scholarly journals Calculations of Internal Oxidation Rate Equations and Boundary Conditions between Internal and External Oxidation in Silicon Containing Steels

2010 ◽  
Vol 51 (3) ◽  
pp. 482-487 ◽  
Author(s):  
Takashi Onishi ◽  
Shouhei Nakakubo ◽  
Mikako Takeda
Keyword(s):  
Boundary Conditions ◽  
Internal Oxidation ◽  
Oxidation Rate ◽  
Rate Equations ◽  
External Oxidation

Calculation of Boundary Conditions between Internal and External Oxidation of Silicon or Chromium Containing Steels

2011 ◽  
Vol 696 ◽  
pp. 88-93 ◽  
Author(s):  
Shohei Nakakubo ◽  
Mikako Takeda ◽  
Takashi Onishi
Keyword(s):  
Boundary Condition ◽  
Diffusion Coefficient ◽  
Boundary Conditions ◽  
Oxygen Concentration ◽  
Internal Oxidation ◽  
Rate Equation ◽  
Oxidation Rate ◽  
Oxidation Rate Constant ◽  
External Oxidation ◽  
Diffusion Coefficient Of Oxygen

The boundary constants between internal and external oxidation of Si or Cr containing steels (Fe-Si alloys or Fe-Cr alloys) at 850°C were calculated in order to clarify the formation mechanism of fayalite scale (Fe2SiO4) or chromite scale (FeCr2O4), which can form as a “sub-scale” in Si or Cr containing steels. The diffusion coefficient of oxygen in the alloy, Do, and the oxygen concentration at the specimen surface, NO(s), which are constituents of the internal oxidation rate constant, (2DONO(s)/NB(O)n), were calculated for various oxidation conditions, and the rate equation for internal oxidation was derived. By comparing the calculated and measured values of (2DONO(s)/NB(O)n), we confirmed that the rate equation determined for internal oxidation was reasonable. The boundary condition between internal and external oxidation of Si or Cr containing steels (Fe-Si alloys or Fe-Cr alloys) at 850°C were also calculated by substituting the calculated values of DO and NO(s) into the rate equation.

Dependence of internal oxidation rate of water atomized Cu-Al alloy powders on oxygen partial pressure

1996 ◽  
Vol 15 (6) ◽  
pp. 465-468 ◽  
Author(s):  
J. Brito Correia ◽  
M. Pereira Caldas ◽  
N. Shohoji ◽  
A. Cabral Ferro
Keyword(s):  
Oxygen Partial Pressure ◽  
Partial Pressure ◽  
Internal Oxidation ◽  
Oxidation Rate ◽  
Al Alloy

Refinement in the Mathematical and Numerical Treatment of the Internal Oxidation of Alloys

2005 ◽  
Vol 237-240 ◽  
pp. 1157-1162 ◽  
Author(s):  
Wiktor Miszuris ◽  
Andreas Öchsner
Keyword(s):  
Boundary Conditions ◽  
Internal Oxidation ◽  
Diffusion Coefficients ◽  
Finite Dimension ◽  
Time Dependent ◽  
Diffusion Equations ◽  
Numerical Treatment ◽  
Constant Diffusion ◽  
Finite Difference Solution ◽  
Oxide Particles

When oxygen dissolves from atmosphere and diffuses into an alloy during oxidation, the less noble alloy components may react to form oxide particles within the metal. This process is termed internal oxidation. Classical approaches to describe this phenomenon were derived under many strong simplifications such as constant diffusion coefficients, certain boundary conditions and semi-infinite sample. The presented general approach is based on the finite difference solution of the general diffusion equations coupled through the stoichiometry of reaction between oxygen and the considered element. The main enhancement is the consideration of concentration dependent diffusion coefficients, concentration dependent source terms and arbitrary time-dependent boundary conditions formulated as a concentration, a flux or mixed conditions. Furthermore, finite dimension of the specimen is incorporated. This general treatment also allows for the incorporation of the energy balance.

Oxidation Behavior of K38 Superalloy with Different Amounts of Yttrium Addition at 1173K in Air

2011 ◽  
Vol 366 ◽  
pp. 40-44 ◽  
Author(s):  
Ping Yu ◽  
Long Shi ◽  
Wen Wang ◽  
Fu Hui Wang
Keyword(s):  
Oxidation Resistance ◽  
Selective Oxidation ◽  
Internal Oxidation ◽  
Oxidation Rate ◽  
Oxidation Behavior ◽  
Rich Phase ◽  
Al2o3 Scales ◽  
Yttrium Addition ◽  
Negative Effect ◽  
Cast Alloys

The oxidation behavior of K38 alloy with 0, 0.05, 0.1, 0.5wt% yttrium concentrations has been investigated during exposures in air at 1173K for 100 hours. The results indicated that Cr2O3 and TiO2 scale mainly formed on the surface of the alloy without yttrium. Yttrium addition promoted the selective oxidation of aluminum and reduced the internal oxidation. The alloy with 0.1 wt.% yttrium addition exhibits excellent oxidation behavior among the four types of the alloys for its decreasing the oxidation rate and forming more continuous and compact Al2O3 scales. Yttrium-rich phase formed in the alloy with 0.5wt.% yttrium, result in a negative effect on the oxidation resistance of cast alloys.

HREM studies on interfaces in internally oxidized alloys

1988 ◽  
Vol 46 ◽  
pp. 730-731
Author(s):  
W. Mader
Keyword(s):  
Internal Oxidation ◽  
Electrical Contact ◽  
Relative Orientation ◽  
Atomic Scale ◽  
Metal Alloys ◽  
Chemical Information ◽  
Dispersion Strengthening ◽  
Low Oxygen ◽  
External Oxidation ◽  
Low Oxygen Pressure

Precipitation of metal oxides by internal oxidation of metal alloys has been widely used for dispersion strengthening of materials in electrical contact applications. Like in other precipitate systems, the oxide precipitates have the freedom to form with any shape and relative orientation with respect to the metal matrix. It is expected that natural, low energy interfaces which are perfectly flat at an atomic scale can be produced by this technique. For these reasons, such interfaces are ideal objects for HREM studies. Interfaces between Nb and Al2O3 and between Ag and CdO, produced using internal oxidation were investigated by HREM techniques in order to extract structural and chemical information at the atomic level.Specimens of Nb containing 3.5 at% A1 were oxidized at 1500°C in a controlled atmosphere with a low oxygen pressure in order to avoid external oxidation. Small plate-like Al2O3 precipitates 15-30 nm thick and 200-800 nm wide were observed.

Study on the Behavior of Internal Oxidation of Ag-Cu-Zn Alloy

2013 ◽  
Vol 395-396 ◽  
pp. 196-200
Author(s):  
Yong Tai Chen ◽  
Ming Xie ◽  
You Cai Yang ◽  
Ji Ming Zhang ◽  
Man Men Liu ◽  
...  
Keyword(s):  
Internal Oxidation ◽  
Short Path ◽  
Oxidation Rate ◽  
Boundary Diffusion ◽  
Oxidation Time ◽  
Diffusion Activation Energy ◽  
Diffusion Channel ◽  
Initial Stage ◽  
Zn Alloy ◽  
Diffusion Activation

the behavior of internal oxidation of Ag-Cu-Zn alloy was studied at various internal oxidation temperatures for different internal oxidation time. The experimental results show that the short path diffusion, such as boundary diffusion and surface diffusion, is the main diffusion channel of oxygen in initial stage of oxidation, oxidation rate is fast, while the internal oxidation exponent n=1. Then the oxygen diffusion translated from short path diffusion into long path diffusion with the extending of internal oxidation time, and the oxidation rate was slowed down, while the internal oxidation exponent n=1.67. The action size is increased with the temperature increase. The diffusion activation energy of oxygen in initial stage of oxidation is lower than that in middle and late stage.

scholarly journals Non-Isothermal Oxidation Behaviors and Mechanisms of Ti-Al Intermetallic Compounds

Materials ◽  
2019 ◽  
Vol 12 (13) ◽  
pp. 2114 ◽  
Author(s):  
Peixuan Ouyang ◽  
Guangbao Mi ◽  
Peijie Li ◽  
Liangju He ◽  
Jingxia Cao ◽  
...  
Keyword(s):  
Internal Oxidation ◽  
Oxidation Rate ◽  
Isothermal Oxidation ◽  
Pure Oxygen ◽  
Scanning Calorimetry ◽  
Β Phase ◽  
Thermal Analyzer ◽  
Wagner’S Theory ◽  
Simultaneous Thermal Analyzer ◽  
Oxidation Behaviors

Non-isothermal oxidation is one of the important issues for the safe application of Ti-Al alloys, so this study aimed to illustrate the non-isothermal oxidation behaviors and the corresponding mechanisms of a TiAl-based alloy in comparison with a Ti3Al-based alloy. The non-isothermal oxidation behaviors of Ti-46Al-2Cr-5Nb and Ti-24Al-15Nb-1.5Mo alloys in pure oxygen were comparatively investigated with a thermogravimetry-differential scanning calorimetry (TGA/DSC) simultaneous thermal analyzer heating from room temperature to 1450 °C with a heating rate of 40 °C/min. When the temperature rose above 1280 °C, the oxidation rate of the Ti-46Al-2Cr-5Nb alloy sharply increased and exceeded that of the Ti-24Al-15Nb-1.5Mo alloy owing to the occurrence of internal oxidation. When the temperature was higher than 1350 °C, the oxidation rate of the Ti-46Al-2Cr-5Nb alloy decreased obviously due to the generation of an oxygen-barrier β-Al2TiO5-rich layer by a chemical reaction between Al2O3 and TiO2 in the oxide scale. Based on Wagner’s theory of internal oxidation, the reason for the occurrence of internal oxidation in the Ti-46Al-2Cr-5Nb alloy is the formation of the α phase in the subsurface, while no internal oxidation occurred in the Ti-24Al-15Nb-1.5Mo alloy due to the existence of the β phase in the subsurface with the enrichment of Nb and Mo.

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