Quantitative Approach for Determining the Critical Volume Fraction for the Transition from Internal to External Oxidation

Zhao, Wei; Kang, Yunyi; Alvarado-Orozco, J.M.; Gleeson, Brian

doi:10.1007/s11085-014-9516-1

Cited by 37 publications

(31 citation statements)

References 16 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In the investigated Co-base alloys, alumina exhibits insufficient lateral growth which is needed to form a diffusion limiting oxide layer. According to Zhao et al the simultaneous formation of numerous discrete oxide precipitates can be attributed to pronounced rates of alumina nucleation [35]. The γ′-precipitates are subjected to a slower oxidation-related attack that is accompanied by an evident shape loss as it is depicted for the STEM-results (for 30 min exposure at 850 °C).…”

Section: Oxidation Kinetics Of Polished Samplesmentioning

confidence: 90%

On the High-Temperature Oxidation Behavior of a Ta-Containing Quaternary Co-Base Model Alloy System with γ/γ′-Microstructure - Influence of γ′-Volume Fraction, Surface State, and Heating Condition on Alumina Growth

et al. 2020

View full text Add to dashboard Cite

The improvement of the high-temperature oxidation resistance remains an ambitious goal for the design of new γ/γ′-strengthened Co-base superalloys, since their oxidation resistance beyond 800 °C still ranks behind their Ni-base counterparts. To better understand the origin of the poor oxidation resistance at higher temperatures, this study focuses on early stages of oxidation of four quaternary (Co-Al-W-Ta system) Co-base model alloys with a two-phase γ/γ′-microstructure and varying γ′-volume fraction at 800 °C, 850 °C and 900 °C. Based on time-resolved isothermal gravimetric analysis (TGA) in synthetic air and detailed electron microscopic analysis, the role of the γ-channel width (or γ′-volume fraction), the surface preparation prior to exposure (polishing versus shot-peening), and the heating conditions (synthetic air versus argon) on protective alumina growth is elucidated. Firstly, for alloys of increased γ′-volume fractions slower oxidation kinetics prevailed. Secondly, the two-phase microstructure was found to decisively affect the propagation of the internal oxidation front at the early stages of oxidation. Thirdly, shot-peening prior to exposure together with a lack of oxygen availability during heating was identified to foster protective alumina growth, accompanied by TCP-phase formation in the substrate. The critical role of a high Al availability in the alloy for a rapid growth of protective alumina and the relating challenges in alloy development regarding, for example, phase stability in this relatively novel Co-base alloy class are discussed in detail.

show abstract

Section: Oxidation Kinetics Of Polished Samplesmentioning

confidence: 90%

On the High-Temperature Oxidation Behavior of a Ta-Containing Quaternary Co-Base Model Alloy System with γ/γ′-Microstructure - Influence of γ′-Volume Fraction, Surface State, and Heating Condition on Alumina Growth

et al. 2020

View full text Add to dashboard Cite

show abstract

“…The critical concentration

N_{B}^{true(0 true)} true(c r i t true)

can be predicted from

N_{B}^{(0)} true(c r i t true) = {(\frac{f_{V}^{*} V_{A l l o y} N_{O}^{false(s false)} D_{O}}{2 ν V_{O x} {\overset{D}{true}}_{B}})}^{\frac{1}{2}}

where B refers to the protective oxide forming element,

f_{V}^{*}

is the critical oxide volume fraction needed for the transition from internal to external oxidation, which is usually taken to be 0.3, following the study of Rapp on silver‐indium alloys. Recent studies by Leblond and Zhao et al showed that this factor is not constant and depends on factors such as the molar volumes of the species and the internal oxide morphology. The quantites V Alloy and V Ox refer to the molar volume of the alloy and the internal oxide, respectively, ν is the stoichiometric coefficient for oxide BO ν ,

{\tilde{D}}_{B}

the interdiffusion coefficient of the oxide forming element in the alloy,

N_{O}^{(s)}

the concentration of dissolved oxygen on the surface of the metal, and D O the diffusion coefficient of oxygen in the alloy.…”

Section: Introductionmentioning

confidence: 99%

Oxygen permeability of Fe‐Ni‐Cr alloys at 1100 and 1150 °C under carbon‐free and carbon‐containing gases

Jullian

Prillieux

Zhang

et al. 2016

Materials & Corrosion

View full text Add to dashboard Cite

Wagner's model of internal oxidation allows the prediction of an alloy's critical concentration of oxide forming metal required to achieve a protective oxide scale at high temperatures. The model depends on oxygen permeability in the alloy, but this parameter has not been evaluated for the Fe‐Ni system, and the influence of carbon‐bearing gases is unknown. Oxygen permeability measurement by internal oxidation of Fe‐Ni‐Cr alloys, reacted at 1100 and 1150 °C is described. Exposures in Rhines packs and flowing CO‐CO2 gas mixtures serve to assess the influence of carbon on oxygen permeability at the Fe‐FeO equilibrium oxygen potential. Oxygen permeability in Fe‐Ni increases with iron content in a non‐ideal manner in both gas environments. Higher permeability is found in carbon bearing gases for iron‐rich alloys, and the size of this effect increases with temperature.

show abstract

“…The halogen effect turned out to slightly decrease the mass-gain after 36 h of exposure in case of polished samples (relative reduction of 7.5%). Since no statistic evaluation of the alumina precipitate size was conducted, it cannot be excluded that this difference might be based on a slight coarsening of the distinct alumina precipitates [37] that is simply not clearly depicted within the ion-milling-based cross sections. Also, an increased internal formation of spinel phase due to halogenation might contribute to the enhancement in oxidation resistance [31].…”

Section: Discussionmentioning

confidence: 99%

Protective Alumina Scale Growth at 900 °C for a Ni- and Cr-Free Co-Base Model Alloy with γ/γ’-Microstructure: Synergistic Effects by Combining Shot-Peening and Halogenation

et al. 2021

View full text Add to dashboard Cite

The oxidation resistance of novel γ/γ’-strengthened Co-base superalloys is clearly outmatched by their Ni-base counterparts within the high-temperature regime. Therefore, surface modification strategies to foster protective alumina growth seem auspicious. This study elucidates the impact of fluorination and shot-peening on protective alumina formation at 900 °C for a quaternary Co-base model alloy (Co-Al-W-Ta system) which is well known for an exceptionally low inherent oxidation resistance. Time-resolved isothermal gravimetric analysis (TGA) in synthetic air, detailed electron microscopic analysis, and X-ray diffraction (XRD) were used. For polished samples, no pronounced enhancement of oxidation resistance could be obtained by halogenation. However, in case of shot-peened samples (halogen-free), an increased tendency for alumina formation is found compared to polished surfaces. The very early stages of oxidation were identified to be especially crucial with respect to sustainable protective scale growth. Most noteworthy is the observation of a strong synergistic effect derived by a combination of halogenation and shot-peening, leading to significantly increased oxidation resistance.

show abstract

Quantitative Approach for Determining the Critical Volume Fraction for the Transition from Internal to External Oxidation

Cited by 37 publications

References 16 publications

On the High-Temperature Oxidation Behavior of a Ta-Containing Quaternary Co-Base Model Alloy System with γ/γ′-Microstructure - Influence of γ′-Volume Fraction, Surface State, and Heating Condition on Alumina Growth

On the High-Temperature Oxidation Behavior of a Ta-Containing Quaternary Co-Base Model Alloy System with γ/γ′-Microstructure - Influence of γ′-Volume Fraction, Surface State, and Heating Condition on Alumina Growth

Oxygen permeability of Fe‐Ni‐Cr alloys at 1100 and 1150 °C under carbon‐free and carbon‐containing gases

Protective Alumina Scale Growth at 900 °C for a Ni- and Cr-Free Co-Base Model Alloy with γ/γ’-Microstructure: Synergistic Effects by Combining Shot-Peening and Halogenation

Contact Info

Product

Resources

About