scholarly journals Deciphering the role of Al2O3 formed during isothermal oxidation in a dual-phase AlCoCrFeNi2.1 Eutectic High-Entropy Alloy

2021 ◽  
Author(s):  
Mainak Saha
Keyword(s):  
Elevated Temperatures ◽  
Isothermal Oxidation ◽  
Tensile Behavior ◽  
Oxidation Behaviour ◽  
High Entropy Alloy ◽  
Dual Phase ◽  
High Entropy Alloys ◽  
High Entropy ◽  
Al2o3 Phase

In recent times, there has been a significant volume of work on Eutectic High Entropy Alloys (EHEAs) owing to their remarkable castability combined with excellent mechanical properties, which aids in clearing obstacles for their technological applications. One of the most common EHEAs, which has been of enormous interest at present, primarily owing to its solidification and tensile behavior, is AlCoCrFeNi2.1. However, to aim for high-temperature applications, oxidation behaviour of material is one of the major aspects that needs to be extensively investigated. To this end, the present work aims to study the phases evolved during oxidation at elevated temperatures as high as 950 and 1000°C in AlCoCrFeNi2.1 using XRD and also to determine the rate law followed for isothermal oxidation of this alloy at 950 and 1000°C, in order to understand the role of Al2O3 phase formed during isothermal oxidation at 950 and 1000°C.

Role of BCC phase on tensile behavior of dual-phase Al0.5CoCrFeMnNi high-entropy alloy at cryogenic temperature

2019 ◽  
Vol 746 ◽  
pp. 443-447 ◽  
Author(s):  
Jeong Min Park ◽  
Jongun Moon ◽  
Jae Wung Bae ◽  
Dong Hyuk Kim ◽  
Yong Hee Jo ◽  
...  
Keyword(s):  
Cryogenic Temperature ◽  
Tensile Behavior ◽  
High Entropy Alloy ◽  
Dual Phase ◽  
High Entropy ◽  
Bcc Phase

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

Metals ◽  
2021 ◽  
Vol 12 (1) ◽  
pp. 41
Author(s):  
Shuaidan Lu ◽  
Xiaoxiao Li ◽  
Xiaoyu Liang ◽  
Wei Yang ◽  
Jian Chen
Keyword(s):  
Oxidation Resistance ◽  
High Temperatures ◽  
Elevated Temperatures ◽  
Early Stage ◽  
Mass Gain ◽  
High Entropy Alloy ◽  
High Entropy Alloys ◽  
X Ray Diffraction ◽  
X Ray ◽  
High Entropy

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.

Oxidation behaviour of a novel refractory high entropy alloy at elevated temperatures

2020 ◽  
Vol 119 ◽  
pp. 106711 ◽  
Author(s):  
Kai-Chi Lo ◽  
Hideyuki Murakami ◽  
Jien-Wei Yeh ◽  
An-Chou Yeh
Keyword(s):  
Elevated Temperatures ◽  
Oxidation Behaviour ◽  
High Entropy Alloy ◽  
High Entropy

scholarly journals Brute Force Composition Scanning with a CALPHAD Database to Find Low Temperature Body Centered Cubic High Entropy Alloys

Entropy ◽  
2018 ◽  
Vol 20 (12) ◽  
pp. 911 ◽  
Author(s):  
T. Klaver ◽  
D. Simonovic ◽  
M. Sluiter
Keyword(s):  
Low Temperature ◽  
Grid Point ◽  
Ternary Alloys ◽  
High Entropy Alloy ◽  
High Entropy Alloys ◽  
Body Centered Cubic ◽  
High Entropy ◽  
Increasing Temperature ◽  
Bcc Phase

We used the Thermo-Calc High Entropy Alloy CALPHAD database to determine the stable phases of AlCrMnNbTiV, AlCrMoNbTiV, AlCrFeTiV and AlCrMnMoTi alloys from 800 to 2800 K. The concentrations of elements were varied from 1–49 atom%. A five- or six-dimensional grid is constructed, with stable phases calculated at each grid point. Thermo-Calc was used as a massive parallel tool and three million compositions were calculated, resulting in tens of thousands of compositions for which the alloys formed a single disordered body centered cubic (bcc) phase at 800 K. By filtering out alloy compositions for which a disordered single phase persists down to 800 K, composition ‘islands’ of high entropy alloys are determined in composition space. The sizes and shapes of such islands provide information about which element combinations have good high entropy alloy forming qualities as well as about the role of individual elements within an alloy. In most cases disordered single phases are formed most readily at low temperature when several elements are almost entirely excluded, resulting in essentially ternary alloys. We determined which compositions lie near the centers of the high entropy alloy islands and therefore remain high entropy islands under small composition changes. These island center compositions are predicted to be high entropy alloys with the greatest certainty and make good candidates for experimental verification. The search for high entropy islands can be conducted subject to constraints, e.g., requiring a minimum amount of Al and/or Cr to promote oxidation resistance. Imposing such constraints rapidly diminishes the number of high entropy alloy compositions, in some cases to zero. We find that AlCrMnNbTiV and AlCrMoNbTiV are relatively good high entropy alloy formers, AlCrFeTiV is a poor high entropy alloy former, while AlCrMnMoTi is a poor high entropy alloy former at 800 K but quickly becomes a better high entropy alloy former with increasing temperature.

scholarly journals Tensile Behavior and Evolution of the Phases in the Al10Co25Cr8Fe15Ni36Ti6 Compositionally Complex/High Entropy Alloy

Entropy ◽  
2018 ◽  
Vol 20 (9) ◽  
pp. 646 ◽  
Author(s):  
Anna Manzoni ◽  
Sebastian Haas ◽  
Haneen Daoud ◽  
Uwe Glatzel ◽  
Christiane Förster ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Gas Turbines ◽  
Heat Treatments ◽  
Tensile Behavior ◽  
High Entropy Alloy ◽  
High Entropy Alloys ◽  
Dendritic Solidification ◽  
Cast State ◽  
High Entropy ◽  
Two Phases

Compositionally complex alloys, or high entropy alloys, are good candidates for applications at higher temperatures in gas turbines. After their introduction, the equiatomic Al17Co17Cr17Cu17Fe17Ni17 (at.%) served as a starting material and a long optimization road finally led to the recently optimized Al10Co25Cr8Fe15Ni36Ti6 (at.%) alloy, which shows promising mechanical properties. Investigations of the as-cast state and after different heat treatments focus on the evolution of the microstructure and provide an overview of some mechanical properties. The dendritic solidification provides two phases in the dendritic cores and two different ones in the interdendritic regions. Three of the four phases remain after heat treatments. Homogenization and subsequent annealing produce a γ-γ’ based microstructure, similar to Ni-based superalloys. The γ phase is Co-Cr-Fe rich and the γ’ phase is Al-Ni-Ti rich. The understanding of the mechanical behavior of the investigated alloy is supported and enhanced by the study of the different phases and their nanohardness measurements. The observations are compared with mechanical and microstructural data from commercial Ni-based superalloys, Co-based alloys, and Co-Ni-based alloys at the desired application temperature of ~800 °C.

scholarly journals High-throughput design of high-performance lightweight high-entropy alloys

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Rui Feng ◽  
Chuan Zhang ◽  
Michael C. Gao ◽  
Zongrui Pei ◽  
Fan Zhang ◽  
...  
Keyword(s):  
High Temperature ◽  
High Throughput ◽  
High Throughput Screening ◽  
Elevated Temperatures ◽  
Alloy System ◽  
Computational Method ◽  
High Entropy Alloy ◽  
High Entropy Alloys ◽  
Theoretical Understanding ◽  
High Entropy

AbstractDeveloping affordable and light high-temperature materials alternative to Ni-base superalloys has significantly increased the efforts in designing advanced ferritic superalloys. However, currently developed ferritic superalloys still exhibit low high-temperature strengths, which limits their usage. Here we use a CALPHAD-based high-throughput computational method to design light, strong, and low-cost high-entropy alloys for elevated-temperature applications. Through the high-throughput screening, precipitation-strengthened lightweight high-entropy alloys are discovered from thousands of initial compositions, which exhibit enhanced strengths compared to other counterparts at room and elevated temperatures. The experimental and theoretical understanding of both successful and failed cases in their strengthening mechanisms and order-disorder transitions further improves the accuracy of the thermodynamic database of the discovered alloy system. This study shows that integrating high-throughput screening, multiscale modeling, and experimental validation proves to be efficient and useful in accelerating the discovery of advanced precipitation-strengthened structural materials tuned by the high-entropy alloy concept.

scholarly journals Dynamic precipitation at elevated temperatures in a dual-phase AlCoCrFeNi high-entropy alloy: an in situ study

2018 ◽  
Vol 98 (9) ◽  
pp. 400-409 ◽  
Author(s):  
Ehsan Ghassemali ◽  
Reshma Sonkusare ◽  
Krishanu Biswas ◽  
Nilesh P. Gurao
Keyword(s):  
Elevated Temperatures ◽  
High Entropy Alloy ◽  
Dual Phase ◽  
Dynamic Precipitation ◽  
High Entropy ◽  
In Situ Study

scholarly journals The Effect of Ge Addition on the Oxidation of Nb-24Ti-18Si Silicide Based Alloys

Materials ◽  
2019 ◽  
Vol 12 (19) ◽  
pp. 3120 ◽  
Author(s):  
Zifu Li ◽  
Panos Tsakiropoulos
Keyword(s):  
Oxidation Resistance ◽  
Refractory Metal ◽  
Isothermal Oxidation ◽  
Oxidation Behaviour ◽  
The Other ◽  
High Entropy Alloys ◽  
High Entropy ◽  
Parabolic Kinetics ◽  
Cast Alloys ◽  
Oxidation In Air

In this paper, we report research about the isothermal oxidation in air at 800 and 1200 °C for 100 h of the as-cast alloys (at.%) Nb-18Si-5Ge (ZF1), Nb-18Si-10Ge (ZF2), Nb-24Ti-18Si-5Ge (ZF3), Nb-24Ti-18Si-5Cr (ZF4), Nb-24Ti-18Si-5Al (ZF5), Nb-24Ti-18Si-5Al-5Cr-5Ge (ZF6), and Nb-24Ti-18Si-5Al-5Cr-5Ge-5Hf (ZF9), the microstructures of which were reported in previous publications. Only the alloys ZF1, ZF2, and ZF3 suffered from pest oxidation at 800 °C. The Ge addition substantially improved the oxidation resistance of the other alloys both at 800 °C and 1200 °C, which followed parabolic kinetics at 800 °C and in the early stages at 1200 °C and linear kinetics at longer times, where there was spallation of the scales. The Nb2O5 and TiNb2O7 oxides were formed in the scales of the alloys ZF4, ZF5, ZF6, and ZF9 at 800 °C and 1200 °C, the GeO2 was observed in all scales and the SiO2 in the scales of the alloys ZF4 and ZF5, the CrNbO4 in the scales of the alloys ZF4, ZF6, and ZF9 and the AlNbO4 in the scales of the alloys ZF5, ZF6, and ZF9. Diffusion zones were formed below the scale/substrate interface only in the alloys ZF4 and ZF5 where the Nbss and Nb5Si3 were contaminated by oxygen. However, these phases were not contaminated by oxygen in the bulk of the alloys ZF4, ZF5, ZF6, and ZF9. The alloys ZF9 and ZF6 exhibited the best oxidation behaviour at 800 °C and 1200 °C, respectively. The alloys were compared with Nb-silicide based alloys of similar compositions without Ge and Hf additions and the alloy ZF9 with refractory metal High Entropy Alloys. Compared with the former alloys, the addition of Ge reduced the vol % of the Nbss. Compared with the latter alloys, the superior oxidation behaviour of the alloy ZF9 was attributed to its higher and lower values respectively of the parameters δ and VEC.

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