Role Of Oxide Films Research Articles

The role of oxide films in preventing liquid metal embrittlement of T91 steel exposed to liquid lead-bismuth eutectic

The effect of oxygen concentration dissolved in liquid lead-bismuth eutectic (LBE) on the low cycle fatigue properties of T91 ferritic-martensitic steel has been investigated under different temperatures, strain rates and total strain ranges, with an emphasis on the role of oxide films in prevention of liquid metal embrittlement (LME). The results showed that the fatigue life in the presence of LBE was strongly temperature-dependent. Specifically, the fatigue life was observed to decrease with increasing the temperature from 160 °C up to 350 °C, and then show an increasing trend up to 450 °C. Only at the relatively high temperature range of 300–450 °C, the oxygen concentration played a role, and the oxygen-saturated condition was found to increase the fatigue life by a factor of 2–3 in comparison to the oxygen-depleted condition. In addition, a significant oxygen effect was also observed under low total strain ranges, and especially the fatigue life was found to be comparable with that in vacuum under a combination of high oxygen, slow strain rates and low total strain ranges. This can be attributed to protective oxide films that were not damaged under this condition and hence had delayed fatigue crack initiation. Once cracks initiated, however, LME occurred at crack tips, causing fast crack propagation. Thus, the nature that T91 is susceptible to LME was not changed by the oxides. The results indicate that under the optimum operation conditions, i.e. adequate LBE oxygen levels, slow strain rates and low applied cyclic deformations, the fatigue life degradation of T91 exposed to LBE can be kept to a minimum.

On the role of oxide film’s cleaning effect into the metallurgical bonding during cold spray

In this work, a novel understanding was proposed to explain bonding process of a cold sprayed Cu particle deposition. The cleaning effect by the extrusion of viscous metal jet was proved for the first time by the observation of oxides fragments located at the periphery of detached particle, which promoted the formation of metallurgical bonding around central area. It is more interests to find the existence of micro-cracks on contact interface, which revealed the clue of interfacial melting. However, the lack of dimple-like fractures suggests that the interfacial melting at the contact interface is not a prerequisite for metallurgical bonding.

Oxide film on bubble surface of aluminum foams produced by gas injection foaming process

Based on A356 aluminum alloy, aluminum foams were prepared by gas injection foaming process with pure nitrogen, air and some gas mixtures. The oxygen volume fraction of these gas mixtures varied from 0.2% to 8.0%. Optical microscopy, scanning electron microscopy (SEM) and Auger electron spectroscopy (AES) were used to analyze the influence of oxygen content on cell structure, relative density, macro and micro morphology of cell walls, coverage area fraction of oxide film, thickness of oxide film and other aspects. Results indicate that the coverage area fraction of oxide film on bubble surface increases with the increase of oxygen content when the oxygen volume is less than 1.2%. While when the oxygen volume fraction is larger than 1.6%, an oxide film covers the entire bubble surface and aluminum foams with good cell structure can be produced. The thicknesses of oxide films of aluminum foams produced by gas mixtures containing 1.6%–21% oxygen are almost the same. The reasons why the thickness of oxide film nearly does not change with the variation of oxygen content and the amount of oxygen needed to achieve 100% coverage of oxide film are both discussed. In addition, the role of oxide film on bubble surface in foam stability is also analyzed.

The Role of Oxide Films on TiS and Ti4C2S2 Inclusions in the Pitting Corrosion Resistance of Stainless Steels

Microelectrochemical polarization, thermodynamic calculations, and Auger electron spectroscopy were performed to determine the predominant factors affecting the pit initiation resistance at sulfide and carbosulfide inclusions in stainless steels. TiS and Ti4C2S2 inclusions did not dissolve in the passive or the trans-passive regions of stainless steels in NaCl solutions, and no pits were initiated at these inclusions in NaCl solutions. The calculations made from the potential-pH diagrams for Ti-S-TiS-H2O and Ti-S-Ti4C2S2-H2O systems indicated a high likelihood that Ti-oxide enriched surface films would form, and this was confirmed by surface analysis. The Ti-oxide enriched layers on the inclusions inhibited the dissolution of the TiS and Ti4C2S2 inclusions in the passive and trans-passive regions of stainless steels. In contrast, MnS inclusions dissolved in NaCl solutions, and pits were initiated at the inclusions. While MnS inclusion surfaces were covered by Mn-oxides, the corrosion resistance of Mn-oxides was not sufficient to prevent inclusion dissolution and subsequent pit initiation. The oxide enriched surface layers on the sulfide and carbosulfide inclusions were shown to significant enhance pit initiation resistance at the inclusions.

Influence of Electrochemical Conditions on CoCrMo Behavior in Simulated Body Fluid by Step Polarization Technique

Corrosion processes occurring at implant surfaces, the role of oxide films in the corrosion process, alloy biocompatibility and the electrochemical response of alloys to mechanical or electrical transients are all important in the behaviour and success of implant alloys. Most transition metal alloys used in medicine (i.e. Titanium, CoCrMo alloys, stainless steels) have a passive film which spontaneously forms on the surface of the alloy and it provides a kinetic barrier to corrosion reactions. Oxide film structure and morphology are susceptible to the potential which exists across the alloy-solution interface. The present study presents an electrochemical technique based on the application of a potential step and measuring the current transient response to the step in potential. Electrochemical Impedance Spectroscopy (EIS) was carried out in order to provide information concerning the electrical character of the interface. The current density response and the properties of the interface (biomaterial/body fluid) depends on the solution chemistry and the way potential is achieved.

Growth and Properties of Oxide Films on Platinum: I. EIS and X-Ray Photoelectron Spectroscopy Studies

Electrocatalysts supporting the oxygen electrode reaction are commonly covered with thin oxide films that may have a profound influence over the kinetics of the reaction. Little is currently known about the role of oxide films on electrocatalysts, particularly with regard to the role of the defect structure. In this work, the physical and defect structures of the oxide film that forms on platinum in under steady-state conditions have been investigated using electrochemical impedance spectroscopy (EIS) and ARXPS (angle-resolved X-ray photoelectron spectroscopy). Mott-Schottky analysis shows that the film is n-type, indicating that the defects in the film are either platinum interstitials or oxygen vacancies, or both. ARXPS analysis shows that, for potentials between 1.0 and , a single-layer film develops, with the principal oxidation state for Pt (in the film) being . However, a bi-layer structure was observed for films formed at potentials greater than and ARXPS analysis shows that these bilayer films comprise an inner layer containing and an outer layer containing . Optimization of the point defect model on the EIS data yields values for various kinetic parameters that are then used to predict the steady-state thickness and current. Good agreement with experiment is obtained.

The intergranular corrosion and stress corrosion cracking of mild steel in clarke's solution

Measurements have been made of the corrosion rates and stress corrosion crack velocities for mild steel exposed to hydrochloric acid containing antimony additions at open circuit and various applied potentials. Cracking occurs within a sharply defined range of potentials, within which markedly slower intergranular corrosion occurs, while general corrosion occurs at potentials above or below those that promote cracking. It is suggested that the role of Sb in the cracking mechanism is essentially the same as the role of oxide films in other environments, of restricting lateral dissolution at the crack sides.

The Nature of the Friction Transition as a Function of Load and Speed for the Steel/Steel System©

In this paper the load-speed diagram of steel/steel rubbing pair wider lubricated conditions was measured using the ball-on-disc lusting machine and the stepwise loading method. The role of the lubricating oil at the various transition regions was examined. It has been shown that the transition between lubrication states in the load-speed diagram was completed within a certain interval of load, i.e. the load-speed diagram was constituted by not three, but five regions. In this paper the composition and valence state of surface film was systematically analyzed by AES and ESC A within the different lubrication states. This paper also discusses the role of oxide film in the transitions of load-speed diagram, and proposes a model about the structure and role of oxide film as well. Presented at the 35th STLE/ASME Tribology Conference in Fort Lauderdale, Florida October 16–19, 1989

高温水中における鋭敏化304ステンレス鋼の粒界応力腐食割れにおよぼす酸化皮膜の役割

高温水中における鋭敏化304ステンレス鋼の粒界応力腐食割れにおよぼす酸化皮膜の役割

Review of oxidational wear Part II: Recent developments and future trends in oxidational wear research

This is the second part of a two-part in-depth review of the oxidational wear of metals. In the first part, the origins of the oxidational theory of wear were described, with special emphasis on the role of oxide films in the wear of metals at relatively low ambient temperatures. Under these conditions, most of the oxidation occurs at the temperature of the real areas of contact between sliding surfaces. In this part of the review, recent developments involving determination of the activation energies and Arrhenius constants for oxidation during wear are described together with an account of some of the research into the use of measurements of oxide film thickness to deduce the contact temperatures at the real areas of contact. Although the effect of partial oxygen pressures upon the wear of metals is covered in this review, it is in the effects of elevated temperatures upon wear that the future of oxidational wear research would appear to lie. Under these conditions, the effect of oxidation upon a given contact area whilst ‘out-of-contact’ must be taken into account. An oxidational wear theory relevant to elevated ambient temperatures is described and the most likely trends in oxidational wear research in the 1980's are discussed.

The role of oxide films in stress corrosion cracking initiation

In the low-potential transition range, passivatable alloys undergo electrolytic crevice corrosion i.e. localized anodic attack at any area prevented from passivating by shielding effects. A possible role of stress in this range may be seen, accordingly, in producing at every film rupture uncontrollable localized attack in critical underfilm crevices at the feet of emerging slip steps. The fundamental condition for s.c.c. would be that the incubation time, i.e. the time of attack required to form a critical notch, must be shorter than the film lifetime. The resulting model for s.c.c. initiation at the active-passive transition fits in with the mostly accepted slip-dissolution mechanism. A simple mathematical treatment is given for such model and applied to three typical systems, that are the combination of steel with K 2CO 3 KHCO 3, NaOH and NH 4NO 3 solutions, respectively. Calculated incubation times are consistent with experimental times to rupture and cracking rates from s.c.c. tests.

The role of oxide films in stress corrosion cracking initiation

In the low-potential transition range, passivatable alloys undergo electrolytic crevice corrosion i.e. localized anodic attack at any area prevented from passivating by shielding effects. A possible role of stress in this range may be seen, accordingly, in producing at every film rupture uncontrollable localized attack in critical underfilm crevices at the feet of emerging slip steps. The fundamental condition for s.c.c. would be that the incubation time, i.e. the time of attack required to form a critical notch, must be shorter than the film lifetime. The resulting model for s.c.c. initiation at the active-passive transition fits in with the mostly accepted slip-dissolution mechanism. A simple mathematical treatment is given for such model and applied to three typical systems, that are the combination of steel with K 2CO 3-KHCO 3, NaOH and NH 4NO 3 solutions, respectively. Calculated incubation times are consistent with experimental times to rupture and cracking rates from s.c.c. tests.

Role of oxide films in stress corrosion cracking of mild steel in nitrate solutions

Time to failure of iron with varying carbon content was determined during stress corrosion at 75°C in various nitrate solutions. Ability of these solutions to passivate iron was estimated. It has been suggested that the high rate of the intergranular stress corrosion cracking of mild steel is connected with the formation of the passive γ-Fe 2O 3 film and its sensitivity to the depassivating action of steel constituents such as carbon, segregated at grain boundaries. It is thought that the Fe 3O 4 film also protects the grain boundaries.

518. Liquid metals. Part V. The role of oxide films in the wetting of iron, cobalt, and nickel by liquid sodium, and by solutions of barium and calcium in liquid sodium

Receding contact angles foi liquid sodium on iron, cobalt, and nickel surfaces in a pure argon atmosphere were studied as a function of time and temperature. All observations can be correlated on the basis that the changes in contact angle reflect the reduction, by sodium, of the invisible oxide film present on the transition-metal surfaces after abrasion to a mirror surface in air. Nickel carries only one oxide, irrespective of temperature, and wetting rates vary uniformly with temperature. The oxide films on iron and cobalt change at about 225 deg and 250 to 300 deg , respectively, and wetting rates also change abruptly at these temperatures. Each metal possesses a critical wetting temperature (Fe 140 deg , Co 190 deg , Ni 195 deg ) below whlch no wetting occurs, and below which it is believed that no reduction of the oxide film is possible. Addition of small quantities of calcium (> 0.07%) or barium to liquid sodium influences wetting rates profoundly. (auth)

Mechanism of the Reaction of Hydrogen with Zirconium: I . Role of Oxide Films, Pretreatments, and Occluded Gases

Previous studies have shown the reaction of zirconium with hydrogen to be sensitive to surface preparation, surface films, heat treating cycles, cold working of the metal, and nonmetallic impurities.Experiments were made on the rate of reaction of high purity zirconium with pure hydrogen using a sensitive microbalance method, and an all glass and ceramic vacuum system to minimize contamination.The effect of a preliminary vacuum heating cycle on rate of reaction with hydrogen at 150°C was studied by varying the temperature of the vacuum heating cycle from 150° to 700°C. Samples having the room temperature oxide present showed only a slow rate of reaction, while samples heated to 700°C for one hour showed a rate of reaction 7700 times as great. Results also showed that the oxide film was effectively removed by heating in a vacuum for one hour at 500°C.A study was made of the thickness and nature of the oxide film. Thus, the film formed in air at room temperature was more resistant to hydrogen attack than thicker oxides formed at higher temperatures. Studies on the effect of small quantities of oxygen and nitrogen in solid solution indicate only minor effects. Results suggest that considerable revision is necessary in concepts of the mechanism of the hydrogen reaction on metals.