Solving oxygen embrittlement of refractory high-entropy alloy via grain boundary engineering

Wang, Zhengqi; Wu, Hong‐Hui; Wu, Yuan; Zhu, Xiangyu; Zhang, Yingjie; Zhu, Huihui; Yuan, Xiaoyuan; Chen, Qiang; Wang, Shudao; Liu, Xiong-Jun; Wang, Hui; Jiang, Suihe; Kim, Moon J.; Liu, Xiongjun

doi:10.1016/j.mattod.2022.02.006

Cited by 121 publications

(12 citation statements)

References 43 publications

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“…Specifically, the plasticity increased from <2% to >10% and the fracture strength increased from 1211 MPa to 1780 MPa, respectively, for the base RHEA and the RHEA alloyed with 5000 ppm B. However, the plasticity of the said RHEA decreased with further increase in the B concentration [ 49 ]. Contamination with oxygen can have a strong effect of the near surface properties of phases and alloy [ 3 ].…”

Section: Introductionmentioning

confidence: 99%

On the Stability of Complex Concentrated (CC)/High Entropy (HE) Solid Solutions and the Contamination with Oxygen of Solid Solutions in Refractory Metal Intermetallic Composites (RM(Nb)ICs) and Refractory Complex Concentrated Alloys (RCCAs)

Tsakiropoulos

2022

Materials

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In as-cast (AC) or heat-treated (HT) metallic ultra-high temperature materials often “conventional” and complex-concentrated (CC) or high-entropy (HE) solid solutions (sss) are observed. Refractory metal containing bcc sss also are contaminated with oxygen. This paper studied the stability of CC/HE Nbss and the contamination with oxygen of Nbss in RM(INb)ICs, RM(Nb)ICs/RCCAs and RM(Nb)ICs/RHEAs. “Conventional” and CC/HE Nbss were compared. “Conventional” Nbss can be Ti-rich only in AC alloys. Ti-rich Nbss is not observed in HT alloys. In B containing alloys the Ti-rich Nbss is usually CC/HE. The CC/HE Nbss is stable in HT alloys with simultaneous addition of Mo, W with Hf, Ge+Sn. The implications for alloy design of correlations between the parameter δ of “conventional” and CC/HE Nbss with the B or the Ge+Sn concentration in the Nbss and of relationships of other solutes with the B or Ge+Sn content are discussed. The CC/HE Nbss has low Δχ, VEC and Ω and high ΔSmix, |ΔHmix| and δ parameters, and is formed in alloys that have high entropy of mixing. These parameters are compared with those of single-phase bcc ss HEAs and differences in ΔHmix, δ, Δχ and Ω, and similarities in ΔSmix and VEC are discussed. Relationships between the parameters of alloy and “conventional” Nbss also apply for CC/HE Nbss. The parameters δss and Ωss, and VECss and VECalloy can differentiate between types of alloying additions and their concentrations and are key regarding the formation or not of CC/HE Nbss. After isothermal oxidation at a pest temperature (800 oC/100 h) the contaminated with oxygen Nbss in the diffusion zone is CC/HE Nbss, whereas the Nbss in the bulk can be “conventional” Nbss or CC/HE Nbss. The parameters of “uncontaminated” and contaminated with oxygen sss are linked with linear relationships. There are correlations between the oxygen concentration in contaminated sss in the diffusion zone and the bulk of alloys with the parameters ΔχNbss, δNbss and VECNbss, the values of which increase with increasing oxygen concentration in the ss. The effects of contamination with oxygen of the near surface areas of a HT RM(Nb)IC with Al, Cr, Hf, Si, Sn, Ti and V additions and a high vol.% Nbss on the hardness and Young’s modulus of the Nbss, and contributions to the hardness of the Nbss in B free or B containing alloys are discussed. The hardness and Young’s modulus of the bcc ss increased linearly with its oxygen concentration and the change in hardness and Young’s modulus due to contamination increased linearly with [O]2/3.

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Section: Introductionmentioning

confidence: 99%

On the Stability of Complex Concentrated (CC)/High Entropy (HE) Solid Solutions and the Contamination with Oxygen of Solid Solutions in Refractory Metal Intermetallic Composites (RM(Nb)ICs) and Refractory Complex Concentrated Alloys (RCCAs)

Tsakiropoulos

2022

Materials

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“…In addition, it is noteworthy that the serrated grain boundary (SEG) architectures can effectively solve this intergranular premature cracking issue in an L1 2 -strengthened HEA (46.23Ni-23Co-10Cr-5Fe-8.5Al-4Ti-2W-1Mo-0.15C-0.1B-0.02Zr, at.%) at 1000 °C. This kind of HEA with SEG structures shows a brittle-toductile transition and achieves a superior strength as high as ~260 MPa while maintaining a uniform elongation of ~6.5% [Figure 10] [75] . This finding further demonstrates that SEGs can produce enhanced resistance to intergranular crack nucleation and propagation at higher temperatures.…”

Section: Ite Mechanisms and Strategies For Hea Systemsmentioning

confidence: 99%

“…The discovery of the HEAs opens a new pathway for the design of HE-resistant alloys, especially for single-phase NiCoCr and FeCoCrNiMn. However, unlike conventional alloys, such HEA [75] . Copyright 2021, Elsevier).…”

Section: Outlook and Future Workmentioning

confidence: 99%

“…Tensile properties of straight grain boundary (STG)-MNiHEA and SEG-MNiHEA samples at (A) room temperature and (B) 1000 °C. Microstructures of fracture surfaces in STG-MNiHEA and SEG-MNiHEA tensioned at 1000 °C: (C and G) scanning electron microscopy images; (D and H) EBSD band contrast maps; (E and I) inverse pole figure map; (F and J) Kernal-angle misorientation maps (Reproduced with permission[75] . Copyright 2021, Elsevier).…”

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Environmental embrittlement behavior of high-entropy alloys

2022

Microstructures

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High entropy alloys (HEAs), as a new class of structural materials, have attracted extensive interest from numerous metallurgical scientists and engineers. Benefiting from their unique microstructural features and outstanding mechanical performance, HEAs have shown significant potential for applications in many engineering fields, even under extreme conditions. In particular, when exposed to hydrogen and/or intermediate-temperature environments, these HEAs inevitably suffer from severe environmental embrittlement (EE) issues, e.g., hydrogen embrittlement (HE) and intermediate-temperature embrittlement (ITE), resulting in serious premature intergranular failure. In this work, we critically review the state-of-the-art advances of EE in previously reported HEA systems. Particular focus is given to novel strategies to enhance the resistance to EE in different HEAs. Two critical embrittlement phenomena, namely, HE and ITE, are highlighted separately. Finally, we provide perspectives on future research directions and opportunities for EE-resistant HEAs.

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“…Boron has also been widely added in alloys to improve the cohesive strength of grain boundaries [ 26 ], e.g., to change the fracture mode of Ni 3 Al from intergranular to transgranular and thus prevent early failure [ 27 ], or to lower the migration rate of grain boundaries and inhibit grain growth at high temperatures [ 28 ]. Additionally, the short-range order in an Fe 40 Mn 40 Co 10 Cr 10 alloy caused by the addition of boron atoms or the precipitation of borides was reported to retard the motion and increase the density of dislocations [ 29 ], and the discontinuous intergranular precipitation of borides in high-strength steels avoided the intergranular fracture [ 30 ], both improving the mechanical properties of the alloys [ 31 , 32 ]. As the grain-boundary brittleness is a major issue for BCC RHEAs, a minor amount of boron element (0.1 at.%) was hence added into an HfMoNbTaTiZr RHEA in the present study for potential precipitation of borides at the grain boundaries and improvement of grain boundary cohesion, then to yield a larger work hardenability and better ductility.…”

Section: Introductionmentioning

confidence: 99%

Microstructure and Mechanical Properties of Intergranular Boride Precipitation-Toughened HfMoNbTaTiZr Refractory High-Entropy Alloy

Lee

Chang

2022

Materials

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To develop strong refractory high-entropy alloys for use at elevated temperatures as well as to overcome grain-boundary brittleness, an equimolar HfMoNbTaTiZr alloy was prepared, and a minor amount of boron (0.1 at.%) was added into the alloy. The microstructures of the alloys were characterized, and their macro-to-microscale mechanical properties were measured. The microstructural observations indicated that the matrices of both the alloys were composed of a body-centered cubic solid-solution structure, and the added boron induced the precipitation of hexagonal close-packed borides (most likely the (Hf, Zr)B2) at the grain boundaries. The modulus and hardness of differently oriented grains were about equivalent, suggesting a diminished anisotropy, and many small slips occurred on multiple {110} planes. While the hardness of the matrix was not increased, the intergranular precipitation of the borides markedly raised the hardness of the grain boundaries. Owing to the enhanced grain boundary cohesion, the work hardenability and ductility were effectively improved with the addition of boron.

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Solving oxygen embrittlement of refractory high-entropy alloy via grain boundary engineering

Cited by 121 publications

References 43 publications

On the Stability of Complex Concentrated (CC)/High Entropy (HE) Solid Solutions and the Contamination with Oxygen of Solid Solutions in Refractory Metal Intermetallic Composites (RM(Nb)ICs) and Refractory Complex Concentrated Alloys (RCCAs)

On the Stability of Complex Concentrated (CC)/High Entropy (HE) Solid Solutions and the Contamination with Oxygen of Solid Solutions in Refractory Metal Intermetallic Composites (RM(Nb)ICs) and Refractory Complex Concentrated Alloys (RCCAs)

Environmental embrittlement behavior of high-entropy alloys

Microstructure and Mechanical Properties of Intergranular Boride Precipitation-Toughened HfMoNbTaTiZr Refractory High-Entropy Alloy

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