Adhesion Of Oxide Layer Research Articles

Improving the Adhesion of a Hard Oxide Layer on Ti6Al4V by a Three‐Step Thermal Oxidation Process

Thermal oxidation is a promising technique to improve the tribological properties of Ti6Al4V. Herein, a single‐step process consisting of oxidation in air, a two‐step process with an additional solid‐state oxide layer reduction step under vacuum, and a three‐step process with an appended final oxidation step in air are applied to Ti6Al4V. The oxide layer adhesion after the three‐step process is improved compared with the single‐step process. This improved adhesion is not due to a different nature of the oxide layers because oxide layers obtained during the single‐step and three‐step process show a similar morphology and composition. Instead, it is ascribed to the presence of an optimized oxygen diffusion zone with two distinct regions: a gradual decrease in oxygen concentration from the maximum possible oxygen concentration at the oxide–substrate interface until a depth of 20 μm followed by a near‐linear decrease until a depth of about 85 μm. Both regions are also visible in the correlated microhardness‐depth profile.

Mechanical, tribological and adhesive properties of oxide layers obtained on the surface of the Ti–6Al–7Nb alloy in the thermal oxidation process

The mechanical, tribological and adhesive properties of oxide layers obtained on the Ti–6Al–7Nb alloy surface through thermal oxidation at temperatures of 600, 700 and 800 °C for 24 h have been identified in the study. The morphology of the scale formed was determined. It was found that with an increasing oxidation temperature, an increase in the continuity of the oxide scale takes place. The surface covered by oxide layers was characterised by 3 times higher hardness compared to the as-received condition. It was shown that the presence of oxide layers on the surface of Ti–6Al–7Nb alloy led to a significant reduction in wear despite an increase in the value of the friction coefficient. The best sliding wear resistance was found in the oxide layer obtained at a temperature of 700 °C (a 70% reduction in wear). The tribological interaction of ZrO2 balls with the surface of the alloy covered with oxide layers also resulted in a significant reduction in their wear (86% for the oxide layer obtained at 800 °C). It was shown that the wear resistance of ZrO2 balls increased with the oxidation temperature. The values of critical load being the measure of adhesion of the formed scale were determined in scratch-test, which showed that the layer obtained at 700 °C had the best adhesion. The tests showed a relationship between the adhesion of oxide layers and sliding wear resistance. The layer with the best adhesion, which was obtained at 700 °C, was also characterised by the highest resistance to sliding wear.

High-temperature Oxidation of Intermetallics Based on Ti-Al-Si System

Ti-Al-Si alloys excel with their low density and good resistance against high-temperature oxidation in comparison with so far commonly used nickel alloys. Silicon in Ti-Al-Si alloys has significant positive effect on high-temperature oxidation due to increasing adhesion of oxide layer. The TiAl20Si20 alloy was evaluated as the best alloy from tested ones, because its oxide layer protected very well the basic material and TiAl20Si20 achieved good hardness after 400 hours of annealing.

Effect of Carbonitriding in a Salt Bath by a QPQ Scheme on Stainless Steel 321 Microstructure and Service Properties

Wear resistance, corrosion properties and structure of reinforced layers deposited on steel AISI 321 with carbonitriding by the quench-polish-quench (QPQ) Tennifer® process with subsequent oxidation are studied. The structure of the layers is investigated by scanning electron microscopy with energy dispersive local analysis and x-ray diffractometry. Steel wear resistance is determined by a pin-on disk test, and oxide layer adhesion is determined by a scratch method. Pitting corrosion resistance is determined by plotting cyclic polarization curves.

Influence of boron contents on oxidation behavior and the diffusion mechanism of Fe–B based alloys at 1073 K in air

The microstructure and oxidation behavior of Fe–B alloys have been investigated. Oxide scale cross-sectional microstructures oxidized at 1073K for 100h have been studied. EPMA investigations show that B2O3–SiO2 oxides accumulates in the inner oxide layer which improves the oxidation behavior and oxide layer adhesion considerably. Cyclic oxidation kinetics data indicates that Fe–B 3.08wt.% alloy presents the best oxidation resistance. The formation of diffusion zone in the Fe–B alloys indicate that the oxidation of the Fe2B boride is controlled by boron diffusion. The diffusion zone increases with time and reaches a maximum width of 60–65μm.

Characterization Of Oxide Layers Formed On 13CrMo4-5 Steel Operated For A Long Time At An Elevated Temperature

Abstract The paper contains results of studies into the formation of oxide layers on 13CrMo4-5 (15HM) steel long-term operated at an elevated temperature. The oxide layer was studied on a surface and a cross-section at the inner and outer surface of the tube wall. The 13CrMo4-5 steel operated at the temperature of 470°C during 190,000 hours was investigated. X-ray structural examinations (XRD) were carried out, microscope observation s using an optical, scanning microscope were performed. The native material chemical composition was analysed by means of emission spark spectroscopy, while that of oxide layers on a scanning microscope (EDS). The studies on the topography of the oxide layers comprised studies on the roughness plane, which were carried out using a AFM microscope designed for 2D and 3D studies on the surface. Mechanical properties of the oxide layer – steel (substrate) were characterised on the basis of scratch test. The adhesion of oxide layers, friction force, friction coefficient, scratching depth were determined as well as the force at which the layer was delaminated.

Studies on the Adhesion of Oxide Layer Formed on Steel Long-Term Operated at an Elevated Temperature

The paper contains results of studies into the formation of oxide layers on steel long-term operated at an elevated temperature. The material studied comprised specimens of steel taken from an steam pipeline and on the flue gas side. The oxide layer adhesion tests were carried out on an automated Revetest XPress Plus instrument using a diamond Rockwell indenter. The adhesion of oxide layers, friction force, friction coefficient, scratching depth were determined as well as the force at which the layer was delaminated. It has been found that the oxide layer formed under the influence of applied pressure is more degradation in the areas where are a pores and cracks.

An Enhanced Three-Step Oxidation Process to Improve Oxide Adhesion on Zirconium Alloys

Oxidation of zirconium-based alloys results in a thermally-grown oxide scale with excellent corrosion resistance, and good wear and friction properties, which make them interesting for tribological applications. Nevertheless, adhesion of the oxide layer to the substrate must be enhanced. A new three-step oxidation process was introduced in order to achieve an improvement. Following an initial oxidation step (1st step), a heat treatment was carried out in vacuum during which the oxide dissolves and diffuses into the metallic zirconium substrate (2nd step). These two steps resulted in an oxygen dissolution layer with increased hardness formed in-between the oxide and the substrate, which serves as a bonding layer with increased thickness. In a 3rd step a new oxide layer was obtained. The improved oxide layer adhesion was characterized by indentation tests on three different groups of oxidized samples of the newly developed alloy.

Studies on the adhesion of oxide layer formed on X10CrMoVNb9-1 steel

The paper contains results of studies on the formation of oxide layers on X10CrMoVNb9-1 (P91) steel long-term operated at an elevated temperature. X10CrMoVNb9-1 steel operated at the temperature of 595°C for 54,144h was the studied material. X-ray structural examinations (XRD) were carried out, microscope observations using an optical and scanning microscope were performed. The native material chemical composition was analysed by means of emission spark spectroscopy, while that of oxide layers on a scanning microscope (EDS). Mechanical properties of the oxide layer – steel (substrate) were characterised on the basis of scratch test. The adhesion of oxide layers, friction force, friction coefficient, scratching depth was determined as well as the force at which the layer was delaminated. It has been found that the oxide layer formed under the influence of applied pressure is more degradeted in the areas where are porous and cracks.

Oxidation behaviour and mechanism of a cobalt based superalloy between 1050 and 1250 °C

A new Co-base superalloy 22Co–21Ni–23Fe–29Cr–2.2Nb (Co22 for short) was developed, and the influence of a trace amount of rare earth (RE) on the oxidation resistance was investigated. Isothermal oxidation behaviour of this Co-base superalloy was investigated at 1050–1250°C in air, analyzed with scanning electronic microscopy and X-ray diffraction. The results show that oxidation mass gain of the samples with or without RE elements obeyed secondary parabolic law, and the effect of 0.03wt.% RE on oxidation resistance is small. The oxidation rate constant of the 0.03wt.% RE added Co22 alloy decreases by about 6.1% to 9.0% compared to that of the Co22 alloy without RE. Oxidation at 1050–1250°C for 100h results in the formation of MnCr2O4, Cr2O3 and SiO2. A continuous and protective MnCr2O4 spinel layer forms as outer layer. The continuous middle oxide layer is confirmed to be Cr2O3, and the innermost layer consists of discontinuous SiO2. The outer and middle layers strongly improve oxidation resistance and oxide layer adhesion because of their continuity and compactness, and the innermost SiO2 layer forms a diffusion barrier to prevent further oxidation. Formation and growth mechanisms of oxide layers were also discussed.

The effect of yttrium on cathodic arc evaporated Ti0.45Al0.55N coating

This work aims to understand the effect of 1at.% Y addition on cathodic arc evaporated Ti0.45Al0.55N coating. Ti0.45Al0.55N coating and Ti0.45Al0.54Y0.01N coating were deposited on WC-Co substrate by cathodic arc evaporation method, and their microstructure and properties were compared. The addition of 1at.% Y does not change the crystalline phase of Ti0.45Al0.55N coating. It still consists of (Ti,Al)N phase with a cubic NaCl-type structure. However, addition of Y leads to reduction of columnar structure and refinement of grains. Compared with Ti0.45Al0.55N coating, the hardness of Ti0.45Al0.54Y0.01N increases by 24%. The residual stress of Ti0.45Al0.54Y0.01N coating is approximately three times that of Ti0.45Al0.55N coating. Ti0.45Al0.54Y0.01N coating exhibits superior oxidation resistance, owing to the retardation of oxide layer growth, the dense fine-grained structure and the improved oxide layer adhesion.

Effect of B and Cr on the high temperature oxidation behaviour of novel γ/γ′-strengthened Co-base superalloys

Isothermal oxidation was carried out on new γ/γ′-strengthened Co-base superalloys of the system Co–Al–W–B and Co–Al–W–B–Cr at 800 and 900 °C in air. ToF-SIMS investigations show that boron accumulates in the inner oxide layer which improves the oxidation behaviour and oxide layer adhesion considerably. B-rich precipitations can be observed in the alloy matrix, as well. Appropriate amounts of chromium as additional alloying element lead to further improvement of the oxidation resistance due to the formation of protective inner Al 2O 3 and Cr 2O 3 scales.

High temperature oxidation of γ/γ′-strengthened Co-base superalloys

Isothermal oxidation was carried out on new γ/γ′ Co-base superalloys of the system Co–Al–W–B. Appropriate B-contents lead to improved oxidation resistance and oxide layer adhesion. Oxidation at 800 and 900 °C results in formation of Co 3O 4, CoO, and complex oxides (containing Co, Al, and W). A continuous and protective inner alumina layer forms only at 800 °C. Furthermore, oxidation leads to phase transformation (γ/γ′ to γ/Co 3W microstructure) at the matrix/oxide layer interface due to Al-depletion. The effect of additional alloying elements such as Ta, Cr, Nb, Si, V, Mo, and Ir on the oxidation behaviour was also investigated.

Microscopic observations of both sides of scale-substrate interfaces after adhesion measurements of chromia-rich scales on ferritic stainless steels using the inverted blister test

Ferritic stainless steels were oxidized cyclically at 850°C in air. Four grades were studied : one reference grade without stabilizers, one stabilized with Ti, one with Nb and one with both Ti and Nb. The mass gain evolution of these grades versus number of cycles was recorded and gave relevant information about their oxidation kinetics. Indeed, very few oxide spallation was noted (<1%). Ti appeared to accelerate kinetics significantly, mainly because of its internal oxidation. Nb seemed to have no effect on kinetics in air at this temperature. The adhesion of oxide layers was quantified by the inverted blister-test. A beneficial effect of titanium on the adhesion was noted. For Ti-containing grades, adhesion energies were about 40 J/m2 whereas for other grades, they were lower, about 10 J/m2. This effect is thought to be due to internal oxidation of titanium, playing a role of mechanical keying of the oxide scale. On the contrary, niobium is not oxidized at the interface and remains as an intergranular intermetallic ironniobium phase. Its influence on oxide adhesion is therefore negligible.

The influence of reactive element additions to β-NiAlCr alloys on the morphology of thermally grown oxides

The effect of the reactive elements (REs), Y and Zr, on oxidation of β-NiCrAl alloy at 1373 K in a gas mixture of argon with 20 vol.% oxygen at atmospheric pressure was evaluated using X-ray diffractometry, scanning electron microscopy, electron probe X-ray microanalysis and secondary ion mass spectroscopy. The oxide surfaces and interface morphologies, compositions and growth kinetics were studied for alloys with 0.32 at.% Zr and 0.24 at.% Y additions and for an undoped alloy. The oxide layer produced on the three different alloys contains mainly α-alumina and some intermediate alumina modification, Cr2O3 and RE-oxides. A needle-like morphology was seen on top of the oxide layer for the undoped and Zr alloy. Needle formation on the Y alloy was suppressed by the formation of a thin Y2O3 layer during the initial stage of oxidation. Needles were maintained to long oxidation times for the undoped alloy, but disappeared on the doped alloys indicating that some cation diffusion is possible when REs are present. Fewer intermediate alumina modifications are seen for the oxide layers on the RE alloys showing that the REs promote the formation of the α-alumina phase. Oxide layer growth occurs in two stages for all alloys. Initially, oxide growth is rapid with outward diffusion of aluminium. The second stage of oxidation is slow and is initiated by the formation of a closed α-alumina layer limiting further oxidation to inward oxygen diffusion. This stage is characterised by parabolic growth kinetics associated with a constant aluminium interface concentration. The oxide layer is thinnest for the Y alloy due the fine Y2O3 layer acting as a diffusion barrier. The oxide/alloy interface for the undoped alloy is flat and shows many voids, whereas voids are not seen for the RE alloys. This is due to the promotion of a closed α-alumina layer giving predominantly inward growth early in the oxidation process. Oxide pegs of the RE are also seen growing into the alloys. The lack of voids and the oxide pegs are advantageous for oxide layer adhesion to the doped alloys.

Oxidation resistance of AlN–(TiB2–TiSi2) ceramics in air up to 1450 °C

Abstract With the aid of DTA, TG, XRD, SEM and EPMA methods the kinetics and mechanism of oxidation of both composite powders and monolithic ceramics of AlN–(TiB2–TiSi2) system with different content of components were studied in the air up to 1450 °C under isothermal and non-isothermal conditions. It was established that the oxidation isotherms of monolithic ceramics follow the parabolic and paralinear rate law. According to the kinetic data and results of investigation of composition, morphology and structure of oxide films that are formed at different temperatures, the AlN–based ceramics containing up to 30% (TiB2–TiSi2) solid solutions are the corrosion-resistant and have the high adhesion of oxide layer in relation to substrate material. The activation energies of oxidation calculated for ceramics with 10% (TiB2–TiSi2) are: E1 =180 kJ/mol for the temperature range up to 1300 °C and E2=630 kJ/mol at 1350–1450 °C. The change of activation energy value is associated with the change of oxide layer composition: at the oxidation till 1300 °C the oxides of individual elements are, mainly, formed on the samples while above 1350 °C the formation of very dense surface film containing β-tialite Al2TiO5 takes place.

Influence of the nature of alloying elements on the adherence of oxide films formed on titanium alloys

In order to study the influence of aluminum, chromium, and silicon on the adherence of oxide layers to the metallic substrate for binary alloys of titanium, adhesion measurements were carried out and the results were correlated with the oxidation behavior of these materials. Ti-Al, Ti-Cr, and Ti-Si alloys were prepared and oxidized at temperatures of 550–700°C in air and in oxygen, for oxidation times from a few hundred to several thousand hours. The reaction kinetics were followed using continuous thermogravity or daily weighing of samples. For Ti-Al and Ti-Si alloys, a slight decrease in the adherence of oxide layers to the substrate was observed for the lowest aluminum contents (1.65 and 3%) and silicon content (0.25%) as compared with the behavior of unalloyed titanium; at higher levels, the adherence increased with the alloying element content. For Ti-Cr alloys, the addition of chromium increased the adhesion of oxide layers to the substrate for all cases; however, the change in adhesion with chromium content was not monotonic.