Surface Of NiTi Alloy Research Articles

Characteristic variations in a pulsed‐anodized NiTi alloy surface by the lower voltage setting

Pulsed anodization of a nearly equiatomic NiTi alloy in HNO3 leads to the formation of a nearly Ni‐free oxide layer, resulting in the suppression of Ni‐ion release from the alloy surface. The core technology involves introduction of a lower‐voltage period, which promostes chemical reactions between the alloy and electrolyte, to obtain a surface layer with better corrosion protection. In this study, a higher voltage of 3.5 V was applied, and the lower voltage was varied within 0–3.5 V. As the lower voltage was increased, nanometer‐sized pores present on the anodized surface gradually expanded, while the layer thickness decreased. Although the corrosion protectivity of the layer did not change significantly during the electrochemical experiments, the amount of Ni‐ion released into the physiological solution significantly decreased when the voltage was below 1.8 V. X‐ray photoelectron spectroscopy analyses revealed the presence of Ni (OH)2 on the topmost surface, and its concentration decreased at a voltage <1.8 V. Lower voltages affected the concentration of Ni (OH)2 on the topmost surface and thus considerably influenced the Ni‐ion release behavior. These findings will contribute to the production of NiTi alloys with improved biocompatibility.

Nickel nitride-mediated nitric oxide generation for combating implant-associated infections

NiTi alloys are widely used in the fabrication of biomedical implants, and it is essential to endow them with selective antibacterial properties to avoid implant-associated infection. In this study, nickel nitride (Ni3N), as a promising new inorganic nitric oxide (NO) donor, was in situ constructed on the surface of NiTi alloys through a straightforward two-step plasma immersion ion implantation (PIII) strategy. Nickel sites were first exposed by physical bombardment with argon or metal plasma, followed by reaction with nitrogen plasma to form Ni3N. Ni3N can disrupt the transmembrane proton electrochemical gradient by capturing protons to produce ammonia species (NHx), resulting in the accumulation of reactive oxygen species (ROS) as a result of bacterial metabolic disruption. On the other hand, the generated NHx can further react with ROS to produce NO and reactive nitrogen species (RNS). As a result, the Ni3N films exhibited more than 99 % antibacterial efficiency against both gram-negative and gram-positive bacteria. They also demonstrated effective antibacterial properties in a rat subcutaneous implant model. In addition, the modified NiTi alloys exhibit good corrosion resistance and cytocompatibility. This study provides a green, safe, and inexpensive method for constructing metal nitride films on implant surfaces and offers new ideas for the clinical design and fabrication of novel antibacterial implants.

Experimental study on ultrasonic-assisted electrochemical polishing of NiTi alloy

NiTi alloy has a wide range of applications due to its unique superelasticity and shape memory, the superelastic function of NiTi alloy made it had been applied in building shock absorption, advanced bearings and other scenes, the shape memory function made it also applied in the fields of aerospace engine heat exchanger, cardiac medical stent and so on. In order to made NiTi alloy better applied in practice and improve its surface quality, it was crucial to polish it. In this paper, a new method of ultrasonic-assisted electrochemical polishing of NiTi alloy was innovatively proposed, and an ultrasonic electrochemical polishing device was built independently. The effects of ultrasonic amplitude, voltage and temperature on roughness were explored by Box-Behnken experimental design method. The results show that after ultrasonic-assisted electrochemical polishing, the roughness Ra had been reduced from about 2 μm to the minimum of 0.048 μm. The surface quality of NiTi alloy was improved. The impact of micro-jet of cavitation bubble on NiTi alloy mainly occurs in the early stage, and the equivalent stress on the surface of NiTi alloy was annular, showing an increasing and decreasing trend. In the whole ultrasonic electrochemical polishing solution, a large number of micro-jets will impact the surface of NiTi alloy, thus realizing the material removal. This study enhances traditional electrochemical polishing techniques by integrating ultrasonic energy fields, thus broadening the scope of electrochemical polishing applications. Additionally, it presents a novel approach and establishes a foundation for the polishing of NiTi alloys with intricate geometries in additive manufacturing.

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.

Enhanced photocatalytic antibacterial activity of Au-coated Ni–Ti–O nanotubes for biomedical applications

Nickel-titanium (NiTi) alloy is a smart material exhibiting superelasticity, contributing to low stiffness and facilitating integration with bone structures. However, NiTi alloy's bioactivity and antibacterial activity limit its dental applications. In this study, we fabricated nickel titanium oxide (Ni–Ti–O) nanotubes with the potential for bioactivity and photocatalytic properties on the surface of NiTi alloy. Specifically, we applied a coating of gold (Au) nanoparticles to the surface of Ni–Ti–O nanotubes, in order to leverage the antibacterial activity through the photocatalytic effect under 470 nm visible light. Field-emission scanning electron microscopy (FE-SEM) and high-resolution transmission electron microscopy (HR-TEM) observations revealed that Au was deposited mainly at the top surface of Ni–Ti–O nanotubes (diameter: 12.76 ± 2.91 nm, height: 721.12 ± 50.25 nm). X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and diffuse reflectance spectroscopy (DRS) analyses revealed that the Ni–Ti–O nanotubes were NiTiO3 crystalline phases with low crystallinity. Therefore, based on the methylene blue (MB) degradation test, the photocatalytic effect was only achieved under visible light at 470 nm, facilitated by the presence of Au. The antibacterial colony forming unit test and enzymatic activity tests demonstrated that Au-coated Ni–Ti–O nanotubes displayed excellent antibacterial activity under 470 nm visible light irradiation, which was also attributed to photocatalytic effect. Consequently, the combination of Au-coated Ni–Ti–O nanotubes and visible light-based photofunctionalization holds promise for expressing antibacterial properties in dental applications.

Effects of adsorption of O2 and H2O molecules on the corrosion behavior of the NiTi alloy surface: a DFT investigation.

The influence of O2 and H2O adsorption significantly affects the electrochemical corrosion of the NiTi alloy, with unresolved corrosion disparities between the NiTi-B2 and NiTi-B19' phases. Density functional theory (DFT) calculations are utilized in this investigation to explore the adsorption of O atoms at varying coverages on the NiTi-B2(110) and NiTi-B19'(010) surfaces. The goal is to elucidate their oxidation behavior differences. Subsequently, the effect of O adsorption on the dissolution trends of these phases is assessed by inducing Ni/Ti vacancies to simulate alloy dissolution thermodynamically. Additionally, interactions between H2O molecules and O-pre-adsorbed NiTi alloy surfaces are examined to simulate the atomic evolution of the oxidized surface under exposure to humid air and corrosive solutions. The findings indicate a propensity of the NiTi-B19' phase to react with O, forming an oxide film more readily than the NiTi-B2 phase. O adsorption facilitates Ni dissolution and retards Ti dissolution on the alloy surface. Higher O coverage promotes easier dissolution of Ni and Ti atoms on the NiTi-B2(110) surface compared to the NiTi-B19'(010) surface, underscoring the greater corrosion resistance of the NiTi-B19' phase. Both clean and O-pre-adsorbed NiTi alloy surfaces physically adsorb H2O molecules. Notably, an O monolayer substantially mitigates the detrimental effects of H2O molecules on the corrosion resistance of alloy surfaces. This research contributes to a deeper comprehension of the corrosion mechanisms in NiTi alloys.

Repetitive Nanosecond Laser-Induced Oxidation and Phase Transformation in NiTi Alloy

NiTi shape memory alloys, known as Nitinol, are highly valuable in medical fields for their unique attributes, including superelasticity, wear resistance, and biocompatibility. Laser treatment provides precise control over surface characteristics, enhancing biocompatibility. This study focuses on the effects of laser irradiation on NiTi alloy surfaces, particularly considering the number of laser scans and their impact on surface features. Even at low laser power, multiple high-frequency scans significantly alter surface roughness and induce phase transformation. After 16 repeated laser irradiations, amorphous Ti oxide transforms into crystalline anatase. Remarkably, anatase can further transform into rutile due to the influence of Ni nearby and TiO, due to insufficient oxygen content. The most notable outcome is the formation of a thick Ti oxide layer, causing unbound Ni to emerge on the surface, resulting in a Ni oxide layer. These findings highlight the importance of precisely adjusting laser parameters to achieve tailored surface properties for medical applications, addressing challenges and enhancing biocompatibility.Graphical abstract

Feasibility study on ultraprecision micro-milling of the additively manufactured NiTi alloy for generating microstructure arrays

Nickel-titanium (NiTi) alloy has unique functional properties in medical and microelectronics products. Recently, additive manufacturing has become an attractive way of fabricating NiTi alloy. However, the study of generating microstructure arrays on additively manufactured (AMed) NiTi alloy surfaces remains unclear. Motivated by this, this study proposes the ultraprecision micro-milling (UMM) process to generate microstructure arrays and perform a systematic investigation. First, selective laser melting, as a popular additive manufacturing way, was utilized to fabricate the AMed NiTi alloy. Then, the UMM process was carried out to machine these samples. After the machining experiments, a mirror surface with a surface roughness of 0.014 μm can be acquired, which demonstrates the good machinability of the AMed NiTi alloy. Moreover, the micro-groove array and micro-pillar array with low machining errors were machined on the AMed NiTi alloy surfaces, which verifies the effectiveness of the proposed machining process. The corresponding cutting forces, tool conditions, and chip morphologies were studied to fully understand the machining mechanism of the AMed NiTi alloy. Besides, the surface wettability of microstructure arrays was also quantitatively analyzed. Therefore, this study provides a facile and effective machining process for generating microstructure arrays on the AMed NiTi alloy surfaces.

Dealloying and polydopamine/silver coating on NiTi alloy for improved antibacterial activity

Improved bone bonding ability and antibacterial activity are two critical requirements for implants. In this work, novel dual surface modifications of dealloying and polydopamine/silver coating on a NiTi alloy were conducted. Scanning electron microscopy (SEM) results show a porous layer with interconnected micro- and nano-pores on the dealloyed NiTi alloy. Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) results confirm the formation of a polydopamine/silver coating on the surface of the dealloyed NiTi alloy. The silver nanoparticles (58.9 nm, in the polydopamine/silver coating) on the dealloyed NiTi alloy surface are smaller when compared with pristine NiTi alloy (73.1 nm). Moreover, the dealloyed NiTi alloy with polydopamine/silver coating exhibits better antibacterial activity against Escherichia coli (99.7%) and Staphylococcus aureus (99.4%) than pristine NiTi alloy with the same coating (97.3% and 96.5%, respectively), due to the larger surface area, higher silver content, and smaller silver nanoparticles that trigger more silver ion release. The combined dealloying and coating method is an effective way of increasing antibacterial activity of NiTi alloys. The findings presented in this work may provide a new guidance for the surface modification of NiTi implant materials.

Construction and parameter optimization of LPBF-NiTi alloy bionic superhydrophobic surface based on laser processing

Nickel-titanium (NiTi) is the most ordinarily used shape memory alloy (SMAs), which has important implications in aerospace, medical devices and so on. However, NiTi parts were limited in their application scope and ability due to the difficulty of processing. Until the appearance of laser powder bed fusion (LPBF) technology, it overcame NiTi alloy preparation's multiple challenges and became the preferred method to fabricate NiTi alloy. Nevertheless, the NiTi parts fabricated by LPBF that have a great shortage still exist in corrosion resistance. Therefore, in this paper, a series of micro-nano structures with different characteristics were constructed in LPBF-NiTi by orthogonal experiment for the first time, which wants to explore the degree of influence of various parameters on the wettability of samples. After variance analysis, the nanolaser processing parameters which are most suitable for constructing lotus leaf structures on NiTi alloy surfaces are obtained. The surface morphology and composition were studied by SEM, XRD, EDS, and XPS, respectively. Finally, the corrosion resistance of samples was tested by electrochemical analysis. The results show that the laser power during processing has the greatest influence on the surface morphology of LPBF-NiTi alloy. And the wettability is affected by surface morphology and –CF/-CF2 adsorption. Furthermore, we compared the corrosion resistance of the superhydrophobic samples which was obtained based on the variance analysis with that of the substrate in 3.5 wt% NaCl solution. The result shows that the corrosion resistance and corrosion stability of superhydrophobic samples are brilliantly increased compared with the substrate.

Preparation of ROS‐Responsive Exosome Coating of Nitinol Material for Making the Neurointerventional Stent

AbstractNitinol (NiTi) alloy is an ideal material for preparing neurointerventional stents due to its excellent mechanical properties and biocompatibility. However, NiTi stents without surface‐specific functionalization cause a high rate of stent thrombosis and in‐stent restenosis after implantation. In ischemic stroke, exosomes have a role in regulating nervous system development, regeneration, vascular remodeling, and neuroinflammation. In this work, the effect of exosome coating on the biocompatibility of NiTi alloy is evaluated. NiTi alloy is successively immersed in relevant solution (sodium alginate, 3‐aminophenylboronic acid, distearoylphosphatidylethanolamine, and exosomes) to form ROS‐responsive exosome coated surfaces. In vitro experiments (platelets, endothelial cells, smooth muscle cells, and macrophages) and in vivo subcutaneous implantation experiments are performed to test coatings for biocompatibility. The results show that the modified NiTi alloy surface has high hydrophilicity, which has the functions of inhibiting platelet aggregation, promoting endothelialization, inhibiting smooth muscle cell migration, anti‐inflammatory, and good tissue biocompatibility. This study develops exosome neurointerventional stent coating as a bioactive drug via reactive oxygen species accumulation in lesions, thus targeting drug release, inhibiting intimal hyperplasia, and reducing inflammation and thrombosis.

Controllable fabrication and adjustment of optical anti-reflectance micro-nano structures on NiTi alloy surface made by nanosecond laser circular scanning

The scanning path plays a very important and novel breakthrough in preparing optical anti-reflectance micro-nano structures on the surface of NiTi alloy. Compared with simple grids and grating structures, circular structures are more likely to form closed structures under high heat accumulation nanosecond laser processing conditions. These relatively closed circular structures will further help reduce optical reflection performance. In this study, some designed surface micro-nano structures are prepared by nanosecond laser circular scanning, which are the scanning pitch (plan A), the scanning angle (plan B), and the multi-pass scanning (plan C), respectively. The influence of the different micro-nano structures, surface roughness and elemental content on the surface optical anti-reflectance are also investigated. The results indicate that the best optical anti-reflectance micro-nano structures is obtained by 10-pass scanning among plan C. and which is 5% during the measurement wavelength of 400 nm ∼ 800 nm. At the same time, the mechanism is also discussed for changes in the light trapping effect of the laser textured surfaces.

Cavitation erosion behavior and anti-cavitation erosion mechanism of NiTi alloys impacted by water jet

The cavitation erosion behavior and anti-cavitation erosion mechanism of NiTi alloys was explored by water jet equipment conforming to ASTMG134 international standard. The cumulative mass loss rate of NiTi alloys changed slowly by water jet impact within 180 min, then increased sharply and decreased obviously after 240 min. When the impact time lengths were prolonged from 30 min to 60 min, the macroscopic deformation did not significantly increase on the surface of the sample. It was mainly due to the superelasticity of NiTi alloys, resulting in a prolonged cavitation incubation period of NiTi alloys impacted by water jet. When the impact time length was 180 min, work hardening occurred along with the plastic deformation, and cavitation pits appeared on the surface of the sample. When the impact time lengths were extended from 240 min to 300 min, there was no obvious increase in cavitation pits and the material spalling. This is mainly due to the formation of new grains by the recombination of dislocations on the surface and the piling up of dislocations on the grain boundaries at a distance from the impact surface of NiTi alloys. The formation of new grains has consumed high-density dislocation and distortion energy, which can reduce the cavitation erosion damage on NiTi alloys caused by water jet impact. With the increase of water jet impact time, the surface of NiTi alloys undergoes a process of plastic deformation→ work hardening→ increase in dislocation density→ grain refinement→ proliferation of refined grains. Additionally, the residual stress of NiTi alloys with different impact time lengths remained high and they could inhibit the initiation and propagation of cavitation cracks.

DFT investigation of the dissolution trends of NiTi alloys with the B2 and B19' phases during the initial oxidation stage.

The selective corrosion of NiTi alloys was studied using density functional theory calculations, and the dissolution trends of the NiTi-B2 and NiTi-B19' phases in the initial oxidation stage were compared to predict their corrosion difference. The dissolution process of Ni and Ti was simulated by creating Ni or Ti vacancies on the unoxidized and oxidized NiTi alloy surfaces. The results show that the surface vacancy formation energy of Ti vacancies is higher than that of Ni vacancies, indicating that Ti is more difficult to dissolve than Ni. Furthermore, oxidation promotes and impedes the dissolution of Ni and Ti, respectively. This study improves the fundamental understanding of the corrosion mechanism of NiTi alloys.

Преимущественное распыление сплава NiTi атомарными и кластерными ионами

X-ray photoelectron spectroscopy was used to study the evolution of NiTi alloy surface composition under bombardment with atomic and cluster argon ions. A strong enrichment of the surface with nickel was found for both atomic and cluster ions, which is inconsistent with contemporary understanding of preferential sputtering. Possible reasons for this result are discussed.

Corrosion characterization of NiTi alloy by femtosecond laser surface processing

AbstractThe study of the corrosion resistance of NiTi alloy surfaces with different wettabilities is important to achieve improvements in biocompatibility. In this study, a femtosecond laser was used to process different wettability surfaces on the NiTi alloy. The corrosion resistance of the surfaces was examined via potentiodynamic polarization and electrochemical impedance spectroscopy. Scanning electron microscopy and X‐ray photoelectron spectroscopy were used to analyze the morphology and chemical composition of the surfaces. The findings demonstrate that when an original oxide film is destroyed by femtosecond laser processing with a low laser fluence, hydrophilic or hydrophobic surfaces are more vulnerable to erosion. The corrosion resistance of superhydrophilic surfaces is improved to a certain extent, whereas superhydrophobic surfaces exhibit excellent corrosion resistance. Superhydrophilic surfaces are protected from further corrosion by the formation of a dense oxide film after corrosion, whereas superhydrophobic surfaces can inhibit corrosion because of their thicker oxide film and additional air film produced by air trapped in the micro/nanostructure.

Formation of tantalum coatings with a given structure on the surface of niti alloy by magnetron sputter deposition

Way for applying tantalum coating with a given structure to the surface of an alloy with a shape memory effect NiTi to increase the biocompatibility of implants from this alloy is presented. The coating was synthesized by direct current (DC) magnetron sputtering. The changes sequence of the structural-phase states depending on the thickness of the coating, that is, the rate of its deposition, has been established. It is shown that at a low magnetron power, ∼14 W in present study, a single-phase α-Ta coating with a bcc structure and a high degree of perfection of the crystal lattice is successfully synthesized on the titanium nickelide surface.

Adhesion and corrosion resistance of polycaprolactone coating on NiTi alloy surface after alkali heat pretreatment

Selective laser melting of nickel-titanium alloy (SLM-NiTi) can precisely control the size of the sample molding structure and has attracted extensive attention due to its special superelasticity and shape memory effect. However, the biological inertness and poor corrosion resistance of SLM-NiTi alloy limit their wide application as biomedical implant materials. In this study, polycaprolactone (PCL) coating was prepared on SLM-NiTi alloy by dipping and pulling method, and the effects of alkali heat pretreatment on the morphology, adhesion, corrosion resistance, long-term stability and biomineralisation of the PCL coatings were investigated. The results showed that PCL coating can substantially improve the performance of SLM-NiTi alloy, and the PCL coating after alkali heat pretreatment has higher adhesion (increased from 1,747 to 2,498 mN) and lower corrosion current density (reduced by about an order of magnitude compared to PCL coating alone). In addition, the necessary stability, biomineralisation and biocompatibility ability of coatings were also further improved. Therefore, the alkali heat pretreated PCL-coated SLM-NiTi alloy has good application prospects in implants due to its superior properties.

Achieve superior interfacial bonding force with excellent corrosion resistance on polycaprolactone coating by nanosecond laser machining of LPBF-NiTi alloy

• Nanosecond laser constructed the surface micro-nano structure of LPBF-NiTi alloy. • Nanosecond laser improves the bonding force of PCL coating. • Nanosecond laser enhanced the corrosion resistance of PCL coating. Polycaprolactone (PCL) is a non-toxic and harmless polymer material with good biocompatibility and histocompatibility and has been widely used in the field of biomedicine, especially as a coating material. However, the interfacial bonding force of PCL coating has always been the key factor affecting their application. In this paper, a micro-nano graded laser powder bed fusion (LPBF) NiTi alloy surface was created by nanosecond laser pretreatment innovatively and observed by scanning electron microscopy. Nano-scratch experiments were performed to assay the interfacial bonding force, and the corrosion behavior was carried out by the potentiodynamic polarization test. The results show that the high surface roughness and micro-nano hierarchical structure of the nanosecond laser machining surface conduce to achieve superior interfacial bonding force compared with the mechanically polished sample. Meanwhile, the 80 μJ-PCLcoated sample can obtain the most excellent corrosion resistance in simulated body fluids (SBF), clearly indicating nanosecond laser machining is a promising pretreatment for enhancing the interfacial bonding force and anti-corrosion of coatings.

Ultrafast flame coating of carbon and chemical vapor deposition of graphene on NiTi alloy to enhance its corrosion resistance

To study their surface protection performance, both graphene and carbon layers have been deposited onto the surface of NiTi alloy via the common chemical vapor deposition (CVD) and a facile flame coating technique, respectively. The latter can be accomplished within tens of seconds with the combustion flame itself as the carbon source and alloy substrate as catalyst. The carbon layer not only inhibits effectively the Ni2+ releasing from NiTi alloy, but also displays lower surface roughness and higher corrosion resistance than that of the graphene coating. The effect of the flame coating time on the performance of resulted carbon layer has been studied comprehensively. The lowest corrosion current density (1.6 μA/cm2) of the flame coated alloy in simulated body fluid has been achieved by adjusting the flame time to be just 30s. This value is much less than that of graphene coating (2.4 μA/cm2) in the same test conditions. And it gets even less in 3.5 wt% NaCl solution (1.3 μA/cm2), implying the potential application of the flame coating method for more corrosive marine environments. Also, the Ni2+ releasing concentration of NiTi/C-30s is decreased to be around one fourth that of bare NiTi. Moreover, the excellent scratch resistance of the carbon layer and its strong adhesion to NiTi substrate have been also confirmed by both the cross-cut and scratching tests. Furthermore, both the elastic modulus and hardness of the alloy decreased marginally after the fast and mild-temperature flame coating process according to the nano-indentation test results. Compared with traditional surface engineering approaches, the flame coating method has many advantages, such as simple and fast process, high protective performance, environmental-friendly fabrication and protection. All of these benefit its promising application in various fields.