scholarly journals Kinetically Limited Phase Formation of Pt-Ir Based Compositionally Complex Thin Films

Materials ◽  
2020 ◽  
Vol 13 (10) ◽  
pp. 2298
Author(s):  
Aparna Saksena ◽  
Dimitri Bogdanovski ◽  
Hrushikesh Sahasrabuddhe ◽  
Denis Music ◽  
Jochen M. Schneider
Keyword(s):  
Thin Films ◽  
Activation Energy ◽  
Surface Diffusion ◽  
Phase Formation ◽  
Single Phase ◽  
Configurational Entropy ◽  
High Entropy Alloys ◽  
X Ray ◽  
High Entropy ◽  
Two Phases

The phase formation of PtIrCuAuX (X = Ag, Pd) compositionally complex thin films is investigated to critically appraise the criteria employed to predict the formation of high entropy alloys. The formation of a single-phase high entropy alloy is predicted if the following requirements are fulfilled: 12 J∙K−1 mol−1 ≤ configurational entropy ≤ 17.5 J∙K−1 mol−1, −10 kJ∙mol−1 ≤ enthalpy of mixing ≤ 5 kJ∙mol−1 and atomic size difference ≤ 5%. Equiatomic PtIrCuAuX (X = Ag, Pd) fulfill all of these requirements. Based on X-ray diffraction and energy-dispersive X-ray spectroscopy data, near-equiatomic Pt22Ir23Cu18Au18Pd19 thin films form a single-phase solid solution while near-equiatomic Pt22Ir23Cu20Au17Ag18 thin films exhibit the formation of two phases. The latter observation is clearly in conflict with the design rules for high entropy alloys. However, the observed phase formation can be rationalized by considering bond strengths and differences in activation energy barriers for surface diffusion. Integrated crystal orbital Hamilton population values per bond imply a decrease in bond strength for all the interactions when Pd is substituted by Ag in PtIrCuAuX which lowers the surface diffusion activation energy barrier by 35% on average for each constituent. This enables the surface diffusion-mediated formation of two phases, one rich in Au and Ag and a second phase enriched in Pt and Cu. Hence, phase formation in these systems appears to be governed by the complex interplay between energetics and kinetic limitations rather than by configurational entropy.

A review on phase prediction in high entropy alloys

2021 ◽  
pp. 095440622110089
Author(s):  
Vinay Kumar Soni ◽  
S Sanyal ◽  
K Raja Rao ◽  
Sudip K Sinha
Keyword(s):  
Solid Solution ◽  
Phase Formation ◽  
Single Phase ◽  
High Entropy Alloy ◽  
High Entropy Alloys ◽  
Modeling Tools ◽  
High Entropy ◽  
Recent Developments ◽  
Phase Prediction ◽  
The Stability

The formation of single phase solid solution in High Entropy Alloys (HEAs) is essential for the properties of the alloys therefore, numerous approach were proposed by many researchers to predict the stability of single phase solid solution in High Entropy Alloy. The present review examines some of the recent developments while using computational intelligence techniques such as parametric approach, CALPHAD, Machine Learning etc. for prediction of various phase formation in multicomponent high entropy alloys. A detail study of this data-driven approaches pertaining to the understanding of structural and phase formation behaviour of a new class of compositionally complex alloys is done in the present investigation. The advantages and drawbacks of the various computational are also discussed. Finally, this review aims at understanding several computational modeling tools complying the thermodynamic criteria for phase formation of novel HEAs which could possibly deliver superior mechanical properties keeping an aim at advanced engineering applications.

Enhancement of Aurivillius Phase Formation Kinetics in SBT Thin Films using Nanoparticle Seeding

2003 ◽  
Vol 784 ◽  
Author(s):  
Yun-Mo Sung ◽  
Woo-Chul Kwak ◽  
Se-Yon Jung ◽  
Seung-Joon Hwang
Keyword(s):  
Thin Films ◽  
Activation Energy ◽  
Phase Transformation ◽  
Phase Formation ◽  
X Ray Diffraction ◽  
Aurivillius Phase ◽  
X Ray ◽  
Si Substrates ◽  
Formation Kinetics ◽  
Kinetics Of

ABSTRACTPt/Ti/SiO2/Si substrates seeded by SBT nanoparticles (∼60–80 nm) were used to enhance the phase formation kinetics of Sr0.7Bi2.4Ta2O9 (SBT) thin films. The volume fractions of Aurivillius phase formation obtained through quantitative x-ray diffraction (Q-XRD) analyses showed highly enhanced kinetics in seeded SBT thin films. The Avrami exponents were determined as ∼1.4 and ∼0.9 for unseeded and seeded SBT films, respectively, which reveals different nucleation modes. By using Arrhenius–type plots the activation energy values for the phase transformation of unseeded and seeded SBT thin films were determined to be ∼264 and ∼168 kJ/mol, respectively. This gives a key reason to the enhanced kinetics in seeded films. Microstructural analyses on unseeded SBT thin films showed formation of randomly oriented needle-like crystals, while those on seeded ones showed formation of domains comprised of directionally grown worm-like crystals.

scholarly journals Laves Phase Formation in High Entropy Alloys

2021 ◽  
Author(s):  
Roman Ryltsev ◽  
Svetlana Estemirova ◽  
Evgenii Sterkhov ◽  
Lubov Cherepanova ◽  
Denis Yagodin ◽  
...  
Keyword(s):  
Phase Formation ◽  
Single Phase ◽  
Laves Phase ◽  
Structural Defects ◽  
Clear Understanding ◽  
High Entropy Alloys ◽  
Laves Phases ◽  
Important Conclusion ◽  
High Entropy ◽  
Chemical Complexity

One of the intriguing recent results in the field of high-entropy alloys is the discovery of single-phase equiatomic multi-component Laves intermetallics. However, there is no clear understanding that a combination of chemical elements will form such high-entropy compounds. Here we contribute to understanding this issue by modifying the composition of duodenary TiZrHfNbVCrMoMnFeCoNiAl (12x) alloy in which we recently reported the fabrication of hexagonal C14 Laves phase. We consider three alloys based on 12x: 7x=12x-VCrMoMnFe, 12x+Sc, 12x+Be and observe that all of them crystalize with the formation of C14 Laves phase as a dominant structure. We report that 12x+Be alloy reveals single-phase C14 structure with very high concentration of structural defects and ultra-fine dendritic microstructure with almost homogenous distribution of the constituted elements over the alloy matrix. The 7x and 12x+Sc alloys contain C14 as a main phase and unknown impurity phases. To characterize the materials, we examine their heat capacity, electrical conductivity and magnetic properties. The measurements reveal that the Laves phases are Curie-Weiss paramagnets, which demonstrate metallic conduction; 7x and 12x alloys also reveal a pronounced Kondo-like anomaly. Analysis of experimental data as well as ab initio calculations suggests that chemical complexity and compositional disorder cause strong s-d band scattering and thus the rather high density of d-states in the conduction band. Analysis of the results suggests that the mechanism of Laves phase formation in multicomponent multi-principal element metallic alloys is may be the same as in polydisperse hardspheres mixtures. Another important conclusion is that the configurational entropy is a negligible factor in the stabilization of multi-element Laves phases.

scholarly journals High-Entropy 2D Carbide MXenes

2021 ◽  
Author(s):  
Srinivasa Kartik Nemani ◽  
BOWEN ZHANG ◽  
Brian C. Wyatt ◽  
Zachary D. Hood ◽  
Sukriti Manna ◽  
...  
Keyword(s):  
Transition Metals ◽  
Photoelectron Spectroscopy ◽  
Single Phase ◽  
Configurational Entropy ◽  
Max Phase ◽  
High Temperature Stability ◽  
Max Phases ◽  
X Ray ◽  
High Entropy ◽  
Synthesis Conditions

<p>Two-dimensional (2D) transition metal carbides and nitrides, known as MXenes, are a fast-growing family of 2D materials. MXenes 2D flakes have <i>n </i>+ 1 (<i>n</i> = 1 – 4) atomic layers of transition metals interleaved by carbon/nitrogen layers, but to-date remain limited in composition to one or two transition metals. In this study, through the use of four transition metals, we report the synthesis of multi-principal element high-entropy M<sub>4</sub>C<sub>3</sub>T<i><sub>x</sub></i> MXenes. Specifically, we introduce two high-entropy MXenes, TiVNbMoC<sub>3</sub>T<i><sub>x</sub></i> and TiVCrMoC<sub>3</sub>T<i><sub>x</sub></i>, as well as their precursor TiVNbMoAlC<sub>3</sub> and TiVCrMoAlC<sub>3 </sub>high-entropy MAX phases. We used a combination of real and reciprocal space characterization (x-ray diffraction, x-ray photoelectron spectroscopy, energy dispersive x-ray spectroscopy, and scanning transmission electron microscopy) to establish the structure, phase purity, and equimolar distribution of the four transition metals in high-entropy MAX and MXene phases. We use first-principles calculations to compute the formation energies and explore synthesizability of these high-entropy MAX phases. We also show that when three transition metals are used instead of four, under similar synthesis conditions to those of the four-element MAX phase, two different MAX phases can be formed (<i>i.e.</i> no pure single-phase forms). This finding indicates the importance of configurational entropy in stabilizing the desired single-phase high-entropy MAX over multiphases of MAX, which is essential for the synthesis of phase-pure high-entropy MXenes. The synthesis of high-entropy MXenes significantly expand the compositional variety of the MXene family to further tune their properties, including electronic, magnetic, electrochemical, catalytic, high temperature stability, and mechanical properties. </p>

scholarly journals High-Entropy 2D Carbide MXenes

2021 ◽  
Author(s):  
Srinivasa Kartik Nemani ◽  
BOWEN ZHANG ◽  
Brian C. Wyatt ◽  
Zachary D. Hood ◽  
Sukriti Manna ◽  
...  
Keyword(s):  
Transition Metals ◽  
Photoelectron Spectroscopy ◽  
Single Phase ◽  
Configurational Entropy ◽  
Max Phase ◽  
High Temperature Stability ◽  
Max Phases ◽  
X Ray ◽  
High Entropy ◽  
Synthesis Conditions

<p>Two-dimensional (2D) transition metal carbides and nitrides, known as MXenes, are a fast-growing family of 2D materials. MXenes 2D flakes have <i>n </i>+ 1 (<i>n</i> = 1 – 4) atomic layers of transition metals interleaved by carbon/nitrogen layers, but to-date remain limited in composition to one or two transition metals. In this study, through the use of four transition metals, we report the synthesis of multi-principal element high-entropy M<sub>4</sub>C<sub>3</sub>T<i><sub>x</sub></i> MXenes. Specifically, we introduce two high-entropy MXenes, TiVNbMoC<sub>3</sub>T<i><sub>x</sub></i> and TiVCrMoC<sub>3</sub>T<i><sub>x</sub></i>, as well as their precursor TiVNbMoAlC<sub>3</sub> and TiVCrMoAlC<sub>3 </sub>high-entropy MAX phases. We used a combination of real and reciprocal space characterization (x-ray diffraction, x-ray photoelectron spectroscopy, energy dispersive x-ray spectroscopy, and scanning transmission electron microscopy) to establish the structure, phase purity, and equimolar distribution of the four transition metals in high-entropy MAX and MXene phases. We use first-principles calculations to compute the formation energies and explore synthesizability of these high-entropy MAX phases. We also show that when three transition metals are used instead of four, under similar synthesis conditions to those of the four-element MAX phase, two different MAX phases can be formed (<i>i.e.</i> no pure single-phase forms). This finding indicates the importance of configurational entropy in stabilizing the desired single-phase high-entropy MAX over multiphases of MAX, which is essential for the synthesis of phase-pure high-entropy MXenes. The synthesis of high-entropy MXenes significantly expand the compositional variety of the MXene family to further tune their properties, including electronic, magnetic, electrochemical, catalytic, high temperature stability, and mechanical properties. </p>

scholarly journals Welding of high-entropy alloys and compositionally complex alloys—an overview

2021 ◽  
Author(s):  
Michael Rhode ◽  
Tim Richter ◽  
Dirk Schroepfer ◽  
Anna Maria Manzoni ◽  
Mike Schneider ◽  
...  
Keyword(s):  
Weld Joint ◽  
Single Phase ◽  
Welding Process ◽  
Industrial Applications ◽  
High Entropy Alloys ◽  
Trade Off ◽  
High Entropy ◽  
Crystalline Defects ◽  
Joint Properties ◽  
Two Phases

AbstractHigh-entropy alloys (HEAs) and compositionally complex alloys (CCAs) represent new classes of materials containing five or more alloying elements (concentration of each element ranging from 5 to 35 at. %). In the present study, HEAs are defined as single-phase solid solutions; CCAs contain at least two phases. The alloy concept of HEAs/CCAs is fundamentally different from most conventional alloys and promises interesting properties for industrial applications (e.g., to overcome the strength-ductility trade-off). To date, little attention has been paid to the weldability of HEAs/CCAs encompassing effects on the welding metallurgy. It remains open whether welding of HEAs/CCAs may lead to the formation of brittle intermetallics and promote elemental segregation at crystalline defects. The effect on the weld joint properties (strength, corrosion resistance) must be investigated. The weld metal and heat-affected zone in conventional alloys are characterized by non-equilibrium microstructural evolutions that most probably occur in HEAs/CCAs. The corresponding weldability has not yet been studied in detail in the literature, and the existing information is not documented in a comprehensive way. Therefore, this study summarizes the most important results on the welding of HEAs/CCAs and their weld joint properties, classified by HEA/CCA type (focused on CoCrFeMnNi and AlxCoCrCuyFeNi system) and welding process.

scholarly journals Entropy Determination of Single-Phase High Entropy Alloys with Different Crystal Structures over a Wide Temperature Range

Entropy ◽  
2018 ◽  
Vol 20 (9) ◽  
pp. 654 ◽  
Author(s):  
Sebastian Haas ◽  
Mike Mosbacher ◽  
Oleg Senkov ◽  
Michael Feuerbacher ◽  
Jens Freudenberger ◽  
...  
Keyword(s):  
Single Phase ◽  
Configurational Entropy ◽  
Solid Solution Phase ◽  
High Entropy Alloys ◽  
Scanning Calorimetry ◽  
High Entropy ◽  
Thermal Entropy ◽  
Fcc Alloys ◽  
Good Agreement

We determined the entropy of high entropy alloys by investigating single-crystalline nickel and five high entropy alloys: two fcc-alloys, two bcc-alloys and one hcp-alloy. Since the configurational entropy of these single-phase alloys differs from alloys using a base element, it is important to quantify the entropy. Using differential scanning calorimetry, cp-measurements are carried out from −170 °C to the materials’ solidus temperatures TS. From these experiments, we determined the thermal entropy and compared it to the configurational entropy for each of the studied alloys. We applied the rule of mixture to predict molar heat capacities of the alloys at room temperature, which were in good agreement with the Dulong-Petit law. The molar heat capacity of the studied alloys was about three times the universal gas constant, hence the thermal entropy was the major contribution to total entropy. The configurational entropy, due to the chemical composition and number of components, contributes less on the absolute scale. Thermal entropy has approximately equal values for all alloys tested by DSC, while the crystal structure shows a small effect in their order. Finally, the contributions of entropy and enthalpy to the Gibbs free energy was calculated and examined and it was found that the stabilization of the solid solution phase in high entropy alloys was mostly caused by increased configurational entropy.

Microstructural Characteristics and Mechanical Behaviors of AlCoCrFeNi High-Entropy Alloys at Ambient and Cryogenic Temperatures

2011 ◽  
Vol 688 ◽  
pp. 419-425 ◽  
Author(s):  
Jun Wei Qiao ◽  
S.G. Ma ◽  
E.W. Huang ◽  
C.P. Chuang ◽  
P.K. Liaw ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Ambient Temperature ◽  
Phase Formation ◽  
Single Phase ◽  
Size Difference ◽  
High Entropy Alloys ◽  
Cryogenic Temperatures ◽  
Mechanical Behaviors ◽  
Microstructural Characteristics ◽  
High Entropy

The phase-formation rule of high-entropy alloys (HEAs) with different microstructures is discussed, based on the atom-size difference in multicomponent alloys. For the single-phase HEA with the composition of AlCoCrFeNi, the yielding strengths and fracture strengths at cryogenic temperatures increase distinguishingly, compared to the corresponding mechanical properties at ambient temperature. However, the plasticity at 298 and 77 K changes very gently, while the fracture modes are intergranular and transgranular, respectively.

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