NiTi Research Articles

Study of ageing and size effects in Nickel–Titanium shape memory alloy using molecular dynamics simulations

ABSTRACT The effect of ageing process at 1073.15 K on the athermal phase transformation in different nanograins (4.5, 6 and 9 nm) of Nickel–Titanium shape memory alloy is studied using molecular dynamics simulations. The martensitic transformation start temperature and transformed martensite volume decrease with decreasing grain size. The two-stage phase transformation with intermediate phase formation is observed only in the smallest grain (4.5 nm) where a single martensite variant is formed. On the contrary, larger grains show a self-accommodated twinned martensite variants with one-stage transformation from austenite to martensite. The ageing process hardly influences the morphology of the martensite phase, however, it rises the martensite start temperature and reduces the austenite start temperature. The nano grain size models demonstrate the constrained transformation due to the transformation barrier and the accumulation of internal stress, while the ageing process shows the tendency for stress relaxation.

Which environmental sample type and statistical approach provides most information about metal exposure in young children from an urban setting?

Identification of sources and pathways is critical in minimizing exposure of young children to toxic materials. We monitored 108 children <5 years old 6-monthly for up to 5 years in a major urban setting. Samples (ñ7000) included interior handwipes (W1) and after exterior playing (W2), interior house dust (PD1) and day care dust (PD2) using petri dishes, exterior dust-fall accumulation, exterior dust sweepings, garden soil, blood and urine. Here we describe multi-element results to determine which sampling method and analysis of the data provide the most reliable indicators of metal exposure to young children. Samples were analysed by ICPMS for Ca, Cd, Cr, Cu, Fe, Mg, Mn, Ni, Pb, Ti, V and Zn. Pearson Correlations showed the highest number of significant correlations are for: W1 and W2, dust sweepings and soil. Mixed model analyses (MMA) for the blood levels as the dependent variable and environmental predictor variables showed the most consistent results were for W1, PD1 and sweepings. MMA to investigate the association between each metal (e.g. Ca) and the other 11 metals showed the largest numbers of significant relationships are for W1 and sweepings. Cluster analyses showed that the ‘best’ clusters in W1 and W2 are for Fe–Zn–Mg and Mn–Pb–Ni. For PD1 and PD2 the ‘best’ clusters were Fe–Zn–Mg, Cr–Ni–Ti, and Cu–Mn–Pb. Clusters for dust sweepings and soil are generally similar. Principal component analysis (PCA) loadings for W1 and PD1 accounted for >50% of the variance. Metals comprising loading 1 component for both sample types included Ca, Fe, Mg, and Mn. Overall cluster analyses provided more information than PCA loadings. In summary: The most suitable methods and analyses are MMA of W1 and sweepings, and cluster analyses of W1and PD1. Resuspension from outdoor surfaces and soils and deposition in the residences is a likely pathway for most metals.

Efficacy of three Nickel Titanium rotary file systems in removal of intracanal filling material (In vitro study)

Efficacy of three Nickel Titanium rotary file systems in removal of intracanal filling material (In vitro study)

Comparison of Different Rotary Nickel–titanium Systems to Evaluate Coronal Leakage of Root Canals: An in Vitro Study

Introduction: The objective of the study was to assess coronal leakage following root canal treatment utilizing four Micro Mega rotary nickel–titanium files, specifically One shape, Two shape (s1), Two shape (s2), and Revo-S, by means of dye penetration analysis using a stereomicroscope set at 20× magnification. Methods: Fifty human lower premolar teeth that were extracted for orthodontic reasons were included in the study, excluding teeth with cracks, caries, severe curvature (&lt;25°), or root resorption. The teeth were randomly assigned to five groups using www.random.org, and standard endodontic treatments were performed as per the manufacturer’s instructions using Micro Mega One shape, Two shape (s1), Two shape (s2), and Revo-S rotary nickel–titanium systems. To measure dye penetration, the teeth were immersed in a 2% methylene blue dye solution for approximately 24 hours and then axially split using a diamond sectioning disc, with measurements taken using a stereomicroscope. Results: The study groups showed statistically significant differences (P &lt; 0.001), and all pairwise comparisons were found to be significantly different according to the post hoc test (P &lt; 0.001). Conclusion: Our results showed that various rotary file designs significantly affect coronal leakage.

Loss of working length in curved canals with rotary nickel–titanium instruments and reciprocating files

ABSTRACT Aim: The aim of the study was to investigate the change of working length in curved molar root canals after preparation with rotary nickel–titanium instruments and reciprocating files. Materials and Methods: Thirty human-extracted maxillary and mandibular molars with curved roots were selected, with the help of a radiographic platform, a constant object sensor distance was arranged to take a digital radiograph of each tooth for determining the angle of curvature of the roots by Schneider’s method. The teeth were divided into Groups I, II, and III based on the instrumentation, ProTaper group, Reciproc group, and control group, respectively. Preoperative and postoperative working length was determined and compared using cone-beam computed tomography. The difference was determined statistically using one-way anova analysis. Results: There was minimum loss of working length found when instrumentation was done with Reciproc files compared with ProTaper. Conclusion: Reciprocating instruments can be an effective alternative used in the preparation of severely curved canals.

Bessel beam generated LIPSS on NiTi wires

Ultrashort laser pulses are used to generate Laser-Induced Periodic Surface Structures (LIPSS). To apply LIPSS on small confined areas, the laser source must be focused to a small spot diameter. Contrary to commonly used high numerical aperture objectives, we present a Bessel beam-based approach to produce LIPSS covered lines with a width of 4 to 10 µm. Therefore, an 800 nm Ti:Sa-laser with a pulse duration of 110 fs and a repetition rate of 5000 Hz was used. The setup convinces with an extended depth of focus. Thus, high reproducibility of the process was proven, while no focus control and no specific requirements for the surface quality are needed. The applicability of this method is demonstrated by structuring the shell surface of nickel–titanium wires.

Electroanalysis of nickel ions released in artificial saliva from three orthodontic arch wires: Stainless Steel (SS), NiTi, and CuNiTi

Background: Nickel titanium wires are superior for first alignment because they have exceptional shape memory and super-elasticity. Increased concerns have been raised about the high rate of nickel (Ni) allergy and the growing usage of dental biomaterials that contain Ni. Aim: The aim of the study was to analyze and evaluate the rate of nickel release from different types of orthodontic arch wires. Materials and methods: A set of arch wires of nickel titanium (NiTi), SS and Cu-NiTi were immersed in artificial saliva for three days and analyzed after three days. The amount of Ni ions released from the sample were evaluated using electrochemical techniques such as Cyclic Voltammetry (CV), Electrochemical Impedance Spectroscopy (EIS) and polarization (Tafel) plot. Results: The EIS and Tafel graph confirmed the s-NiTi, s-CuNiTi showed an excellent corrosion resistance than the s-SS. From all the above measurements, we can conclude that the saliva can affect the corrosion resistance property of the SS, NiTi, CuNiTi day by day. Conclusion: From this study it was concluded that the saliva can affect the corrosion resistance property of the SS, NiTi, CuNiTi day by day, and there was nickel ion release but at a very negligible rate.

Computational study of Na diffusion and conduction in P2- and O3-Na2x[NixTi1-x]O2 materials with machine-learning interatomic potentials

Sodium-ion batteries (SIBs) provide a feasible solution for large-scale energy storage applications of sustainable energy resources like wind and solar energy. Layered sodium nickel titanates (Na2x[NixTi1-x]O2) (SNTL) are considered a promising electrode material for SIBs since they can function as either a positive or negative electrode due to the coexistence of high redox potential element Ni (V = 3.7 V vs. Na/Na+) and low redox potential element Ti (V = 0.7 V vs. Na/Na+). There have been both experimental and computational studies on the family of Na2x[NixTi1-x]O2 materials, investigating their structures, electrochemical performance, electronic and ionic conductivity, etc. However, the current understanding of the Na migration mechanism is still very limited at an atomic level because of the restrictions of simulation methods: density-functional theory (DFT) simulation is restricted to a small length and time scale, whereas the conventional empirical interatomic potential (IP) is restricted by a limited accuracy. To solve this efficiency-versus-accuracy dilemma, herein we developed a neural network (NN)-based machine-learning interatomic potential (MLIP), which is trained using DFT data. Our MLIP demonstrates a DFT-approaching accuracy in terms of atomic forces. Moreover, the extracted Na self-diffusivity, ionic conductivity, and activation energy values from MLIP-MD simulation agree well with experimental data. In general, P2-SNTL demonstrates a higher Na self-diffusivity and ionic conductivity than O3-SNTL, mainly due to the larger bottleneck size through which Na ions migrate. We also employed the incoherent density correlation function to study the Na migration mechanism. The Singwi-Sjölander (SS) model and Chudley-Elliot (CE) model were used to fit the jump-diffusion behavior in P2- and O3-SNTL, respectively. The obtained jump distance values match well with the typical distance between the nearest Na sites in P2- and O3-SNTL, confirming that the hopping events happen mostly between neighboring Na sites in SNTL. The decrease of residence time and jump distance values with temperature is a result of higher ion mobility and level of delocalization, as validated by the nuclear density maps. In addition, our study also confirmed that both the “straight” and “curved” Na migration paths exist in O3-SNTL, in contrast to previous studies which only mention the “curved” migration path. In the end, our calculated Haven ratios have a value <1, indicating that it is more likely for the Na hopping events to occur via a concerted migration of several atoms other than the jump of an isolated atom.

ELECTROCHEMICAL ARC DRILLING OF NICKEL–TITANIUM SHAPE MEMORY ALLOY USING MOLYBDENUM ELECTRODE: INVESTIGATION, MODELING AND OPTIMIZATION

In the present scenario, electrochemical arc machining (ECAM) (hybrid of electric discharge erosion and electrochemical dissolution) is an evolving procedure for difficulty in machining the materials due to constraints of existing processes. This research aims to investigate the machinability of Ni[Formula: see text]Ti alloy through electrochemical arc drilling using molybdenum electrode. Electrolyte concentration (ethanol with ethylene glycol and sodium chloride), supply voltage, and tool rotation are considered as the variable factors to evaluate the ECAM performance characteristics in drilling blind hole operation concerning overcut (OC), tool wear rate (TWR) and materials removal rate (MRR). Consequently, response surface methodology is implemented for predictive modeling of various performance characteristics. Finally, multi-objective optimization through desirability function approach (DFA) has produced a set of optimal parameters to improve the productivity along with the accuracy, which is the prime requirement for the industrial applicability of the ECAM process. Results demonstrated that supply voltage is the influential key factor for improvement of machining rate. Scanning electron microscope (SEM) photographs revealed the development of heat affected zone (HAZ), white layer, melted droplet, craters, re-solidified material, ridge-rich surface and voids as well as cavities around the end-boundary surfaces of a blind hole. Composition analysis through energy dispersive spectroscopy (EDS) indicated the oxygen content on the machined surface because electrolyte breakdown causes oxidation to take place at elevated temperatures across the machining zone. Moreover, carbide precipitation like TiC was found in the melting zone of the drilled hole, as revealed by X-ray diffraction (XRD) analyses, which has the affinity to reduce the SMA properties in HAZ.

A numerical study on the superheater tubes bundle of a 660 MW coal-fired supercritical boiler

Coal-fired thermal power plants are currently converting their technology to supercritical and ultra-supercritical in order to meet the world’s energy demands. An important component in this technology is the superheater of the boiler, which operates at higher temperatures and above the critical pressures. For the design and reliable operation of a superheater tube bundle, thermal and structural analyses are crucial. This study focuses on the superheater tubes bundle of a 660[Formula: see text]MW coal-fired supercritical boiler. The superheater model is simulated to investigate the thermal characteristics such as temperature distribution, total heat flux and directional heat flux and structural parameters such as von Mises stresses, equivalent strains and total deformations. Different materials such as martensitic steel, austenitic steel and nickel–titanium are compared based on thermal and structural analysis. It is claimed that thermal performances of martensitic steel are more impressive as compared to superheater materials. The lower strain appeared for austenitic steel as compared to martensitic steel.

Inhibition of Localized Corrosion of Ni–Ti Superelastic Alloy in Sodium Hypochlorite Solution by Sodium Carbonate Addition

Inhibition of Localized Corrosion of Ni–Ti Superelastic Alloy in Sodium Hypochlorite Solution by Sodium Carbonate Addition

Diffusivity and atomic mobility for Fcc Ni–Ti–V alloys: Experiment and modeling

Ni–Ti–V is one key sub-system of the Ni-based superalloys. However, there is a lack of the investigation on diffusion kinetics for Fcc Ni–Ti–V alloys. In order to remedy this situation, we combined the diffusion couple experiment and calculation by CALTPP (CALculation of ThemoPhysical Properties) software to investigate diffusion kinetics for Fcc Ni–Ti–V alloys. Totally, 12 ternary Fcc Ni–Ti–V diffusion couples were prepared and annealed at 1273, 1373 and 1473 K, for which the composition profiles were measured by EPMA (Electron Probe MicroAnalysis). Based on the measured composition profiles and available thermodynamic descriptions, the interdiffusivities and atomic mobility parameters for Fcc Ni–Ti–V system were then calculated by the numerical inverse method integrated with CALTPP software. The simulated composition profiles by CALTPP software agree well with the measured ones. Moreover, the interdiffusivities obtained by CALTPP software were confirmed to be reliable through the good consistence with those calculated by M − K (Matano-Kirkaldy) method. Thus, the present numerical calculation by CALTPP software was verified to be reasonable. Finally, based on the presently obtained mobility parameters and available thermodynamic descriptions for Fcc Ni–Ti–V alloys, the three-dimensional surfaces of the interdiffusivities, activation energies and frequency-factors against Ti and V composition were predicted. The present work provides reliable kinetic parameters for Fcc Ni–Ti–V alloys, which can be included in the diffusion database of Ni-based superalloys for material design.

Structural properties and sensing performance of Ni–Ti alloy films for extended-gate field-effect transistor pH sensors

This study presents a facile Ni–Ti alloyed film grown on the n+-type Si through a DC sputtering technique for electrochemical pH sensing and its comprehensive structural, morphological, compositional, profiling, microstructural, and elemental characterization. In addition to pH sensing measurements, the properties of the sensing layer were analyzed using X-ray diffraction, atomic force microscopy, X-ray photoelectron spectroscopy, secondary ion mass spectroscopy, transmission electron microscopy, and energy dispersive X-ray spectroscopy analysis. The impact of rapid thermal annealing (RTA) treatment (500–700 °C) on the alloyed Ni–Ti sensitive films was extensively studied. The structural feature of the alloyed Ni–Ti sensitive films is more closely related to their relative sensing performances. The performance of the alloyed Ni–Ti sensitive film at the RTA temperature of 600 °C showed a higher pH sensitivity of 60.73 mV/pH in a wide pH range of 2–12 in comparison with other RTA temperatures. Moreover, the stability of this 600 °C-annealed EGFET sensor exhibited a small drift rate of 0.21 mV/h in pH 7 and a low hysteresis voltage of 1 mV in a loop of pH 7 → 4→7 → 10→7. The alloyed Ni–Ti sensitive film is fully compatible with a standard CMOS process and demonstrates better sensing performance than other metal nitride sensitive films (e.g. RuN, TiN), suggesting it may be a strong candidate for future sensor and biosensor applications.

Synergies of material and geometrical non-linearities allow for the tuning of damping properties of functionally graded composite materials

In this study, we present an alternative fabrication technique to obtain functionally graded polymer–metal composites. The aim is to obtain a composite material with a graded damping factor, which is provided by the presence of pseudoelastic nickel–titanium (NiTi) fibres within an epoxy resin matrix. A preliminary dynamic mechanical characterisation of the NiTi wire revealed a pre-strain dependency of its damping factor. By fabricating wires with curved geometries in the free state, we were able to obtain fibres with a graded level of pre-strain when straightened. This feature in turn imparts a graded damping response. When encapsulating the straightened fibres in an epoxy resin, the graded damping response is transferred to the composite.

Roughness Analysis of Powder-Bed Fused Nickel–Titanium Surfaces with Chemical Etching Enhancement by a Safe Aqueous Fluoride Solution

Roughness Analysis of Powder-Bed Fused Nickel–Titanium Surfaces with Chemical Etching Enhancement by a Safe Aqueous Fluoride Solution

How to grow single-crystalline and epitaxial NiTi films in (100)- and (111)-orientation

Understanding the martensitic microstructure in nickel–titanium (NiTi) thin films helps to optimize their properties for applications in microsystems. Epitaxial and single-crystalline films can serve as model systems to understand the microstructure, as well as to exploit the anisotropic mechanical properties of NiTi. Here, we analyze the growth of NiTi on single-crystalline MgO(100) and Al2O3(0001) substrates and optimize film and buffer deposition conditions to achieve epitaxial films in (100)- and (111)-orientation. On MgO(100), we compare the transformation behavior and crystal quality of (100)-oriented NiTi films on different buffer layers. We demonstrate that a vanadium buffer layer helps to decrease the low-angle grain boundary density in the NiTi film, which inhibits undesired growth twins and leads to higher transformation temperatures. On Al2O3(0001), we analyze the orientation of a chromium buffer layer and find that it grows (111)-oriented only in a narrow temperature range around 500 ∘C. By depositing the Cr buffer below the NiTi film, we can prepare (111)-oriented, epitaxial films with transformation temperatures above room temperature. Transmission electron microscopy confirms a martensitic microstructure with Guinier Preston-zone precipitates at room temperature. We identify the deposition conditions to approach the ideal single crystalline state, which is beneficial for the analysis of the martensitic microstructure and anisotropic mechanical properties in different film orientations.

Impact of rapid thermal annealing on structural and sensing properties of Ni–Ti sensitive films for extended-gate field-effect transistor pH sensors

In the present work, a facile Ni–Ti film deposited on n+-type Si substrate is introduced as a sensitive film for the development of a solid-state extended-gate field-effect transistor (EGFET) pH sensor. Influence of rapid thermal annealing (RTA) treatment (500–700 °C) on structural properties of the Ni–Ti sensitive films was extensively investigated. The film structures, surface morphologies, element profiles, film microstructures, and chemical compositions of the Ni–Ti sensitive films were characterized by a combination of X-ray diffraction, atomic force microscopy, secondary ion mass spectroscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy, respectively. The structural features of the Ni–Ti sensitive films are most closely related to their sensing characteristics. The experimental results indicated that the Ni–Ti sensitive film annealed at the RTA temperature of 600 °C exhibited better sensing performances (a higher pH sensitivity of 71.01 mV/pH, a lower hysteresis voltage of 1 mV and a smaller drift rate of 0.15 mV/h) than other RTA temperatures. The proposed Ni–Ti sensitive film is expected to be effectively useful for various long-term pH sensor and biosensor applications, since it satisfies the typically required sensing performances such as sensitivity and stability.

A Novel Endodontic Approach in Removing Smear Layer Using Nano and Submicron Diamonds with Intracanal Oscillation Irrigation.

Sodium hypochlorite (NaOCl) and ethylenediaminetetraacetic acid (EDTA) are commonly recommended for effectively removing organic and inorganic components in the smear layer. This layer is found on root canal walls after root canal instrumentation. However, high-concentration EDTA reduces the strength of dentin and the dissolution efficacy of organic substances in NaOCl solution. The objective of this study was to investigate the efficacy of applying nano and submicron diamonds in irrigation solutions with sonic and ultrasonic oscillation for removing the smear layer during endodontic treatment. Extracted single-rooted human teeth were instrumented with ProTaper® Gold (Dentsply Sirona) nickel-titanium rotary instruments. Subsequently, each canal was irrigated with 3% NaOCl, 17% EDTA, distilled water, and 10-1000 nm-sized nano and submicron diamond irrigation solutions, respectively. Sonic and ultrasonic instruments were compared for oscillating the irrigation solutions. The teeth were processed for scanning electron microscopy to observe the efficiency of smear layer removal on the canal walls. Our results indicated that diamond sizes of 50 nm and above irrigation solutions showed significant effectiveness in removing the smear layer following the oscillation of sonic instruments for 10 s. Ultrasonic assisted 500 nm and 1000 nm diamond solutions significantly differed from the other diamond-sized solution in their ability to remove the smear layer. These results suggest that sonic and ultrasonic oscillation with specific sizes of nano and submicron diamond irrigation solution can be used as an alternative approach to removing the smear layer during endodontic treatment. The potential clinical application of root canal treatments can be expected.

Effects of different Y compounds on the microstructure and properties of laser cladding NiTi coatings in a semi-open environment

In recent years, nickel–titanium (NiTi) coatings have shown excellent tribological performance due to their unique phase transition characteristics. However, in the laser cladding of NiTi coatings in a semi-open environment, there are still issues with nitrogen and oxygen impurities arising in the coatings due to their exposure to air. In this study, three rare earth (RE) compounds were used to modify NiTi coatings in a semi-open environment to obtain coatings without any impurities. The effect of different RE compounds (Y2O3, YF3 and YCl3) on phase composition, surface oxidation and mechanical properties were studied. NiTi, NiTi2 and the impurity phase titanium nitride (TiN) were observed in the original and Y2O3 modified coating. In addition, incompletely melted Y2O3 exists in the Y2O3-modified coating. The coatings with YCl3 and YF3 were composed of NiTi and NiTi2 phase and the TiN impurity phase was not observed in either coating. In addition, the oxidation phenomenon at the top of the coating gradually weakened in the original, Y2O3, YCl3 and YF3-modified coatings. Furthermore, the R-phase was characterised in the YF3-modified coatings. The average microhardness values of the original, Y2O3, YCl3 and YF3-modified coatings were 669.68 HV0.3, 755.1 HV0.3, 579.1 HV0.3 and 390.47 HV0.3, respectively, of which the microhardness of the YF3-modified coating was the lowest. Although RE compounds did not significantly change the tribological properties, the Y2O3-modified coating exhibited the best tribological properties (∼0.886 mm, 2.6 mg). The results show that YF3 can isolate pollutants from the air in the coating and protect the coating in a semi-open environment.

Characterization of Hydrogen Thermal Desorption Behavior and Enhancement of Hydrogen Embrittlement in Ni–Ti Superelastic Alloy Induced by Cathodic Hydrogen Charging in the Presence of Chloride Ions

Characterization of Hydrogen Thermal Desorption Behavior and Enhancement of Hydrogen Embrittlement in Ni–Ti Superelastic Alloy Induced by Cathodic Hydrogen Charging in the Presence of Chloride Ions