Surface characteristics, nano-indentation and corrosion behavior of Nb implanted NiTi alloy

NiTi shape memory alloy has been modified by Nb implantation with different implantation parameters including incident dose and current. The surface morphology and chemical components are determined by atomic force microscopy (AFM), Auger Electron Spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). The results show that Nb implantation leads to the formation of compact Nb₂O₅/TiO₂ thin film about 30 nm in thickness on the surface of the NiTi alloy and decreases the surface concentration of Ni. A larger incident dose or incident current causes a higher surface roughness and a higher Nb content in the implantation layer of NiTi alloy. The nano-indentation measurements indicate the obvious reduction of both nano-hardness and Young's modulus of the Nb implanted NiTi alloy in the implantation layer and even in deeper NiTi matrix. The results of potentiodynamic polarization test show that the corrosion resistance of NiTi alloy in Hanks's solution has been evidently improved by Nb implantation. The NiTi alloy with a moderate implantation parameter of 1.5 × 10¹⁷ ions/cm² and 2 mA exhibits the best corrosion resistance ability.     

电流密度对ZK60镁合金表面超疏水涂层的制备及耐腐蚀性的影响

为了提高镁合金的耐腐蚀性能,基于层状双氢氧化物（LDHs）膜在ZK60镁合金表面制备了超疏水（SH）涂层。涂层制备过程中引入电场辅助,研究了工作电流密度对涂层性能的影响。结果表明,工作电流密度显著影响LDHs膜的微观结构,这对SH涂层的疏水性具有重要影响。当工作电流密度为25 mA/cm²时,SH涂层表面呈现均匀的微纳米结构,并表现出超疏水性。超疏水涂层的腐蚀电流密度（I_corr=9×10^-7 A·cm^-2）比ZK60基体的腐蚀电流密度（I_corr=3×10^-5 A·cm^-2）低了2个数量级,表现出优异的耐腐蚀性。     

Effect of Surface Treatment on Bio-corrosion in Aluminum Alloy 2024-T3

Bio-corrosion is one of the major problems faced in any engineering/aerospace industry. The present study focuses on understanding the effect of surface treatment on AA2024-T3 on bio-corrosion in aircraft fuel tanks. The microbial attack on aluminum alloy (2024-T3) in aircraft fuel tanks by Pseudomonas aeruginosa was studied. Substrates with (1) chromate-free surface treatment (anodization; 2) Ormosil coatings doped with inhibitors/derivatives known for antimicrobial properties were evaluated for their bio-corrosion protection efficiency as compared to bare coupons. The coupons were immersed in aviation fuel spiked with the test culture. The changes in chemical parameters of test solution like pH were monitored periodically. A probable relationship between number of organisms, changes in pH and the extracellular protein (hypothesized to be produced by organisms) were evaluated. Our studies indicated that pH did not appear to play a crucial role in biofilm formation. Surface morphology of bare and anodized AA2024-T3 coupons before and after electrochemical impedance studies (EIS) was analyzed using FE-SEM. Anodized samples with least i_corr value of (0.075?×?10^?6 A cm^?2) and corrosion rate of (0.12?×?10^?2 mm/y) after 60 days showed distinct corrosion protection than bare and the coated samples. Additional evidence in support of corrosion protection efficiency of anodized was obtained by the biofilm barrier efficiency of 98.94%.     

Corrosion characterization of microarc oxidation coatings formed on Mg–7Li alloy

Ceramic coatings with thickness of 27 µm were fabricated on Mg–7Li alloy in Na₂SiO₃–C₆H₁₈O₂₄P₆ solution by microarc oxidation (MAO). The morphology and phase composition of MAO coatings were characterized by scanning electron microscopy (SEM) and X‐ray diffraction (XRD). The corrosion behavior of the bare and MAO coated Mg–7Li alloy was investigated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). Results showed that the MAO coatings were composed of MgO, Li₂O, and Mg₂SiO₄, and there existed some micropores on the coating surface with a diameter of 3–20 µm. The corrosion potential (E_corr) and corrosion current density (I_corr) of the MAO coated alloy were about ?1.4761 V and 7.204 × 10^?7 A/cm², respectively. The E_corr of the MAO coated alloy increased by 109.6 mV and its I_corr decreased by three orders compared with that of the bare Mg–7Li alloy. The EIS plots indicated that the impedance of the MAO coated alloy was 15 times higher than that of the bare alloy. The fitting parameters showed that the resistance of the MAO coatings was far greater than that of the bare alloy. The dense intermediate layer and the transition layer of the MAO coatings acted as a barrier to hinder the proceeding of solution permeation, remarkably improving the corrosion resistance of the Mg–7Li alloy.     

Effect of Surface Alloying by Silicon on the Corrosion Resistance and Biocompatibility of the Binary NiTi

This paper presents the study on changes in element and phase compositions in the near-surface layer and on surface topography of the NiTi specimens after the silicon ion-beam treatment. The effect of these parameters of the near-surface layer on corrosion properties in biochemical solutions and biocompatibility with mesenchymal stem cells of rat marrow is studied. Ion-beam surface modification of the specimens was performed by a DIANA-3 implanter (Tomsk, Russia), using single-ion-beam pulses under oil-free pumping and high vacuum (10^?4 Pa) conditions in a high-dose ion implantation regime. The fluence made 2 × 10¹⁷ cm^?2, at an average accelerating voltage of 60 kV, and pulse repetition frequency of 50 Hz. The silicon ion-beam treatment of specimen surfaces is shown to bring about a nearly twofold improvement in the corrosion resistance of the material to attack by aqueous solutions of NaCl (artificial body fluid) and human plasma and a drastic decrease in the nickel concentration after immersion of the specimens into the solutions for ~3400 and ~6000 h, respectively (for the artificial plasma solution, a nearly 20-fold decrease in the Ni concentration is observed). It is shown that improvement of NiTi corrosion resistance after treatment by Si ions occurs mainly due to the formation of two-layer composite coating based on Ti oxides (outer layer) on the NiTi surface and adjacent inner layer of oxides, carbides, and silicides of the NiTi alloy components. Inner layer with high silicon concentration serves as a barrier layer preventing nickel penetration into biomedium. This, in our opinion, is the main reason why the NiTi alloy exhibits no cytotoxic properties after ion modification of its surface and leads to the biocompatibility improvement at the cellular level, respectively.     

Corrosion Behavior and Microhardness of Ni-P-SiO<Subscript>2</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Nano-composite Coatings on Magnesium Alloy

In the present work, nano-composites of Ni-P-SiO₂-Al₂O₃ were coated on AZ91HP magnesium alloy. The surface morphology of the nano-composite coating was studied by field emission scanning electron microscopy (FESEM). The amount of SiO₂ in the coating was determined by energy-dispersive analysis of x-ray (EDX), and the crystalline structure of the coating was examined by x-ray diffractometer (XRD). All the experiments concerning the corrosion behavior of the coating carried out in 3.5 wt.% NaCl solution and evaluated by electrochemical impedance spectroscopy (EIS) and polarization technique. The results showed that an incorporation of SiO₂ and Al₂O₃ in Ni-P coating at the SiO₂ concentration of 10 g/Land 14 g/LAl₂O₃ led to the lowest corrosion rate (i _corr = 1.3 µA/cm²), the most positive E _corr and maximum microhardness (496 VH). Furthermore, Ni-P-SiO₂-Al₂O₃ nano-composite coating possesses less porosity than that in Ni-P coating, resulting in improving corrosion resistance.     

Studies on copper-semiconducting layer-electrolyte systems—I. Electrode potentials of copper and electrodeposited copper sulphide in S2− and Cu2+ media

Copper sulphide layers electrodeposited from a Na₂S bath consist chiefly of cuprous sulphide. Calculated values of the specific conductance of the deposited sulphide average around 3·8 × 10^?5 ohm^?1.cm^?1.Electrode potentials, E_H, of the Cu/Cu_2?δS in unbuffered Na₂S solutions and in solutions buffered at pH 9, correspond to the behaviour of a Cu/Cu_2?δS, overlayered with CuS/electrolyte. Steady reproducible potentials are obtained with the above electrodes in 0·5–10^?3M CuSO₄ solutions, closely comparable with those of the reversible Cu/Cu²⁺ couple.     

Preventing or accelerating galvanic corrosion through the application of a proper external magnetic field

The effect of an external magnetic field on the corrosion behaviour of a galvanic couple, zinc (Zn)–stainless steel (SS 316L), has been investigated in a 0·055 mol L^?1 potassium chloride (KCl) solution. The impact of the orientation as well as the magnetic flux density B (Wb m^?2) on the corrosion progression of the galvanic couple, is evaluated heuristically by monitoring the corrosion potential E_corr (mV) and the current density I_corr (μA cm^?2) of the system. A strong influence of the magnitude and orientation of the magnetic field on the Zn–SS316L galvanic couple corrosion was observed, whereas the field was proven to act either protective or accelerating in terms of corrosion.     

Atmospheric corrosion of clad palladium and palladium-silver alloys: film growth and contamination effects

Claddings of Pd, Pd-40 Ag and Pd-60 Ag on CA725² copper alloy, exposed for up to 40 months in certain air-conditioned telephone central offices, do not show significant film growth or surface contamination effects. When exposed for similar periods in a non-air-conditioned room of a central office, these claddings had dust particles containing salts of Ca, Na and Cl on a hydrated palladium dichloride film for Pd, and on a mixed hydrated PdCl₂ and silver chloride film for Pd-40 Ag and Pd-60 Ag. The growth rate of the chloride film was parabolic with rate constants of 1.11 × 10^?11 cm²/month for Pd, 2.77 × 10^?12 cm²/month for Pd-60 Ag and 5.82 × 10^?13 cm²/month for Pd-40 Ag. The Pd-60 Ag alloy also reacted with other contaminants and was the most degraded with respect to total film growth, followed by Pd and Pd-40 Ag.     

Effect of velocity and elevated temperature on pitting of Al 6013-20SiCp composite in 3·5 wt-%NaCl

Abstract

This paper presents new data on the effect of temperature and velocity on the pitting potential E_p, corrosion potential E_corr, and pitting morphology of O, F, and T4 tempers of alloy 6013-20SiC_p in 3·5 wt-%NaCl in the temperature range 30–130°C and at velocities of 0·5–1·0 m S_?1. The pitting potential of tempers T4 and O tended to increase with increasing temperature and flow velocity, but the pitting potential of temper F showed the opposite behaviour. Temper T4 of the alloy showed the best resistance to pitting. Alloy 6013-20SiC_p in temper T4 is therefore considered to be suitable for application in chloride containing environments.     

Surface modification of NiTi/PZT heterostructure thin films using various protective layers for potential MEMS applications

The present study explored the in-situ deposition of hard and adherent nanocrystalline protective coatings on NiTi/PZT/TiO_x thin film heterostructure prepared by dc/rf magnetron sputtering. Protective layers (AlN, CrN and TiCrN) of approximate thickness (~ 200 nm) were used to improve the surface, mechanical and corrosion properties of NiTi/PZT/TiO_x heterostructure without sacrificing the shape memory effect and ferroelectricity of the NiTi and PZT layers, respectively. The influence of the protective layer on structural, electrical and mechanical properties of NiTi/PZT/TiO_x heterostructure was systematically investigated and the results were compared. Nanoindentation studies were performed at room temperature to determine the hardness and reduced modulus. The surface modified NiTi/PZT/TiO_x heterostructures were found to exhibit high hardness, high elastic modulus and thereby better wear resistance as compared to pure NiTi/PZT/TiO_x films. From the results of potentiodynamic polarization test conducted in 1 M NaCl solution, the CrTiN coated NiTi/PZT/TiO_x heterostructure showed the best corrosion resistance with the lowest corrosion current density (1.52 × 10^? 8 A cm^? 2) and the highest protective efficiency (96.8%). The results presented here prove the potential of a surface modified NiTi/PZT/TiO_x heterostructure to be used in various microelectromechanical (MEMS) applications.     

Oxidation Behavior of ZrB<Subscript>2</Subscript>–SiC Composites at 1650 °C

The oxidation behavior of ZrB₂–SiC composites in air was studied at 1650 °C. Diffusion-controlled oxidation kinetics were found for the composites studied. A parabolic rate constant of 1.2 × 10^?8 g² cm^?4 s^?1 was measured for ZrB₂–10 % SiC composite. A transition in the oxidation kinetics was observed for ZrB₂–30 % SiC composite with the initial parabolic rate constant being 1.3 × 10^?8 g² cm^?4 s^?1. After exposure for 60 min, the parabolic rate constant was found to be 0.3 × 10^?8 g² cm^?4 s^?1. A single ZrO₂-rich oxide layer was found in the oxide scale structure of ZrB₂–10 % SiC composite. On the other hand, three-layer oxide structures, namely SiO₂-rich top layer, followed by ZrO₂-rich oxide scale and SiC-depleted layer, were found for ZrB₂–30 % SiC composite. The outer layer in the oxide scale structure of ZrB₂–SiC composite was tapered with enhanced oxidation at the corners of the sample. Vortex formation during the viscous flow of B₂O₃–SiO₂–ZrO₂ liquid near the corners on the surface was proposed as the root cause for enhanced oxidation at the corners of the sample.     

Effect of La-Substitution on the Electrical Conductivity of Sr1−x La x MoO4+δ (x = 0-0.3) Compounds

Various compositions of Sr_1?x La _x MoO_4+δ (x = 0.05, 0.1, 0.2, and 0.3) compounds were prepared by solid state reaction route. The samples were characterized by powder-XRD, TG-DTA, and SEM-EDAX techniques. Formation of single crystalline phases of Sr_1?x La _x MoO_4+δ was confirmed from powder-XRD patterns. The thermal stability of La-doped SrMoO₄ compounds was investigated by TG-DTA. Uniform grain distribution was observed in the SEM image of 10-20 mol.% La-substituted compositions. Needle-shaped structures were observed in the SEM image of Sr_0.3La_0.1MoO_4+δ and were confirmed to be La₂Mo₂O₉ by XRD examination. The electrical conductivity of these compounds was measured by AC-impedance technique in the temperature range of 373-1073 K in air ambience and compared with that of pristine SrMoO₄. The electrical conductivity was found to decrease for La-substituted SrMoO₄ compared to pristine SrMoO₄. The diffusion coefficient calculated from the electrical conductivity was found to be in the range of 1.94 ± 0.02 × 10^?13 to 1.15 ± 0.01 × 10^?11 cm²/S at 873-1173 K for substituted composition and 3.47 ± 0.02 × 10^?13 to 2.48 ± 0.01 × 10^?10 cm²/S for pristine SrMoO₄ at 673-1073 K temperature range.     

Structural, electrical and mechanical properties of magnetron sputtered NiTi/PZT/TiOx thin film heterostructures

Shape memory alloy (NiTi) thin films coupled to ferroelectric lead zirconate titanate (PZT) produce an intelligent material capable of performing both sensing and actuating functions. In the present study, we report on the in-situ growth of NiTi/PZT/TiO_x heterostructure on Pt/Ti/SiO₂/Si substrates using magnetron sputtering technique. Deposition processing, microstructure, surface morphology, electrical properties and mechanical properties of these heterostructures were systematically investigated. The top NiTi films exhibit austenitic B2 structure with preferred (110) orientation. The varying thickness of NiTi films had a significant influence on properties of NiTi/PZT/TiO_x heterostructure. The bottom TiO_x layer was observed to favor the growth of perovskite PZT films with (100) orientation. Nanoindentation tests of these heterostructures were performed at room temperature. The mechanical hardness of the top NiTi layer of lower thickness was found to be highly influenced by underneath PZT layer. The heterostructure exhibited an interesting martensite to austenite phase transformation and polarization-electric field hysteresis behavior with remanent polarization (P_r) and the coercive field (E_r) of 17.1 μC/cm² and 69.6 kV/cm, respectively. These heterostructures having a layer of SMA material coupled to a ferroelectric material with underneath TiO_x layer are of immense technological importance for MEMS devices.     

Rapid Obtaining of Nano-Hydroxyapatite Bioactive Films on NiTi Shape Memory Alloy by Electrodeposition Process

Nano-hydroxyapatite (n-HA) crystalline films have been developed in this study by electrodeposition method on NiTi shape memory alloy (SMA). The electrodeposition of the n-HA films was carried out using 0.042 mol/L Ca(NO₃)₂ · 4H₂O + 0.025 mol/L (NH₄) · 2HPO₄ electrolytes by applying a constant potential of ?2.0 V for 120 min and keeping the solution temperature at 70 °C. The characterization of n-HA films is of special importance since bioactive properties related to n-HA have been directly identified with its specific composition and crystalline structure. AFM, XRD, EDX, FEG-SEM and Raman spectroscopy shows a homogeneous film, with high crystallinity, special composition, and bioactivity properties (Ca/P = 1.93) of n-HA on NiTi SMA surfaces. The n-HA coating with special structure would benefit the use of NiTi alloy in orthopedic applications.     

The polarization characteristics of Pb-free Sn-8.5Zn-XAg-0.1Al-0.05Ga alloy in 3.5% NaCl solution

The polarization characteristics of Pb-free Sn-8.5Zn-XAg-0.1Al-0.05Ga alloy with varying Ag content were investigated in 3.5% NaCl solution. The value of Ag content i.e X varied from 0.1 wt% to 2 wt%. An increase in the Ag content up to 2 wt% resulted in a progressive increase in the corrosion current density and shifted the corrosion potential (E_corr) towards more active values. These changes were also reflected in the corrosion rate of the solder alloy. However the linear polarization resistance values decreased with increase in the weight content of silver. Increasing the Ag content from 0.1 to 2 wt% did not show a significant improvement in the passivation behaviour of the solder alloy as reflected in the passivation current density (i_p) and critical current density (i_cc) values. XPS and SIMS depth profile results revealed that the oxides of Zn and Sn were present in high concentrations on the outer surface of the solder alloy along with very low concentration of Al₂O₃.     

A Study on the Passivation Behavior and Semiconducting Properties of Gamma Titanium Aluminide in 0.1 N H2SO4, HNO3, and HClO4 Acidic Solutions

The study focuses on the passivation behavior of single-gamma-phase titanium aluminide in acidic solutions with a particular emphasis on the role of oxidizing strength in characteristics of passive layer. The report includes potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) studies along with Mott-Schottky analysis in order to determine the corrosion behavior of the alloy and the semiconducting properties of the scale formed during exposure to acidic environment. Passive current density measured from potentiodynamic polarization curve, polarization resistance (R _p) estimated by EIS, defect density, and flatband potential drawn from Mott-Schottky analysis are mainly used in estimating the ability of passive film formed on alloy in protecting it against high corrosion rates in Sulfuric acid (a non-oxidizing acid), perchloric acid, and nitric acid (oxidizing acid with different oxidizing strength). The results show that passive current density (i _pass) in Sulfuric acid is 2.67 × 10^?5 A cm^?2, which is 2.5 and 3 times greater than the values obtained in perchloric acid (i _pass = 9.91 × 10^?6) and nitric acid (i _pass = 7.98 × 10^?6), respectively. EIS data reveal that the value of R _p in sulfuric acid (20 kΩ cm²) is about three and five times smaller than that its value in perchloric acid and Nitric acid, respectively. Mott-Schottky analysis shows that the passive layer exhibits an n-type semiconducting characteristics irrespective of acidic environment. The greatest and the smallest values of donor density (N _D) are obtained for the passive scale formed in sulfuric acid (N _{D, H2SO4} = 18.36 × 10¹⁹) and nitric acid (N _{D, HNO3} = 13.13 × 10¹⁹), respectively. The report concludes that characteristics of the passive scale are directly affected by reduction potential of the acid, which is the criterion of its oxidizing strength. An increase in the oxidizing strength of the acidic solution results in formation of more protective and less conductive layer on γ phase titanium aluminide.     

Isothermal Oxidation Comparison of Three Ni-Based Superalloys

Ni-based superalloys are used for high-temperature components of gas turbines in both industrial and aerospace applications due to their ability to maintain dimensional stability under conditions of high stress and strain. The oxidation resistance of these alloys often dictates their service lifetime. This study focuses on the isothermal oxidation behavior of three Ni-based superalloys, namely, polycrystalline cast IN738LC, single-crystal N5, and a ternary Ni-Fe-Cr (TAS) powder metallurgy alloy. The isothermal oxidation tests were conducted at 900 °C in the static air up to 1000 h, and the specific aspects studied were the oxidation behavior of these chromia-forming and alumina-forming alloys that are used extensively in industry. In particular, the behavior of oxide scale growth and subsurface changes were analyzed in detail using various techniques such as SEM, EDS, and AFM. From the isothermal oxidation kinetics, the oxidation rate constant, k _p, was calculated for each alloy and found to be; k _p = 2.79 × 10^?6 mg² cm^?4 s^?1 for IN738LC, k _p = 1.42 × 10^?7 mg² cm^?4 s^?1 for N5 and k _p = 1.62 × 10^?7 mg² cm^?4 s^?1 for TAS. Based on a microstructural analysis, IN738LC exhibited a continuous dense outer scale of Cr₂O₃ and discontinuous inner scale of Al₂O₃, whereas N5 and TAS showed a dense outer scale of Al₂O₃ alone. The results suggested that the N5 and PM-TAS alloys are more oxidation resistant than the IN738LC under these conditions.     

Investigation of the Corrosion Inhibition of CTAB and SDS on Carbon Steel Using an Experimental Design Strategy

The corrosion inhibition performance of sodium dodecyl sulfate (SDS) and cetyltrimethyl ammonium bromide (CTAB) on carbon steel was investigated in sodium chloride solutions. Using an experimental design strategy pH, chloride concentration, SDS/CTAB concentrations, and temperature were optimized by conducting only 30 experiments. The optimum value of each factor was obtained from the designed matrix of the experiments based on the lowest log I _corr value calculated for each experimental condition. The 3D surface plots of the electrochemical response (log I _corr) against each factor were constructed. The optimum conditions in which the lowest log I _corr can be achieved were found as follows: pH 12, [Cl^?] ≈ 1 M, [SDS] ≈ 200 ppm, [CTAB] ≈ 20 ppm, and T ≈ 10 °C.     

Temperature-Dependent Properties of Spray-Deposited ITO Thin Films

Sprayed indium tin oxide (ITO) thin films are synthesized by mixing adequate quantities of ethanolic solutions of indium trichloride and stannic chloride at different substrate temperatures. The pyrolytic decomposition temperature affects the properties and morphology of ITO samples. X-ray diffraction results showed that the films are polycrystalline with cubic structure and exhibit preferential orientation along (222) plane. The SEM and AFM studies indicated that the surface morphology of the samples increases with substrate temperature. The typical I₅₀₀ sample is composed of cubic grains and has carrier concentration of 3.26 × 10²⁰ cm^?3 and mobility of 9.77 cm²/V s. The electrical resistivity of ITO films decreased with increasing deposition temperature. The highest figure of merit of film is 4.4 × 10^?3 Ω^?1. Optical absorption studies reveal that films are highly transparent in the visible region and band gap increases with substrate temperature owing to Moss-Burstein effect.