| 1. |
- Sun, Xiaoyu, et al.
(författare)
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Revealing microstructural degradation mechanism induced by interdiffusion between Amdry365 coating and IN792 superalloy
- 2024
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Ingår i: Materials and Design. - : ELSEVIER SCI LTD. - 1873-4197 .- 0264-1275. ; 241
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Tidskriftsartikel (refereegranskat)abstract
- Metallic coatings are widely employed to improve the oxidation resistance of superalloys. However, the interdiffusion between the metallic coatings and the superalloys leads to microstructural degradation in both. Some of the underlying degradation mechanisms are still elusive, e.g., the γ′ (Ni3Al) phase depletion in superalloys, where a large amount of γ′ precipitates are dissolved in the γ matrix even though the incoming Al from coatings indeed increases the Al content. Here, we investigated the interdiffusion behavior between the Amdry365 coating and the IN792 superalloy at 1100 °C, using multiple microscopic techniques and thermodynamics calculations. Our results showed an excellent agreement between experiments and thermodynamics simulations, indicating the dominant role of Al on the initial diffusion-induced phase transitions. We proposed the Al-Cr interference effect to account for the pile-up behavior of Cr and the reduced Al content near the coating/superalloy interface. The local phase equilibrium calculations revealed that the γ′ depletion in the superalloy is primarily attributed to the loss of γ′-forming elements, such as Ta and Ti. Our findings opened up an avenue for studies on the superalloy/coating interdiffusion, contributing to reducing this damaging impact.
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| 2. |
- Balpande, A. R., et al.
(författare)
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Excellent specific strength-ductility synergy in novel complex concentrated alloy after suction casting
- 2024
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Ingår i: Materials and Design. - 1873-4197 .- 0264-1275. ; 242
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Tidskriftsartikel (refereegranskat)abstract
- Lightweight alloys are known to improve the fuel efficiency of the structural components due to high strength-to-weight ratio, however, they lack formability at room temperature. This major limitation of poor formability is most of the time overcome by post-fabrication processing and treatments thereby increasing their cost exponentially. We present a novel Ti50V16Zr16Nb10Al5Mo3 (all in at. %) complex concentrated alloy (Ti-CCA) designed based on the combination of valence electron concentration theory and the high entropy approach. The optimal selection of constituent elements has led to a density of 5.63 gm/cc for Ti-CCA after suction casting (SC). SC Ti-CCA displayed exceptional room temperature strength (UTS ∼ 1.25 GPa) and ductility (ε ∼ 35 %) with a yield strength (YS) of ∼ 1.1 GPa (Specific YS = 191 MPa/gm/cc) without any post-processing treatments. The exceptional YS in Ti-CCA is attributed to hetero grain size microstructure, whereas enormous strength-ductility synergy is due to the concurrent occurrence of slip and deformation band formation in the early stages of deformation followed by prolonged necking event due to delayed void nucleation and growth. The proposed philosophy of Ti-CCA design overcomes the conventional notion of strength-ductility trade-off in such alloy systems by retaining their inherent characteristics.
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| 3. |
- Li, Xiaolong, 1991
(författare)
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Alloy Design for Refractory High Entropy Alloys with Better Balanced Mechanical Properties at Both Room Temperature and Elevated Temperatures
- 2023
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Motivated by the desire to improve the energy efficiency of gas turbines by operating them at higher temperatures (HT), which will contribute to a more energy efficient and carbonless society, the quest for novel ultrahigh-temperature materials can never be overwhelming. High entropy alloys, the recently emerged multi-component alloys with equiatomic or close-to-equiatomic compositions, are considered highly promising as next-generation ultrahigh-temperature materials. In particular, refractory high entropy alloys (RHEAs), one category of HEAs comprising refractory elements with high melting points, are thought to hold the greatest potential to surpass the current state-of-the-art HT materials, Ni-based superalloys, whose upper bound of service temperature has been limited by the melting point of Ni. The alloy design of RHEAs for HT applications is highly challenging though. Specifically, how to balance HT strength, room-temperature (RT) ductility and oxidation resistance is a formidable materials challenge. For instance, the solid solution hardening (SSH) strategy has been proved to work nicely to enable excellent HT strength for singe-phase bcc structured RHEAs, however, at the cost of losing tensile ductility at RT. Another example is that adding Al, Cr or Si into RHEAs could improve their oxidation resistance, which however harms their RT ductility due to the easy formation of undesirable intermetallics. Innovative strategies to design RHEAs that can meet these demanding materials requirements, i.e., simultaneously possessing excellent HT strength, acceptable RT ductility and excellent oxidation resistance, are desperately in need and constitute the main topic of this licentiate thesis. Here in this work, the solid solution softening (SSS) strategy was utilized to soften selected RHEAs to achieve RT ductility without compromising HT strength. Minor additions of substitutional transition metals, Mn, Al and Cu, were confirmed to soften a Hf20Nb31Ta31Ti18 RHEA from RT to 1000oC. Further, with the solo Mn additions into a (HfNbTi)85Mo15 RHEA, a concurrent SSS at RT and SSH at intermediate temperatures was achieved, which led to better-balanced mechanical properties at both RT and elevated temperatures. Combining SSS at low temperatures and SSH at intermediate temperatures holds the potential to induce non-zero tensile ductility for those RHEAs with decent HT strength, hence, to deliver desirable mechanical properties required by ultrahigh-temperature materials, and contributes to accelerate the alloy development and engineering applications of RHEAs.
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| 4. |
- Li, Xiaolong, 1991, et al.
(författare)
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Solid solution softening at room temperature and hardening at elevated temperatures: a case by minor Mn addition in a (HfNbTi) 85 Mo 15 refractory high entropy alloy
- 2023
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Ingår i: Materials Research Express. - 2053-1591. ; 10:11
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Tidskriftsartikel (refereegranskat)abstract
- To address the conflict between room-temperature (RT) ductility and high-temperature (HT) strength in single phase bcc-structured refractory high entropy alloys, here we propose to use minor alloying to achieve solid solution softening at RT and simultaneously, solid solution hardening at HT. Our strategy was manifested by minor Mn additions in a RT brittle (HfNbTi)85Mo15 refractory high entropy alloy, where nominal Mn additions ranging from 2 at. % down to 0.03 at. % were seen to soften the base (HfNbTi)85Mo15 alloy at RT, while to harden the base alloy at the temperature range from 400 to 800 °C. The yield stress in all studied alloys showed a three-stage pattern, characterized by a temperature dependent stage at temperatures below 400 °C, followed by a temperature independent stage at intermediate temperatures ranging from 400 to 800 °C, and finally another temperature dependent stage at temperatures higher than 800 °C. The mechanisms for solid solution softening and solid solution hardening in single phase bcc-structured refractory high entropy alloys were discussed, together with their temperature dependence.
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| 5. |
- Li, Xiaolong, 1991, et al.
(författare)
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Solid solution softening or hardening induced by minor substitutional additions in a Hf 20 Nb 31 Ta 31 Ti 18 refractory high entropy alloy
- 2023
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Ingår i: AIP Advances. - 2158-3226 .- 2158-3226. ; 13:8
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Tidskriftsartikel (refereegranskat)abstract
- The effect of minor additions of substitutional elements such as Al, Cu, Mn, and Fe on the room-temperature (RT) and elevated-temperature hardness of a single bcc phase Hf20Nb31Ta31Ti18 refractory high entropy alloy is studied here. Interestingly, 2.5 at. % nominal addition of Fe hardened the base Hf20Nb31Ta31Ti18 alloy in the temperature range from RT to 800 °C, while the same nominal content of addition of Al, Cu, and Mn softened the base alloy from RT to 1000 °C. Regardless of solid solution hardening or solid solution softening, the hardness variation with temperature essentially showed the same three-stage pattern for all studied alloys here: a temperature-dependent decrease in hardness below 300 °C/400 °C, followed by a temperature-independent hardness plateau between 300/400 and 800 °C, and finally a temperature-dependent decrease in hardness at temperatures higher than 800 °C. The mechanism for solid solution hardening or softening in bcc-structured refractory high entropy alloys is discussed, together with their temperature dependence.
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| 6. |
- Reddy, S. R., et al.
(författare)
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High Strain Rate Superplastic Flow and Fracture Characteristics of a Fine-Grained Eutectic High Entropy Alloy
- 2024
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Ingår i: Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science. - 1073-5623. ; 55, s. 173-182
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Tidskriftsartikel (refereegranskat)abstract
- A fine-grained micro-duplex AlCoCrFeNi2.1 eutectic high entropy alloy exhibited high strain rate superplasticity with an elongation to failure of ~ 960 pct at 1173 K and a strain rate of 10-1 s-1. Optimum superplasticity was associated with a strain rate sensitivity of ~ 0.5, and there were transitions to non-superplastic flow with strain rate sensitivities of < 0.5 at both low and high strain rates. Superplasticity is attributed to grain boundary sliding with the observed retention of an equiaxed grain morphology, with some grain growth. Cavities with dimensions in the range of 1 to 5 μm were observed in specimens pulled to failure. Although analysis revealed that cavity nucleation is likely under the experimental conditions, cavity growth was slow because of control by a plasticity growth rate that was proportional to the cavity size. Graphical Abstract: [Figure not available: see fulltext.]
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