scholarly journals An Investigation of the Miscibility Gap Controlling Phase Formation in Refractory Metal High Entropy Superalloys via the Ti-Nb-Zr Constituent System

Metals ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 1244
Author(s):  
Tamsin E. Whitfield ◽  
George J. Wise ◽  
Ed J. Pickering ◽  
Howard J. Stone ◽  
Nicholas G. Jones
Keyword(s):  
Spinodal Decomposition ◽  
Phase Field ◽  
Refractory Metal ◽  
Miscibility Gap ◽  
High Entropy ◽  
Long Duration ◽  
Three Phase ◽  
Miscibility Gaps ◽  
Bcc Phase

Refractory metal high entropy superalloys (RSAs) have been heralded as potential new high temperature structural materials. They have nanoscale cuboidal bcc+B2 microstructures that are thought to form on quenching through a spinodal decomposition process driven by the Ta-Zr or Nb-Zr miscibility gaps, followed by ordering of one of the bcc phases. However, it is difficult to isolate the role of different elemental interactions within compositionally complex RSAs. Therefore, in this work the microstructures produced by the Nb-Zr miscibility gap within the compositionally simpler Ti-Nb-Zr constituent system were investigated. A systematic series of alloys with compositions of Ti5NbxZr95−x (x = 25–85 at.%) was studied following quenching from solution heat treatment and long duration thermal exposures at 1000, 900 and 700 °C for 1000 h. During exposures at 900 °C and above the alloys resided in a single bcc phase field. At 700 °C, alloys with 40–75 at.% Nb resided within a three phase bcc + bcc + hcp phase field and a large misfit, 4.7–5%, was present between the two bcc phases. Evidence of nanoscale cuboidal microstructures was not observed, even in slow cooled samples. Whilst it was not possible to conclusively determine whether a spinodal decomposition occurs within this ternary system, these insights suggest that Nb-Zr interactions may not play a significant role in the formation of the nanoscale cuboidal RSA microstructures during cooling.

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.

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 Liquid Phase Separation in High-Entropy Alloys—A Review

Entropy ◽  
2018 ◽  
Vol 20 (11) ◽  
pp. 890 ◽  
Author(s):  
Nicholas Derimow ◽  
Reza Abbaschian
Keyword(s):  
Phase Separation ◽  
Liquid Phase ◽  
Liquid Phase Separation ◽  
Miscibility Gap ◽  
Mixing Enthalpy ◽  
High Entropy Alloys ◽  
High Entropy ◽  
Entropy Of Mixing ◽  
Miscibility Gaps ◽  
Alloy Systems

It has been 14 years since the discovery of the high-entropy alloys (HEAs), an idea of alloying which has reinvigorated materials scientists to explore unconventional alloy compositions and multicomponent alloy systems. Many authors have referred to these alloys as multi-principal element alloys (MPEAs) or complex concentrated alloys (CCAs) in order to place less restrictions on what constitutes an HEA. Regardless of classification, the research is rooted in the exploration of structure-properties and processing relations in these multicomponent alloys with the aim to surpass the physical properties of conventional materials. More recent studies show that some of these alloys undergo liquid phase separation, a phenomenon largely dictated by low entropy of mixing and positive mixing enthalpy. Studies posit that positive mixing enthalpy of the binary and ternary components contribute substantially to the formation of liquid miscibility gaps. The objective of this review is to bring forth and summarize the findings of the experiments which detail liquid phase separation (LPS) in HEAs, MPEAs, and CCAs and to draw parallels between HEAs and the conventional alloy systems which undergo liquid-liquid separation. Positive mixing enthalpy if not compensated by the entropy of mixing will lead to liquid phase separation. It appears that Co, Ni, and Ti promote miscibility in HEAs/CCAs/MPEAs while Cr, V, and Nb will raise the miscibility gap temperature and increase LPS. Moreover, addition of appropriate amounts of Ni to CoCrCu eliminates immiscibility, such as in cases of dendritically solidifying CoCrCuNi, CoCrCuFeNi, and CoCrCuMnNi.

scholarly journals Understanding the Links between the Composition-Processing-Properties in New Formulations of HEAs Sintered by SPS

Metals ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 888
Author(s):  
Paula Alvaredo-Olmos ◽  
Jon Molina-Aldareguía ◽  
Alvaro Vaz-Romero ◽  
Estela Prieto ◽  
Jesús González-Julián ◽  
...  
Keyword(s):  
High Hardness ◽  
Processing Parameters ◽  
Heating Rates ◽  
High Entropy ◽  
Plasma Sintering ◽  
Mechanical Study ◽  
Spark Plasma ◽  
Processing Properties ◽  
Bcc Phase ◽  
Hardness Values

This work presents two new compositions of high entropy alloys (HEAs) that were designed with the aim of obtaining a body-centered cubic (BCC) phase with high hardness values and a moderate density. Sintering was performed using Spark Plasma Sintering (SPS) with different heating rates to determine the influence of the processing parameters on the phase formation. The microstructural study revealed that the presence of Ni in the composition promoted phase separation, and the mechanical study confirmed a clear influence on the mechanical properties of both the composition and heating rate. The combination of microscopy with compression and nanoindentation tests at room and high temperature made it possible to advance our understanding of the relationships between the composition, processing, and properties of this emerging group of alloys.

scholarly journals EEG Correlates of Old/New Discrimination Performance Involving Abstract Figures and Non-Words

2021 ◽  
Vol 11 (6) ◽  
pp. 719
Author(s):  
Monika Toth ◽  
Anke Sambeth ◽  
Arjan Blokland
Keyword(s):  
Recognition Memory ◽  
Current Knowledge ◽  
Discrimination Performance ◽  
Correct Identification ◽  
Memory Strength ◽  
Verbal Stimuli ◽  
Brain Responses ◽  
Three Phase ◽  
New Item

The processing of pre-experimentally unfamiliar stimuli such as abstract figures and non-words is poorly understood. Here, we considered the role of memory strength in the discrimination process of such stimuli using a three-phase old/new recognition memory paradigm. Memory strength was manipulated as a function of the levels of processing (deep vs. shallow) and repetition. Behavioral results were matched to brain responses using EEG. We found that correct identification of the new abstract figures and non-words was superior to old item recognition when they were merely studied without repetition, but not when they were semantically processed or drawn. EEG results indicated that successful new item identification was marked by a combination of the absence of familiarity (N400) and recollection (P600) for the studied figures. For both the abstract figures and the non-words, the parietal P600 was found to differentiate between the old and new items (late old/new effects). The present study extends current knowledge on the processing of pre-experimentally unfamiliar figurative and verbal stimuli by showing that their discrimination depends on experimentally induced memory strength and that the underlying brain processes differ. Nevertheless, the P600, similar to pre-experimentally familiar figures and words, likely reflects improved recognition memory of meaningless pictorial and verbal items.

Turnover among medical clowns early in their career

2021 ◽  
Vol 30 (2) ◽  
pp. 106-116
Author(s):  
Abira Reizer ◽  
Meni Koslowsky ◽  
Rivki Antilevich-Steg
Keyword(s):  
Job Satisfaction ◽  
Individual Differences ◽  
Traumatic Experiences ◽  
Mediating Role ◽  
Humor Appreciation ◽  
Three Phase ◽  
Research Findings ◽  
Turnover Behavior ◽  
Actual Turnover

In recent years, several investigations of the medical clowning profession have appeared in the literature. However, few studies have focused on factors associated with turnover among medical clowns early in their careers. The current study examined whether individual differences in humor disposition predicted turnover behavior. Participants were 111 medical clowns in a three-phase longitudinal study. Humor disposition was measured in the first week of their training, clowns' job satisfaction two months later, and turnover six months after that. Results showed that humor appreciation decreased actual turnover through the mediating role of job satisfaction, whereas individual differences in humor creation directly decreased turnover. In addition, previous traumatic experiences moderated the associations between humor appreciation and turnover. Overall, our research findings support the notion that humor disposition can help predict which clowns remain in the hospital.

Phase-Field Modeling of Multiple Emulsions Via Spinodal Decomposition

Langmuir ◽  
2021 ◽  
Vol 37 (17) ◽  
pp. 5275-5281
Author(s):  
Haodong Zhang ◽  
Yanchen Wu ◽  
Fei Wang ◽  
Fuhao Guo ◽  
Britta Nestler
Keyword(s):  
Spinodal Decomposition ◽  
Phase Field ◽  
Phase Field Modeling ◽  
Multiple Emulsions ◽  
Field Modeling

A framework ensemble facilitates high Pt utilization in a low Pt loading fuel cell

2021 ◽  
Vol 11 (8) ◽  
pp. 2957-2963
Author(s):  
Jian Wang ◽  
Guangping Wu ◽  
Wenhui Xuan ◽  
Lishan Peng ◽  
Yong Feng ◽  
...  
Keyword(s):  
Fuel Cell ◽  
Phase Field ◽  
Active Sites ◽  
Catalyst Layer ◽  
Three Phase ◽  
Pt Utilization ◽  
The Cross ◽  
Low Pt Loading ◽  
Effective Transfer

Rationally designing the structure of catalyst layer in MEA to achieve the dispersion of active sites at the cross of three-phase field and the effective transfer network paths for protons through catalysts and catalyst layer.

scholarly journals Refractory Metal (Nb) Intermetallic Composites, High Entropy Alloys, Complex Concentrated Alloys and the Alloy Design Methodology NICE—Mise-en-scène † Patterns of Thought and Progress

Materials ◽  
2021 ◽  
Vol 14 (4) ◽  
pp. 989
Author(s):  
Panos Tsakiropoulos
Keyword(s):  
Solid Solution ◽  
Refractory Metal ◽  
Design Methodology ◽  
Alloy Design ◽  
High Entropy Alloys ◽  
Laves Phases ◽  
High Entropy ◽  
High Temperature Materials ◽  
Mise En Scene ◽  
Intermetallic Composite

The paper reflects on the usefulness of the alloy design methodology NICE (Niobium Intermetallic Composite Elaboration) for the development of new Nb-containing metallic ultra-high-temperature materials (UHTMs), namely refractory metal (Nb) intermetallic composites (RM(Nb)ICs), refractory high entropy alloys (RHEAs) and refractory complex concentrated alloys (RCCAs), in which the same phases can be present, specifically bcc solid solution(s), M5Si3 silicide(s) and Laves phases. The reasons why a new alloy design methodology was sought and the foundations on which NICE was built are discussed. It is shown that the alloying behavior of RM(Nb)ICs, RHEAs and RCCAs can be described by the same parameters. The practicality of parameter maps inspired by NICE for describing/understanding the alloying behavior and properties of alloys and their phases is demonstrated. It is described how NICE helps the alloy developer to understand better the alloys s/he develops and what s/he can do and predict (calculate) with NICE. The paper expands on RM(Nb)ICs, RHEAs and RCCAs with B, Ge or Sn, the addition of which and the presence of A15 compounds is recommended in RHEAs and RCCAs to achieve a balance of properties.

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