Numerical modeling of high-temperature corrosion processes

Nesbitt, James A.

doi:10.1007/bf01046731

Cited by 39 publications

(20 citation statements)

References 28 publications

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“…Detailed descriptions of the occurring processes were for instance described by Durham et al [15] using FeCrC model alloys as example. For the alumina forming NiCoCrAlY coatings analytical [16,17] as well as numerical models [18][19][20][21] describing the diffusion and dissolution processes as a result of oxide scale formation have been presented.…”

Section: Introductionmentioning

confidence: 99%

Sub-Scale Depletion and Enrichment Processes During High Temperature Oxidation of the Nickel Base Alloy 625 in the Temperature Range 900–1000 °C

et al. 2010

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Numerous chromia-forming austenitic steels and nickel-base alloys contain chromium-rich strengthening precipitates, e.g. chromium-base carbides. During high temperature exposure the formation of the chromia base oxide scale results in chromium depletion in the alloy matrix and consequently in dissolution of the strengthening phase in the sub-surface zone. The present study describes the oxidation induced phase changes in the chromium depletion layer in case of alloy 625, a nickel base alloy in which the strengthening precipitates contain hardly any or only minor amounts of chromium. Specimens of alloy 625 were subjected to oxidation up to 1000 h at 900 and 1000°C and analyzed in respect to oxide formation and microstructural changes using light optical microscopy, scanning electron microscopy, energy and wavelength dispersive analysis, glow discharge optical emission spectroscopy, and X-ray diffraction. In spite of the fact that the alloy precipitates d-Ni 3 Nb and/or (Ni, Mo) 6 C contain only minor amounts of chromium, the oxidation induced chromium depletion results in formation of a wide sub-surface zone in which the precipitate phases are depleted. However, in parallel, substantial niobium diffusion occurs towards the alloy surface resulting in formation of a thin layer of d-Ni 3 Nb phase adjacent to the alloy/oxide interface. By modeling phase equilibria and diffusion processes using Thermo-Calc and DICTRA it could be shown that the phase changes in the sub-scale zone are governed by the influence of alloy matrix chromium concentration on the thermodynamic activities of the other alloying elements, mainly niobium and carbon. The d-phase depletion/ enrichment process is caused by a decreasing niobium activity with decreasing chromium concentration whereas the (Ni,Mo) 6 C dissolution finds its cause in the increasing carbon activity with decreasing chromium content.A. Chyrkin (&) Á P. Huczkowski Á V. Shemet Á L. Singheiser Á W. J. Quadakkers

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Section: Introductionmentioning

confidence: 99%

Sub-Scale Depletion and Enrichment Processes During High Temperature Oxidation of the Nickel Base Alloy 625 in the Temperature Range 900–1000 °C

et al. 2010

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“…The time at which C i (t) drops down to C b is the time to breakaway. In parallel, numerical methods to solve the diffusion equations were developed to account for non-parabolic oxidation kinetics [21] extending their applicability to multicomponent [22][23][24][25] and multiphase [26][27][28] alloys, imposing twodimensional restrictions on the specimen geometry. [29][30][31] In the present study the finite-difference software DIC-TRA [32] was used to simulate the chromium depletion in a spherical particle of a Ni-22%Cr alloy.…”

Section: Lifetime Modeling Using Dictramentioning

confidence: 99%

Oxidation Limited Lifetime of Ni‐Base Metal Foams in the Temperature Range 700–900 °C

et al. 2010

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Metal foams are potentially suitable for various high temperature applications in which low-density components with relatively high mechanical properties are required. Examples of such applications are materials for walls of combustion chambers (or furnaces), high temperature catalyst supports, heat-exchangers, and filters. [1][2][3] The high temperature oxidation behavior of metal foams is therefore of substantial technological as well as scientific interest. However, only a very limited number of publications are available which deal with the oxidation behavior of porous metallic components. [4,5] Due to their excellent mechanical properties and oxidation resistance NiCr-base alloys are attractive materials for the manufacturing of metallic foams. These chromium-rich heat-resistant alloys rely for their high temperature oxidation resistance on the selective oxidation of chromium to form a dense, well-adherent, and protective Cr 2 O 3 oxide scale on the component surface. The formation of the oxide layer is associated with a continuous depletion of Cr from the alloy which may, after long service times, eventually result in breakdown of the Cr 2 O 3 scale due to an insufficient flux of Cr toward the oxide/metal interface. [6][7][8] This breakaway type oxidation is the result of the formation of fast growing base-metal oxides after a critical Cr depletion in the alloy has occurred. The time t B at which the Cr concentration at the oxide/metal interface reaches this critical value of the Cr concentration C b at which breakaway oxidation occurs, is a very important technological parameter defining the service lifetime limit of the components. Numerous studies [6,7,9] have shown that at a given temperature the time to breakaway is a function of oxidation rate, specimen dimensions, and geometry: (i) faster oxidation leads to accelerated chromium depletion, i.e., shortening of the lifetime, (ii) a thinner component possesses a smaller chromium reservoir and thus t b tends to be smaller than for thicker components, and (iii) the overall specimen geometry affects the supply of chromium from the bulk alloy, cylindrical, and spherical components having lower chromium supply compared to a flat sample of identical thickness because of the larger surface to volume ratio. [10] COMMUNICATION [*] Dr. [**] This work has been funded by the German Research Foundation within the framework of the SFB 561 project. Mr. H. Cosler and Ms. A. Kick are gratefully acknowledged for their assistance in carrying out the oxidation tests, and Mr. E. Wessel for the SEM/ EDX analyses.INCONEL 625 metal foams produced from alloy powder by the slip-reaction-foam-sinter-process are tested in respect to cyclic oxidation behavior in air in the temperature range 700-900 8C. The structure of the oxide scales formed on the foam particles is characterized using optical microscopy and SEM/ EDX analysis. Main emphasis is put on studying the oxidation limited lifetimes of the foams as function of temperature and foam microstructure. It is shown that mechanical...

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“…However, modeling of more complex internal-precipitation reactions that involve more than one compound or moderate stability of the reaction product and varying boundary conditions (e. g. temperature changes) require a numerical treatment of both the diffusion and the thermochemical processes in the alloy [17,18]. For this purpose, a computer simulation was developed in which the commercial thermodynamic software ChemApp is combined with a finite-difference diffusion calculation using the explicit method [19].…”

Section: Materials and Corrosionmentioning

confidence: 99%

Thermodynamic characteristics and numerical modeling of internal nitridation of nickel base alloys

Christ¹,

Chang

Krupp

2003

Materials & Corrosion

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Kinetics and thermodynamics of the process of internal nitridation of various nickel-base alloys have been investigated in oxygenfree nitrogen atmospheres. Furthermore, the influence of formation and spalling of a protective oxide scale on the internal nitridation behavior of the alloys was studied by isothermal and cyclic oxidation tests in air. In general, nitridation kinetics of model nickel-base alloys of the system Ni-Cr-Ti was found to obey a parabolic rate law indicating that the nitridation process is diffusion-controlled. The temperature dependence of the nitridation rate constants is well described by an equation of the Arrhenius type. A thermodynamic calculation of the Ni-Cr-Ti-Al-N system was used to determine the nitrogen solubility in respective alloys as a function of temperature and alloy composition. The results show that a higher chromium content gives rise to an increase in the nitrogen solubility of Ni-Cr-Ti alloys leading to an increased nitridation rate in accordance with the experimental observations. From the calculated values for the nitrogen solubility, the diffusion coefficients of nitrogen were assessed using Wagner's classical theory of internal oxidation. A computer model of internal nitridation was developed that combines a commercial thermodynamic software (ChemApp) with a finite-difference diffusion calculation. It was found that this model describes the internal nitridation process in reasonable agreement with the experimental results and allows to treat the case of simultaneous formation of different nitrides. The dependence of internal nitridation behavior on spalling and cracking of the oxide was incorporated into the simulation on the basis of simple assumptions showing that this calculation method successfully applies also to complex internal corrosion processes.

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Numerical modeling of high-temperature corrosion processes

Cited by 39 publications

References 28 publications

Sub-Scale Depletion and Enrichment Processes During High Temperature Oxidation of the Nickel Base Alloy 625 in the Temperature Range 900–1000 °C

Sub-Scale Depletion and Enrichment Processes During High Temperature Oxidation of the Nickel Base Alloy 625 in the Temperature Range 900–1000 °C

Oxidation Limited Lifetime of Ni‐Base Metal Foams in the Temperature Range 700–900 °C

Thermodynamic characteristics and numerical modeling of internal nitridation of nickel base alloys

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