artificial metal canal submerged in either sodium hypochlorite or saline solution until fracture. Time to fracture was recorded. For torsional fatigue testing, the file tip was secured while the file was allowed to rotate at a fixed rate until fracture. Torque at failure was recorded. The two experiments were performed at simulated body temperature and the length of fractured segments was measured. Statistical analysis was carried out with a significance level (p-value) set at 5%. The mean cycles to fracture for RE were superior to that of TTB irrespective of the solution used (p &lt; 0.05). TTB’s cyclic fatigue resistance decreased in NaOCl (p &lt; 0.0001). RE demonstrated lower torque at failure (p = 0.002). All files were fractured at comparable lengths (p = 0.218). Although RE is considered more resistant to cyclic fatigue, it showed inferior torsional resistance compared with TTB. The NaOCl negatively affected the TTB’s cyclic fatigue resistance.

A comparison of spreader penetration depth and load required in curved canal using two types of spreaders

The aim of the present study was to compare nickel titanium and stainlesssteel spreaders penetration depth and load in lateral compaction. Thirty curved mesialcanals of extracted mandibular molars were used in the study. The canals wereprepared using step-back technique with Gates-Glidden. Afterward the teeth weredivided randomly into 2 groups. In part 1 of the study, the force required to inserteach spreader to within 1 mm of the working length in an empty canal was measured .In part 2, the force required to insert each spreader to within 2 mm of the workinglength was measured in canal containing a master cone. ln part 3, the depth ofpenetration of each spreader with a master cone in place using a 1.5 kg force wasmeasured. Using a t-test for paired samples, the results from pan 1 showed that nickeltitanium spreader required high significantly less force than stainless steels reader P&lt;0.01 . ln part 2, a nickel titanium s reader re uired high si niticantl lessforce than a stainless steel spreader .As expected in part 3, a nickel titanium spreaderpenetrated to a significantly high depth than stainless steel spreader (P&lt;0.0l

Evaluation of the dentinal wall adaptation ability of Mineral Trioxide Aggregate Fillapex, EndoSequence BC, and AH Plus sealers using Scanning Electron Microscope: An in vitro study

ABSTRACT Introduction: The present study was conducted to evaluate the dentinal wall adaptation ability of different root canal sealers (mineral trioxide aggregate Fillapex [MTA], EndoSequence BC [ESBC] Sealer, and AH Plus) using a scanning electron microscope (SEM). Materials and Methods: Forty-five extracted single-rooted human maxillary incisor teeth were selected and divided into three equal groups (n = 15). Working length was established using a #15 K-type file. Canals were prepared with rotary Ni–Ti system to size 30/0.06 or 40/0.06 file using endomotor at 250 rpm, irrigated with 17% ethylenediaminetetraacetic acid, 3% NaOCl, and normal saline solution, and dried with paper points. Prepared canals were obturated with gutta-percha cones using the single-cone technique and appropriate sealers. Specimens were stored in saline solution at 37°C for 48 h and evaluated using a SEM. Statistical Analysis: Unpaired t-test, one-way analysis of variance, and post-hoc tests verified the differences between groups and were considered significant at alpha = 5%. Results: None of the specimens showed a gap-free interface. Gaps compared between MTAF and ESBC did not show any statistically significant differences (coronal [P = 0.9757], middle [P = 0.5464], and apical [P = 0.2136] thirds). However, gaps found at the interface of sealer and dentinal wall in root canals filled with AH Plus showed extremely statistically significant differences when compared with MTAF and ESBC (P &lt; 0.0001). Conclusion: Specimens obturated with MTAF and ESBC Sealer showed smaller gaps on SEM analysis than specimens filled with AH Plus.

Osteoblast differentiation of Gli1⁺ cells via Wnt and BMP signaling pathways during orthodontic tooth movement

ObjectivesFactors that induce bone formation during orthodontic tooth movement (OTM) remain unclear. Gli1 was recently identified as a stem cell marker in the periodontal ligament (PDL). Therefore, we evaluated the mechanism of differentiation of Cre/LoxP-mediated Gli1/Tomato+ cells into osteoblasts during OTM. MethodsAfter the final administration of tamoxifen to 8-week-old Gli1-CreERT2/ROSA26-loxP-stop-loxP-tdTomato mice for 2 days, nickel–titanium closed coil springs were attached between the upper anterior alveolar bone and the first molar. Immunohistochemical localizations of β-catenin, Smad4, and Runx2 were observed in the PDL on 2, 5, and 10 days after OTM initiation. ResultsIn the untreated tooth, few Gli1/Tomato+ cells were detected in the PDL. Two days after OTM initiation, the number of Gli1/Tomato+ cells increased in the PDL on the tension side. On this side, 49.3 ± 7.0% of β-catenin+ and 48.7 ± 5.7% of Smad4+ cells were found in the PDL, and Runx2 expression was detected in some Gli1/Tomato+ cells apart from the alveolar bone. The number of positive cells in the PDL reached a maximum on day 5. In contrast, on the compression side, β-catenin and Smad4 exhibited less immunoreactivity. On day 10, Gli1/Tomato+ cells were aligned on the alveolar bone on the tension side, with some expressing Runx2. ConclusionsGli1+ cells in the PDL differentiated into osteoblasts during OTM. Wnt and bone morphogenetic proteins signaling pathways may be involved in this differentiation.

Metallurgical analysis of laser welded AZ31/5A06 lap joints with Ti–Ni interlayer

The presence of brittle Mg–Al intermetallic compounds (IMCs) in Mg/Al welded joints significantly degrades their mechanical properties. Understanding of the joint interfacial metallurgical reactions is essential for improving the performance of Mg/Al joints. Various single element interlayers, such as Ti, Ni, Zn, Fe, Ce and Cu, have been introduced to improve the joint performance, and the Miedema model has been applied to analyze the priority of phase generations in binary systems. However, the metallurgical reactions in the Mg/Al interface with bi-alloy interlayers cannot be fully explained using only a binary system. In this study, laser welding of AZ31-5A06 using a Ti–Ni interlayer was comprehensively investigated Then, the aggregation tendency of the elements in the Mg–Ni–Ti–Al system was explained using the Toop model and the ternary phase diagram was used to analyze the solidification process in the interlayer. With the increasing of laser power, the interlayer became from intact to incomplete, and finally completely destroyed. As a result, the Mg–Al IMCs with a thickness of 4.5 μm (1617 W) increased to 17–21 μm (1815 W) and 130 μm (2013 W) respectively. The distribution of Mg–Al IMCs also changed from being distributed between Mg-interlayer (1617 W) to being discontinuously distributed within the joint (1815 W) and continuously distributed within the joint (2013 W). When the interlayer remained intact at 1617 W, the maximum shear strength of the joint was 145.76 MPa, and the fracture exhibited a mixed fracture pattern consisting of brittle and ductile fracture. At 1617 W, the distribution of elements at the joint interface revealed that the interlayer was composed of Al, Ni, and Ti without Mg, which successfully blocked the diffusion between Mg and Al. The Gibbs free energy calculated from the Toop model indicated that the minimum Gibbs free energy of an Al–Ni–Ti system was −59.3 kJ/mol, which is lower than that of a Mg–Ni–Ti system (−48.1 kJ/mol); therefore, the Al–Ni–Ti system would be preferentially generated in the joint. The composition of the interlayer was mainly concentrated in the α-Ti and β-Ti phase region of the liquid-phase projection phase diagram and in the TiAl+τ3-Al3NiTi2 and Ti3Al+τ3-Al3NiTi2 phase regions of the isothermal cross-section phase diagram. Consequently, the interlayer consists of multiple phases such as Ti3Al, TiAl, and Al3NiTi2. The Ti3Al and TiAl with superior strength and deformability in the interlayer inhibited the generation of Mg–Al IMC, and the partially melted Ni layer facilitated the connection between Mg/Ni/Ti, thus improving the strength of Mg–Al dissimilar alloy joints.

Impact of Prophylactic Fluoride Agents On the Surface Roughness of Newer orthodontic arch wires

Fluorides serve an important part in orthodontic therapy as a prophylactic strategy. However, the harmful effects of fluoride are typically disregarded due to its widespread use as an anti-cariogenic agent in a variety of dental materials. The effects of these fluoride agents on conventional arch wires have been studied extensively but not on newer wires such as coated wires or braided wires. Hence this study was undertaken to assess the effects of prophylactic fluoride agents on the surface properties of non-coated Nickel-Titanium orthodontic wires and compare it with coated esthetic Ni-Ti wires and braided Ni-Ti wire. Materials and methods: In this study, we compared three packages of 270 orthodontic arch wires made of nickel titanium. For the control, the third set of 30 wires was stored in plastic vials containing 5ml of artificial saliva for two months. Subgroup a did not make use of any fluoride treatments. Samples from subgroup b were treated with Phos-flur gel for one minute every day for 2 months, while those from subgroup c were treated with Prevident 5000. An optic profilometer was used to measure the wires roughness. Results: The investigation found that both the acidulated fluoride agent (Phos-flur gel) and neutral fluoride agent (Prevident 5000) had an effect on the surface attributes of all three sets of wires. Coated esthetic Ni-Ti wires showed highest surface roughness followed by braided Ni-Ti wire. Conclusion: The findings of the research showed that using fluoride preventive treatments (such as mouthwash or gels) during orthodontic treatment decreases the arch wires characteristics. Bangladesh Journal of Medical Science Vol.23 (Special Issue) 2024 p.S107-S114

Understanding the role of interface in deformation behavior of additively manufactured bimetallic structures of pure metals

Directed energy deposition (DED)-based additive manufacturing (AM) was employed to fabricate three distinct bimetallic compositions to understand the role interface for the deformation behavior of bimetallic structures under compressive loading. Commercially pure titanium (CP Ti) with a hexagonal closed packed (HCP) structure, nickel (Ni) with a face-centered cubic (FCC), and tantalum (Ta) with a body-centered cubic (BCC) structure were selected to understand the deformation behavior within the pure metals and damage accumulation at the bimetallic interface. By incorporating the combination of these materials, such as Ni–Ti, Ni–Ta, and Ta–Ti, we aimed to manufacture layered-base polycrystalline composite structures with FCC-HCP, FCC-BCC, and BCC-HCP crystal unit cells, respectively. In Ni–Ti and Ni–Ta bimetallic structures, it was determined that deformation is controlled by the Ni region, where the highest deflection occurs when Ni bulges out and makes lateral stress at the interface, resulting in crack initiation, propagation, and failure of the structure. Structural edges were found to experience the highest deformation, prompting grain inclination towards the <111> crystal orientation, resulting in a favorable orientation for dislocation slip and a higher Taylor factor. However, strong interfacial bonding and similar Young's modulus between Ta and Ti altered the deformation mechanisms to twinning formation in the Ti region and observed buckling of the entire structure without significant failure at the interface.

Shaping Ability of Three Different Rotary Nickel Titanium Systems An In Vitro Study

Shaping Ability of Three Different Rotary Nickel Titanium Systems An In Vitro Study

Electrochemical degradation of the hydrogen-absorption-induced passive film on an Ni–Ti superelastic alloy in an NaCl solution

This study was conducted to investigate the effects of electrochemically generated hydrogen on the passivation behaviour of Ni–Ti alloy surfaces. Hydrogen charging via galvanostatic polarisation increased the passive current density during cyclic potentiodynamic polarisation experiments. Electrochemical impedance spectroscopy and Mott–Schottky analyses revealed an increase in the electrochemical conductivity of the film, indicating that hydrogen charging increased the donor density. Changes in the compositions were detected by Auger electron spectroscopy and X-ray photoelectron spectroscopy. Scanning transmission electron microscopy revealed film degradation after hydrogen charging. These results demonstrate that the electrochemical conductivity of the passive film increased owing to hydrogen absorption.

Thermodynamic analysis of production parameters and microstructural evolution in shape memory Ni(50-x)Ti(50)Fe(x) (x = 5, 10) alloy synthesized by combustion synthesis

This study represents an initial effort to produce NiTiFe shape memory alloys via the self-propagating high-temperature synthesis (SHS) process. The synthesis successfully yielded Ni45Ti50Fe5 and Ni40Ti50Fe10 alloys from elemental Ni, Ti, and Fe powders at three distinct preheating temperatures (240, 330, 420 °C). To support empirical findings, thermodynamic analysis using Factsage Thermodynamic Software was employed to correlate reaction propagation behavior with chemical composition. The calculation showed that the addition of 5 at.% Fe to the B2 phase did not hinder reaction self-propagation. This conclusion was supported with the ∆Hf/Cp ratio and transient liquid ratio, computed using the sub-lattice model, which closely resembled that of NiTi. Whereas 10 at.% Fe that synthesized at preheating temperature of 240 °C exhibits struggle, thus an increase in triggering time causes an effect on crystallite size and a decrease in porosity. Empirical results confirmed these findings, albeit influenced by ignition times. An increase in the liquid ratio due to the adiabatic temperature rise can also result in a reduction of NiTi content when the Fe ratio is increased, consequently diminishing the driving force for the reaction. In the sample containing – 5% Fe, the main phase is B2, and the R martensitic phase is also present. Ms is determined to be – 38.7 °C. SEM analyses revealed the presence of Ti2Ni and Ti2Ni3 phases in the upper and lower regions, while the distribution in the middle section is more homogeneous. No martensitic transformation was observed in 10% Fe. Additionally, nanocrystalline regions were detected within the samples by transmission electron microscopy, contributing to a nuanced understanding of their structural properties.Graphic abstract

Application of CALPHAD Method for Predicting of Concentration Range of Amorphization of Transition Metals Melts

Early, the efficiency of the CALPHAD (Calculation of Phase Diagrams) method to a targeted search for compositions of amorphous alloys has been shown. The method for predicting the ranges of amorphization is based on the calculation of diagrams of metastable phase transformations between supercooled melts and boundary solid solutions on the base of pure elements. In this work, the model parameters for thermodynamic properties of liquid alloys and boundary solid solutions were summarized in a self-consistent database for the multicomponent Cu–Fe–Ni–Ti–Zr–Hf system. Such database for the multicomponent system is based on a common set of model parameters for boundary binary and ternary systems. This database was used to predict the concentration ranges of amorphization for the quinary Cu–Fe–Ni–Ti–Zr, Cu–Fe–Ni–Ti–Hf and boundary ternary and quaternary systems. The results of calculations are presented along sections in quaternary and quinary systems. The ternary and quaternary equiatomic alloys along with high entropy CuFeNiTiZr and CuFeNiTiHf alloys are trapped into prognosed composition ranges of amorphization. Predicted composition space of amorphization for melts of the Fe–Ni–Ti–Zr system is shown on the concentration tetrahedron. Based on the obtained results, a new criterion for predicting the concentration regions of amorphization of multicomponent melts is proposed, according to which the presence of a sufficient content of metals that are electron acceptors and donors is a chemical factor that affects the thermodynamic stability of melts and determines their glass-forming ability. For multicomponent melts of the Cu–Fe–Ni–Ti–Zr–Hf system the concentration ranges of amorphization correspond to the simultaneous fulfillment of the conditions xFe + xNi + xCu &gt; 0.25 and xTi + xZr + xHf &gt; 0.15, where Fe, Ni, and Cu are electron acceptors and Ti, Zr, and Hf are electron donors.

Shape-Setting of Self-Expanding Nickel–Titanium Laser-Cut and Wire-Braided Stents to Introduce a Helical Ridge

PurposeAltered hemodynamics caused by the presence of an endovascular device may undermine the success of peripheral stenting procedures. Flow-enhanced stent designs are under investigation to recover physiological blood flow patterns in the treated artery and reduce long-term complications. However, flow-enhanced designs require the development of customised manufacturing processes that consider the complex behaviour of Nickel-Titanium (Ni-Ti). While the manufacturing routes of traditional self-expanding Ni–Ti stents are well-established, the process to introduce alternative stent designs is rarely reported in the literature, with much of this information (especially related to shape-setting step) being commercially sensitive and not reaching the public domain, as yet.MethodsA reliable manufacturing method was developed and improved to induce a helical ridge onto laser-cut and wire-braided Nickel–Titanium self-expanding stents. The process consisted of fastening the stent into a custom-built fixture that provided the helical shape, which was followed by a shape-setting in air furnace and rapid quenching in cold water. The parameters employed for the shape-setting in air furnace were thoroughly explored, and their effects assessed in terms of the mechanical performance of the device, material transformation temperatures and surface finishing.ResultsBoth stents were successfully imparted with a helical ridge and the optimal heat treatment parameters combination was found. The settings of 500 °C/30 min provided mechanical properties comparable with the original design, and transformation temperatures suitable for stenting applications (Af = 23.5 °C). Microscopy analysis confirmed that the manufacturing process did not alter the surface finishing. Deliverability testing showed the helical device could be loaded onto a catheter delivery system and deployed with full recovery of the expanded helical configuration.ConclusionThis demonstrates the feasibility of an additional heat treatment regime to allow for helical shape-setting of laser-cut and wire-braided devices that may be applied to further designs.

Effect of Sintering Temperature on Microstructure Characteristics of Porous NiTi Alloy Fabricated via Elemental Powder Sintering.

To investigate the effect of the sintering temperature on the microstructure characteristics of porous NiTi alloys, two types of porous NiTi alloys with equal atomic ratios were fabricated via elemental powder sintering at 950 °C and 1000 °C. Afterwards, optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were collectively applied to investigate the pore characteristics and microstructure of the fabricated porous NiTi alloy. The results show that when the sintering temperature increases from 950 °C to 1000 °C, the average pore size increases from 36.00 μm to 181.65 μm, owing to the integration of these newly formed small pores into these pre-existing large-sized pores. The measured density increases from 2.556 g/cm3 to 3.030 g/cm3, while the porosity decreases from 60.4% to 51.8%. This is due to the occurrence of shrinkage after the sufficient diffusion of atoms. Furthermore, the characterization results confirm that a change in the sintering temperature would not change the phase types within a porous NiTi alloy; namely, the matrix consists primarily of B2 NiTi, with a significant amount of Ni4Ti3 precipitates and a small amount of Ni3Ti precipitates and Ti2Ni precipitates. However, as the sintering temperature increases, the number of Ni4Ti3 precipitates decreases significantly. The formation of a Ni4Ti3 phase in the present study is closely related to the enrichment of Ni content in the matrix owing to the diffusion rate difference between Ni atoms and Ti atoms and the absence of a transient liquid phase (TLP) during the sintering process owing to the relatively low sintering temperature (lower than the eutectic temperature). Moreover, the increasing sintering temperature speeds up the atom diffusion, which contributes to a reduction in the enrichment of Ni as well as the number of formed Ni4Ti3 precipitates.