NiTi Alloy Research Articles

Past and Recent Progress on Metallic Digestive Tract Stents.

The implantation of digestive tract stents at various lesion sites can effectively improve digestive tract patency, opening up an excellent treatment method for diseases that are currently incurable or resistant to conventional surgery. Digestive tract stents have been extensively studied and widely used worldwide due to their unique advantages of simple implantation, low trauma, satisfactory effect, and low complication rate. Among the various types of stents, metallic stents have been developed to improve surgical efficacy due to their excellent mechanical properties and are constantly being improved. This review provides an overview of the design and development of conventional nonbiodegradable metallic digestive tract stents such as nitinol (NiTi alloy), stainless steel, and cobalt-based alloy stents. Furthermore, biodegradable metallic stents for the digestive tract, such as magnesium-based, iron-based, and zinc-based stents, are described. This paper also evaluates the advantages and disadvantages of existing metallic digestive stents as well as future research directions and challenges in the development of metallic digestive tract stents.

Machine learning in additive manufacturing——NiTi alloy’s transformation behavior

The laser powder bed fused NiTi alloys (LPBF-NiTi) demonstrate shape memory functionality and superelasticity as a result of their distinctive phase transition characteristics. Nevertheless, achieving precise control and regulation of the phase transition temperature poses a challenge, influenced by factors like powder composition and process parameter. In this study, a feature screening strategy and machine learning (ML) method were employed to predict and regulate the phase transition temperature of LPBF-NiTi alloy, offering a more efficient and cost-effective alternative to traditional experimental methods of regulation and control. Specifically, accuracy analysis was performed on LPBF-NiTi phase transition datasets with varying compositions and process conditions utilizing generalized regression neural network (GRNN), and other methods. The findings indicate that the interpretable features extracted through the selection strategy outlined in this study when combined with the GRNN model, demonstrate a high level of prediction accuracy (R2 = 0.97). To investigate the accuracy of the model, this study utilized various process parameters to fabricate NiTi alloys with different compositions from Ni50.8Ti49.2 alloy powder. Using this model, the study identified a novel, larger window of optimal LPBF processing that allows for controllable complex phase transitions.

Fabrication and tribological properties of bionic surface texture self-lubricating 60NiTi alloy via selective laser melting and infiltration

Due to its low elastic modulus, low density, non-magnetic and good lubricity, 60NiTi alloy is considered a novel fourth-generation aerospace bearing material. In this paper, 60NiTi biomimetic surface textured self-lubricating composites were fabricated by selective laser melting (SLM) and high-temperature fusion infiltration (HTFI). The effects of different slit widths (NTD), edge lengths (NTA), and soft metal Sn-Pb-Ag (SPA) infiltration on its tribological properties were studied. The results show that the NTA-SPA structural samples with medium texture density (ρ=16%) promoted the diffusion of the lubricant phase to the friction surface, resulting in a complete lubricant film. The COF stabilized at 0.2, and the wear rate decreased to 0.56×10-3 mm3/Nm, providing a more stable self-lubrication effect compared to the NTD-SPA sample.

Study of atomic diffusion behavior in diffusion welding of NiTi alloy - based on molecular dynamics

NiTi alloy with nearly equiatomic ratios of Ni and Ti, has a unique shape memory effect and biocompatibility. Atomic diffusion is a determinant factor for the diffusion welding of NiTi alloys joining. In general, the atomic diffusion may be mediated by the temperature, time and pressure and so on. Despite the importance of technology, Ni and Ti atoms’ diffusion mechanism, however, still remains un-elucidated. Few works have investigated the movement rules of atoms from the atomic scale. Molecular dynamics simulations of diffusion welding were performed for 200-800ps to investigate the diffusion process of the NiTi alloy composite plate at temperatures of 1000, 1100, 1200, and 1300K. The results show that the holding temperature had the greatest effect on diffusion, with pressure having the least effect. The diffusion coefficients of NiTi, Ni, and Ti were calculated at temperatures of 1000, 1100, 1200, and 1300K, respectively. The diffusion degree of Ni atoms was higher than that of Ti atoms. The diffusion coefficients of Ni and Ti atoms satisfied the Arrhenius equation, and the diffusion activation energy of Ni atoms was lower than that of Ti atoms. Furthermore, this study demonstrates at the atomic scale that the growth of the diffusion layer at high temperatures follows the parabolic growth kinetics law.

A cotton-derived carbon coating by thermolysis method for enhanced mechanical and bio-compatibility of NiTi alloy

To elevate the performance of NiTi alloy in medical devices, carbon coating derived from natural cotton has been successfully deposited onto the alloy surface using a one-step thermolysis method. Natural cotton soaked in copper sulfate was utilized as carbon raw material, and the deposition process was carried out at low vacuum and temperature requirements. The mechanical and bio-compatibility of the coating performance of resulted carbon layer has been studied comprehensively. The uniformity and mechanical properties of the carbon film prepared at 390 °C, with a holding time of 1–2 h, indicate that it should retain the alloy's excellent mechanical properties and superelasticity. Furthermore, the carbon coating improves the corrosion resistance compared to the raw alloy material. Observations of the proliferation and morphology of adhered human umbilical vein endothelial cells confirm the non-toxic effect of the carbon film. Additionally, the application of the carbon film significantly reduces the contact angle and enhances the adsorption of albumin in blood, suggesting that employing carbon films as bio-active layers is a viable approach to enhance the performance of NiTi-based blood implants and components.

Optimizing laser parameters and exploring building direction dependence of corrosion behavior in NiTi alloys fabricated by laser powder bed fusion

The microstructure and materials performance of Laser Powder Bed Fusion-fabricated (LPBFed) NiTi shape memory alloys (SMAs) varies depending on the laser parameters and building directions. This study initially optimized the laser processing parameters (laser power and scanning speed) for LPBFed NiTi SMAs to enhance their printing quality and mechanical properties. We determined that with fixed hatch spacing of 80 μm and layer thickness of 30 μm, the laser power of 105 W, and scanning speed of 600 mm/s produced the best results. Subsequently, the corrosion behavior of LPBFed NiTi SMAs built in three different building directions (0°, 45°, 90°) was investigated in 0.9 wt.% NaCl solution at 37 °C. The electrochemical data revealed that the corrosion current density (Icorr) decreased with increasing building direction angle (Icorr-90° <Icorr-45° <Icorr-0°). The corrosion resistance followed the order of 0° sample ˂ 45° sample ˂ 90° sample. These findings were attributed to the difference in the grain size and boundary density. Higher boundary densities enhanced the electron activity capacity and the element diffusion rates, facilitating the rapid formation of a protective film and thus improving the corrosion resistance. This new insight into the anisotropy of corrosion behavior relative to building directions can inform the design of NiTi-SMA products and improve their reliability in tissue engineering applications.

Mechanical behaviour of low-, medium- and high-entropy Ti-Hf-Zr-Ni-Cu-Co shape memory alloys

The mechanical behaviour was studied in twelve senary Ti-HfXZrX-Ni-CuXCoX alloys with various configuration entropies, which were regulated by the X value - concentration of doping elements (Hf, Zr, Cu, and Co) that varied from 1 at% to 17 at% and the concentration of the Ni group (Ni+Cu+Co) that varied from 49 to 51 at%. The stress vs strain curves were obtained at three temperatures (-100oC, 22oC and 100oC) at which the alloys were in different states (martensite, austenite, or a mixture of both). It was found that the senary Ti-Hf-Zr-Ni-Cu-Co alloys could undergo deformation via martensite reorientation, stress-induced martensitic transformation, and dislocation slip. The activation of the mechanisms depends on the deformation temperature compared to the temperatures of the martensitic transformations, as in the binary NiTi alloys. An increase in the X value from 1 to 10 at% increased the yield limit for dislocation slip in the austenite phase, while a further rise in the X value by 17 at% decreased this limit. An increase in the X value decreased the strain up to failure. The larger the [Ni] concentration or deformation temperature, the more pronounced the reduction in strain up to failure. An increase in X value from 1 to 5 at% significantly changed the fracture mechanisms from ductile to brittle due to the suppression of the dislocation movement.

Effect of grain size on precipitation and microstrain of nanocrystalline NiTi alloys

The effect of aging treatment on the microstructure, phase transformation behavior and mechanical properties of nanocrystalline NiTi alloy was studied. The nanocrystalline NiTi alloys with different grain sizes were acquired by cold drawing followed by annealing at 350–500 °C for 10 min. The annealed samples were aged at 250–400 °C for 48 h. The Ti3Ni4 precipitates were found in aged nanocrystalline NiTi alloys. In the sample with smaller average nanograin size, the precipitates were found at the edge of grain boundaries and little lattice strain was shown in R phase matrix. In the sample with larger average grain size, the precipitates were found in the nanograins and exhibited a coherent interface with the matrix. The nanocrystalline R phase NiTi matrix exhibited a significant compressive stress at the end of the coherent precipitate. The coherent precipitates in sample aged at 250 °C after annealing at 500 °C suppress the stress-induced R → B19′ phase transformation and increased the upper plateau stress. The precipitation in sample aged at 250 °C after annealing at 350 °C unable to suppress the martensitic transformation effectively.

Investigation of the Effect of Milling Time on Elemental Powders of Oxi‐Reduction Nickel and Hydrogenation–Dehydrogenation Titanium

Mechanical alloying (MA) is widely applied in the synthesis of blended elemental or prealloyed powders. This work evaluates the effect of milling time on elemental nickel and titanium powders produced by oxi‐reduction and the hydrogenation–dehydrogenation process, respectively. The powders are characterized by scanning electron microscopy, X‐ray diffraction, particle size, powder yield, and differential scanning calorimetry. It is observed that increasing the milling time promotes the formation of a structure composed of thin lamellae of nickel and titanium, which results in the beneficial effect of lowering the temperature for the formation of the intermetallic of the Ni–Ti system and in the powder yield achieved. The reduction of milling time in the MA process of NiTi alloys enhances technological efficiency by decreasing their overall processing time.

Effect of Addition of Rare Earth Metal (Ce) on the Microstructure, Mechanical Properties and Corrosion Behavior of NiTi Alloys

Effect of Addition of Rare Earth Metal (Ce) on the Microstructure, Mechanical Properties and Corrosion Behavior of NiTi Alloys

Mechanical properties of lander bionic buffer structure based on additive manufacturing

In order to meet the energy absorption requirements of the landing buffer, this paper starts with the buffer filling material of the buffer, draws on the Kelvin structure and spiral structure, and applies the engineering bionics principle to design and establish two structural models: a soccerball-like bionic structure and a multi-spiral bionic structure. Considering the energy absorption and reusability requirements of the lander buffer structure, the bionic structure sample is prepared by additive manufacturing technology and NiTi alloy with shape memory effect. The mechanical properties, energy absorption and recoverability of the sample are analyzed and verified by simulation and experiment. The results show that the accuracy of the numerical simulation is verified by comparing the force-displacement curves of the simulation test and the isometric static pressure test; the multi-spiral bionic structure has better mechanical properties, and its maximum energy absorption is 3096.23 J; the recovery rates of the two structures are as high as 98.02%and respectively 97.12%, and the recovery rate of the soccerball-like bionic structure is slightly higher. This study uses additive manufacturing to prepare the leg-type lander buffer bionic structure, which provides a reference for the bionic design of the lander buffer structure.

Selective laser melting fabrication of body-temperature shape memory NiTi alloy for 4D-printed orthopedic implants

ABSTRACT SLM fabrication of NiTi alloy is receiving increasing attention. However, the relatively high austenite transformation finish (Af) temperature is the main problem for biomedical applications. In this study, it was found that phase transformation temperature (PTT) increased with increasing laser power, decreasing scanning speed, and decreasing hatch spacing. The combination of PPs with an energy density of less than 75 J/mm³ is expected to yield the Af temperature below 37 °C. P = 80 W, v = 600 mm/s, and h = 70 μm were identified as the optimal combination because of a good tensile strength of 612 MPa and a peak shape recovery rate of 96.94%. Biocompatibility assessment showed that SLM-NiTi porous scaffolds supported pre-osteoblast survival and proliferation. A patient-specific mesh-like supporting prosthesis was designed to show the prospect of 4D-printed orthopedics implant. In clinical application, SLM-NiTi prosthesis could reduce bony window and facilitate easier insertion through compressive deformation.

Effect of Cu Alloying and Heat Treatment Parameters on NiTi Alloy Phase Stability and Constitutive Behavior

Effect of Cu Alloying and Heat Treatment Parameters on NiTi Alloy Phase Stability and Constitutive Behavior

Phase transition in the shape memory alloy NiTi described by the SCAN meta-GGA functional.

Climbing the ladder of density functional approximations has long been proposed to systematically improve the accuracy of first-principles calculations employing the density functional theory (DFT); however, up until now, the Perdew-Burke-Ernzerhof (PBE) functional at the second rung of the ladder, has dominated. Here, we present a study of the martensitic phase transition in NiTi based on abinitio molecular dynamics simulations and thermodynamic integration using the third-rung approximation of the strongly constrained and appropriately normalized (SCAN) meta-generalized gradient approximation (GGA). Although the predicted equilibrium lattice constants and formation enthalpy agree well with experimental data, the martensitic transition temperature (MTT) is overestimated by 94% (or 324K too high), compared with only 22% (77K) overestimation by PBE. The latent heat (q) is severely overestimated by SCAN as well. This deteriorated performance originates from the enlarged energy difference (ΔE) between the austenite and martensite phases, compared with the PBE result. Furthermore, a large variation (over 50meV/atom) in ΔE using different meta-GGAs indicates large variations in computed MTTs (∼400-500 K) and q, i.e., the predicted thermodynamic properties depend sensitively on the choice of meta-GGA. This would pose a serious problem when upgrading DFT calculations to the third rung. One possible solution is to add NiTi as a normsystem so that the revised SCAN meta-GGA could reproduce the PBE results of the relevant energy difference.

Enhanced mechanical properties and structural stability of Hf-modified NiTi alloy for advanced bearing materials

Ni-rich NiTi alloys suitable for bearing materials exhibit excellent properties such as high hardness, low modulus, non-magnetic, and corrosion resistance. In this study, the addition of Hf elements enhanced the mechanical properties and improved the structural stability of the alloys. The results indicate that the aging-treated Ni55Ti37Hf8 alloy demonstrates outstanding properties, with a Vickers hardness of 738.7 ± 12.5 HV, a nano-hardness of 9.6 ± 0.3 GPa, and an elastic modulus of 106.1 ± 2.2 GPa. The microstructure is primarily composed of the NiTi, Ni4Ti3 phase, and the H-phase. The structural stability of Ni55Ti37Hf8 alloy reached unprecedented levels, with hardness remaining at 673.1 ± 4.6 HV after heat treatment at 600°C for 100 h, meeting the requirements for bearing materials (exceeding 58 HRC). The Ni55Ti37Hf8 alloy exhibits superior thermal stability, making it a revolutionary option for the development of next-generation wear-resistant materials.

Directed energy deposition combined with interlayer remelting for improving NiTi wear resistance by grain refinement

Directed energy deposition of NiTi coatings has received much attention, however, its performance is difficult to meet the increasing requirements in the engineering field. In order to refine the grains to improve wear resistance, a novel interlayer remelting method for fabricating NiTi alloys by directed energy deposition is proposed in this study. The influence of laser interlayer remelting parameters on lattice structure, phase transformation behavior, microstructure, crystallographic evolution, and microhardness was thoroughly analysed in comparison. Good formability is demonstrated after interlayer remelting, while the high energy density leads to microstructure refinement and eutectic regions are observed between dendrites. The grain size decreases with increasing remelting speed, which is due to the faster cooling rate having a greater degree of subcooling with more nucleation points. The faster interlayer remelting speed shows a higher microhardness (586 HV0.2) with higher wear resistance, which is attributed to its finer grain size and significant grain boundary strengthening. Reciprocating sliding wear experiments show that the wear resistance is improved after interlayer remelting, especially at a load of 30 N, the specific wear rate is 1.35 * 10−4mm3/Nm, which is only 47 % of that of the untreated sample. This study proposes a technique to achieve synergistic enhancement of microhardness and sliding wear properties of reinforced coatings, which provides a theoretical basis for the application of NiTi coatings in engineering and extends the field of additive manufacturing.

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.