Oxidation mechanism of refractory high entropy alloys Ta-Mo-Cr-Ti-Al with varying Ta content

Schellert, Steven; Gorr, Bronislava; Laube, Stephan; Kauffmann, Alexander; Heilmaier, Martin; Christ, Hans‐Jürgen

doi:10.1016/j.corsci.2021.109861

Cited by 44 publications

(19 citation statements)

References 40 publications

(64 reference statements)

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“…An experimental investigation into the oxidation resistance of several HEAs at T = 1373 K yielded the conclusion that the presence of Ta reduced the evaporation of MoO 3 in the alloy TaMoCrAl. 11 A similar result for Ta was reported by Schellert et al, 13 with the addition that Ta content of <10% failed to enhance the oxidation performance of TaMoCrAl. It could be that, when present in high enough amounts, the Ta−O charge interaction prohibits the formation of the MoO 3 covalent bonds, 45 thus weakening the oxygenassisted outward movement of Mo, which leads to the eventual evaporation of MoO 3 .…”

Section: ■ Introductionsupporting

confidence: 82%

“…Müller et al studied TaMoCrTiAl, NbMoCrTiAl, NbMoCrAl, and TaMoCrAl and reported the formation of a protective oxide layer containing Al 2 O 3 , Cr 2 O 3 , and CrTaO 4 in the quinary Ta-containing alloy with the general conclusion that increased Ta content reduced MoO 3 evaporation and increased oxidation resistance. Schellert et al performed an analysis similar to that in ref on the same HEA where they found that a Ta content of <10% resulted in poor oxidation performance. In the computational domain, Taylor et al reported metal oxide formation energies calculated with density functional theory (DFT) that suggested Zr, Ta, Nb, Ti, and Al are among the top candidates for oxide resistance, with oxide formation energies exceeding 8 eV/atom.…”

Section: Introductionmentioning

confidence: 99%

“…Here, the focus is restricted to refractory HEAs (RHEAs), which are promising candidate materials for high-temperature structural applications, such as their use in jet propulsion systems as the structural material for the engine turbine blades and discs. Senkov and associates have carried out extensive experimental investigations on the mechanical properties, phase stability, and high-temperature oxidation behavior of refractory alloy systems to examine the viability of deploying them in aircraft propulsion systems. − Several RHEAs have been thoroughly discussed and recently reviewed by Couzinie et al Experimental studies on the high-temperature oxidation resistance of RHEAs and the role different metals play are ongoing. − Butler and Weaver explored Al x (NiCoCrFe) 1– x in which the Al content was varied. They reported a combination of Al 2 O 3 and AlN beneath an external Cr 2 O 3 scale across all samples with the general conclusion that increasing Al content improved the oxidation resistance by bolstering the position and continuity of the Al 2 O 3 scale.…”

Section: Introductionmentioning

confidence: 99%

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Adsorption of Oxygen to High Entropy Alloy Surfaces for up to 2 ML Coverage Using Density Functional Theory and Monte Carlo Calculations

Doležal

Samin

2022

Langmuir

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High-entropy alloys (HEAs) manufactured with refractory elements are candidates for high-temperature structural applications. To enhance our understanding of oxidation in these complex systems, the early stages of oxidation on the surface of Al 10 Nb 15 Ta 5 Ti 30 Zr 40 were studied using density functional theory and thermodynamic modeling. Surface slabs were generated from bulk configurations sampled from equilibrium using a multicell Monte Carlo method for phase prediction. The bulk structure was found to be a single BCC phase in good agreement with experimental observations. The oxygen adsorbed with a strong preference for sites with Ti and Zr and avoided sites with Nb−Al and Nb−Ta. The surface was shown to be highly reactive to oxygen, yielding a dominating oxygen coverage of two monolayers over the temperature range of 100 to 2600 K and an oxygen pressure range of 10 −30 to 10 5 bar. Recovering a clean surface slab was not achieved until pressures approached vacuum conditions and temperature exceeded 1900 K, demonstrating the difficulty of oxygen removal from the surface. Grand canonical Monte Carlo simulations showed that high Nb content in the top surface layer reduced the surface reactivity to incoming oxygen. Inward oxygen diffusion at low coverage was preferred in regions rich with Zr but slowed with the addition of Ti and Al. Diffusion rates drastically decreased at 1 ML, especially in the region rich with Ti and Zr, where strong metal−oxygen bonds were reported. Our results indicated that a high content of Ti and Zr increased the reactivity of the HEA surface to oxygen. The presence of Nb also enhanced the resistance to oxygen adsorption, especially when partnered with Al and Ta. Inward oxygen diffusion was likely to occur at low coverage in regions rich with Zr but could be protected against with the addition of Al and Ti. The limitations of the present work are discussed. This study may provide insights that assist with devising short-and long-term mitigation strategies against material degradation related to high-temperature oxidation.

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Section: ■ Introductionsupporting

confidence: 82%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Adsorption of Oxygen to High Entropy Alloy Surfaces for up to 2 ML Coverage Using Density Functional Theory and Monte Carlo Calculations

Doležal

Samin

2022

Langmuir

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“…CrNbO 4 and CrTaO 4 have been found to form dense, protective layers in refractory high-entropy alloy oxides scales. [28][29][30][31] Investigation of AlTaO 4 in this regard may be promising, whereas no rutile-type compound is known in the Al-Nb-O system.…”

Section: Discussionmentioning

confidence: 99%

High‐Temperature Ternary Oxide Phases in Tantalum/Niobium–Alumina Composite Materials

et al. 2022

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Refractory metal (molybdenum, niobium, and tantalum) matrix composite materials in combination with refractory ceramics (alumina, zirconia, and mullite) are of particular interest for high-temperature applications, e.g., in refractory linings in the casting industry. [1] However, besides the high-temperature applicability, other aspects need consideration as well for the choice of material combination, such as: 1) the reaction between the metal and ceramic particles, 2) the chemical interaction with the environment, and 3) the thermal mismatch between the ceramic and the metallic phases. [2] The majority of the past publications dealt with so-called fine-grained refractory composites. [3][4][5][6][7] However, their disadvantages are high shrinkage on sintering, thus resulting in limited thermal shock ability. The refractory metals Nb and Ta are promising candidates for application with Al 2 O 3 due to their similar thermal expansion behavior. Wang et al. [8] and White et al. [9] showed for temperatures between 1000 and 2000 K a similarly linear increase of the linear thermal expansion coefficient for the three elements, with 8.8 to 11.2 Â 10 À6 K À1 for α-Al 2 O 3 , [8] 8.3 to 10.4 Â 10 À6 K À1 for Nb, and 7.1 to 8.4 Â 10 À6 K À1 for Ta. [9] Recently, Zienert et al. [10] demonstrated the fabrication of coarse-grained refractory composites based on alumina with niobium or tantalum, while Weidner et al. [11] reported first mechanical properties at high temperatures (1300-1500 °C) under compressive load. In these coarse-grained refractory composites, alumina with different particle classifications from 0-20 μm up to 2-5 mm (with different volume

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“…The investigation of WMoTaNb alloys has been focused on their structure and mechanical properties; however, the oxidation behaviors of these alloys at elevated temperatures determine the application and have rarely been studied [9,10]. It is known that RHEAs, especially WMoTaNb alloys, suffer from poor oxidation resistance at elevated temperatures, which may be attributable to the evaporation of volatile oxides (MoO 3 , WO 3 and V 2 O 5 ) and the scale fractures caused by the high Pilling-Bedworth ratio (PBR) of Ta 2 O 5 (2.47) and Nb 2 O 5 (2.74) [11][12][13][14]. Researchers have undertaken a large number of studies on improving the oxidation resistance of HEAs by alloying beneficial elements, such as Al, Ti, Cr and Si [15][16][17][18].…”

Section: Introductionmentioning

confidence: 99%

Effect of V and Ti on the Oxidation Resistance of WMoTaNb Refractory High-Entropy Alloy at High Temperatures

Liang

et al. 2021

Metals

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Alloying with V and Ti elements effectively improves the strength of WMoTaNb refractory high entropy alloys (RHEAs) at elevated temperatures. However, their effects on the oxidation resistance of WMoTaNb RHEAs are unknown, which is vitally important to their application at high temperatures. In this work, the effect of V and Ti on the oxidation behavior of WMoTaNb RHEA at 1000 °C was investigated using a thermogravimetric system, X-ray diffraction and scanning electron microscopy. The oxidation of all alloys was found to obey a power law passivating oxidation at the early stage. The addition of V aggravates the volatility of V2O5, MoO3 and WO3, and leads to disastrous internal oxidation. The addition of Ti reduces the mass gain in forming the full coverage of passivating scale and prolongs the passivation duration of alloys.

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Oxidation mechanism of refractory high entropy alloys Ta-Mo-Cr-Ti-Al with varying Ta content

Cited by 44 publications

References 40 publications

Adsorption of Oxygen to High Entropy Alloy Surfaces for up to 2 ML Coverage Using Density Functional Theory and Monte Carlo Calculations

Adsorption of Oxygen to High Entropy Alloy Surfaces for up to 2 ML Coverage Using Density Functional Theory and Monte Carlo Calculations

High‐Temperature Ternary Oxide Phases in Tantalum/Niobium–Alumina Composite Materials

Effect of V and Ti on the Oxidation Resistance of WMoTaNb Refractory High-Entropy Alloy at High Temperatures

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