Surface characteristics and corrosion behavior of Ti-Al-Zr alloy implanted with Al and Nb

Ti-Al-Zr alloys were implanted with Al and Nb to doses ranging from 1 × 10¹⁷ to 1 × 10¹⁸ ions cm⁻². The valence states of element on the sample surfaces were analyzed by X-ray photoelectron spectroscopy (XPS). Glancing angle X-ray diffraction (GAXRD) was employed on the as-implanted specimens to understand phase formation. X-ray diffraction (XRD) measurement revealed α-Ti on Al-implanted samples and (α + β)-Ti on Nb-implanted samples. The tendency was observed in increasing corrosion resistance from α- toward (α + β)-phase. In deaerated 5 M HCl, the ion-implanted Ti-Al-Zr surface containing Nb-stabilized β-phase was spontaneously passive, while Al-implanted surface displaying an active/passive behavior. In the aerated solution with pH = 10, all the implanted surfaces are passive. Enhanced reoxidation was confirmed on implanted surfaces by Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) analysis. The corrosion in the solution with pH = 10 was governed by a predominantly TiO₂ surface film. The cathodic kinetics was seen to affect the corrosion behavior in 5 M HCl.     

Surface characteristics, corrosion behavior, and antibacterial property of Ag-implanted NiTi alloy

NiTi shape memory alloy was modified by Ag ion implantation with different incident doses to improve its antibacterial property. The atomic force microscopy, auger electron spectroscopy, and X-ray photoelectron spectroscopy show that the surface of NiTi alloy is covered by TiO₂ nano-film with embedded pure Ag with a peak concentration of 5.0 at% at the incident dose of 1.5 × 10¹⁷ ions·cm^?2, and Ni concentration is reduced in the superficial surface layer. The surface roughness reaches the maximum value nearly twice higher than the control sample at the incident dose of 1.5 × 10¹⁷ ions·cm^?2. The potentiodynamic anodic polarization curves show that the Ag-implanted NiTi samples possess higher self-corrosion potential (E _corr) and lower self-corrosion current density (i _corr) but lower breakdown potential (E _br). Therefore, the corrosion resistance of the Ag–NiTi is comparable to, if not better than, the untreated NiTi. The antibacterial tests reveal that there is a distinct reduction of the germ numbers on the Ag–NiTi, which is due to the direct contact between Ag and germ, and enhanced by the leaching Ag ions.     

Surface treatment of NiTi shape memory alloy and its influence on corrosion behavior

Influence of various surface treatments of a NiTi alloy on its surface chemistry and corrosion resistance was studied. NiTi (50.9 at.% Ni) alloy was subjected to mechanical polishing (MP), chemical etching (CHE) in an acidic bath, combination of mechanical polishing and oxidation at 530 °C/10 min in air (MPO) and combination of chemical etching and oxidation at 530 °C/10 min in air (CHEO). Scanning electron microscopy, X-ray photoelectron spectroscopy and Raman spectrometry were used for the surface examination. Corrosion behavior was determined by measuring potentiodynamic curves and nickel release into a model physiological solution with pH = 2. It was shown that oxidation at 530 °C has a slightly retarding effect on the nickel release in the case of MP material. However, in the case of CHE material, oxidation negatively influences corrosion, i.e. it strongly accelerates the nickel release, despite that it produces a relatively thick Ni-depleted oxide layer. Chemical etching was evidenced to produce the best corrosion performance in terms of nickel release. By comparing the MP and MPO sample, it was evidenced that oxidation significantly enhances susceptibility to the pitting corrosion. The findings obtained in our work were discussed in relation to variations in the surface chemistry and structure after different treatments.     

Enhanced wear resistance of NiTi alloy by surface modification with Nb ion implantation

Niobium ion implantation is found to significantly decrease the friction coefficient and improve wear resistance of NiTi shape memory alloy. Scanning electron microscope(SEM) observations indicate that surface grooves formed on NiTi during the mechanical polishing are removed after Nb ion implantation. Dry friction tests show that Nb implanted NiTi samples exhibit a lower friction coefficient, narrower wear tracks, fewer wear debris generated, 46 %–62 % reduction in wear width, and29 %–49 % reduction in wear depth compared with the untreated NiTi. Wear resistance is related to the incident parameters, and the Nb implanted NiTi with the incident dose of 2.5 9 1017ionsácm-2, and incident current of2 mA behaves the best wear performance. The lubricating of Nb2O5, good oxidation resistance of Nb in NiTi, and increased micro-hardness of NiTi are responsible for the enhanced wear resistance.     

Nitrogen ion implantation and in vitro corrosion behavior of as-cast Ti-6Al-7Nb alloy

In the present investigation, surface modification of Ti-6Al-7Nb alloy with nitrogen ions is considered as a method to improve its performance with respect to corrosion. Nitrogen ion was implanted on Ti-6Al-7Nb alloy at an energy of 70 and 100 keV using a 150 keV accelerator at different doses between 1×10¹⁶ and 3×10¹⁷ ions/cm². Gracing incidence X-ray diffraction was employed on the implanted specimens to understand the phases formed with increasing doses. The implanted samples were subjected to electrochemical study in Ringer's solution in order to determine the optimum dose that can give good corrosion resistance in a simulated body fluid condition. The OCP of the implanted specimens were found to shift in the noble direction in comparison with unimplanted specimen. The passive current density and area of the repassivation loop were found to decrease as the dose values increased. The electrochemical impedance spectroscopic results indicate that the polarization resistance was higher for the dose of 2.5×10¹⁷ ions/cm² implanted at both energy of 70 and 100 keV. Nitrogen ion implantation enhanced the passivability and reduces the corrosion kinetics of the alloy surface with increasing tendency for repassivation. Nature of the surface and reason for the variation and improvement in corrosion resistance are discussed in detail.     

Surface characterization and mechanical property of TiN/Ti-coated NiTi alloy by PIIID

A hard and adherent TiN/Ti thin film of approximately 3 μm in thickness was deposited on the surface of Ti-50.6 at.% Ni alloy by the PIIID technique. The surface composition and chemical state of the coated samples were evaluated by XPS. The XPS results indicate that titanium oxide and titanium oxynitride were present on the TiN surface. The spectra of Ti 2p, N 1s, O 1s and C 1s electrons before and after the film being sputter etched were also discussed. Scanning electron microscopy (SEM) and energy disperse spectroscopy (EDS) analyses demonstrate that an interfacial layer, containing Ti, N and Ni, was formed at the interface between the TiN and Ti coatings. Sliding wear tests show that the TiN coating significantly reduces the friction coefficient and improves wear resistance of the NiTi alloy.     

In vitro corrosion behavior of TiN layer produced on orthopedic nickel-titanium shape memory alloy by nitrogen plasma immersion ion implantation using different frequencies

In the present work, the NiTi surface was modified by nitrogen plasma immersion ion implantation (PIII) in an effort to improve the corrosion resistance and mitigate nickel release from the materials. The implanted nitrogen depths and thicknesses of the surface TiN barrier layers were varied by changing the pulsing frequencies during PIII. In order to determine the optimal parameters including the pulsing frequencies, electrochemical tests including open circuit potential (OCP) measurements and potentiodynamic polarization tests were conducted on the untreated and N-implanted NiTi in simulated body fluids (SBF). Our results reveal that the nitride layer produced using a frequency of 50 Hz has the best stability under the OCP conditions and the TiN layer produced using 200 Hz has the highest potentiodynamic stability after immersion in SBF for a long time. The observation can be correlated to the temperature during PIII and the thickness of TiN layer. The TiN layer on the NiTi surface favors deposition of Ca-P composites thereby compensating for the instability of the TiN layer produced at a higher frequency.     

Surface analysis and corrosion behavior of zirconium samples implanted with yttrium and lanthanum

Zirconium specimens were implanted with yttrium and lanthanum ions with a fluence ranging from 1×10¹⁶ to 1×10¹⁷ ions/cm² at approx. 130 °C, using a metal vapor vacuum arc source at an extraction voltage of 40 kV. The surfaces of the implanted samples were then analysed. The valence states of elements in implanted surface layer were analysed by X-ray photoelectron spectroscopy (XPS), which showed that yttrium existed in the form of Y₂O₃, and lanthanum existed in the form of La₂O₃. Depth distributions of elements in the implanted surface of samples were obtained by Auger electron spectroscopy (AES), which showed that the oxide film of zirconium substrate became thicker with increasing implantation fluence, the thicknesses of the oxide films reached the maximum approximately to the fluence of 1×10¹⁷ ions/cm². Rutherford back-scattering indicates that a profile of La appears in Zr around the depth of 30 nm, which also indicates that a serious sputtering occurred during the (La+Y) 1×10¹⁷ ions/cm² implantation. The potentiodynamic polarization technique was employed to evaluate the aqueous corrosion resistance of the implanted-zirconium samples in 0.6 M H₂SO₄. It was found that a significant improvement was achieved in the aqueous corrosion resistance of zirconium compared with that of as-received zirconium when the fluence is smaller than 5×10¹⁶ (Y+La)/cm². The mechanism of the corrosion behavior of the implanted-zirconium samples was discussed.     

In-situ synchrotron X-ray diffraction investigation on deformation behavior of Nb/NiTi composite during pre-straining process

The mechanisms responsible for deformation behavior in Nb/NiTi composite during pre-straining were investigated systematically using in-situ synchrotron X-ray diffraction, transmission electron microscopy and tensile test. It is shown that upon loading, the composite experiences elastic elongation and slight plastic deformation of B19′, B2 and β-Nb phases, together with the forward stress-induced martensitic (SIM) transformation from B2 to B19′. Upon unloading, the deformation mechanisms of the composite mainly involve elastic recovery of B19′, B2 and β-Nb phases, compression deformation of β-Nb phase and incomplete B19′→B2 reverse SIM transformation. In the tensile loading?unloading procedure, besides the inherent elastic deformation and SIM transformation, the (001) compound twins in B19′ martensite can also be conducive to the elastic deformation occurring in B19′-phase of the composite. Therefore, this composite can exhibit a large recoverable strain after unloading owing to the elastic deformation, and the partially reversible and consecutive SIM transformation together with the (001) compound twins.     

铸态镍钛形状记忆合金的断裂行为及显微组织(英文)

通过真空自耗电极熔炼法制备等原子比镍钛形状记忆合金。为了研究其断裂力学性能,进行铸态镍钛形状记忆合金的拉伸和压缩实验。为了更好地理解镍钛形状记忆合金的组织演变及断裂行为,分析铸态镍钛形状记忆合金及其断裂样品的显微组织。在拉伸加载下,镍钛形状记忆合金在750°C时具有较高的塑性,表现为韧性断裂,但在室温和-100°C时表现出较差的塑性,具有解理断裂和穿晶断裂的特征。在-100°C的压缩加载下,铸态镍钛形状记忆合金发生剪切断裂,剪切断裂面法线与压缩轴呈45°,具有解理断裂的特征,裂纹经由穿晶断裂而扩展。     

Surface characterization of passive film formed on nitrogen ion implanted Ti-6Al-4V and Ti-6Al-7Nb alloys using SIMS

The aim of this paper is to study the effect of N⁺ ion implantation on corrosion and phase formation on the implanted surfaces of Ti-6Al-4V and Ti-6Al-7Nb alloys. Nitrogen ion was implanted on Ti-6Al-4V and Ti-6Al-7Nb alloys at an energy of 70 and 100 keV, respectively using a 150 keV accelerator at different doses ranging from 5 × 10¹⁵ to 2.5 × 10¹⁷ ions/cm². Electrochemical studies have been carried out in Ringer’s solution in order to determine the optimum dose that can give good corrosion resistance in a simulated body fluid condition. The implanted surfaces of such modified doses were electrochemically passivated at 1.0 V for an hour. Secondary ion mass spectroscopy was used to study and characterize titanium oxide and titanium nitride layers produced on implanted surface and to correlate them with the corrosion resistance. The nature of the passive film of the implanted-passivated specimen was compared with the unimplanted-passivated as well as as-implanted specimens.     

Cr离子注入镍钛合金的表面组织结构

针对镍钛合金(NiTi)进行3种不同浓度Cr离子注入,采用扫描电子显微镜、三维白光形貌干涉仪、小角度掠射X射线衍射仪、X射线光电子能谱仪分析了离子注入前后镍钛合金表面形貌、粗糙度、组织结构及化合态。结果表明,随着注入Cr离子浓度的增大,镍钛合金表面更加平整,粗糙度变小。所有注入试样表面形成了近60nm厚的注入膜层,主要成分为三氧化二铬和铬碳化合物,并且随Cr离子注入剂量的增加,三氧化二铬和铬碳化合物的含量增加。     

Preparation and characterization of hydroxyapatite/titania composite coating on NiTi alloy by electrochemical deposition

NiTi alloy is used as biomaterial due to its unique properties, but the high content of Ni (about 50 at.%) in biomedical NiTi is of concern. Hydroxyapatite/titania composite coating was directly electrodeposited on the surface of NiTi alloy. The coated samples were characterized using X-ray diffraction, scanning electron microscopy, infrared spectroscopy, bonding strength test, polarization and electrochemical impedance spectroscopy (EIS). Results showed that addition of TiO₂ to the electrolyte changed the morphology of hydroxyapatite from thin flake-flower-like crystals to needle-flower-like crystals, and the coating was much denser. Besides, hydroxyapatite crystal grains in the coating were preferentially arranged in the [001] direction, which was perpendicular to the surface of NiTi alloy. The addition of TiO₂ improved the bonding strength between the coating and the substrate. Corrosion resistance of NiTi in the simulated body fluid at 37 °C was significantly improved by more than 50 times by electrodeposition of the hydroxyapatite/titania composite coating.     

Surface mechanical attrition treatment induced phase transformation behavior in NiTi shape memory alloy

The phase constituents and transformation behavior of the martensite B19′ NiTi shape memory alloy after undergoing surface mechanical attrition treatment (SMAT) are investigated. SMAT is found to induce the formation of a parent B2 phase from the martensite B19′ in the top surface layer. By removing the surface layer-by-layer, X-ray diffraction reveals that the amount of the B2 phase decreases with depth. Differential scanning calorimetry (DSC) further indicates that the deformed martensite in the sub-surface layer up to 300 μm deep exhibits the martensite stabilization effect. The graded phase structure and transformation behavior in the SMATed NiTi specimen can be attributed to the gradient change in strain with depth.     

60NiTi合金的热变形行为及本构方程

60NiTi合金具有强度高、耐磨性好等一系列优异的性能。但由于它难热成型,因此大大限制了在工业领域的广泛应用。为了确定60NiTi合金最优的热加工工艺,研究了铸态60NiTi合金在750～1 050℃,0.01～1 s^-1变形速率下的热变形行为,并采用包含Arrhenius项的Z参数法构建了高温变形本构方程。结果显示：仅在1 000℃、1 s^-1速率下高温变形时60NiTi合金发生了明显的动态再结晶,温度升高能提高60NiTi合金的热成型性能。在高温(1 050℃)大变形速率下(1 s^-1)加工60NiTi合金的热成型性能最好。     

Deformation characteristics of the intermetallic alloy 60NiTi

The deformation behavior of a Ni-rich Ni₅₅Ti₄₅ (at.%) alloy, commonly known as 60NiTi (as designated in wt.%), was analyzed using neutron and synchrotron x-ray diffraction during in situ isothermal tension and compression loading, and pre and post-test electron microscopy. The alloy was shown to exhibit remarkable strength and high hardness resulting from a high density of fine Ni₄Ti₃ precipitates (size ∼67 nm), which were uniformly dispersed throughout the matrix after a solution treatment and oil quench. The precipitate volume fraction was 55 ± 3%, determined from both the neutron Rietveld refinement and conventional x-ray measurements. Non-linear stress-strain behavior was observed in tension (but not in compression) and was attributed to reversible stress-induced martensite (SIM) that forms to accommodate the stress as revealed by neutron diffraction measurements. The tensile and compressive neutron data also showed peak broadening and residual lattice strains. Transmission and scanning electron microscopy revealed stress-induced coarsening of Ni₄Ti₃ precipitates in both tension and compression tested samples, but precipitation and growth of the stable Ni₃Ti phase was observed only after tensile testing. Finally, the potential ramifications of these microstructural changes are discussed.     

Electrochemical behavior of YAG laser-welded NiTi shape memory alloy

Electrochemical behaviors of laser-welded Ti-50.6%Ni（mole fraction） shape memory alloy and the base metal in 0.9% NaCl solution were investigated by electrochemical techniques as corrosion potential measurement, linear and potentiodynamic polarization. The results indicate that the laser-welded NiTi alloy is less susceptible to pitting and crevice corrosion than the base metal, which is demonstrated by the increase in polarization resistance（Rp） and pitting potential（φpit） and decrease in corrosion current density（Jcorr） and mean difference between φpit and φprot values. It is confirmed by scanning electron microscope micrographs that pits could be observed on the surface of base metal but not on the surface of laser-welded alloy after potentiodynamic tests. An improvement of corrosion resistance of laser-welded NiTi alloy could be attributed to almost complete dissolution of inclusions upon laser welding.     

Effects of surface alloying on electrochemical corrosion behavior of oxygen-plasma-modified biomedical magnesium alloy

Mg–3Nd–0.2Zn–0.4Zr alloy with good mechanical properties is a new type of biodegradable magnesium alloy. In order to improve the surface stability in the initial healing stage and foster tissue growth on biomedical implants made of this Mg alloy, oxygen plasma immersion ion implantation (O-PIII) is conducted to modify the alloy surface. Although O-PIII increases the thickness of the surface oxide, no significant improvement in the surface corrosion resistance is observed. Hence, surface alloying with Al and Cr by means of high-energy ion implantation is conducted prior to O-PIII. The electrochemical data obtained in simulated body fluids, including polarization curves and electrochemical impedance spectra (EIS), reveal that the surface corrosion resistance is improved after surface alloying. Our results show that surface alloying with Cr produces the best result in this study. The improvement stems from the formation of Al or Cr-containing oxide films in the implanted layer.     

Modification of biomedical NiTi shape memory alloy by TiC/Ti films using PIIID

TiC/Ti coatings were deposited on the surface of Ti-50.6 at.% Ni alloy by plasma immersion ion implantation and deposition (PIIID) technique. The microstructure, mechanical properties and hemocompatibility of the samples were investigated by means of XRD, AFM, nanoindentation, and scratch and platelet adhesion tests. The result of XRD analysis shows that the crystalline TiC coating has a preferential orientation of (111) in the normal direction. The surface presents a very smooth and dense microstructure with 1.517 nm root mean square roughness (RMS). The average hardness and modulus values of the TiC coating are much higher than those of the NiTi substrate. In the initial stage of scratching, some obvious transversal cracks and worm-like cracks spreading into the film from both side of the scratch track were observed. At higher normal loads for the scratching test, the film delaminated from the substrate at the margins of the substrate. Platelet adhesion tests demonstrate that the hemocompatibility of the coated sample is improved.