NiTi Alloy Research Articles

Influence of Torque on Cutting Efficiency of Heat Treated NiTi Alloy Endodontic Rotary Files

Influence of Torque on Cutting Efficiency of Heat Treated NiTi Alloy Endodontic Rotary Files

Improved Super-Elastic Ti-Ni Alloy Wire for Nonsurgical Treatment of Skeletal Class II Malocclusion Combined with Large Overjet and Gummy Smile Case

Improved Super-Elastic Ti-Ni Alloy Wire for Nonsurgical Treatment of Skeletal Class II Malocclusion Combined with Large Overjet and Gummy Smile Case

Unleashing the elastocaloric cooling potential of 3D-printed NiTi alloy with heterogeneous microstructures and Ni4Ti3 nanoparticles

Toward the development of elastocaloric (eC) refrigeration applications, this study examines how Ni4Ti3 nanoparticles improve the eC properties of laser powder bed-fused (LPBF) NiTi alloys, with a focus on the formation of a NiTi/Ni4Ti3 nanocomposite. The LPBF-produced microstructure offers significant advantages: i) a heterogeneous grain structure that provides complementary benefits—fine grains offer higher deformation resistance while coarse grains initiate phase transformation (PT) earlier, releasing more latent heat; ii) a strong <001>//building direction texture that enhances recoverability. However, these benefits are partially limited by grain boundary slip during PT, leading to lower cooling efficiency and increased energy dissipation in as-built NiTi alloys. To address these issues, Ni4Ti3 nanoparticles are introduced through aging treatment, forming a composite structure that strengthens grain boundaries. Given the challenges of applying severe plastic deformation to 3D-printed components, this approach may offer a more practical solution. The study also reveals that Ni4Ti3 nanoparticles contribute to: 1) reducing Ni content in the matrix, increasing lattice size and enthalpy, which enhances the temperature drop (ΔTad); and 2) promoting R phase formation, which hinders the B2↔B19' PT, reducing energy dissipation and improving the coefficient of performance (COPmat). The balance of these effects depends on nanoparticle size, with smaller particles (∼5–12 nm) amplifying the second effect, while larger particles (∼130 nm) increase the first effect. At 350°C aging, the optimized nanocomposite exhibits a maximum COPmat of 15 and ΔTad of 14K, representing a 163% improvement over the as-built alloy. This work highlights the potential of NiTi composites in 3D-printed eC components.

Laser microwelding of NiTi/PtIr alloys with laser beam offset

The NiTi and PtIr alloy joint has been employed in biomedical devices to combine the superelasticity of NiTi alloy with the X-ray visibility of PtIr alloy. Laser microwelding is usually used for the joints, but there is a risk of forming brittle intermetallic compounds (e.g., Ni3Ti, Ti2Ni, and Ti3Pt) in the fusion zone (FZ), which could deteriorate joint strength. In this study, laser beam offset (laser offset) was implemented for a butt joint of Ni-49.8 at.% Ti and Pt-10.0 at.% Ir alloy wires to control the intermetallic compound formation in the FZ. Welding with 300 μm laser offset on the NiTi side achieved 2.3 times higher joint breaking stress and 13.0 times higher joint breaking strain than welding without laser offset. The joint breaking stress and strain were enhanced from 221 MPa and 0.9% to 502 MPa and 11.7% by 300 μm laser offset on the NiTi side, respectively. In the absence of laser offset, the dissolution of Pt and Ir into the FZ facilitated the M3Ti (M = Ni, Pt, Ir) formation in the FZ, resulting in crack propagation within the M3Ti. In contrast, the 300 μm offset on the NiTi side inhibited the M3Ti formation by mitigating Pt and Ir dissolution into the FZ. Laser offset on the NiTi side can be an attractive option to enhance the strength and ductility of NiTi and PtIr butt joints.

Enhanced structural stability of Si electrode employing TiNi/Si pillars with oriented Li diffusion pathway

As the anode materials of Li-ion batteries, pillar-shaped TiNi/Si particles fabricated by employing electrochemical etching of (100) Si wafers and TiNi alloy coating, were investigated for their structural and electrochemical properties. The most suitable porous wafer for producing Si pillars was obtained at a current density of 2.5 mA/cm2 during etching. The deposited TiNi alloy film consisted of a crystallized austenitic (B2) phase capable of inducing phase transformation through annealing at 500°C. Particularly, by coating with the inactive materials, only the (100) plane of single crystalline Si was exposed during the initial charging process to restrict Li ion movement exclusively along the <100>Si direction. The TiNi/Si electrode exhibited a lower capacity compared to the Si electrode but demonstrated improved cycling performance. It showed a charge capacity of 1110 mAh/g at 0.1 C with an initial efficiency of 77 % and maintained a capacity retention of 49 % (543 mAh/g) up to 100 cycles. After the initial cycle, Si electrodes exposed to various lithium insertion directions exhibited severe structural damage such as cracking and particle pulverization, whereas TiNi/Si electrodes demonstrated enhanced structural stability due to surface coating and restricted reaction pathway.

Research on corrosion behavior and biocompatibility of NiTi alloy processed with combined dealloying and annealing treatment

This paper presents a novel method to prepare hydrophilic nanoporous functional surface with combined dealloying and annealing treatment to improve the corrosion resistance and biocompatibility of NiTi components. Surface modification mechanism is discussed with microscopic characterization of NiTi nanoporous structures. Hydrophilic and biocompatible performance is achieved through specifically tailoring the dimensions and chemical compositions of nanoporous layer. The corrosion resistance of NiTi samples is investigated in 0.9 wt% NaCl solution and evaluated with potentiodynamic polarization and electrochemical impedance spectroscopy tests. The results indicate that material corrosion resistance is significantly enhanced with TiO2 formation during dealloying treatment, while annealing promotes the oxidation and densification of dealloyed layer raising the energy barrier for ion transportation during corrosion. Furthermore, as the dealloying temperature increases, the surface defects of the sample decrease resulting in better corrosion resistance. The research can provide guidance for NiTi surface modification to enhance its biomedical applications.

Microstructure, Mechanical Properties and Corrosion Performance of Laser-Welded NiTi Shape Memory Alloy in Simulated Body Fluid.

Laser-welding is a promising technique for welding NiTi shape memory alloys with acceptable tensile strength and comparable corrosion performance for biomedical applications. The microstructural characteristics and localized corrosion behavior of NiTi alloys in a simulated body fluid (SBF) environment are evaluated. A microstructural examination indicated the presence of fine and equiaxed grains with a B2 austenite phase in the base metal (BM), while the weld metal (WM) had a coarse dendritic microstructure with intermetallic precipitates including Ti2Ni and Ni4Ti3. The hardness decreased from the BM to the WM, and the average hardness for the BM was 352 ± 5 HV, while it ranged between 275 and 307 HV and 265 and 287 HV for the HAZ and WM, respectively. Uni-axial tensile tests revealed a substantial decrease in the tensile strength of NiTi WM (481 ± 19 MPa), with a reduced joint efficiency of 34%. The localized corrosion performance of NiTi BM was superior to the WM, with electrochemical test responses indicating a pitting potential and low corrosion rate in SBF environments. The corrosion rate of the NiTi BM and WM was 0.048 ± 0.0018 mils per year (mpy) and 0.41 ± 0.019 mpy, respectively. During welding, NiTi's strength and biocompatibility properties changed due to the alteration in microstructure and formation of intermetallic phases as a result of Ti enrichment. The performance and safety of welded medical devices may be impacted during welding, and it is essential to preserve the biocompatibility of NiTi components for biomedical applications.

Elastocaloric effect of NiTi shape memory alloys manufactured by laser powder bed fusion

To address the challenges posed by the complex processing of NiTi alloys, the additive manufacturing technology has been employed for the preparation of NiTi alloys samples. Up to now, there is limited research on the elastocaloric effects of NiTi alloys manufactured by LPBF. This study focused on the utilization of laser powder bed fusion (LPBF) to fabricate NiTi samples, with a particular emphasis on the influence of laser power, scanning speed and hatch spacing on the microstructure and properties of NiTi alloys. The results indicated that the process parameters affect the stress hysteresis of superelasticity by influencing the Ni content in the NiTi alloys. The higher Ni content, the lower the stress hysteresis. In addition, the critical stress for plastic deformation of the texture in the <001> direction in NiTi alloys is the smallest. When only the P was changed, the proportion of the texture in the <001> direction in the sample increased with the increase of P, the proportion of plastic deformation increased, and the degree of recovery also gradually decreased. Furthermore, at a specific temperature, 10 K higher than the end temperature of austenite transformation, each sample exhibited good superelasticity. In particular, the 1st cooling capacity of the sample with the best elastocaloric effect reached 11.0 K, which was superior to other results obtained by LPBF under similar compressive strain levels.

Experimental analysis of extrusion-based additive manufacturing process of bio-composite NiTi alloy

Experimental analysis of extrusion-based additive manufacturing process of bio-composite NiTi alloy

Microstructural evolution and phase transformation behavior of Ni-Ti alloys prepared by accumulative roll bonding-deformation diffusion process

Ni-Ti shape memory alloys were prepared by accumulative roll bonding-deformation diffusion (ARB-DD) process. Effects of deformation heat treatment on the microstructural evolution and phase transition behavior of ARB-DD Ni-Ti alloy were investigated by thermodynamic calculations, and the intrinsic mechanism was revealed. The results show that strong shear is induced by intensified plastic flow of the metal at the interface, resulting the interfaces engage with each other. The simultaneous opening and cross-tangling of multi-directional dislocations leads to the dislocation cells and Taylor lattice interact near the interface, and the compounds are preferentially formed. The ARB-DD treatment resulted in a one-step phase transition for the Ni-Ti alloy. After deformation heat treatment, R-phases appear and the phase transition is transformed into two-step. During heating and cooling the phase transitions are B19’→R→B2 and B2→R→B19’, respectively. The thermal hysteretic temperature increases and reaches 57.0 °C. The microstructure transforms from dislocations to nano-twin. A lattice distortion zone with a width of about 10 nm exists at the interface between precipitates and the matrix. It reduces the energy barrier required for phase transformation, leading to stabilization of the B2 phase and de-stabilization of the B19’ phase. Eventually, a wider temperature interval for the phase transformation is obtained. This process is an effective way to prepare Ni-Ti alloys with favorable shape memory effect.

Thermodynamic Investigation of Propagating Behavior in SHS for Equiatomic and Non-Equiatomic NiTi Alloys Using Factsage Software

Thermodynamic Investigation of Propagating Behavior in SHS for Equiatomic and Non-Equiatomic NiTi Alloys Using Factsage Software

Decomposition features and mechanical properties of aging Ti49Ni51 alloy with shape memory effects subjected to heat treatment

The features of the microstructure of the Ti–51 at.%Ni shape memory alloy have been studied after aging at various temperatures. In combination with studies using optical and electron microscopy and X-ray analysis, mechanical properties were tested for tensile strength at room temperature. It has been established that the aged alloy is distinguished by a high level of mechanical properties (tensile strength up to 1200 MPa with a relative elongation of up to 35 %) due to highly dispersed homogeneous decomposition and the effect of simultaneous hardening and increased plasticity as a result of deformation-induced martensitic transformation.

Experimental Investigation of the Impact of Loading Conditions on the Change in Thin NiTi Wire Resistance during Cyclic Stretching.

This paper presents the results of an experimental study designed to evaluate the effect of repeated stretching cycles on the electrical resistance change in a NiTi alloy wire. In particular, tests were carried out to determine the effect of the type of loading on resistance change in the investigated wires. Wires with a diameter of 100 μm were used in the research. The experiment was carried out on a dedicated test stand designed for this purpose. During the test, the samples were subjected to 40 identical tensile cycles. The electrical resistance, sample elongation, and tensile force during successive stretching cycles were measured. The conducted research demonstrated the impact of elongation and reorientation of the structure on the resistance change in NiTi alloy thin wires. The research included a comparison of the effect of two different types of loading on the electrical resistance change in the sample. During cyclic stretching of a NiTi alloy sample with constant displacement, a decrease in electrical resistance was observed after each successive stretching cycle. Alternatively, when stretching with a constant force, the value of electrical resistance increased. In both types of loads, the greatest change in resistance value was observed at the initial cycles.

A first step towards the detection of damage processes in endodontic Ni-Ti alloy files, using acoustic emission

Despite major instrumental developments over the last decade, endodontic files are still not infallible. It is well known that NiTi rotary files can break without any visible sign of deformation. Instrument breakage under combined flexion-torsion loading is still common in clinical practice. Unfortunately, breakage of this type of instrument mainly occurs in narrow canals, through pinching in the apical region. When such an incident occurs, the endodontist must adopt a debris retrieval strategy that is both stressful and not guaranteed success. This study proposes a new method for experimental damage detection leading to the fracture of Ni-Ti shape memory alloy endodontic files. It is based on the acoustic emission (AE) technique and mechanical parameters measured in real-time and image analysis. It has been shown that the AE results correlate with the damage observations and torque and force measurements recorded during the tests.Having carried out numerous root canal treatment on resin blocks, it appears that this new detection and analysis technique can be used to analyze and anticipate the first signs of damage leading to endodontic file failure. The technological development of such a method, at the level of the engine itself, associated with the act in service procedure, would constitute a revolution in the field of endodontics.

Adapting the Mn content within a Fe-Mn-Si-based shape memory alloy by in situ parameter variations in laser-based additive manufacturing

Shape memory alloys exhibit unique properties ideal for functionally integrated components, such as actuators. While commonly used Ni-Ti alloys are well established, especially in biomedicine and aerospace, their high cost limits wider applications. Fe-based shape memory alloys present an affordable alternative, suitable for diverse applications, with a larger thermal hysteresis but lower recovery strain. Nonetheless, their functional properties can be enhanced through optimized processing methods like laser powder bed fusion and adjustments to their alloy composition. In the present study, laser powder bed fusion was used for modifying the composition and microstructure of a Fe-30Mn-6Si-5Cr alloy. For this purpose, laser parameters were varied to evaporate up to 47.3% of the initial Mn in the manufacturing process. In this context, the amount of Mn evaporated was dependent on both the line energy and more considerably on the volume energy density introduced in the manufacturing process. Subsequently, the impact of the resulting compositional changes on the microstructure was analyzed, and the functional properties were visualized using a demonstrator. Lowering the Mn content below 24.1% led to a higher degree of ferrite in the otherwise austenitic microstructure. This also affected the functional properties. These findings highlight the potential of laser-based additive manufacturing for modifying the composition and microstructure of shape memory alloys in situ and, thus, tailoring their functional properties.

Evaluation of titanium dioxide and tantalum pentoxide nanoparticles for coating NiTi archwires in orthodontics: An in vitro study

Background: This study aims to enhance the biocompatibility of Nickel–Titanium (NiTi) alloy by developing a new coating using titanium dioxide (TiO2) and titanium pentoxide (Ta2O5) through direct current (DC) reactive sputtering technology. Materials and methods: Two distinct coating materials, namely, TiO2 and Ta2O5, were used to fabricate NiTi orthodontic archwires with improved surface properties. TiO2 nanoparticles, with thickness ranging from 21.90 nm to 31.93 nm, were deposited onto NiTi alloy substrates through DC reactive sputtering deposition under different power conditions. Results: X-ray diffraction and field emission scanning electron microscopy validated the uniformity and morphology of the coatings. Immersion tests in simulated body fluid (SBF) revealed significant hydroxyapatite layer growth on TiO2-coated NiTi, especially at a sputtering power of 240 W. Reduced nickel ion release was observed on TiO2 nanoparticles with a thickness of 21.90 nm at 50 W sputtering power compared with 31.93 nm-thick nanoparticles at 240 W. Ta2O5 thin films were deposited on NiTi substrates through DC magnetron reactive sputtering at ~100 °C with a deposition power of 50 W. Structural and morphological analyses through optical microscopy and X-ray diffraction, atomic force microscopy, and scanning electron microscopy revealed the homogeneity and low roughness of the coatings. Biocompatibility assessments in artificial saliva and SBF solutions established that Ta2O5-coated NiTi alloys exhibited superior electrochemical behavior, enhanced corrosion resistance, and diminished Ni ion release compared with uncoated specimens. Conclusion: TiO2 and Ta2O5 coatings not only improved the biocompatibility of NiTi orthodontic archwires but also presented a promising path for advanced biomedical applications. These coatings have potential in improving the cellular behavior and performance of NiTi-based orthodontic devices.

Dynamic damage response of sing-crystal NiTi alloys induced by shear localization

Dynamic damage response of sing-crystal NiTi alloys induced by shear localization

Comparison of Key Properties of Ag-TiO2 and Hydroxyapatite-Ag-TiO2 Coatings on NiTi SMA.

To functionalize the NiTi alloy, multifunctional innovative nanocoatings of Ag-TiO2 and Ag-TiO2 doped with hydroxyapatite were engineered on its surface. The coatings were thoroughly characterized, focusing on surface topography and key functional properties, including adhesion, surface wettability, biocompatibility, antibacterial activity, and corrosion resistance. The electrochemical corrosion kinetics in a simulated body fluid and the mechanisms were analyzed. The coatings exhibited hydrophilic properties and were biocompatible with fibroblast and osteoblast cells while also demonstrating antibacterial activity against E. coli and S. epidermidis. The coatings adhered strongly to the NiTi substrate, with superior adhesion observed in the hydroxyapatite-doped layers. Conversely, the Ag-TiO2 layers showed enhanced corrosion resistance.

A comparative study of the microstructure and shape memory behaviour of NiTi, NiTiHf, and Pt-added NiTiHf alloys

The microstructure, substructure, transformation temperature, and recovery ratio of a novel Ni45Pt 5 Ti30Hf20 alloy are reported in the current work. The properties of binary TiNi and ternary TiNiHf alloys are also characterized to establish a comparative basis for shape memory behaviour. The microstructure of the cast structure of Ni45Pt5Ti30Hf20 alloy showed a dendritic matrix and interdendritic eutectic-like mixture, and that of the homogenized structure consisted of martensitic matrix and secondary phase of dark contrast having the composition (Ti+Hf)2(Ni+Pt). Pt substitution of Ni in the ternary alloy with 20 at.% Hf by 5 at.% leads to a decrease in the Af, As, Ms, and Mf . Ms and Mf represent the temperatures at which austenite to martensite transformation starts and completes, respectively, while As and Af represent the temperatures at which martensite to austenite transformation starts and completes, respectively. The XRD studies showed that the structure of martensite is B19′ and TEM studies showed that the substructure of martensite in Pt modified NiTiHf alloy is similar to that of ternary NiTiHf alloy. The shape memory recovery of the Pt-modified alloy is similar to the ternary alloy at higher strength levels. The recovery ratio determined using Vickers indentation is compared with that determined using compression tests to provide an efficacy of small volume tests for screening of these alloys.

Regulation of microstructure, phase transformation behavior, and enhanced high superelastic cycling stability in laser direct energy deposition NiTi shape memory alloys via aging treatment

The remarkable mechanical properties, fatigue resistance, wear and corrosion resistance, biocompatibility, shape memory effect, and superelasticity of NiTi shape memory alloys make them applied in diverse engineering areas, including satellite antennas, oil pipelines, and vascular stents. This paper focuses on the preparation of Ni50.8Ti49.2 alloy via laser directed energy deposition (LDED) utilizing pre-alloyed powder and the heat treatment of solid solution at 950 °C for 8 h followed by subsequent aging at 350 °C, 450 °C and 550 °C for 2 h. The influence of varying aging temperature on the microstructures, phase transformation behavior and superelastic cyclic stability of them was comprehensively summarized and discussed. The martensitic transformation temperatures of NiTi alloys after aging decrease as the aging temperature increases. Specifically, NiTi alloys aged at 450 °C for 2 h exhibit excellent superelasticity and high cyclic stability. After an initial loading-unloading cycle with an 8.079 % pre-strain, the alloy achieves 100 % complete recovery. Even after 10 cycles, the recoverable strain remains at approximately 7.374 %, with a recovery rate exceeding 90 %. These outstanding properties of high superelasticity and superior cyclic stability are significantly better than most other LDED NiTi alloys. This exceptional performance is primarily attributed to the synergistic effects of the R-phase and Ti3Ni4 precipitates on the shape memory alloy.