Formation Of Protective Oxide Film Research Articles

The Kinetics and Mechanism of the Selective Oxidation of 20Fe–40Ni–10Mn–30Cr Alloy

Process environments of high carbon activity (a c > 1) and low oxygen partial pressures (p O2) are often encountered in the petrochemical industry. Under these conditions a type of corrosion known as metal dusting occurs. Previous work has identified a 20Fe–40Ni–10Mn–30Cr high temperature alloy as a potential metal dusting resistant material. Knowledge of the kinetics and mechanism of the oxidation of the alloy under low p O2 conditions would provide a better understanding of its corrosion resistant behavior and guide future alloy development. The present work examines the selective oxidation of Mn and Cr in the 20Fe–40Ni–10Mn–30Cr alloy under low p O2 conditions. The conditions for oxidation were selected by fixing the p O2 value such that only Mn and Cr would oxidize. These p O2 values are representative of the conditions that exist in metal dusting type environments. A comparison of the oxide film chemistry and morphology with those formed under metal dusting conditions will inform whether the high carbon activity is playing a role in protective oxide film formation. Low p O2 values are obtained by using a 90:10 CO:CO2 mixture at 1,000 K. Under these conditions an oxide film rapidly forms on the surface of the alloy. Analysis of the oxidized alloy by electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy reveals that the oxide consists of a continuous spinel with the approximate stoichiometry of MnCr2O4, as well as islands of MnO and fibrillar structures of MnCr2O4 stoichiometry. The parabolic rate constant for the growth of the spinel is determined from thermogravimetric analysis [k p = (3.72 ± 0.01) × 10−14 g2 cm−4 s−1], TEM analysis [k p = (6 ± 3) × 10−14 g2 cm−4 s−1] and cross-sectional SEM [k p = (3 ± 1) × 10−14 g2 cm−4 s−1].

EFFECT OF THE TEMPERATURE ON THE FRICTION AND WEAR PROPERTIES OF BULK AMORPHOUS ALLOY

The present paper report the results of an experimental investigation of the temperature effect on the sliding friction and wear properties of the bulk metallic glass (BMG). To improve the friction and wear properties of the BMG, the disk specimens were developed in the alloy system of Fe 67.6 C 7.1 Si 3.3 B 5.5 P 8.7 Cr 2.3 Mo 2.6 Al 2 Co 1.0 using hot metal and industrial ferro-alloys. The friction and wear test was performed using flat-on-flat contact configuration of unidirectional tribometer and Si 3 N 4 ceramic disk used as a counterpart. The worn surfaces of the BMG were observed by using scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS). The results indicated that the friction and wear properties of the BMG depend on the glass transition and the formation of protective oxide film. The friction coefficient decreased with increasing temperature, while it increased slightly when the temperature passed the glass transition temperature (Tg). The worn specimens were exposed to abrasion, adhesion, oxidation and plastic deformation. In addition, obvious surface flow characteristics was accompany during wear test.

Effect of Lead and Lead–Bismuth Eutectic Melts on the Fatigue Life of Steels of the Martensitic and Austenitic Classes

We study the effect of lead and lead-bismuth eutectic melts on the fatigue properties of martensitic Fe-13Cr and austenitic Fe-18Cr-10Ni steels within the temperature range 200-450°С. It is shown that the liquid-metal medium contributes to a significant decrease in the fatigue life of steels and the action of eutectic melt is more negative. The fatigue properties of austenitic Fe-18Cr-10Ni steel undergo weaker changes under the influence of lead and lead-bismuth eutectic melts. The realization of the projects of nuclear power plants of new generation requires the solution of a series of materials-science problems dealing with the development of reactor materials (1−4). It is supposed that steels of the austenitic and ferritic-martensitic classes may serve as the main structural materials of nuclear power plants. Despite the well-known susceptibility of steels of the austenitic class (based on the Fe−Cr−Ni system) to the de- velopment of vacancy porosity in the course of their high-temperature neutron irradiation, it is proposed to make the vessel of a BREST-type fast-neutron reactor and some in-vessel workpieces of chromium-nickel steel, which does not require additional thermal treatment after welding (5). Steels of the ferritic-martensitic class (based on the Fe−Cr system), due to their high thermal and mechanical characteristics, compatibility with the main cooling media, and lower sensitivity to swelling as compared with steels of the austenitic class, remain promising mate- rials for the first wall and blanket of fusion reactors, as well as for fuel elements, steam generators, and structural elements of the coolant pumps in the fast-neutron reactors (6, 7). The melts of heavy metals (Рb, Ві, and their eutectic mixture Pb−Bi), due to their nuclear and thermal prop- erties are regarded as promising cooling media for fast-neutron reactors (of the BREST-, SVBR-, and MBIR- types) and also for the subcritical hybrid systems controlled by accelerators (8−10). The problem of corrosion activity of these media in contact with steels is solved by using lead coolants with controlled oxygen contents, which promotes the formation of protective oxide films on the steel surface (11). Another hazard encountered in the course of operation of nuclear power plants is connected with liquid-metal embrittlement, which manifests itself in the degradation of the mechanical properties of structural materials in the course of their interaction with the melts of heavy metals. Unlike the studies of corrosion processes, the investigations of the influence of liq- uid-metal media on the degradation of the mechanical properties of steels are not systematic. This fact compli- cates the analysis of the mechanisms of crack initiation and propagation and the character of failures depending on the media and operating temperature and does not enable one to predict various manifestations of the interac- tions between liquid and solid metals and, hence, to predict the behavior of structural materials. Therefore, the analysis of the scientific aspects of the effect of lead melts (Рb, Рb−Bi) on the mechanical properties of steels of

(Invited) Metal Oxide Nano Film Characterization for CMP Optimization

This paper focuses on the planarization of metallic films in microelectronics manufacturing by CMP through investigation of metal oxide thin films forming as a result of the chemical component of the process. Tungsten planarization is discussed as a model to establish the role of metal oxide nano-films in achieving material removal through their formation characteristics during polishing. The findings indicate a protective oxide film formation on tungsten, which tends to nucleate at high concentrations of oxidizers and enables material removal through the interaction of nano-particles in the slurry with the surface oxide hillocks.

Sliding wear behavior of Fe-based bulk metallic glass at high temperature

In the past decade Fe-based bulk metallic glasses (BMGs) have attracted increasing attention due to their beneficial properties, including high glass forming ability (GFA), high strength and hardness and high fracture toughness in both fundamental science and engineering application. Most research using these materials has been conducted at room temperature environment, and research that assesses their behavior especially at high temperature has been scarce. We present the results of high temperature effect on the friction and wear behavior of Fe-based bulk metallic glass (BMG), and we tested that this material may satisfy wear and oxidation resistance at high temperature as well as to explore the high temperature wear mechanism of the Fe-based BMG. The dry sliding tribological behaviors of Febased BMG against Si3N4 ceramic were conducted with a pin-on-disc friction and wear tribometer. The morphology of the worn surfaces of Fe-based BMG was examined by scanning electron microscopy (SEM) and the chemical composition characterized with energy dispersive spectroscopy (EDS) to observe the wear characteristics and investigate the wear mechanisms. The overall average friction coefficient value generally decreased with increasing temperature, and the glass transition and the formation of protective oxide film played an important role in the tribological behavior of BMG. The wear resistance of Fe-based BMG was not only from their hardness but also from the formation protective oxide layer. Analysis of the worn surface revealed abrasion, plastic deformation and oxidation during sliding test.

Wear behavior of self-lubricating Fe-Cr-C-Mn-Cu alloys: Smearing effect of second phase particles

Newly developed self-lubricating Fe-Cr-C-Mn-Cu cast composite alloys were investigated to study the role of Cu-rich second phase particles which smear on the wear surface during sliding. The wear resistance of the material was improved with an increasing copper concentration. The improved wear resistance was probably obtained by forming a protective tribofilm, which prevented metal-to-metal contact through smearing of the embedded Cu-rich second phase particles. This formation of protective oxide films during sliding is likely to improve the wear resistance of austenitic Fe-Cr-C-Mn-Cu cast composite alloys.

High temperature cyclic oxidation and hot corrosion behaviours of superalloys at 900°C

Oxidation and hot corrosion are serious problems in aircraft, marine, industrial, and land-base gas turbines. It is because of the usage of wide range of fuels coupled with increased operating temperatures, which leads to the degradation of turbine engines. To obviate these problems, superalloys, viz. Superni 75, Superni 718 and Superfer 800H superalloys (Midhani grade), are the prominent materials for the high temperature applications. It is very essential to investigate the degradation mechanism of superalloys due to oxidation and hot corrosion and substantiate the role of alloying elements for the formation of protective oxide films over the surface of the superalloys. Therefore, the present work investigates the oxidation and hot corrosion behaviour of superalloys exposed to air and molten salt (Na2SO4–60% V2O5) environment, respectively, at 900°C under cyclic conditions. The weight change measurements made on the superalloys during the experiments are used to determine the kinetics of oxidation and hot corrosion. X-ray diffraction (XRD), X-ray mapping and field emission scanning electron microscope (FESEM, FEI, Quanta 200F company) with EDAX Genesis software attachment, made in Czech Republic are used to characterize the corroded products of the superalloys. It is observed that the formation of scale rich in Cr2O3, NiO and spinel NiCr2O4 has contributed for the better oxidation and hot corrosion resistance of Superni 75; whereas relatively lesser hot corrosion resistance of Superfer 800H is due to the formation of non-protective oxides of iron and sulphides of iron and nickel. The parabolic rate constants calculated for the superalloys show that the corrosion rate is minimum in air as compared to molten salt environment.

Metal CMP Optimization Based on Chemically Formed Thin Film Analysis

The conventional demands for development in semiconductor industry are changing as the Moore's Law is approaching to its limits. This paper demonstrates a theoretical optimization approach for the planarization of metal films by Chemical Mechanical Polishing (CMP) process. Optimal removal rate and a smooth surface finish post CMP can be achieved by the combined effect of the chemical and mechanical components of the process. Metal CMP necessitates a protective oxide film formation in the presence of surface active agents, corrosives, pH regulators etc' to achieve global planarization. Formation and mechanical properties of the chemically modified films determine the stresses develop in the film structure delineating the stability of the chemically altered films on the surface of the metal wafer. The balance between the stresses built in the film structure versus the mechanical actions provided during the process can be used to optimize the process variables and furthermore help define new planarization techniques for the next generation microelectronic device manufacturing which is expected to deal with atomic level structures.

Using ToF-SIMS and EIS to evaluate green pretreatment reagent: Corrosion protection of aluminum alloy by silica/zirconium/cerium hybrid coating

Increasing environmental concern has led to the restrictive use of chromate conversion coatings to protect Al-alloys from corrosion. Our research is under way to find environmentally compliant substitute coating such as Si/Zr/Ce hybrid coating. The corrosion protection effect of green pretreatment reagent consisted of Si-containing base solution, Ce- and Zr-containing sealing solutions on the corrosion protection of Al-alloys was studied with a 3.5% NaCl aqueous testing solution. The correlation between the corrosion resistance measured by electrochemical impedance spectroscopy (EIS) and surface chemical composition of the hybrid coating measured by time-of-flight secondary ion mass spectroscopy (ToF-SIMS) was studied. The proposed green pretreatment reagent was found improve the corrosion protection of Al-alloys, presumably due to the formation of protective oxide film acting as an oxygen barrier.

Corrosion and oxidation resistance study of reactive ion beam mixed 316 SS

Corrosion and oxidation resistance behaviour has been studied after reactive ion beam mixing (RIBM) treatment of 316 SS. The RIBM treatment was carried out on 28 nm Al- or 34 nm Si-deposited 316 SS using 30 keV N 2 + ions, at room temperature, at different doses ranging from 4 × 10 16 to 2 × 10 17 ions/cm 2. Structural characterization was done using the GXRD technique. Potentiodynamic polarization studies in 0.5 N H 2SO 4 solution were carried out to determine the corrosion resistance. Oxidation studies were done using the weight gain method. The RIBM-treated 316 SS show the increase in corrosion and oxidation resistances with the dose. The weight gain curves of the RIBM-treated 316 SS follow the logarithmic law indicating the formation of protective oxide film, which helps in preventing further oxidation. The improvements in corrosion and oxidation properties have been concluded to be due to the presence of AlN or Si 3N 4 in the near-surface region of 316 SS. The potentiodynamic polarization studies indicate that 316 SS containing Si 3N 4 has relatively better corrosion resistance than that containing AlN.

Enhancing the corrosion resistance of magnesium alloy AZ91D in 3.5 per cent NaCl solution by cerate conversion coatings

PurposeTo develop new eco‐environmentally friendly surface treatments based on cerate compounds as alternatives to the process involving toxic chromates for the corrosion protection of magnesium alloys.Design/methodology/approachA treatment process in which a surface was alkaline‐etched prior to ceria treatment is proposed. The process involves cleaning, etching in potassium hydroxide followed by treatment in ceria conversion coatings. The effect of surface preparation prior to ceria treatment on the corrosion resistance of AZ91D in 3.5 per cent NaCl solution was measured using AC impedance spectroscopy and DC polarization techniques. Surface examination was performed by scanning electron microscopy, energy dispersive X‐ray.FindingsIt was shown that the ceria treatment can be used as a localized corrosion inhibitor for alloy AZ91D in NaCl solution. The level of inhibition strongly depended on the cerium concentration. Moreover, ceria treatments improved the pitting corrosion resistance due to the formation of protective oxide films which act as a barrier to oxygen diffusion to the metal surface. According to the EIS and polarization measurements, alkaline etching in KOH is more effective in reducing the pitting corrosion of AZ91D than was HCl. It was shown that surface treatment in alkaline solution (KOH) prior to ceria treatments played an important role in inhibiting the active surface sites, rejecting the chloride ions from the surface and forming uniformly distributed oxide film.Originality/valueCeria conversion coatings seem very promising as alternatives to toxic chromating for the corrosion protection of magnesium alloys in NaCl solution.

Oxidation tuning in AlCrN coatings

In this work, we have studied the influence of the coating design and composition on the oxidation behavior of Al x Cr 1− x N ( x = 0.70) coatings. In particular, we have studied the effect brought about by the deposition of an additional subsurface titanium nitride barrier layer as well as by the doping of the AlCrN-based coatings by tungsten, boron and silicon. The coatings studied have been deposited using the cathodic arc vacuum (CAV) technique. The multilayered AlCrN/TiN coatings with TiN sublayer were oxidized in air at 900 °C over 3 h and then analyzed by Glow Discharge Optical Emission Spectroscopy (GDOES) and X-ray photoelectron spectroscopy (XPS). Oxidation tests were performed in air at 900 and 1100 °C for the AlCrN and AlCrWN, AlCrSiN, and AlCrBN coatings. In each case weight gain was measured and the surface morphology of the oxidized samples were studied using Secondary Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS). The results obtained showed that the oxidation behavior of the aluminum rich AlCrN-based coatings could be improved in two ways: (1) by controlling the chromium outward diffusion rate in multi-layered coatings and (2) by alloying the AlCrN-based coatings with Si. Both improvements are related to the enhancement of the protective oxide film formation.

Corrosion resistance of Cu–Zr–Al–Y and Zr–Cu–Ni–Al–Nb bulk metallic glasses

Electrochemical tests of amorphous Cu 46Zr 42Al 7Y 5 in comparison to amorphous Zr 58.5Cu 15.6Ni 12.8Al 10.3Nb 2.8 (Vit106a) were conducted by potentiodynamic polarization at room temperature in 0.001–0.1 M NaCl aq (pH 8). The influence of corrosion on the surface topography was studied by X-ray diffraction and SEM. Electrochemical measurements indicate a good corrosion resistance of both bulk metallic glasses in NaCl solutions with low molarity at pH 8 due to the formation of protective oxide films. However, at high NaCl molarity the Cu–Zr–Al–Y glass shows no passive layer and is very susceptible to pitting corrosion. The mechanisms of the formation of the oxide films as well as the nucleation and growth of pitting were clarified by associating microstructural investigations with the results of electrochemical measurements.

Advanced nano-particles anti-corrosion ceria based sol gel coatings for aluminum alloys

Chromate conversion coatings can be successfully used for the corrosion protection of aluminum alloys. However, the environmental laws in many countries have imposed severe restrictions on chromate use due to its high toxicity and consequent environmental hazards. Many attempts have been made to find alternatives to chromating such as cerate. In this work, the effect of surface preparation prior to ceria treatment was studied. A series of specimens was prepared under the following conditions: (a) as polished, (b) directly treated, (c) etched, (d) oxide thickened, and (e) etching followed by oxide thickening. After surface preparation, the specimens dipped in ceria solutions prepared by sol–gel method. Electrochemical Impedance Spectroscopy (EIS) and polarization measurements have been used to evaluate the coating performance in 3.5% NaCl. The optimum conditions under which ceria treatments can provide good corrosion protection to the aluminum substrate were determined. Generally, ceria treatments improve the corrosion resistance due to the formation of protective oxide films which act as a barrier to oxygen diffusion to the metal surface. According to the EIS and polarization measurements, a combination between etching and oxide thickening has a vital role on the corrosion protection performance of AA6061-T6 in NaCl.

Corrosion protection of aluminum composites by silicate/cerate conversion coating

The effect of silicate surface treatments on the corrosion inhibition characteristics of AA6061 T6-10% Al 2O 3 composite were studied in 3.5% NaCl. A series of specimens was carried out at different silicate concentrations using different application methods alone or combined with a sealing step in cerium solutions. The effect of surface etching and oxide thickening were also studied. Electrochemical impedance spectroscopy (EIS) was used to investigate the corrosion behavior of treated and untreated specimens. The pitting corrosion behavior and the perfect passivity domain were measured using potentiodynamic tests. The occurrence of localized corrosion due to chloride ion attack was examined by optical microscopy and SEM. Generally, silica/ceria treatments improve the corrosion resistance due to the formation of protective oxide films which act as a barrier to oxygen diffusion to the metal surface. Ceria sealing specimens showed a superior corrosion resistance indicating that cerate and not silicates plays the main part in the passivation mechanism. According to the EIS results, the etching process has a negative effect on the corrosion resistance.

Characterisation of co-sputtered Nb:Cr coatings grown by the combined cathodic arc/unbalanced magnetron sputtering technique

Niobium and chromium are both well known for their corrosion resistance due to the formation of protective oxide films. Sputtering is the preferred physical vapour deposition technique to deposit refractory metals such as Nb, but owing to its high melting point high ion bombardment and/or high deposition temperatures are necessary to grow dense Nb films. Further disadvantages of Nb are its relatively low hardness values and the low oxidation resistance of Nb. The present paper discusses experiments of co-sputtering Cr and Nb using the combined cathodic arc/unbalanced magnetron technique. The corrosion resistance of the 1 μm thick coatings deposited on 304 stainless steel substrates at 250 and 420°C is investigated by potentiodynamic polarisation measurements in a 3% NaCl solution. The formation of solid solutions of Cr in Nb and of the intermetallic phase of Cr2Nb were found to increase the microhardness, as well as the oxidation resistance, of the sputtered coatings substantially in comparison with pure Nb films.

An evaluation of potential material–coolant compatibility for applications in advanced fusion reactors

In assessing possible potential issues for fusion applications, the compatibility of several metallic structural materials was examined using high temperature/pressure steam as test environment. High corrosion resistance associated with protective oxide film formation was regarded as essential for the function of protecting from tritium permeation and corrosion damage. A Ti–Al-based intermetallic compound with V addition, recently developed, showed excellent performance. A low-activation ferritic/martensitic steel, F82-H, was comparable with the current advanced materials for modern supercritical fossil boilers, while some potential vanadium alloys, although not intended for use in steam, were found less compatible.

Tem characterization of diffusion bonding of superplastic 8090 Al-Li alloy

In recent years there has been a growing interest in developing a joining process compatible with other fabrication technologies used in the aeronautical industry for superplastic aluminum-lithium alloys, and it is shown in numerous publications. There have been important advances in the research of the aluminum-lithium alloys diffusion bonding, and specially for the AA8090. However, joining of aluminum alloys by diffusion bonding encounters inherent problems which have not been solved yet. Most of these limitations come from the formation of protective oxide film (Al{sub 2}O{sub 3}) which covers the aluminum based materials. In spite of these unresolved difficulties, most of the investigators, among them are the present authors, have agreed that aluminum alloys which contain lithium as alloying element, present a higher weldability than Li-free aluminum ones. To explain this enhanced diffusion weldability in Li-doped alloys, it has been argued that Li favors the partial elimination of the unsoluble and tenacious alumina film, which acts as a diffusion barrier, through the formation of more soluble and brittle complex spinel (Al-Li-O). Nevertheless, the elimination of these oxides is not complete, resulting, in the most advantageous conditions, in a discontinuous distribution of oxide particles along the bonding interface which controls the finalmore » properties of the bond.« less

Elevated-temperature environmental embrittlement and alloy design of L1 2 ordered intermetallics

Ordered intermetallic alloys with L1 2, crystal structure such as Ni 3Si exhibit environmental embrittlement with much lower ductilities in air than in vacuum when being tested at elevated temperatures. The environmental embrittlement is sensitive to test temperature, alloy composition and grain geometry. The embrittling behavior at elavated temperatures is a dynamic phenomenon, i.e. gaseous oxygen in test environments is chemically absorbed at the tip of cracks induced on alloy surfaces by deformation and then drives into the metal along grain boundaries, leading to a reduction of the grain boundary cohesion. The embrittlement can be alleviated by formation of protective oxide films on alloy surfaces, control of grain shape or addition of beneficial elements such as chromium. In contrast, ordered intermetallics based on b.c.c. crystal structures such as FeAl(B2) and Fe 3Al(DO 3) do not show environmental embrittlement at elevated temperatures. The embrittling behavior as well as alloy design to alleviate the embrittlement is discussed in this paper.

Formation of protective oxide film on chromium-depleted stainless steel

AbstractCoupon specimens of a niobium-stabilized 20Cr–25Ni stainless steel were annealed in a dynamic vacuum at 1273K to produce preferential evaporation of chromium. Two sets of specimens, one coarse grain with a surface-chromium concentration of ∼ 14% and the other having a bimodal grain size distribution and surface concentration of ∼ 16%, were subsequently oxidized at 1123 K in a CO2-CO gas mixture. The coarse-grain samples produced uniformly duplex non-protective oxides while those of mixed grain size exhibited a non-homogeneous reaction. Regions of coarse grains on the latter again developed a duplex pitting-type attack but fine grains were protected by a thin chromia-rich layer. The reasons for this difference are discussed. It is argued that the protective film was not produced as a result of a significantly greater supply of chromium ions but was due to easier nucleation on the fine-grain substrate.