Microstructure and composition of multi-layered oxide scale evolved during isothermal exposure of ZrB2–SiC–LaB6 composite to air at 1500°C

2021 ◽  
pp. 1-12
Author(s):  
Sunil Kumar Kashyap ◽  
Rahul Mitra
Keyword(s):  
Oxide Scale ◽  
Isothermal Exposure ◽  
Layered Oxide

Diffusion Enhanced Rumpling Associated with Martensitic Transformation upon Cycling of Aluminide Bond-Coats

2009 ◽  
Vol 289-292 ◽  
pp. 227-233 ◽  
Author(s):  
B. Bouchaud ◽  
J. Balmain ◽  
F. Pedraza
Keyword(s):  
Martensitic Transformation ◽  
Oxide Scale ◽  
Alumina Scale ◽  
Scale Spallation ◽  
Protective Oxide ◽  
Isothermal Exposure ◽  
Growth Stresses ◽  
Bond Coats ◽  
Aluminide Coatings ◽  
L10 Structure

In this work, β-NiAl aluminide coatings (cubic B2 structure) deposited on a DS substrate have been isothermally as well as cyclically oxidised at 1100°C for up to 240 h to study the diffusion mechanisms associated with the growth of the oxide scales. A 24 h cycle has been shown to promote enhanced Al depletion, thus requiring a sufficient Al flux to maintain a protective oxide scale. Glancing incidence X-ray diffraction (GI-XRD) combined to electron microscopy (FEG-ESEM / EDS) has been carried out to characterize the evolution of the phases induced by the progressive Al depletion into the coating. The results show that upon cycling, specimens undergo significant oxide scale spallation and increased roughness that can be ascribed to both the growth stresses and the phase transformation contribution whereas the coating has barely evolved after 240 h of isothermal exposure. In particular, the martensitic transformation (tetragonal L10 structure) that accompanies thermal cycling was found to be much more significant than the evolution of the γ’-Ni3Al (cubic L12 structure) phase over the same thermal cycle and therefore the B2 to martensite transformation could originate the progressive roughening of the surface. Conversely, upon isothermal exposure, the coating exhibited a typical alumina scale with almost no spallation and the appearance of rumples.

scholarly journals Discontinuities in Oxidation Kinetics: A New Model and its Application to Cr–Si-Base Alloys

2021 ◽  
Author(s):  
Anke S. Ulrich ◽  
Uwe Glatzel ◽  
Mathias C. Galetz
Keyword(s):  
Oxide Scale ◽  
Oxidation Kinetics ◽  
Parabolic Rate Constant ◽  
Mass Gain ◽  
Linear Mass ◽  
Isothermal Exposure ◽  
Growth Stresses ◽  
Scale Failure ◽  
Insight Into ◽  
Rapid Mass

AbstractSome alloys such as many Cr-based systems show mass gain discontinuities during thermogravimetric measurements which strongly affect the oxidation kinetics. The behaviour cannot be described by the current models available in the literature. Thus, a novel $$k_\mathrm{para}$$ k para –$$k_\mathrm{lin}$$ k lin -P-model was developed to describe oxidation kinetics during the isothermal exposure of materials which show such behaviour. Beside the parabolic rate constant $$k_\mathrm{para}$$ k para and the linear mass loss constant $$k_\mathrm{lin}$$ k lin , the P-value and $$f_P$$ f P are introduced to take into account spontaneous rapid mass gains due to local oxide scale failure. The parameter P serves as a measure for the mass gain due to discontinuous events and $$f_P$$ f P is the frequency of such events. The both parameters can be related to oxide scale detachment and growth stresses. The application of the model is demonstrated for the oxidation of Cr–Si-based alloys in synthetic air at $$1200^{\circ }\hbox {C}$$ 1200 ∘ C for 100 h. For these alloys, the origin of the mass gain discontinuities is discussed and the meaning of P and $$f_P$$ f P is explained in more detail. Using this newly developed model, an insight into growth and nitridation resistance of oxide scales as well as scale adhesion is gained.

Structural Imperfections in thin Oxide Films Formed on Some Fe- and Ni-Base Alloys

1970 ◽  
Vol 28 ◽  
pp. 510-511
Author(s):  
L. P. Lemaire ◽  
D. E. Fornwalt ◽  
F. S. Pettit ◽  
B. H. Kear
Keyword(s):  
Oxide Scale ◽  
Oxidation Process ◽  
Short Circuit ◽  
Protective Oxide ◽  
Protective Oxide Scale ◽  
Thin Oxide Films ◽  
Diffusion Paths ◽  
Oxidation Resistant ◽  
Structural Imperfections ◽  
Short Circuit Diffusion

Oxidation resistant alloys depend on the formation of a continuous layer of protective oxide scale during the oxidation process. The initial stages of oxidation of multi-component alloys can be quite complex, since numerous metal oxides can be formed. For oxidation resistance, the composition is adjusted so that selective oxidation occurs of that element whose oxide affords the most protection. Ideally, the protective oxide scale should be i) structurally perfect, so as to avoid short-circuit diffusion paths, and ii) strongly adherent to the alloy substrate, which minimizes spalling in response to thermal cycling. Small concentrations (∼ 0.1%) of certain reactive elements, such as yttrium, markedly improve the adherence of oxide scales in many alloy systems.

Morphologies of Nonadherent Al2O3 and Matching Substrate Surfaces

1972 ◽  
Vol 30 ◽  
pp. 524-525
Author(s):  
C. S. Giggins ◽  
J. K. Tien ◽  
B. H. Kear ◽  
F. S. Pettit
Keyword(s):  
Electron Microscopy ◽  
Oxide Scale ◽  
Oxidation Resistance ◽  
Substrate Surface ◽  
Morphological Features ◽  
Thermally Induced ◽  
Oxide Spallation ◽  
Oxidation Resistant ◽  
Induced Stresses ◽  
Substrate Surfaces

The performance of most oxidation resistant alloys and coatings is markedly improved if the oxide scale strongly adheres to the substrate surface. Consequently, in order to develop alloys and coatings with improved oxidation resistance, it has become necessary to determine the conditions that lead to spallation of oxides from the surfaces of alloys. In what follows, the morphological features of nonadherent Al2O3, and the substrate surfaces from which the Al2O3 has spalled, are presented and related to oxide spallation.The Al2O3, scales were developed by oxidizing Fe-25Cr-4Al (w/o) and Ni-rich Ni3 (Al,Ta) alloys in air at 1200°C. These scales spalled from their substrates upon cooling as a result of thermally induced stresses. The scales and the alloy substrate surfaces were then examined by scanning and replication electron microscopy.The Al2O3, scales from the Fe-Cr-Al contained filamentary protrusions at the oxide-gas interface, Fig. 1(a). In addition, nodules of oxide have been developed such that cavities were formed between the oxide and the substrate, Fig. 1(a).

A new lithium diffusion model in layered oxides based on asymmetric but reversible transition metal migration

2020 ◽  
Vol 13 (4) ◽  
pp. 1269-1278 ◽  
Author(s):  
Kyojin Ku ◽  
Byunghoon Kim ◽  
Sung-Kyun Jung ◽  
Yue Gong ◽  
Donggun Eum ◽  
...  
Keyword(s):  
Transition Metal ◽  
Diffusion Model ◽  
Layered Oxides ◽  
Layered Oxide ◽  
Reversible Transition ◽  
Lithium Diffusion ◽  
Metal Migration

We propose a new lithium diffusion model involving coupled lithium and transition metal migration, peculiarly occurring in a lithium-rich layered oxide.

Oxide-Scale and α-Casing Characterization in Ti6Al4V Alloy Oxidised in Oxygen Gas

2006 ◽  
Vol 43 (11) ◽  
pp. 559-574
Author(s):  
M. N. Mungole ◽  
M. Surender ◽  
S. Bhargava
Keyword(s):  
Oxide Scale ◽  
Ti6al4v Alloy ◽  
Oxygen Gas

The effect of water vapor in increasing growth stresses in the oxide scale on martensitic steam plant alloys

2005 ◽  
Vol 22 (1) ◽  
pp. 139-146 ◽  
Author(s):  
Alexander Donchev ◽  
Harald Fietzek ◽  
Vladislav Kolarik ◽  
Daniel Renusch ◽  
Michael Schütze
Keyword(s):  
Water Vapor ◽  
Oxide Scale ◽  
Growth Stresses ◽  
Effect Of Water ◽  
Steam Plant

New Precursor Route Using a Compositionally Flexible Layered Oxide and Nanosheets for Improved Nitrogen Doping and Photocatalytic Activity

2018 ◽  
Vol 1 (4) ◽  
pp. 1734-1741 ◽  
Author(s):  
Kazuhiko Maeda ◽  
Yuki Tokunaga ◽  
Keisuke Hibino ◽  
Kotaro Fujii ◽  
Hiroyuki Nakaki ◽  
...  
Keyword(s):  
Photocatalytic Activity ◽  
Nitrogen Doping ◽  
Layered Oxide ◽  
Precursor Route

Improved interfacial chemistry and enhanced high voltage-resistant capability of in-situ polymerized electrolyte for LiNi0.8Co0.15Al0.05O2-Li batteries

2021 ◽  
Author(s):  
Yue Ma ◽  
Qifang Sun ◽  
Zhenyu Wang ◽  
Su Wang ◽  
Ying Zhou ◽  
...  
Keyword(s):  
Energy Density ◽  
High Voltage ◽  
Lithium Batteries ◽  
Interfacial Chemistry ◽  
Layered Oxide ◽  
Li Batteries

Ni-rich layered oxide LiNi0.8Co0.15Al0.05O2 (NCA) is one of the most promising cathode candidates for higher energy density lithium batteries. However, the extensive application of NCA is hindered due to the...

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