Isothermal Oxidation Kinetics Research Articles

Cyclic oxidation of coated and uncoated single-crystal nickel-based superalloy MC2 analyzed by continuous thermogravimetry analysis

Abstract The previously developed cyclic thermogravimetry analysis (CTGA) [Monceau D, Poquillon D. Oxid Met 2004;61:143–163] method is applied to the cyclic oxidation at 1150 °C of a NiCoCrAlYTa-coated and an uncoated single-crystal nickel-based superalloy MC2. A new procedure to correct the buoyancy effect is proposed in order to evaluate the amount of oxide formed during the heating periods, which can be important for alloys forming fast-growing transient oxides or during cycling with slow heating rates. It is shown that cyclic thermogravimetry is an useful technique for quantifying the oxidation resistance of an industrial alloy. Moreover, the behaviour of the alloy is better described with CTGA than with a classic cyclic gravimetric test, because both isothermal oxidation kinetics and spalling behaviour are assessed independently. In the present case, it is shown clearly that the NiCoCrAlYTa coating greatly improves the cyclic oxidation resistance without decreasing the isothermal oxidation kinetics. Finally, the use of CTGA for performance and time-of-life evaluations is demonstrated.

Oxidation behavior of sputter-deposited Ti–Ni thin films at elevated temperatures

The isothermal oxidation kinetics of sputter-deposited equiatomic Ti–Ni thin films in pure oxygen from 823 to 923 K is studied using thermo-gravimetric analysis. The structure, composition-depth distribution and surface morphology of oxidized Ti–Ni thin films are investigated by X-ray diffraction (XRD), Auger electron spectroscopy (AES) and atomic force microscope (AFM), respectively. The results show that the oxidation kinetics of Ti–Ni thin films obeys a near-parabolic law. TiO2, TiNi3 and parent B2 phase are the compositions of oxidized Ti–Ni thin films. A double-layered scale including the outermost layer and the Ni-rich layer is formed outside the B2 matrix of oxidized Ti–Ni thin films. Moreover, thermal oxidation induces a surface smoothening of Ti–Ni thin films and surface roughness of oxidized Ti–Ni films decreases with the increasing oxidation temperature.

Phenomenological Kinetics of Isothermal Wet Air Oxidation: Operating Severity Factor and Recalcitrance Index

In the present investigation, the kinetics governing wet air oxidation (WAO) of organic pollutants is modeled by two distinct parallel kinetic terms corresponding to a readily oxidizable and a recalcitrant structural parts of the pollutant molecule involving the concept of thermodynamic severity factor. The developed model was successfully applied to several classes of organic water pollutants including phenolic compounds as well as mono- and di-carboxylic acids. In the offshoot of the model, a recalcitrance index was proposed classifying the pollutant molecules according to their resistance to oxidation. For the carboxylic acids, it was found that the recalcitrance towards WAO was inversely correlated to the molecular size and weight. Acetic acid proved to be the more recalcitrant component. As for the phenolic compounds, the oxidation efficiency was shown to be affected by the nature of the substitutents present on the phenolic ring. The electron donating substitutents such as alkyl groups (CH3 or –C2H5) confer to the molecule an enhanced reactivity towards WAO. On the contrary, electron-accepting substitutents, such as methoxy groups, lower the oxidation and consequently enhance the recalcitrance.

Multi-Sample Thermobalance for Rapid Cyclic Oxidation under Controlled Atmosphere

When testing the resistance to oxidation of high temperature materials, the cyclic oxidation test is used as a reference because it integrates isothermal oxidation kinetics, oxide scale adherence, mechanical stresses, metallic alloy and oxide mechanical behavior and their evolution with time, in conditions close to the actual conditions of use. To fill the gap between the measurements of physical data (oxidation kinetics, interfacial energy, oxide toughness, growth stresses, coefficients of thermal expansion, mechanical properties of the alloy under the oxide scale,...) and the cyclic oxidation test, comprehensive scientific work is necessary, but also technological development and understanding of the practice of the cyclic oxidation test. This paper presents a new experimental tool, which allows the simultaneous measurement of the mass of several samples placed in the same controlled atmosphere during fast thermal cycles. This multi-sample thermobalance is described, in association with the description of the measurement methodology (i.e. “cyclic thermogravimetry”). First tests of performance of the apparatus are given, including heating and cooling rates and continuous Samass measurements for a P91 alloy.

Cyclic Oxidation Kinetics Modeling of NiAl Single Crystal

For alumina forming nickel-based alloys, sulfur content is a key element as it modifies the onset and extent of spalling of the oxide scale. To get a better understanding of that effect, isothermal and cyclic oxidation of two NiAl single crystals (with two S contents) have been carried out at 1050 and 1150°C on (100) and (110) orientated surfaces. Continuous thermogravimetry in cyclic conditions allows to follow isothermal oxidation kinetics and spalling at each cycle. Oxidation kinetics are compared between the two compositions and the two crystallographic orientations. Low sulfur NiAl oxidizes with slightly lower kinetics for both (100) and (110) surface orientations, and, in both isothermal as well as in cyclic conditions at 1150°C in O2 . Experimental results of cyclic oxidation are compared to those obtained with simulations using a previously published simple statistical model and using a more complex Monte-Carlo code. Spalling is found to be an increasing function of the average oxide thickness and seems to depend on the square of the average oxide thickness.

High-temperature oxidation kinetics of NiAl single crystal and oxide spallation as a function of crystallographic orientation

Isothermal and cyclic high-temperature oxidation of NiAl single crystal samples are presented. Oxidations have been carried out at 900, 1050, 1100 and 1150 ◦ C on (1 0 0) and (1 1 0) oriented surface. Continuous thermogravimetry in cyclic conditions allows isothermal oxidation kinetics and spalling at each cycle to be followed. Oxidation kinetics are compared between (1 0 0) surface and (1 1 0) surface. (1 0 0) oriented surfaces appeared to oxidize slightly faster than (1 1 0) oriented surfaces. Experimental results of cyclic oxidation are compared to simulated results using a previously published statistical model. Spalling increases when the average oxide scale thickness increases with the number of cycles. Longer tests are necessary to study this evolution during the ’steady-state’ but no critical oxide thickness was found.

Oxidation of Zr55Cu30Al10Ni5 bulk metallic glass in the glassy state and the supercooled liquid state

The oxidation behavior of Zr55Cu30Al10Ni5 bulk metallic glass in air in the glassy state and the supercooled liquid state was studied using a thermogravimetric analyzer, X-ray diffraction and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy. It was found that the isothermal oxidation kinetics of the glass in both states follows a two-step parabolic law. The oxidation process is governed by the inward diffusion of oxygen and the outward diffusion of Cu, with the first being dominant. The faster diffusion of atoms in the supercooled liquid state led to a network precipitation of crystalline Cu, and the crystallization that occurred in this state in the later stage of oxidation caused a reduction in the rate of oxidation. Two types of Zr oxides, i.e. t-ZrO2 and m-ZrO2, were formed in the oxidation process in both the glassy and supercooled liquid states. t-ZrO2 mainly formed in the outer layer of the oxide scale, while m-ZrO2 tended to form in the inner layer. The formation of m-ZrO2 is possibly activated by the crystallization of the glass near the interface of the oxide scale and the substrate alloy. In addition, oxidation also has a substantial effect on the formation of crystallized phases. The formation of a Cu-rich phase of Cu10Zr7 occurred in the oxidizing atmosphere. However, the formation of a Zr-rich phase of Zr2(Ni, Cu) mainly took place in a vacuum environment.

Electrical Discharge Surface Alloying of Superalloy Haynes 230 with Aluminum and Molybdenum

Surface alloying of superalloy Haynes 230 was performed using either Al-Mo mixture powders suspended in kerosene or Al-Mo composite electrode during the electrical discharge alloying (EDA). For suspending Al-Mo powders in kerosene, the Cr23C6, WC1−x, and graphite phases exist in the alloyed layer of the EDA specimen with negative electrode polarity, while the specimen with positive electrode polarity exhibits no alloying phase except the raw material phase. For employing the Al-Mo electrode with negative polarity, the specimen represents many discontinuous piled-layers, with Al3Mo8 and AlMo3 phases accumulating on the substrate surface. The specimen produced using Al-Mo electrode with positive polarity shows an alloyed layer constituted mainly with NiAl phase. This specimen also shows the smallest surface roughness and highest hardness among the four EDA specimens. The kinetics of isothermal oxidation at 1000°C in static air demonstrate that the specimen using Al-Mo electrode with positive polarity possesses the best oxidation resistance among the tested specimens.

Composition and oxidation resistance of Ti–B–C and Ti–B–C–N coatings deposited by magnetron sputtering

Nanocomposite Ti–B–C and Ti–B–C–N coatings were deposited from a TiB2–TiC target using RF magnetron sputtering. In this paper, the composition and oxidation kinetics of Ti–B–C and Ti–B–C–N coatings are presented. The film composition was characterized using XPS. Compared to the target composition, preferential sputtering of the carbon component was observed. Introducing nitrogen into the sputtering gas resulted in the formation of TiN, with nitrogen of approximately 30 at.%, and shifted the C1s peak from the typical position for carbide to a higher binding energy position, which is typical of graphite. Both dynamic and isothermal oxidation kinetics were studied using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The oxide compositional depth profile, structure and morphology were characterized by Rutherford backscattering spectrometry (RBS), X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The results show that: (1) catastrophic oxidation started at 920 K; (2) TiB2 and TiC in Ti–B–C coatings oxidized in sequence; (3) isothermal oxidation of Ti–B–C coatings in the temperature range from 1173 to 1323 K obeyed a parabolic rate law with an activation energy of 1.64 eV/atom, indicating a diffusion-controlled mechanism; and (4) well-crystallized oxide scales formed after oxidation in air at 1173 K for 2 h are mainly rutile TiO2, with XRD-detectable hexagonal B2O3 and hematite Fe2O3 resulting from iron outward diffusion.

Thermal and microstructural characterizations of nickel nanoparticles at elevated temperatures

The isothermal oxidation behavior and the oxidized structure of nanometer-sized nickel powders have been investigated over a temperature range 300–1100 °C in ambient air. The oxidation began at about 300 °C and the weight gain increased linearly as the isothermal time lengthened. The isothermal oxidation kinetics became parabolic as the temperature was raised above 500 °C. A nickel chromium oxide (NiCr2O4) was formed in addition to the nickel oxide (NiO) as the temperature exceeded 700 °C, due to the presence of chromium as a major impurity in the as-received nickel nanoparticles. A reaction of NiO+Cr2O3→NiCr2O4 was suspected to occur concurrently in addition to the Ni+1/2O2→NiO oxidation reaction at the temperatures (≥700 °C) involved.

On physical and thermochemical properties of high-purity Ti 3SiC 2

Dense polycrystalline Ti3SiC2 of high purity was successfully fabricated from Ti/Si/2TiC powders by reactive hot-isostatic pressing (HIPing) at 1688 K, 100 MPa for 7.2 ks. A flexural strength of 537±16 MPa and a Vickers hardness of 4.0±0.2 GPa was obtained. The partial pressure of Si is important to maintain the stability of Ti3SiC2 at high temperatures. Ti3SiC2 tended to decompose in N2, O2 or C atmosphere at temperatures above 1623 K. The isothermal oxidation kinetics of Ti3SiC2 became parabolic in the temperature range of 1423–1523 K with an activation energy of 295 ±20 kJ/mol. At temperatures above 1573 K, the oxidation kinetics became linear.

Investigation of a New Methodology in High Temperature Oxidation Application to Commercial Austenitic Steels

Avesta Sheffield R&D has evaluated a scaling temperature for heat resistant steels from laboratory gravimetric measurements of cyclic exposures. In this paper, this old method is described. A new methodology, based on the results of isothermal and cyclic tests, is proposed and discussed. It includes isothermal and cyclic oxidation kinetics of different commercial austenitic steels. Oxidation of Avesta Sheffield 153MA, 253MA and 353MA and standard commercial heat resistant steels 309S, 310S and A800 have been investigated under isothermal and cyclic conditions, in air, in the temperature range 800-1200°C. For all alloys, oxidation rates obey a parabolic law below a critical temperature. The activation energies have been calculated. Kinetics of the cyclic tests show that a critical mass change corresponding to a critical thickness of the oxide scale is responsible for the spallation start. This thickness depends on the composition of the alloys, and is very much increased by alloying minor elements like Ce.

Isothermal Oxidation of β-NiAl Alloys and Sputtered Coating at 1000°C in Air

The isothermal oxidation of a NiAl and a NiAlY alloy and of a sputtered NiAl microcrystalline coating were investigated at 1000C in air by TGA, XRD and SEM. The isothermal oxidation kinetics of both NiAl and NiAlY alloys and NiAl microcrystalline coating followed the parabolic rate law with two subsequent stages A phase transformation from metastable θ-Al 2 O 3 to stable α-Al 2 O 3 occurred in the oxide scales and produced a significant decrease of the oxidation rate after an initial transient stage. This phase transformation was accelerated by microcrystallization.

Effects of Pt incorporation on the isothermal oxidation behavior of chemical vapor deposition aluminide coatings

The effects of Pt incorporation on the isothermal oxidation and diffusion behavior of low-sulfur aluminide bond coatings were investigated. Aluminide (NiAl) coatings and Pt-modified aluminide (Ni,Pt)Al coatings were synthesized on a low-sulfur, yttrium-free single-crystal Ni-based superalloy by a high-purity, low-activity chemical vapor deposition (CVD) aluminizing procedure. The isothermal oxidation kinetics and scale adhesion behavior of CVD NiAl and (Ni,Pt)Al coatings before and after isothermal oxidation were determined by electron microprobe analysis. Platinum did not reduce oxide-scale growth kinetics. No significant differences in bulk refractory metal (W, Ta, Re, and Mo) distributions were observed as a result of Pt incorporation. Spallation of the alumina scale and the formation of large voids along the oxide-metal interface were commonly observed over the NiAl coating grain boundaries after 100 hours at 1150 °C. In contrast, no spallation of Al2O3 scales occurred on (Ni,Pt)Al coating surfaces or grain boundaries, although the sulfur content in the CVD (Ni,Pt)Al coatings was higher than that of the CVD NiAl coatings. Most significantly, no voids were observed at the oxide-metal interface on (Ni,Pt)Al coating surfaces or cross sections after 200 hours at 1150 °C. It was concluded that a major beneficial effect of Pt incorporation on an aluminide coatings oxidation resistance is the elimination of void growth at the oxide-metal interface, likely by mitigation of detrimental sulfur effects.

Oxidation behaviour of FeAl intermetallics.The effects of Y and/or Zr on isothermal oxidation kinetics

Abstract The isothermal oxidation behaviour of doped and undoped Fe–37 at% Al intermetallic compounds in an ambient atmosphere over the temperature range of 1000–1200°C was studied. The oxidation products were identified by X-ray diffraction (XRD). Characterisation of the specimens after oxidation was conducted using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The rate constants of the isothermal oxidation were determined using three methods. The effective diffusion coefficients for the oxidation of doped and undoped Fe–37Al are discussed based on oxide grain size and the effects of reactive elements in lattice and grain boundaries. The effects of reactive elements on the isothermal oxidation kinetics of Fe–37Al were analysed based on oxide morphologies and microstructures.

Influence of post-implantation annealing on the oxidation behavior of Nb implanted γ-TiAl based alloy

Abstract The influence of post-implantation annealing on the isothermal oxidation behavior of Nb implanted (3×10 17 ions/cm 2 ) Ti–48 at.%Al was investigated. The kinetics of isothermal oxidation at 900°C for 100 h in air revealed that appropriate post-implantation annealing (800°C/5 h) could remarkably further improve the oxidation resistance of the as-implanted alloy; possible mechanisms were discussed considering the results of element distribution, oxidation product and its surface morphology examined by Auger electron spectra (AES), X-ray diffraction (XRD) and scanning electron microscope (SEM). It indicated that both the eliminating of the lattice damage induced by ion implantation and element redistribution in the implanted region caused by post-implantation annealing might be responsible for the further decrease of the oxidation rate.

High temperature oxidation behaviour of FeAl intermetallics—oxide scales formed in ambient atmosphere

Iron aluminides (Fe-Al) are intermetallic compounds that possess a number of advantages including low materials cost, conservation of Ni and Cr, relatively low densities, and good corrosion and oxidation resistances. The authors have studied the high temperature oxidation and sulfidation behaviors of Fe-Al, including isothermal and cyclic oxidation kinetics, scale structure and spallation tendency, and the reactive elements effects (REE) in an effort to use these materials in industries. This paper reports their results on the structures and formation mechanisms of the scales formed on Fe-Al during oxidation. The scales formed on alloys after exposure to high temperatures often have a complex structure and composition. It is known that when some alloys were oxidized in air at high temperatures, nitrides were formed underneath the oxide scale. It was reported that the oxidation of TiAl alloys in an ambient atmosphere led to the nitration of the base metal beneath the oxide scales. After a long exposure time a multilayered scale was formed which consisted of metal, Ti{sub 2}AlN, TiN, TiO{sub 2} and Al{sub 2}O{sub 3}. Cr was oxidized in air at 1,200 C, forming a Cr{sub 2}O{sub 3} scale with a layer of Cr{sub 2}N beneath the oxide. When binary Crmore » alloys containing Ti,Zr, or Nb were oxidized in air at 1,150 C, a layer or internally distributed Cr{sub 2}N formed beneath the oxide scales. However, the structures and formation mechanisms of these types of scales are not clear. The authors have also found that the scales formed on Fe-Al at 1,100 C in air have a complex structure containing nitrides. This paper reports the authors' studies on this subject.« less

Modeling of the DTG Curves for Oxidation of a Nanosized Molybdenum Ferrite Coupling Mechanics and Diffusion

From a model for isothermal oxidation kinetics in nanosized ferrite spinels based on a diffusion-induced stress effect, the authors present a modeling of the DTG curves for the oxidation of Fe2+ and Mo3+ cations on octahedral sites of a molybdenum ferrite. This has been made by considering that the chemical diffusion coefficient is given by the relation $$\tilde D = D_o \exp \left( {\frac{{E'_{\text{a}} + pV_{\text{a}} }}{{RT}}} \right)$$ , when D o is a pre-exponential factor, E a ′ an activation energy and V a an activation energy induced by the oxidation.

Oxidation behavior of niobium aluminide intermetallics protected by aluminide and silicide diffusion coatings

The isothermal and cyclic oxidation behavior of a new class of damage-tolerant niobium aluminide (Nb3Al-xTi-yCr) intermetallics is studied between 650 °C and 850 °C. Protective diffusion coatings were deposited by pack cementation to achieve the siliciding or aluminizing of substrates with or without intervening Mo or Ni layers, respectively. The compositions and microstructures of the resulting coatings and oxidized surfaces were characterized. The isothermal and cyclic oxidation kinetics indicate that uncoated Nb-40Ti-15Al-based intermetallics may be used up to ∼750 °C. Alloying with Cr improves the isothermal oxidation resistance between 650 °C and 850 °C. The most significant improvement in oxidation resistance is achieved by the aluminization of electroplated Ni interlayers. The results suggest that the high-temperature limit of niobium aluminide-based alloys may be increased to 800 °C to 850 °C by aluminide-based diffusion coatings on ductile Ni interlayers. Indentation fracture experiments also indicate that the ductile nickel interlayers are resistant to crack propagation in multilayered aluminide-based coatings.

Oxidation phenomena in a Ti 3Al base-alloy

In this study we present some results regarding phase and surface thermal stability, with particular reference to the oxidation of an intermetallic alloy with the composition Ti23Al10.3Nb4.5V0.9Cr (at.%). The isothermal oxidation kinetics were studied by thermogravimetric analysis. From the experimental results we evaluated the parameters of the process. The weight gain curves showed a parabolic trend for time up to 25 h. For longer than 50 h treatments, the kinetics tend to follow a linear trend with the formation of a non-protective surface oxide layer. The microstructure of the oxide scale was investigated with scanning electron microscopy and energy dispersive X-ray analysis and mapping. The identification of the crystalline phases was carried out with X-ray diffraction analysis.