Μm Thick Oxide Layer Research Articles

Effect of H2S on the corrosion behavior of austenitic and martensitic steels in supercritical CO2 at 550 °C and 20 MPa for Brayton cycle system

Corrosion of alloy materials significantly influences the stability and efficiency of the supercritical carbon dioxide (S-CO2) Brayton cycle. In this study, we investigated the corrosion behavior of the austenitic alloy SP2215 and the martensitic alloy X19CrMoNbVN11-19 (X19) in S-CO2 at 550°C and 20 MPa. The effect of impurities, H2S, on corrosion behavior was studied. After 900 hours, SP2215 formed a 1.1 μm thick oxide layer (Cr2O3). X19 formed a loose and porous double oxide layer of 4.1 μm (outer: Fe3O4, inner: FeCr2O4). After H2S doping, SP2215 had an oxide layer of 6.2 μm (FeS, SiO2, and Cr2O3), while X19 was 9.8 μm (outer: Fe3O4, SiO2, FexSy and Fe2O3, inner: FeCr2O4, Fe2SiO4 and Cr2S3). Metal sulfides formed and the corrosion layer thickened. This indicates that H2S not only changes the corrosion mechanism but also aggravates the corrosion. However, the corrosion of CO2 is dominant. SP2215 has better corrosion resistance than X19.

Hydrodynamic Flexible Spindle (HydroFlex) Polishing of turbine blade internal cooling channels for oxide removal

Internal cooling channels are essential to turbine blades for high efficiency power generation. Effective removal of aluminum oxide build-up in turbine blade cooling channels is of critical importance to refurbishment and prolonged service life of turbine blades. Conventional internal polishing processes, including abrasive flow machining, chemical polishing, and electrical discharge machining cannot effectively remove the oxide layer within the internal cooling channels due to the complex geometry with high aspect ratio and diameter variation and the electric insulation of the oxide layer. In this case study, we investigated the application of a novel hydrodynamic flexible-spindle (HydroFlex) polishing process to remove the oxide layer within the internal cooling channels of an Inconel 738 turbine blade that was taken out of serve due to oxide build-up. For a 350 mm long cooling channel featured with an inner diameter transition from ϕ4 mm to ϕ2.5 mm, within 12 min, at the grinding wheel rotational speed of 50,000 rpm and 30,000 rpm, HydroFlex was able to completely remove the 14.31 µm thick oxide layer off from the wall of the turbine blade internal cooling channel, improve the channel circularity by 54.7 %, and decrease the channel surface roughness by up to 64.3 %. The results demonstrated the effectiveness of HydroFlex in polishing complex internal cooling channels of turbine blades for oxide removal and potential blade service life extension.

The oxidation-resistant Mo30Si60B10 coating for protection of the T2 phase-based molybdenum alloy

This study focuses on fabrication of a Mo30Si60B10 coating with elevated silicon content, which enhances working properties of Mo-alloy based on the Т2 phase (t-Mo5SiB2). The Mo30Si60B10 coating has a columnar structure. The alloy is characterized by hardness of 17 GPa; Young's modulus of 304 GPa, and elastic recovery of 29 %. Deposition of the coating increased hardness by 40 %; the Young's modulus, by 18 %; and elastic recovery, by 25 %. Oxidation tests at 1200 °C demonstrated that the specific mass loss of the alloy with Mo30Si60B10 coating was 1.5-fold lower than that of the uncoated alloy. An 18 μm thick oxide layer based on a-SiВO and containing MoO2 particles was formed on the alloy surface. The coating contributes to a ∼14-fold reduction of oxide layer thick. The increase in oxidation resistance of alloy after coating deposition is related to sealing of substrate defects and formation of an a-SiВO layer with elevated silicon content.

Accelerated Formation of Oxide Layers on Zircaloy-4 Utilizing Air Oxidation and Comparison with Water-Corroded Oxide Layers.

For the dry storage of Canada Deuterium Uranium (CANDU) spent nuclear fuels, the integrity of Zircaloy-4 fuel cladding has to be verified. However, the formation of ~10 µm-thick oxide layers in typical CANDU reactor operating conditions takes several years, which makes sample preparation a slow process. To overcome such limitations, in this study, an accelerated formation of an oxide layer on Zircaloy-4 cladding tube was developed with a combination of high-temperature water corrosion (HT-WC) and air oxidation (AO). First, Zircaloy-4 tubes were corroded in oxygenated (2 ppm dissolved oxygen) high-temperature water (360 °C/19.5 MPa) for 500 h. Then, the tubes were air-oxidized at 500 °C for 30 h. Finally, the tubes were corroded again in HT-WC for 500 h to produce ~10 µm-thick oxide layers. The morphology and characteristics of the oxide layer in each step were analyzed using X-ray diffraction, scanning and transmission electron microscopy. The results showed that the oxide layer formed in the accelerated method was comparable to that formed in HT-WC in terms of morphology and oxide phases. Thus, the accelerated oxide formation method can be used to prepare an oxidized Zircaloy-4 cladding tube for CANDU fuel integrity analysis.

Analysis of Thermally Grown Oxides on Microperforated Copper Sheets

Copper oxides have some interesting photocatalytic properties and reasonably low price which makes them applicable as PN transistors. However, to obtain the best performance it is necessary to increase the specific working surface of materials which plays a key role in many applications. Furthermore, by ordered spacing and heterojunction formation it is possible to fabricate the systems with specific dedicated properties, like for example PN photovoltaic junction. The conducted research analyses the mechanical properties, stress distributions, and thermal stability of metal–oxide structures with such advanced geometries. Micro-perforation of thin Cu sheet was selected for the study, as it can both enhance the free surface of the substrate and decrease the number of sites of thermal stress occurrence. Both Cu-Cu2O and Cu-CuO layers were simulated using finite element analysis. The model based on fixed geometry of square shaped samples of dimensions of 156 × 156 mm was applied to thin metal plates holes-patterned covered on top by 1-3 μm thick oxide layers. On the other hand, the influence of plate thickness was found to be important in terms of structure durability. A good agreement between the simulation and the experimental data was achieved. The critical delamination temperature of c.a. 473-483 K was estimated for both oxide layers. The verification of the simulation/computation model was done by analyzing perforated and non-perforated Cu Electrolytic Tough Pitch (ETP) sheets. Two methods, FIB-TEM and surface scan using a profilometer, were selected. The first verified the decohesion of the oxide coatings from the metal support after exceeding the temperature of 523 K The issue that was also noticed is the susceptibility for peeling in the inner surface of the holes.

Thermal oxidation of a porous Ti[sbnd]23Nb alloy for wear related biomedical applications: Effect of oxidation duration

In this study, an attempt has been made for tailoring the surface features of an 18 vol% porosity containing Ti23Nb alloy manufactured via powder metallurgy method. The aim was enhancing the wear resistance without sacrificing the mechanical properties. For this purpose, porous Ti23Nb alloys having hardness of 280 HV0.025 were subjected to thermal oxidation (TO) at 600 °C in air for two different holding times. TO duration of 6 h, which introduced a ~ 0.5 μm thick TiO2-rutile type exterior oxide layer (OL), provided surface hardness of 620 HV0.025. Extension of TO duration to 60 h caused covering of the surfaces with a ~ 3.0 μm thick OL and increase of surface hardness to 980 HV0.025. As the result of the increased surface hardness, TO'ed. alloys showed superior sliding wear resistance coupled with a reduction in friction coefficient (COF) against alumina ball in 1.5× simulated body fluid (SBF) when compared to the as-sintered state. Despite having the highest surface hardness, the alloy TO'ed. for 60 h exhibited slightly higher wear loss and COF than the alloy TO'ed. for 6 h. More important than this, the alloy TO'ed. for 60 h collapsed at a compressive stress well below the yield strength of the alloy TO'ed. for 6 h, which exhibited almost similar compressive stress-strain curve with that of the as-sintered alloy. From this perspective 6 h appeared as a promising TO duration for the examined porous alloy to be used in biomedical applications as it preserves the mechanical properties while providing remarkable enhancement in the wear resistance.

Development and certification of chromic acid-free anodizing process for aircraft grade aluminium alloys

Chromic acid (Cr 6+ ) anodization process is widely used for the corrosion protection of aircraft aluminium alloys. Hexavalent chromium being toxic in nature need to be phased out by eco-friendly alternatives. In the present study modified tartaric-sulphuric acid (TSA) process has been developed followed by sealing in permanganate based bath to obtain 4 to 6 µm thick anodic oxide layer on 2024-T3, 6061-T6 and 7075-T6 aluminium alloys. The process was carried out using a pilot scale anodizing plant. The anodized specimens were characterized for visual observation, thickness, adhesion, electrical breakdown voltage, corrosion resistance and tensile behaviour. All the tests were carried out as per MIL-A-8625F specifications. The specimens were also subjected for about 800 hrs to real time corrosion testing, 200 metres away from sea shore at Mandapam Camp, Rameshwaram, India. The performance of the permanganate sealed TSA anodized aluminium alloys are comparable with that of the conventional chromic acid anodized coatings. This chromic acid-free anodization process has been qualified to airworthiness regulating standards by Indian military certification authorities. Efforts are in progress to commercialize this technology for use on aero platforms.

High resolution, high channel count mid-infrared arrayed waveguide gratings in silicon.

Arrayed waveguide gratings (AWGs) working in the 4.7 µm wavelength range are reported on silicon-on-insulator waveguides with 1500 nm thick silicon and 2 µm thick buried oxide layers. For eight channel devices, three different channel spacings (200 GHz, 100 GHz, and 50 GHz) with cross talk levels of -32.31dB, -31.87dB, and -27.28dB and insertion loss levels of -1.43dB, -4.2dB, and -2.3dB, respectively, are demonstrated. Fourteen channel AWGs with 170 GHz channel spacing and 16 channel AWGs with 87 GHz channel spacing are shown to have a cross talk value of -21.67dB and -24.30dB and insertion loss value of -4.2dB and -3.8dB, respectively. Two AWGs with 10 nm difference in channel peak are designed, and the measurements show a 9.3 nm difference. The transmission spectrum shift as a function of temperature is found to be 0.22 nm/°C.

Edge-Coupling of O-Band InP Etched-Facet Lasers to Polymer Waveguides on SOI by Micro-Transfer-Printing

O-band InP etched facets lasers were heterogeneously integrated by micro-transfer-printing into a 1.54 μm deep recess created in the 3 μm thick oxide layer of a 220 nm SOI wafer. A 7 × 1.5 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> cross-section, 2 mm long multimode polymer waveguide was aligned to the ridge post-integration by e-beam lithography with <; 0.7 μm lateral misalignment and incorporated a tapered silicon waveguide. A 170 nm thick metal layer positioned at the bottom of the recess adjusts the vertical alignment of the laser and serves as a thermal via to sink the heat to the Si substrate. This strategy shows a roadmap for active polymer waveguide-based photonic integrated circuits.

Structural, physical, chemical, and biological surface characterization of thermomechanically treated Ti-Nb-based alloys for bone implants.

Metastable near-beta Ti-21.8Nb-6Zr and Ti-19.7Nb-5.8Ta (at%) alloys were subjected to a thermomechanical treatment comprising cold rolling (CR) with a true strain of e = 0.3 and post-deformation annealing (PDA) in the 500-900°C temperature range to ensure the superelastic behavior which is important for bone implants. It was found that PDA resulted in formation of about 1-2 μm-thick oxide layer on the Ti-Nb-Zr and Ti-Nb-Ta alloy samples; the layer was mainly composed of TiO2 , in rutile and anatase modifications. The structure, the phase and chemical compositions, and some surface-sensitive properties of the alloys were compared to those of Ti-50.7Ni and Ti-Grade2 reference materials. These surface layers (especially that of the Ti-Nb-Zr alloy) demonstrated a promising combination of high cohesion strength (load causing surface layer fracture is over 25 N), hardness (∼12 GPa), and hydrophilicity (contact angle ∼40°). Surface modification by controlled oxidation during air annealing increases corrosion resistance and enhances in vivo osteoinductive properties of Ti-Nb-Zr alloys by changing the surface microrelief, increasing the surface wettability, and improving the mechanical characteristics, thus laying the foundation for the development of medical implants with prolonged service life. So, it was confirmed that the same thermomechanical treatment, which creates conditions for the superelastic behavior of the bulk metal (CR: e = 0.3 + PDA = 500-700°C for 1 hr), would also create a strong, protective and biocompatible layer on the implant surface.

Formation of Surface Deposits on Steel and Titanium Aviation Fuel Tubes under Real Operating Conditions.

In this study, stainless steel and titanium (Ti) tubes obtained from a turbofan engine after the end of its lifetime were analyzed in order to compare the amount of pyrolytic coke present and its influence on the parent, base material. Various analytical techniques including microhardness and topographical evaluations, optical emission spectrometry (OES), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS) were applied. On steel surfaces, a thick pyrolytic coke deposition layer consisting of carbon and oxygen and also containing elements from the tube material, fuel, and fuel additives was found. The concentration of elements from the pyrolytic coke continuously decreased with distance from the surface of the deposit, while the concentrations of elements from the tube material continuously increased, with the concentrations of elements from the fuel and the fuel additives being relatively constant. With ultrasonic cleaning in distilled water, most of the deposits could be removed. Only carbon-rich patches with a thickness of more than 300 nm remained adhered to the surface and/or had diffused into the original material. On Ti surfaces, the thickness of the C-rich fuel deposit layer was significantly thinner as compared to that on the stainless steel; however, the surface was covered with an ∼3 μm-thick oxide layer, which consisted of elements from the fuel additives. It is believed that the beneficial properties of Ti covered with a thin layer of TiO2, such as low adhesion and/or surface energy, have promoted different deposition mechanisms compared to those of stainless steel and thus prevented pyrolytic coke deposition and the related material deterioration observed on stainless steel.

Nickel-chromium (Ni–Cr) coatings deposited by magnetron sputtering for accident tolerant nuclear fuel claddings

Nickel-chromium coatings were deposited on Zr1Nb alloy using magnetron sputtering systems with «hot» Ni and cooled Cr targets. The effect of coating composition on high-temperature oxidation resistance and hydrogen uptake of Zr1Nb was studied. Hydrogen uptake of the alloy was measured in situ under gas-phase hydrogenation at 633 K. High-temperature oxidation was performed in air atmosphere at 1173–1373 K for 20 min. It was shown that the coating with high Ni content (83 at.%) drastically increases hydrogen uptake of the Zr1Nb alloy and demonstrates low oxidation resistance even at 1173 K. The coatings with Cr content ≥45 at.% have low hydrogen permeability which reduces the rate of hydrogen uptake of the alloy. The oxidation resistance of the NiCr coatings increases with Cr content in the as-deposited coatings. The pure Cr coating exhibits the best oxidation resistance: only 8 μm-thick oxide layer was observed. There is also found the intensive diffusion of nickel into the alloy during high-temperature oxidation of the samples coated by NiCr films with 55 and 17 at.% Ni. The as-deposited NiCr coatings are less brittle than the pure Cr coating, but their mechanical properties degrade stronger than for the Cr coating after the oxidation test.

Significant effect of oxide on mechanical properties of friction-stir-welded AA2024 joints

A 30–40 μm thick oxide layer was prefabricated on the top, butt or bottom surfaces of AA2024 sheets by micro-arc oxidation, which were then friction stir welded. Sheets without oxide layer were also welded with blowing oxygen along the weldline during welding for comparison purposes. Results reveal that the tensile properties depend on the amount and distribution of the residual oxide impurities in the joints. The oxide layer on the butt surface leads to continuously distributed oxide impurities in the shoulder-affected zone near the advancing side, and a 159 MPa maximum degradation in tensile strength was noticed. Moreover, the oxygen blowing during welding has a little influence on the joint tensile strength and no oxide was detected in the joint.

Fabrication and characterization of suspended beam structures for SiO2 photonic MEMS

This paper proposes a microfabrication process for the reliable release of SiO2 beam structures. These structures are intended to be utilized in SiO2 photonic MEMS. A major fabrication challenge is the release of thick (>10 μm) SiO2 structures with high yield. A single mask process is developed based on temporary reinforcement of the SiO2 structure. A supporting layer of Si functions as a reinforcing layer during etching and release, thereby enabling a high fabrication yield. Furthermore, the process allows to create structures of which the final Si support thickness is configurable from tens of micrometers to zero, thereby providing additional design freedom.The fabrication process is tested on a silicon wafer with a ∼15 μm thick thermal oxide layer. The obtained suspended structures are mechanically characterized. Two deformation effects can be distinguished: a curvature of the beam and a slope at the base of the beam. These effects are caused by the compressive mean stress and the gradient stress in the thermal SiO2. The curvature of the SiO2–Si beams corresponds to a concave downward profile while the SiO2 beams without supporting Si reveal a small curvature in the opposite direction (concave upward). The slope at the base is approximately for the SiO2 beams and between and 0° for the SiO2–Si beams. The acquired bending stiffness of long SiO2 beams is in the newton per meter range (e.g. 0.8 N m−1 for a cantilever measuring 1000 μm in length and 13 μm in width).

Oxidation behavior of nickel coating on ferritic stainless steel interconnect for SOFC application

The oxidation behavior of nickel coated ferritic stainless steel SS441 has been investigated. A nickel coating layer is deposited on the steel which is employed in a solid oxide fuel cell stack as interconnect. The nickel film is about 8 μm thick and is topped by an additional 4 μm thick La0.67Sr0.33MnO3 (LSM) film on the interconnect cathode-contacting surface for the prevention of chromium evaporation from the steel substrate. A 10,000-h 800 °C isothermal ageing on 10 × 10 mm2 steel coupons shows a continuous growth of oxide scales up to ∼200 μm in thickness on the surface, consisting of a 100 μm thick iron oxide layer followed by a complex Fe–Ni–Cr spinel structure. A single-cell stack is tested at 800 °C for up to 1226 h and an average degradation rate of 7.5% kh−1 is observed. Oxidation characteristics of the coating system are analyzed after testing. A Fe–Ni spinel phase is found covering most of the surface area. This is attributed to the intensive interdiffusion of iron and nickel during the stack operation and the high intersolubility of the two elements. In both the tests of the steel coupons and the stack, LSM film structures are damaged by the thermally grown Fe–Ni oxides, and the expected Cr-preventing function is limited. The Fe–Ni spinel layer initially forms an effective obstacle against Cr out-migration. However, the increasing content of iron in the spinel phase induces oxide scale spallation afterwards. Though the fast grown Fe–Ni oxide scale can serve as an effective barrier against chromium out-migration, the iron-enriched scale structure is susceptible to corrosion attacks after an extended stack operation period.

Influence of High-temperature Oxidation on Soft Magnetic Properties of Fe78Si9B13 Amorphous Alloy

Abstract The influence of high-temperature oxidation on soft magnetic properties of Fe78Si9B13 amorphous alloy was investigated using various analysis methods. The results reveal that a 10 μm thick iron oxide layer with high resistivity can be obtained on the surface of Fe78Si9B13 amorphous ribbons by high temperature oxidation treatment. It is found that the amorphous alloy magnetization becomes harder and the saturation induction density changes after the high-temperature oxidation. The saturation induction density value changes from Bs=1.42∼1.46 T without chemical oxidation, to Bs=1.29∼1.38 T after high-temperature oxidation. The factors which have a great effect on the magnetization difficulties of the amorphous ribbons were discussed.

A new wafer level TSV build-up stacking using oxide bonding

A new through-silicon via (TSV) build-up stacking method using oxide bonding is proposed and implemented in this work. The proposed method can be applied to the fabrication of a TSV stack chip. Thermal stress analysis was carried out to compare the structural reliability between conventional TSV and the proposed TSV model. The simulation results indicate that the proposed TSV model is more reliable than the conventional model with respect to stress in the stack chip. Experiments were conducted by oxide bonding of chips and the oxide bonding energy was acquired by a four point bending test. The obtained bonding energy sufficiently exceeds the energy criteria of 3D stacking. Thus, two oxide wafers with an 8 inch diameter were bonded by oxide bonding at the wafer level. The 0.6 µm thick oxide layers were located between bonded wafers and the top wafer was thinned down to fabricate blind via at the top of bonded wafer. The thickness of the top and bottom wafer is to 70 and 725 µm, respectively, after the top chemical mechanical polishing (CMP) process. Then blind vias were fabricated by deep reactive ion etching; the diameter and depth of the via is 20 µm and 150 µm, respectively. A through hole was formed by bottom CMP; total thickness of the oxide bonded wafer is 140 µm. The dielectric layer (SiO2), adhesion and diffusion barrier (TiN, Ti) and wetting layer (Cu) were deposited sequentially to improve the wettability of the via wall. Since the molten solder cannot be filled in the via if there is no wetting layer at the via wall. Finally, the vias were successfully filled with molten solder within 10 s.

Study of edge termination structures for high power GaN Schottky diodes

AbstractDifferent structures of field plate termination were analysed by numerical simulation to enhance the breakdown voltage of quasi‐vertical GaN Schottky diodes. A bevel shaped field plate achieved a maximum breakdown voltage of 1990 V for 1.5 µm thick oxide layer with 18 µm bevel width. Maximum breakdown voltage was achieved when the bevel angle is 5°. A fabrication friendly 4 step field plate structure achieved a breakdown voltage of 1650 V and 1970 V respectively, with oxide and silicon nitride passivation. The width and thickness of the first step were the most influential factors in deciding the maximum breakdown voltage. A multi‐step field plate structure, which is an emulation of bevel structure, achieved a breakdown voltage of 1600 V and 1850 V with oxide and silicon nitride passivation layers, respectively. (© 2011 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Influence of target design on the damage threshold for optically powered MEMS thermal actuators

Bent-beam, polycrystalline silicon MEMS thermal actuators were optically powered using laser illumination. The actuators were designed with a target suspended between angled legs that expand creating displacement and force when the target is heated by a laser. The laser power threshold for immediate damage and extent of the damage exhibited a strong dependence on the target design. The optically powered thermal actuators were fabricated using a five-layer surface micromachining process from combinations of 2.25 μm thick polysilicon layers (poly3 and poly4) and a 2.0 μm thick sacrificial layer. The target compositions listed in decreasing order of laser damage threshold are: the poly3–poly4 laminate targets, the poly3–poly4 targets with an intermediate 2.0 μm thick oxide layer, the poly3–poly4 targets with a 2.0 μm thick air gap, and the poly4 only targets. The laser damage thresholds for the poly3–poly4 targets with connecting posts and an air gap increases with increasing post size, which allows for better thermal transport from the irradiated poly4 layer to the underlying poly3 layer. The laser damage thresholds ranged from a maximum of 475 mW for an oval poly3–poly4 laminate actuator target to a minimum of 190 mW for a circular poly4 only actuator target.

Al and Ti secondary neutral and secondary ion emission from oxide samples in the high-frequency sputtering mode of HF-plasma SNMS

A strong Al+ and a minor Ti+ peak without a proportional increase of the O+ signal in SNMS high-frequency sputtering mode (HFM) time profiles of an insulating µm-thick oxide layer on Ti-48Al-2Cr-2Nb led us to check for a possible contribution of positive secondary ions (SI+). SI+ and SI– (negative secondary ions) can be detected in ion energy spectra. This is shown using Al+, O–, AlO–, and AlO2– ions sputtered from massive Al2O3. Similarly, and depending on stoichiometry, also Ti+ from mixed sintered, microscopically inhomogeneous Al2O3-TiO2-SiO2 pellets has been identified to be partly SI+. The subtraction of an assumed contribution of ionized secondary neutrals (SN+) suggests that SI+ may form several 10% of the detected ions obtained in the HFM sputtering and plasma processes. However, the positive surface potential of some 10 V being necessary to cause detectable SI+ contributions does not build up on µm-thin insulating layers. Therefore, we have to conclude that the Al+ and Ti+ peaks in the sputter time profiles of the µm-thick oxide layer on Ti-48Al-2Cr-2Nb which are accompanied by an O+ deficiency cannot have been caused by SI+. Instead, their more probable origin is the inhomogeneous Al2O3 interlayer itself. Together with the residues of a topmost TiO2 layer which has strongly been depleted in O by preferential sputtering, the relative O+ deficiency may be explained without assuming SI+ contributions.