NiTi形状记忆合金薄膜的制备及形变特性

研究了适用于微器件的溅射态NiTi形状记忆合金薄膜.讨论了溅射工艺及织构对薄膜结构和相变特征的影响.利用薄膜热相变特性制成了微驱动器,观察并分析了该器件的形变特性.结果表明:原位加热溅射可以获得具有织构的晶化薄膜;用该薄膜制备的驱动器回复率为0.76%.     

Characterization of Sol-gel-derived TiO2 and TiO2-SiO2 Films for Biomedical Applications

In order to improve the corrosion resistance and biocompatibility of NiTi surgical alloy, TiO2 and TiO2-SiO2 thin films were prepared by sol-gel method. The surface characteristics of the film, which include surface composition, microstructure and surface morphology, were studied by X-ray diffraction (XRD), atomic force microscopy (AFM) and X-ray photoelectron spectra (XPS), respectively. A scratching test was used to assess the interface adhesive strength between the film and substrate. The corrosion resistance of NiTi alloy coated with oxide films were studied by anodic polarization curves measurement in biological solution. Additionally, a preliminary study of the in vitro bioactivity of the films was conducted. The results indicated that TiO2 and TiO2-SiO2 (Ti/Si=4:1) films have higher electrochemical corrosion resistance and can be used as protective layers on NiTi alloy. In addition, TiO2-SiO2 composite films have better bioactivity than TiO2 film.     

PZT基体沉积条形分布NiTiSMA薄膜复合材料的介电性能

使用模具并采用磁控溅射法在铁电陶瓷PZT基体上沉积具有条形分布结构的Ni Ti SMA薄膜。显微组织结构观察发现,以条形分布结构方式沉积的Ni Ti SMA薄膜晶化处理后具有等轴晶结构。比较所制备PZT/Ni-Ti SMA薄膜复合材料与纯PZT的介电常数及介电损耗发现,两者的介电损耗水平接近;复合材料的介电常数比纯PZT的提高约18%。Ni Ti SMA的沉积使基体中靠近薄膜区域的Zr/Ti物质的量比恰好落在准同型相界区内,致使所制备复合材料的介电性能优于纯PZT。     

Surface nanomechanical behavior of ZrN and ZrCN films deposited on NiTi shape memory alloy by magnetron sputtering

Surface nanomechanical behavior under nanoindentation of ZrN and ZrCN film on NiTi substrate was studied. The surface hardness and modulus of the films increase initially with larger nanoindentation depths and then reach their maximum values. Afterwards, they diminish gradually and finally reaching plateau values which are the composite modulus and composite hardness derived from the ZrN/ZrCN film and NiTi substrate. They are higher than those of electropolished NiTi SMA due to the properties of ZrN and ZrCN. In comparison, the surface nanomechanical properties of electropolished NiTi exhibit a different change with depths.     

Pitting initiation of 316L stainless steel in the media of sulfate-reducing and iron-oxidizing bacteria

Pitting corrosion behavior of stainless steel 316L in the presence of aerobic and anaerobic bacteria isolated from cooling water system in oil refinery was investigated using open circuit potential measurement, electrochemically impedance spectroscopy, scanning electron microscopy examinations, and energy dispersive spectrum analysis. The results show the corrosion potential (E _cor) and polarization resistance (R _p) decrease in the presence of sulfate-reducing bacteria (SRB), iron-oxidizing bacteria (IOB), and a combination of SRB and IOB, in comparison with those observed in the sterile medium for the same exposure time. The presence of SRB demonstrated higher corrosion rates than IOB. The combination of SRB and IOB created the highest corrosion rate. The metabolic activity of bacteria and the integrality and compactness of biofilm influenced the pitting corrosion process, increased the corrosion damage degree of the passive film, and accelerated the pitting corrosion. It is suggested that SRB and IOB in influencing the pitting corrosion of 316L SS is highlighted. The text was submitted by the authors in English.     

Amorphous alloys resistant to corrosion in artificial saliva solution

The tailoring of new corrosion-resistant alloys with specific properties has recently been performed mostly by the sputter deposition technique. The aim of this work was to investigate corrosion resistance of aluminum–tungsten (Al–W) amorphous alloys in artificial saliva solution, pH=5.5, based on the electrochemical methods of cyclic voltammetry and linear polarization. Thin alloy films were prepared on a sapphire substrate by magnetron codeposition. Completely amorphous films were obtained in the Al₈₀W₂₀–Al₆₇W₃₃ composition range. Amorphous Al–W alloys exhibit very high corrosion resistance due to their homogeneous single-phase nature. The passive films spontaneously formed at their surface are uniform with characteristics of an insulator film and prevent corrosion progression in the bulk in a very demanding oral environment. The mechanism of increasing resistivity of Al–W alloys to pitting corrosion and generalized corrosion has been discussed in the view of increasing tungsten content in the alloy. Considering these exceptional corrosion properties and microhardness which falls in the range 7.5±1.6 Pa, Al–W alloys represent promising materials for dental applications.     

XPS and biocompatibility studies of titania film on anodized NiTi shape memory alloy

A dense titania film is fabricated in situ on NiTi shape memory alloy (SMA) by anodic oxidation in a Na₂SO₄ electrolyte. The microstructure of the titania film and its influence on the biocompatibility of NiTi SMA are investigated by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), inductively coupled plasma mass spectrometry (ICPMS), hemolysis analysis, and platelet adhesion test. The results indicate that the titania film has a Ni-free zone near the surface and can effectively block the release of harmful Ni ions from the NiTi substrate in simulated body fluids. Moreover, the wettability, hemolysis resistance, and thromboresistance of the NiTi sample are improved by this anodic oxidation method.     

Effects of anodic oxidation in H2SO4 electrolyte on the biocompatibility of NiTi shape memory alloy

Effects of anodic oxidation in H₂SO₄ electrolyte on the biocompatibility of NiTi shape memory alloy (SMA) were investigated by characterizing surface structure, blood compatibility, wettability, release of harmful Ni ions of anodized NiTi SMA. Although titania film resulting from anodic oxidation in H₂SO₄ electrolyte has a porous structure, it can effectively block out-diffusion of Ni from NiTi SMA to simulated body fluid (SBF). Comparing with chemical polishing, anodic oxidation in H₂SO₄ electrolyte can also improve the wettability, blood compatibility, thromboresistance of NiTi SMA.     

Improvement in corrosion resistance of NiTi by anodization in acetic acid

NiTi was galvanostatically anodized in acetic acid to increase the oxide film thickness for improving corrosion resistance. The galvanostatic anodization behavior of NiTi in acetic acid differed markedly from that of Ti. In particular, the anode potential reached was much lower for NiTi, and thus only thin oxide films could be obtained. With a suitable choice of anodizing conditions, the anodic oxide film formed had a thickness of 20–25 nm, as determined by profilometric measurement. Atomic force microscopy (AFM) revealed that the surface roughness was increased after anodization. Analysis by X-ray photoelectron spectroscopy (XPS) showed a low Ni/Ti ratio of 0.04 at the anodic oxide surface versus a value of 0.30 for bare NiTi. Electrochemical impedance measurements of the anodized sample in Hanks' solution at 37 °C recorded a 9-fold increase in polarization resistance, and cyclic polarization tests also recorded a matching reduction in the passive current density. These observations indicate that anodization of NiTi can serve as a simple low-temperature method to enhance the corrosion resistance of NiTi when used as an implant material.     

Surface structure and biomedical properties of chemically polished and electropolished NiTi shape memory alloys

The surface structure and biomedical properties of NiTi shape memory alloy (SMA) samples after undergoing electropolishing and chemical polishing are determined and compared employing scanning electron microscopy, X-ray photoelectron spectroscopy, inductively-coupled plasma mass spectrometry, hemolysis analysis, blood platelet adhesion test, and MTT test. The results indicate that after chemical polishing, there is still a high Ni concentration on the surface of the NiTi SMA. On the other hand, electropolishing can form a thin surface titanium oxide film (about 10 nm thickness) with depleted Ni. In addition to the TiO₂ phase, some titanium suboxides (TiO and Ti₂O₃) are found in the surface film. Compared to chemical polishing, electropolishing can more effectively mitigate out-diffusion of Ni ions and the wettability, blood compatibility, and thromboresistance are also better. However, no difference on the cytocompatibility can be observed from samples that have been chemically polished or electropolished.     

医用NiTi合金表面溶胶-凝胶法制备TiO2-SiO2薄膜

采用溶胶－凝胶法在ＮｉＴｉ形状记忆合金表面制备了ＴｉＯ_２－ＳｉＯ_２复合薄膜,在提高医用ＮｉＴｉ合金的抗腐蚀性方面,收到了显著的效果．运用电化学方法对不同组成的ＴｉＯ_２－ＳｉＯ_２薄膜在模拟体液中的腐蚀行为进行了研究,结果表明,随薄膜中 Ｔｉ／Ｓｉ比的增加,ＴｉＯ_２－ＳｉＯ_２薄膜的抗腐蚀性增强．划痕试验表明 ＴｉＯ_２－ＳｉＯ_２（Ｔｉ／Ｓｉ＝４：１）膜与ＮｉＴｉ合金基体具有较高的界面结合强度．用原子力显微镜（ＡＦＭ）对ＴｉＯ_２－ＳｉＯ_２薄膜的表面形貌及表面粗糙度进行观察和分析,解释并讨论了ＴｉＯ_２－ＳｉＯ_２薄膜的配方组成与其抗腐蚀性的关系,ＳｉＯ_２含量较少时,薄膜结构致密,膜层均匀平滑,且膜基结合力好,作为医用ＮｉＴｉ合金的表面保护层,可以使其耐腐蚀性有显著提高．     

Advanced resonant ultrasound spectroscopy for measuring anisotropic elastic constants of thin films

This paper presents an advanced resonant ultrasound spectroscopy (RUS) method to determine the elastic constants C_ij of thin films. Polycrystalline thin films often exhibit elastic anisotropy between the film growth direction and the in‐plane direction, and they macroscopically show five independent elastic constants. Because all of the C_ij of a deposited thin film affect the mechanical resonance frequencies of the film/substrate layer specimen, measuring resonance frequencies enables one to determine the C_ij of the film with known density, dimensions and the C_ij of the substrate. Resonance frequencies have to be measured accurately because of low sensitivity of the C_ij of films to them. We achieved this by a piezoelectric tripod. Mode identification has to be made unambiguously. We made this measuring displacement–amplitude distributions on the resonated specimen surface by laser Doppler interferometry. We applied our technique to copper thin film and diamond thin film. They show elastic anisotropy and the C_ij smaller than bulk values of C_ij. Micromechanics calculations indicate the presence of incohesive bonded regions.     

Comparison of their electrical,optical, and electrochemical properties of as-grown plasma polymerized organic thin films by PECVD

Plasma polymerized organic thin films have been deposited on Si(100), glass and metal substrates at 25∼100 °C using thiophene and toluene precursors by plasma enhanced CVD method. In order to compare physical and electrochemical properties of the as-grown thin films, the effect of the RF (13.56 MHz) plasma power in the range of 30∼100 W and the deposition temperature on the corrosion protection efficiency and optical property were mainly studied in this work. Corrosion protection efficiency (P_k), which is one of important factors for corrosion protection in the interlayer dielectrics of microelectronic devices application, provided an increasing tendency with increasing RF power. The highest P_k value of plasma polymerized toluene film (85.27% at 70 W) was higher than that of the plasma polymerized thiophene film (65.17% at 100 W). The result of contact angle measurement showed that the plasma polymerized toluene films have more hydrophobicity than that of the plasma polymerized thiophene films.     

Effect of nitrogen on mechanical properties of thin films of the Ta-B-N system

Amorphous-crystalline thin films of the Ta-B-N system on steel substrates have been produced by high-frequency magnetron reaction sputtering of a TaB₂ target in a nitrogen-argon gas mixture. The effect of the nitrogen content of the mixture on the film mechanical properties has been studied. It has been found that the formation of an amorphous-crystalline structure causes the Ta-B-N film nanohardness and elastic modulus to decrease and the plasticity to increase as compared to TaB₂ nanocrystalline films. The amorphous boron formation results in the viscoelastic mechanical behavior of thin films of the Ta-B-N system.     

Corrosion and stress corrosion cracking behavior of 316L austenitic stainless steel in high H2S–CO2–Cl− environment

In oil and gas production environments, H₂S and Cl^? can coordinate to cause pitting or stress corrosion cracking (SCC) of stainless steels. There has been limited work conducted on corrosion and SCC of autenitic stainless steels in high H₂S–CO₂–Cl^? environments. In this paper, by four-point bending test method and scanning electron microscopy analysis, SCC of 316L steel was investigated under high H₂S–CO₂ pressures with 150,000 ppm Cl^? at 60 °C. The effect of high H₂S–CO₂ pressure was discussed. The results indicated that the higher H₂S–CO₂ pressure can accelerate anodic dissolution process, deteriorate passive films, and aggravate SCC sensitivity. Using cyclic potentiodynamic polarization measurements, the corrosion behavior of 316L steel was studied in high H₂S–CO₂–Cl^? environments. The effect of pH on pitting corrosion was discussed. Lower pH can promote both cathodic and anodic actions on 316L steel and facilitate passive film breakdown.     

Effect of pH, temperature and Cl− concentration on electrochemical behavior of NiTi shape memory alloy in artificial saliva

The cooperation of pH, temperature and Cl⁻ concentration on electrochemical behavior of NiTi shape memory alloy in artificial saliva was studied using orthogonal test method. The results showed that the pitting potential for NiTi in artificial saliva decreased at low and high pH; at 25^∘C, the pitting potential was the lowest compared to those at 10^∘C, 37^∘C and 50^∘C; when the Cl⁻ concentration was not less than 0.05 mol/L the pitting potential decreased with the increase of Cl⁻ concentration. The free corrosion potential of austenitic NiTi was lower than that of mixture of austenite and martensite.     

The biocompatibility and mechanical properties of cylindrical NiTi thin films produced by magnetron sputtering

Superelastic nickel titanium shape memory alloys (NiTi–SMA) are of biomedical interest due to the large obtainable strains and the constant stress level. Production of NiTi–SMA thin films by magnetron sputtering was developed recently. NiTi sputtered tubes have a high potential for application as vascular implants, e.g. stents. Magnetron sputtering, three dimensional lithography and wet etching were used in order to produce Ti and NiTi stent devices (thickness: 5–15 μm; diameter: 1–5 mm). For tensile tests, specimens were prepared in radial and axial directions in order to compare the mechanical properties of the film in both directions. The specimens – produced for cell culture experiments – were incubated with human mesenchymal stem cells (hMSC) for 7 days. Cell viability was analyzed via fluorescence microscopy after live/dead staining of the cells. Cytokine release from cells was quantified via ELISA. Cylindrical NiTi films showed a strain up to 6%. Tensile parameters were identical for both directions. Best material properties were obtained for deposition and patterning in the amorphous state followed by an ex-situ crystallization using rapid thermal annealing in a high vacuum chamber. First biological tests of the Ti and NiTi–SMA samples showed promising results regarding viability and cytokine release of hMSC.     

Properties of multilayer composite thin films based on morphotropic phase boundary Pb(Mg1/3Nb2/3)O3-PbTiO3

It has been reported that ferroelectric and piezoelectric properties of Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ (PMNT) thin films, with compositions close to the morphotropic phase boundary (MPB), show lower values than those reported for bulk ceramics with the same composition, which has been attributed to a reduction of the remnant polarization caused by the small size of the grains in the films. An alternative has been proposed to take full advantage of the excellent piezoelectric properties of polycrystalline PMNT in thin film form: a multilayer configuration that uses ferroelectric layers with large remnant polarization, in this case PbTiO₃, to generate an internal electric bias within the PMNT layers and, thus, anchor an induced polarization on them, resulting in a consequent large piezoelectric behavior. The detailed study of the properties of these multilayer composite films reveals the complex correlations that arise in these heterostructures, which are key for the design of optimized piezoelectric films based on MPB PMNT.     

Formation of a nano-pattering NiTi surface with Ni-depleted superficial layer to promote corrosion resistance and endothelial cell-material interaction

Zirconium ion implantation was performed on NiTi alloy to suppress Ni ion release as well as to improve corrosion resistance and cell-material interaction. A thicker Ni-depleted nano-scale composite layer formed after Zr implantation and the corrosion resistance was evidently increased in aspects of increased E _br ? E _corr (difference between corrosion potential and breakdown potential) and decreased corrosion current density. 2.5/2 NiTi sample possessed the highest E _br ? E _corr, more than 500 mV higher than that of untreated NiTi, suggesting a significant improvement on pitting corrosion resistance. Ni ion release rate of Zr–NiTi was decreased due to the depletion of Ni in the superficial surface layer and the diffusion resistance effect of the ZrO₂/TiO₂ nano-film. Increased surface wettability induced by increased surface roughness was obtained after Zr implantation. Zr–NiTi samples were found to be favorable to endothelial cells (ECs) proliferation, especially after 5 and 7 days culture.     

Optical properties of the c-axis oriented LiNbO3 thin film

C-axis oriented Lithium Niobate (LiNbO₃) thin films have been deposited onto epitaxially matched (001) sapphire substrate using pulsed laser deposition technique. Structural and optical properties of the thin films have been studied using the X-ray diffraction (XRD) and UV-Visible spectroscopy respectively. Raman spectroscopy has been used to study the optical phonon modes and defects in the c-axis oriented LiNbO₃ thin films. XRD analysis indicates the presence of stress in the as-grown LiNbO₃ thin films and is attributed to the small lattice mismatch between LiNbO₃ and sapphire. Refractive index (n = 2.13 at 640 nm) of the (006) LiNbO₃ thin films was found to be slightly lower from the corresponding bulk value (n = 2.28). Various factors responsible for the deviation in the refractive index of (006) LiNbO₃ thin films from the corresponding bulk value are discussed and the deviation is mainly attributed to the lattice contraction due to the presence of stress in deposited film.