钛膜表面氧气氧化层研究

研究了钼基钛膜表面氧气氧化工艺;用XRD分析了氧气氢化层的物相,其物相随氧化条件而异,含有Ti、TiO2、TiO、Ti2O、Ti3O和Ti6O等多种物相;用XPS研究了氧气氧化层钛的主要价态,其主要价态为 4、 3和 2价;用AES深度剖析研究了氧气氧化层的厚度,并研究了温度、氧气压力和时间对氧气氧化层厚度影响的规律;所有氧气氧化层均不与腐蚀介质发生作用,证明了该氧化层致密连续.     

Degradation behavior of a commercial 13Cr ferritic stainless steel (SS405) exposed to an ambient air atmosphere for IT-SOFC interconnect applications

The objective of this work was to verify the feasibility of using low Cr ferritic stainless steels to improve IT-SOFC interconnect properties in terms of electrical conductivity and Cr evaporation resistance by taking advantage that low Cr ferritic stainless steels may form conductive and moisture-stable oxide layers of chromite spinels. In this context, surface degradation of a commercial 13Cr ferritic stainless steel (SS405) was studied at 700 °C in ambient air (containing ca. 3% H₂O by volume) for up to nearly 5000 h. The results showed a slow, nearly linear oxidation rate indicating that the oxide scale could not act as a fully protective barrier during a prolonged exposure at 700 °C. Oxidation-induced degradation was mainly due to the effects of Cr depletion in the subscale matrix region and internal oxidation attack. However, analysis of the oxide scale after long-term exposure revealed the presence of an interesting example of all-spinel structure consisting of outer layer of iron-substituted Mn–Cr spinel particles on the top of an inner and continuous Fe–Cr spinel layer. Since SS405 steel contains also Al and Si as minor additions, the distribution of these elements in the spinel oxide scale was studied and found to be rather different. Whereas Si was present exclusively in the inner oxide regions, Al migrated also to the outermost part of the oxide scale. Possible explanations for this unexpected Al surface enrichment are discussed.     

High-Temperature Oxidation Behavior of a Ni-Cr-W-Al Alloy

A study was conducted to examine the isothermal oxidation behavior of a new Ni-Cr-W-Al alloy in air at 1250℃ with different time. Oxidation kinetics was determined from weight-change measurements. The microstructure and composition of the oxide scale were investigated by means of scanning electron microcopy and X-ray diffraction. The results showed that the oxide scales of the alloy were a compact and continuous outer Cr2O3 and NiCr2O4 layer and an inner Al2O3 layer that was in dendrite shape. Oxides scales with good adherence were formed on the surface of the alloy, which made the alloy perform excellent high-temperature oxidation resistance.     

Improvement on the Oxidation Resistance of a Ti3Al Based Alloy by Cr1-xAlxN （0≤x≤0.47） Coatings

Cr1-xAlxN coatings have been deposited on a Ti3Al based alloy by reactive sputtering method. The results of the isothermal oxidation test at 800-900℃ showed that Cr1-xAlxN coatings could remarkably reduce the oxidation rate of the alloy owing to the formation of Al2O3＋Cr2O3 mixture oxide scale on the surface of the coatings. No spallation of the coatings or oxide scales took place during the cyclic oxidation at 800℃. Ti was observed to diffuse into the coatings, the diffusion distance of which was very short, and the diffusion ability of it was proportional to the AI content in the coatings. Compared to Ti, Nb can diffuse much more easily through the whole coatings and oxide scales.     

9Cr低活化马氏体钢在超临界水中的腐蚀行为

利用扫描电子显微镜(SEM)、电子能谱(EDS)以及X射线衍射(XRD)技术研究了9Cr低活化马氏体钢在650℃/25MPa超临界水中的腐蚀行为。结果表明,9Cr低活化马氏体钢腐蚀产物的晶粒随腐蚀时间的延长而长大,晶粒尺寸从200h的5.7μm长大到1000h的10.1μm。表面形成的氧化膜为双层结构,外层为Fe3O4,内层由Fe3O4和FeCr2O4共同组成。由氧化增重结果获得了9Cr低活化马氏体钢在超临界水中腐蚀的氧化动力学表达式,同时其腐蚀机理表现为吸氧腐蚀。     

Improvement on the Oxidation Resistance of a Ti3Al Based Alloy by Cr1-xAlxN (0≤x≤0.47) Coatings

Cr1-xAlxN coatings have been deposited on a Ti3Al based alloy by reactive sputtering method. The results of the isothermal oxidation test at 800-900 ℃ showed that Cr1-xAlxN coatings could remarkably reduce the oxidation rate of the alloy owing to the formation of Al2O3 Cr2O3 mixture oxide scale on the surface of the coatings. No spallation of the coatings or oxide scales took place during the cyclic oxidation at 800℃. Ti was observed to diffuse into the coatings, the diffusion distance of which was very short, and the diffusion ability of it was proportional to the Al content in the coatings. Compared to Ti, Nb can diffuse much more easily through the whole coatings and oxide scales.     

Prediction of surface oxidation weight gain on 7.8 wt% Cr-containing stainless steel electrode during electroslag remelting

The surface oxidation weight gains on 7.8 wt% Cr-containing stainless steel at different temperatures were studied by thermogravimetric analysis and scanning electron microscope (SEM) equipped with energy-dispersive spectroscopy (EDS). The results show that there are two layers of oxide scales covering the surface of steel matrix after 100 min high-temperature oxidation. The inner oxide scale consists of (Fe, Cr) oxide and the outer oxide scale is composed of Fe oxide due to the stronger affinity of Cr with O. The growth of outer oxide scale is dominated by the combined effects of chemical reaction rate and mass transfer. Based on the study of the oxidation kinetics at different temperatures, a prediction model for surface oxidation weight gain on 7.8 wt% Cr-containing stainless steel electrode during electroslag remelting is acquired, providing a reference for the determination of the amount of deoxidiser added into the molten slag during electrode remelting.     

Effect of admixtures of oxygen on the oxidation of iron and Fe−Cr alloys in lead melts

We study the process of oxidation of Armco iron and Fe−16Cr and Fe−16Cr−1Al model alloys held in lead melts with different concentrations of oxygen for 1000 h at 650°C. It was discovered that the intensity of oxidation, the structure, and phase composition of oxide layers are determined by the activity of oxygen in the liquid metal. By the methods of layer-by-layer X-ray diffraction analysis and microscopic X-ray diffraction analysis, it was shown that, for low concentrations of oxygen in lead (C ₀≤10⁻⁶ wt.%), a thin (1–5μm) oxide [magnetite (Fe₃O₄] film is formed on the surface of iron. If alloys are held under the same conditions, then we also observe an increase in the concentration of chromium in the subsurface layers. For higher concentrations of oxygen (up to 10⁻⁵ wt.%), a film of magnetite (with inclusions of pure lead) is formed on the surface of unalloyed iron. In alloys, under the layer of magnetite, we detect the formation of oxide layers with the same composition as a solid solution of Fe₃O₄ and FeCr₂O₄ and the structure of spinel. These layers efficiently suppress the process of penetration of lead but do not completely terminate the process of diffusion of oxygen into the bulk of the material, which eventually leads to the internal oxidation of alloy. Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 33, No. 3, pp. 97–101, May–June, 1997.     

Initial oxidation of Fe–Cr alloys: in situ STM and ex situ SEM observation

Abstract

In order to understand the initial oxidation of Fe–Cr alloys a single crystal of Fe–15Cr (100) was oxidized at 440°C under controlled oxygen partial pressure in a UHV system and the surface morphology was observed using in situ STM (basic pressure 1×10^?10 mbar); in addition, polycrystalline Fe&15Cr was oxidized at 400°C in an IR-furnace in atmospheric air and the morphology was observed using ex situ SEM. The chemistry of the surface oxide layers was studied by XPS.

Preparation of the single crystal in the UHV system did not lead to segregation of Cr to the surface during heating. In situ STM investigation showed that oxidation of Fe–Cr commenced by nucleation of Cr oxide on the surface, due to selective oxidation of Cr. When the Cr at the surface and at the interface was completely consumed by nucleation of Cr oxide, Fe oxidized and covered the initial Cr oxide nuclei, resulting in an Fe oxide layer on the surface. Ex situ experiments showed that initial oxidation of the mechanically prepared polycrystalline alloy depended on the defect distribution in the surface. It started with formation of whisker-type Fe oxides along defects and proceeded with spherical-type nucleation and growth of Fe oxide. In both experiments, the final product on the surface was Fe₂O₃.     

Influence of Cr content on high-temperature oxidation behaviour of arc sprayed Ni–Cr coatings

In this study, the high-temperature oxidation behaviour of arc-sprayed Ni–Cr coatings with high Cr contents of 30, 45 and 50 at.% was investigated in comparison with reference AISI 1020 steel. X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy were utilised to characterise the oxide scales. The oxidation resistance of the steel substrates was found to be enhanced after the application of the Ni–Cr coatings since the oxidation kinetics followed the parabolic law. In addition, the oxidation rate of Ni–50Cr coating was 56.5% lower than that of Ni–30Cr coating, indicating that the oxidation performance of coatings was improved with increasing Cr content. The oxide layers of Ni–Cr coating were found to be a double layer structure protecting the substrate from severely oxidation, which composed of a top layer of NiO and a basal layer of Cr₂O₃ and NiCr₂O₄. The surface of Ni–30Cr coating contained lots of multi-angle NiO crystals, while the surface of Ni–50Cr coating contained a dense Cr₂O₃ structure, suggesting that the growth of NiO crystals was limited due to the large amount of Cr-rich oxides.     

A Novel Deflection Method for Measuring the Growth Stress of Thermally Growing Oxide Scales

A kind of new deflection technique has been developed for measuring the growth stress of thermally growing oxide scales during high temperature oxidation of alloys. The average growth stresses in oxide scales such as Al2O3, NiO and Cr2O3 formed on the surface of the superalloys can be investigated by this technique. Unlike the comventional deflection method, the novel method does not need to apply a coating for preventing one main face of thin strip specimen from oxidizing and can be used under the condition of longer time and higher temperature.     

pH值对Cu-Co合金镀层结构及中温氧化行为的影响

为探索适合用作铁素体不锈钢表面的保护涂层,在不同pH值条件下,通过电沉积法在SUS430铁素体不锈钢表面共沉积Cu-Co合金镀层,并在750℃下进行中温氧化试验,利用X射线衍射(XRD)、扫描电镜(SEM)、能谱分析(EDS)等手段,分析镀层及氧化膜的形貌和组成,结合增重法研究Cu-Co合金镀层的中温抗氧化性能。结果表明:随着pH值的增加,镀层中Co元素的含量逐渐增大,Cu元素含量逐渐减小;在750℃中温氧化时,pH=6试样氧化速率最小;经400 h氧化后,基体表面的氧化物为Cr_2O_3和Fe_3O_4,pH=4镀层的氧化物主要为CuO,pH=5镀层的氧化物开始形成(Cu,Co)_3O_4尖晶石氧化物,pH=6镀层的氧化物中(Cu,Co)_3O_4和CuO成为主相;随着氧化时间的延长,pH=4,5镀层的氧化物晶粒缓慢长大,pH=6镀层的氧化物颗粒逐步细化;Cu-Co合金镀层氧化后的氧化层与SUS430钢的热匹配性较好,且镀层中Co含量较高时,其抗氧化性也较好,因此,pH=6镀液中获得的合金镀层适合用作铁素体不锈钢表面保护涂层。     

Microstructural evidence for counter-diffusion of aluminum and oxygen during the growth of alumina scales

Abstract

A novel, two-stage oxidation experiment is described that enables the outward diffusion of cations in alumina scales during high-temperature oxidation to be analyzed on the basis of microstructural changes in the surface morphology of the scale. Using this technique, observations of aluminum out-diffusion along α-Al₂O₃ grain boundaries during oxidation of Fe–Cr–Al alloys, nickel aluminides and platinum-modified NiAl bond-coats are made. Although microstructural evidence for the inward grain boundary diffusion of oxygen is more difficult to obtain, it still can be demonstrated by the growth of the oxide above interface cavities on nickel aluminides and inside internal cracks in the alumina scales during cyclic oxidation of zirconia top-coated material. SEM examination of the crack surfaces after scale spallation provides a vivid illustration of two simultaneous processes, aluminum outward and oxygen inward diffusion along grain boundaries in the scale.     

Oxidation of Ion Plated Ni—Cr Alloy Film at 300℃

Investigation by using LAS 3000 surfaceanalysis system showed that the oxide of Fe,Cr,Al formed during oxidation were Cr_2O_3,Fe_2O_3and Al_2O_3,but only small amount of nickel oxidewas found.The composition of oxide layers for differentoxidation durations varied in a similar way.In all cases,there exists an oxygen concentrationpeak in the composition profile of oxide layer.There is a transitional zone between oxide layerand alloy film.The thickness of oxide layerincreases logarithmically with the time of oxida-tion.The ion plated Ni-Cr alloy film has verydense oxide layer and good oxidation resistance.     

Spectroscopic ellipsometry studies on various zinc oxide films deposited by ion beam sputtering at room temperature

Various zinc oxide films were deposited by ion-beam sputter deposition (IBSD) under different oxygen partial pressures (P(O2)) at room temperature. The as-deposited ZnO films fabricated at P(O2)>1.0×10(-4) Torr had poly-crystalline structures to absorb water on the surface at ambient condition. Simultaneously, the film surfaces were covered and smoothed by the surface layers formed with the water, hydroxyl (OH(-)) groups, and ZnO materials investigated by X-ray photoelectron spectroscopy (XPS). When the compositions of the surface layers were used in a multilayer fitting model of spectroscopic ellipsometry, the actual optical refractive index of the ZnO film deposited at P(O2)=1.2×10(-4) Torr was found to be about 1.9618 at λ=550 nm.     

Oxygen Permeation Behaviors and Hardening Effect of Titanium Alloys at High Temperature

In order to improve the surface hardness and wear resistance of Ti and Ti alloy components, an oxygen permeationtreatment (OPT) was developed. The oxygen permeation behaviors of three Ti alloys, TA2, TB5 and TC11, treatedin air with O-P medium at high temperature have been studied. The results show that the O-P treatment cansignificantly improve the surface hardness of Ti alloys. The oxidation mass-gain of β-Ti alloy (TB5) is much higherthan α-Ti alloy (TA2) under the same condition, while α β Ti alloy (TC11) is the lowest. All the Ti alloys treatedat this condition produce two surface layers: the outer layer consists mainly of TiO2, as well as trace of other oxides,and the inner layer consists of a Ti-O interstitial solid solution formed by the diffusion of oxygen in α crystal latticeThick scales of β Ti alloy (TB5) are easily formed depending mainly on the poor solid solution content of oxygen,while deep solution layer can be formed since partial β phase has been transformed into α phase. The scales of α-βTi alloy (TC11) are very thin and compact. Aluminum-rich zone, as well as deficient zone, is found in oxide layerrs.A crystallographic characterization of oxygen solution layer has been performed and evaluated by crystallographiclattice constant.     

Effect of sputtered TiAlCr coatings on oxidation and hot corrosion resistance of Ti-24Al-14Nb-3V

The effect of sputtered Ti-50Al-10Cr and Ti-50Al-20Cr coatings on both isothermal and cyclic oxidation resistance at 800 similar to 900 degreesC and hot corrosion resistance at 850 degreesC of Ti-24Al-14Nb-3V was investigated. Results indicated that Ti-24Al-14Nb-3V alloys exhibited poor oxidation resistance due to the formation of Al2O3+TiO2+AlNbO4 mixed scales in air at 800 similar to 900 degreesC and poor hot corrosion resistance due to the spallation of scales formed in Na2SO4+K2SO4 melts at 850 degreesC. Both Ti-50Al-10Cr and Ti-50Al-20Cr coatings remarkably improved the oxidation and hot corrosion resistance of Ti-24Al-14Nb-3V alloy.     

Scale growth on 2·25Cr–1 Mo steel

Abstract

A 2·25Cr–1 Mo steel was oxidised at 600°C in dry flowing oxygen for periods of up to 100 h. The change in the structure of the oxide scale with time was studied thermogravimetrically and microstructurally by use of SEM and EDX analyses. It was shown that an oxide layer of Fe₃O₄ nucleated and spread laterally between layers of α-Fe₂O₃ and a doped spinel oxide.

MST/931     

溅射Ni11Co26Cr6Al0.5Y涂层对镍基合金在1000 ℃氧化行为的影响

通过对有/无Ni11Co26Cr6Al0.5Y涂层镍基合金在1000℃进行氧化动力学曲线测定,及组织结构观察,研究了Ni11Co26Cr6Al0.5Y涂层对镍基合金高温氧化行为的影响。结果表明:高温氧化期间,合金发生外氧化和内氧化,外氧化层由NiO、NiCrO_4、CoWO_4构成,中间氧化物由TiO_2、Al_2O_3、NiWO_4构成,中间层氧化物层抑制了基体中Al元素向外扩散,形成平直连续的Al_2O_3内氧化物层;合金氧化动力学曲线呈现起伏波动的特征。镍基合金经溅射Ni11Co26Cr6Al0.5Y涂层,可有效改善合金的抗氧化性能;涂层的氧化动力学曲线仅在氧化初期有轻微增重而后趋于平稳,遵循抛物线规律,其形成的Al_2O_3氧化膜未发生明显剥落,仅在涂层内及近涂层/基体界面区域存在少量Al_2O_3内氧化物。     

Electrochemical Performance of Surface-Modified LiMn2O4 Prepared by a Melting Impregnation Method

The surface of as-prepared LiMn2O4 was modified with ZnO, Al2O3, CoO and LiCoO2 using a simple nitrate melting impregnation method. Transmission electron microscopy （TEM） studies indicated that oxide nano- particles in the range of 10～50 nm are coated on the surface of the spinel. The surface modified samples show better capacity retention than the unmodified LiMn2O4 spinel at both room temperature and 55℃. Among these samples, the ZnO-modified LiMn2O4 shows the best combination of a high capacity and a low capacity fading rate of 0.036% per cycle at room temperature and 0.064% per cycle at 55℃. The improvement for surface modified LiMn2O4 can be attributed to the inhibition of Mn dissolution and O losses on the surface.