Papers by Keyword: Oxide Layer

Abstract: Binary TiNi alloys containing 50.0 at.% Ni and 50.7 at.% Ni were tested under bending. Shape memory effect (SME) and two-way SME (TWSME) parameters were measured. Low-temperature thermomechanical treatment (LTMT) by drawing with true strain e ≈ 0.6 and post-deformation annealing (PDA) was performed in the temperature range 300600С for 0.3  1 hr permitted obtaining different types of initial austenite structure. The wires with 0.3 and 0.45 mm in diameter were studied. The curves of element distribution through the surface layer were graphed. The SME training procedure was carried out in bending with the constrained strain 0.7 and 8 %. Thickness, structure and element composition of the oxide film strongly depend on PDA regimes. In all cases titanium quantity in the boundary layer correlates with the oxygen quantity, diffused from the surface. Evidently, it is caused by their chemical reaction and oxide formation. Nickel atoms remain in uncombined state, and their migration is directed from the surface deep into the sample. LTMT permits decreasing the film thickness more than by 10 times. Surface state strongly affects all studied parameters: characteristic temperatures, recovery strain and TWSME value. Increasing of wire diameter from 0.3 to 0.45 mm leads to significant changes of studied parameters. Forecasting of said influence is difficult because of its ambiguity. Therefore, the oxide film must be eliminated by etching in order to obtain the reliable results

Abstract: The hardness of SiC single crystal is very closer to that of diamond, which makes it greatly difficult to process SiC single crystal. It is usually machined by lapping, but this technique requires a long machining time, resulting in low productivity, So we examine the possibility of ELID grinding in SiC single crystal. Results show that with the use of ELID, mirror surfaces can be achieved with high efficiency.

Abstract: In this paper, a study on the electrochemical behaviour and electrical properties of Al-Zn and Al-Zn-Sn alloys in tropical seawater using open circuit potential (OCP) measurement and electrochemical impedance spectroscopy (EIS) are reported. The results from both the OCP and EIS tests show that surface activation was observed in the Al-Zn alloy with the addition of 1.34 wt.% Sn which can be manifested by the shift of OCP values towards more electronegative direction. The EIS spectra of Al-Zn alloy exhibits a semicircle loop, while the EIS spectra for the Al-Zn-Sn alloy exhibits a semicircle with a semicircle inductive loop. The change in EIS spectra for Al-Zn-Sn alloy is correlated to the increase of surface activation resulting in a less stable passive layer. Equivalent circuits models were proposed to fit the impedance spectra and the corresponding electrical parameters with optimum values were deduced. The modulus impedance in the low frequency region or polarization resistance, R_pol obtained for the Al-Zn-Sn alloy, R_pol = 2.76 kΩ cm²) is slightly decreased compared to the corresponding value of the Al-Zn alloy, R_pol = 3.97 kΩ cm²), indicating a considerable reduction in the protective capability of the oxide layer on the Al-Zn-Sn alloy. It appears that the heterogeneous oxide film and pores formed on the Al-Zn-Sn alloy play a key role in reducing total resistance to the flow of electron at the alloy-electrolyte interface.

Abstract: Plasma Electrolytic Oxidation (PEO) is a powerful technique allowing hardening and corrosion protection of valve metals due to formation of an oxide layer on the metal surface. The addition of fluoride ions to the alkaline electrolyte for the PEO processing of aluminum and magnesium alloys produces significant changes in the structure and properties of the coating [1-, however the mechanism of these changes is not clear. A study of the influence of the fluoride concentration on the composition, structure and morphology of thin (to 20 µm) PEO layers was performed. The oxide layer thickness on aluminum is significantly smaller than that on magnesium. Fluorine is detected as an amorphous phase in the vicinity of the base metal.

Abstract: In order to measure thickness and Study on growth behaviors of oxide layers on grinding wheel surface in ELID, the measurement system consisted of a laser sensor and an eddy current sensor was constructed to do a preliminary research on oxide layer replaced by rust. Through the comparison of the values of the thickness obtained by measurement system and the electron microscope of high precision, in this paper, the accuracy of the measurement result and the feasibility of the system ware verified.

Abstract: In order to measure thickness and Study on growth behaviors of oxide layers on grinding wheel surface in ELID, measurement system accuracy is verificated with laser and eddy current sensor for simulation measurement of oxide layers, Growth behaviour of oxide layers were measured in pre-dressing process, the results indicate inward growth speed of oxide layer is greater than outward growth speed along the radius of grinding wheel in the early , oxide layers keep linear growth and growth speed is the fastest; In the late ,inward growth speed of oxide layer slows, outward growth speed is slightly faster, but overall oxide layer growth slows down.

Abstract: The paper reported the effect of zirconia incorporation on the oxide layer modification of the valve metal such as magnesium coated by plasma electrolytic oxidation (PEO). To incorporate zirconia particles into the oxide layer, PEO coatings were carried out under AC condition in electrolytes containing zirconia powder. After PEO coatings, structure observation revealed that a number of zirconia particles were distributed uniformly throughout the oxide layer while the size and distribution of pores remained unchanged as compared to the results coated by PEO without zirconia. It was found that fine zirconia particles incorporated into the oxide layers played an important role in enhancing the anti-corrosion properties of bare metal.

Abstract: As intravascular biomedical devices, metallic stents are particularly susceptible to corrosion induced by the physiological environment, causing the degradation of mechanical properties and leading to the release of toxic and carcinogenic ions from the SS316L bulk. Therefore, several works have been focused on the development of an ultra-thin fluorocarbon coating that could act both as a drug-carrier for in-stent restenosis and as an anti-corrosion barrier. However, the increase of the corrosion performance was limited by the inevitable permeability of the coating, which exposed some of the sensitive interfacial region to the corrosive environment. Indeed, in previous works, adhesion and growth rate of the film were promoted by the removal of the native oxide layer of the stainless steel which is inhomogeneous, brittle and mechanically unstable. Further refinements of the interface are therefore required in order to enhance the overall corrosion performance without compromising the fluorocarbon film properties and adhesion. Hence, the aim of this work was to enhance the corrosion behaviour of coated SS316L by the creation of a controlled interfacial oxide layer. The native oxide layer was first removed under vacuum and the bare metal surface was subjected to a plasma-reoxidation treatment. Tafel measurements were used to assess the corrosion rates of the specimens. Coated and uncoated modified interfaces were also characterized by X-Ray Photoelectron Spectroscopy (XPS) and Atomic Force Microscopy (AFM).

Abstract: The corrosion behaviors of ferritic/martensitic steel P92, austenitic stainless steel TP347HFG and HR3C have been investigated in supercritical water (SCW) at 550°C under 25MPa with 2ppm dissolved oxygen. After 600h exposue, all the samples formed a stable oxide layer, but of varying thickness and microstructure. A typical dual-layered oxide film on P92 and a single-layered structure on TP347HFG and HR3C were observed by SEM and EDS. Further XRD studies indicated the compositions of oxide layers weren’t independent to the type of the used steel. In comparison with ferritic/martensitic steel, austenitic steel showed a higher corrosion resistance.

Abstract: An enhanced photovoltage is reported to occur in Ge/Si structures with a SiOx layer having a thickness of 0.5-2 nm and placed between a Si substrate and Ge nanoislands. The effect is interpreted in terms of an increased separation distance for photoexcited electrons and holes occurring in the stress fields generated in the oxidized Ge/SiOx/Si structure. The electron-hole separation is modeled utilizing finite-element method techniques, and a good agreement between the experimentally observed enhancement and the computationally increased inter-charge distance is obtained. It is also found that insertion of the oxide layer accelerates the photovoltage decay. This result is interpreted in terms of competing processes, involving the direct recombination of the separated electrons and holes and multi-trapping behavior typical of disordered systems caused by Ge islands.