Low Entropy Alloy Research Articles

HyStor: An experimental database of hydrogen storage properties for various metal alloy classes

In this work, we introduce the HyStor database, consisting of 1282 metal alloys along with their maximum hydrogen storage capacity (H2wt%) at a given absorption temperature. The curated HydPark database consist of 831 entries. We sourced compositions from research articles and various patent documents, resulting in addition of 451 compositions to the HydPark database. The addition is reflected in the data across all existing classes of alloys. Further, low entropy alloys (LEA), medium entropy alloys (MEA) and high entropy alloys (HEA) have been newly included classes. This has broadened the scope of the database to encompass the latest materials of interest for hydrogen storage. HyStor contains representation of 54 elements, with a temperature range of 200–800 K, and H2wt% ranging from 0.1 to 7.19. We conducted thorough checks for duplicate entries, erroneous data, and conflicting compositions within the database to ensure data quality. Furthermore, we conducted multiple tests to identify potential outlier compositions. The data curation and updation reflects into slight improved error metrics of the HYST model, reducing the Mean Absolute Error (MAE) from 0.31 to 0.29 and increasing the R2 score from 0.77 to 0.79.

Thermodynamic and elastic properties of laves phase AB2-based alloys and their hydrides: A density functional theory (DFT) study

A first-principles method based on the density functional theory (DFT) was employed in conjunction with quasi-harmonic Debye model to investigate the structural, elastic, and thermodynamic properties of a series of AB2-based Laves phases alloys and their hydrides. Simulation results revealed that the studied materials possess the Laves phase structure with lattice parameters comparable to experimental findings. For the first time, to the best of our knowledge, mixing entropy determined using Debye model was used to classify alloys into (Low- Medium-High Entropy Alloys) LEA, MEA and HEA categories rather than the commonly used ideal solution model, which is often inaccurate and ignores the impact of temperature. Lattice analyses of the alloy materials indicated that cell volume increases with the addition of elements, while the enthalpy of hydride formation indicates that hydrogen absorption in these alloys is exothermic and that the 3.00 H/F.U configuration is energetically stable. The alloys and their hydrides are metallic with no band gap at the Fermi level. The thermodynamic properties were studied using the quasi-harmonic Debye model and it was found that Bulk modulus decreases with increasing volume, and the hydrides possess lower bulk modulus compared to their metallic counterparts. Moreover, Debye temperature decreases with the gradual addition of elements, indicating weaker chemical bonds in ternary and other alloys. All hydrides have lower Debye temperature than their parent alloy materials. Finally, The alloys are classified into low-, medium-, and high-entropy alloys based on mixing entropy calculated using the Debye model. TiMn2 is classified as a low-entropy alloy, ZrMn2, Ti0.5Zr0.5Mn2, and Ti0.5Zr0.5MnFe as medium-entropy alloys, and Ti0.5Zr0.5(MnCr)2, Ti0.5Zr0.5Mn2/3Fe2/3Cr2/3, and Ti0.5Zr0.5Mn0.5Fe0.5Cr0.5Ni0.5 as high-entropy alloys.

Layered High-Entropy Metallic Glasses for Photothermal CO2 Methanation.

High entropy alloys and metallic glasses, as two typical metastable nanomaterials, have attracted tremendous interest in energy conversion catalysis due to their high reactivity in nonequilibrium states. Herein, a novel nanomaterial, layered high entropy metallic glass (HEMG), in a higher energy state than low-entropy alloys and its crystalline counterpart due to both the disordered elemental and structural arrangements, is synthesized. Specifically, the MnNiZrRuCe HEMG exhibits highly enhanced photothermal catalytic activity and long-term stability. An unprecedented CO2 methanation rate of 489mmol g-1 h-1 at 330°C is achieved, which is, to the authors' knowledge, the highest photothermal CO2 methanation rate in flow reactors. The remarkable activity originates from the abundant free volume and high internal energy state of HEMG, which lead to the extraordinary heterolytic H2 dissociation capacity. The high-entropy effect also ensures the excellent stability of HEMG for up to 450 h. This work not only provides a new perspective on the catalytic mechanism of HEMG, but also sheds light on the great catalytic potential in future carbon-negative industry.

The influence of the chemical composition of the Ti-Hf-Zr-Ni-Cu-Co shape memory alloys on the structure and the martensitic transformations

Twelve senary alloys were manufactured with different concentrations of doping elements (Hf, Zr, Ni, and Cu) that varied from 1 to 17 at%, and the concentration of the Ni equivalent (Ni, Cu, and Co) atoms changed from 49 to 51 at%. It allowed the production of Ti-Hf-Zr-Ni-Cu-Co alloys with various configuration entropies. It was found that, regardless of the entropy value, all alloys crystallised in the B2 phase, in which the lattice parameter increased upon a rise in the doping elements’ concentration (X parameter) and was hardly affected by the Ni group concentration ([Ni] = Ni + Cu + Co). In the alloys with low and medium entropy, the chemical composition of the B2 phase was homogeneous and close to the composition of the alloy. In the alloys with high entropy, the core and edge of dendrite cells in the matrix were characterised by different concentrations of doping elements, while the concentration of the Ni group was constant. Besides the B2 phase, the secondary phase existed in all alloys, whose type [Ti]2[Ni] or [Ni]4[Ti]3 depended on the [Ni] value, as was observed in the binary NiTi alloys. It was found that the Ti-Hf-Zr-Ni-Cu-Co alloys with low and medium entropy underwent the B2 ↔ B19′ martensitic transformation on cooling and heating. An increase in the [Ni] and X values initiated the formation of the strain nanodomains on cooling before the forward transformation. In the high-entropy alloys with X = 10 at%, the strain nanodomains formed on cooling to − 180 °C without the formation of the B19′ phase. In the alloys with X = 17 at%, strain nanodomains, and martensitic transformation were not found on cooling, but the martensitic transformation was initiated by loading at − 100 °C. It was shown that the variation in the Ni group concentration affected the martensitic transformation parameters only in the low-entropy alloys. In the medium- and high-entropy alloys, the concentration of the doping element had a more significant effect on the transformation than the [Ni] value.

The influence of the doping elements on the structure and the martensitic transformations in the Ti50-2xHfxZrxNi50-2xCuxCox shape memory alloys

The structure and the martensitic transformation were studied in the Ti50-2xHfxZrxNi50-2xCuxCox alloys. An increase in X parameter from 1 to 17 changed the configuration entropy from 0.89R (low-entropy alloy) to 1.79R (high-entropy alloy). All alloys crystallized in (Ti,Hf,Zr)50(Ni,Cu,Co)50 phase which occupied more than 90 % of the volume. The chemical composition and the volume fraction of precipitates depended on X parameter. If X is equal to 10, (Ti,Hf,Zr)2(Ni,CuCo) particles were observed; if X = 17, the (Ni,Cu,Co)4(Ti,Hf,Zr)3 precipitates were found. An increase in X parameter decreased the temperatures of the martensitic transformation. If X ≥ 10, the martensitic transformation was not found on cooling to −170 °C.

Interdiffusion behaviors between NiCrFe alloy and low-/medium-/high-entropy alloys

Six groups of fcc solid/solid diffusion couples, including Ni-Cr-Fe/ low-entropy (pure Ni, and NiCo, NiCr, and NiCoCr) alloys, Ni-Cr-Fe/ medium-entropy (CoCrNi) alloys, and Ni-Cr-Fe/ high-entropy (CoCrFeNi) alloys, were prepared, and their composition profiles were experimentally measured. Concentration-dependent interdiffusion and tracer diffusion coefficients in fcc Ni-Co-Cr-Fe system at 1473 K were retrieved with the aid of High-throughput Determination of Interdiffusion Coefficients (HitDIC) software and their reliability was validated. In most cases, D˜CrCrNi>D˜FeFeNi>D˜CoCoNi. The comprehensive comparison between the interdiffusivities/tracer diffusivities in the NiCo, NiCr, NiCoCr low-entropy, CoCrNi medium-entropy, and CoCrFeNi high-entropy alloys and those reported data available in the literatures indicates that the interdiffusivities Co, Cr, and Fe in low-entropy alloys are the largest than those in the other two types of alloys. While the tracer diffusivity in Co-Cr-Fe-Ni HEAs may have no sluggish phenomenon when the absolute temperature is used.

Synthesis and Characterization of aluminium based multicomponent alloys

In general, the traditional alloys are essentially based on the domination of a single principle element, such as the aluminium (Al)-base alloys, magnesium (Mg)-base alloys, iron (Fe)-base alloys, nickel (Ni)-base super alloys, etc. For the traditional lightweight alloys, such as the alloys of aluminum, the concentration of minor alloying elements added to the major element (Al) is typically less than or equal to [ ≤] five atomic percent. In this research paper, the intricacies specific to the development of aluminium-based multicomponent alloys as a viable option to engineer the development of advanced lightweight alloys is presented and adequately discussed. The alloys, Alx(LiMgCuZn)100-x were designed based on the multi-element alloying approach in which the concentration of each alloying element was either greater than or equal to [≥] five atomic percent, except for the element aluminum [70 atomic percent and 75 atomic percent]. The multicomponent alloys, Al70Li10Mg10Cu5Zn5 and Al75Li10Mg5Cu5Zn5, were synthesized using the technique of disintegrated melt deposition [DMD]. The calculated mixing entropy of the Al70Li10Mg10Cu5Zn5 alloy was > 1R [R is gas constant, 8.314 J/K mol], classifying it to be a medium entropy alloy (MEA). For the Al75Li10Mg5Cu5Zn5 alloy, the mixing entropy was less than 1R, classifying it to be a low entropy alloy (LEA). Characterization studies were carefully done on the as-synthesized multicomponent alloys. The microstructure and mechanical properties of the two alloys is presented and briefly discussed. Particular emphasis will be given to both examining and understanding microstructural evolution and the resultant influence of microstructure on mechanical properties of the engineered alloys. A comparison of the properties of the two alloys [Medium Entropy Alloy and Low Entropy Alloy] is highlighted.

Entropy and glass formation

Entropy is a state function of the real physical system, which relates to the chaos of a system. During the long-term exploring glass-forming systems, many empirical rules are put forward, including “confusion principle” and three empirical rules.Over a long period of exploring, many glass-forming alloys are developed based on those principles, while some questions have been raised in recent years based on the experimental results, because some other uncertain factors also have influence on the glass-forming ability (GFA) except a number of constituents, e.g., entropy. Greer claimed that in the “confusion principle” the higher the entropy value, the better the glass-formation ability will be, which does not accord with the recent experimental results.The effects of entropy on the glass-formation ability are summarized from the viewpoints of thermodynamics, kinetics, and complexity of atomic structures. In the aspects of thermodynamics and structure, the increase of entropy has a positive effect on glass formation, while in kinetics, the influence is negative. From the viewpoint of thermodynamics, the increase of entropy leads to the decrease of the entropy difference between solid phase and liquid phase, and therefore, the difference in Gibbs free energy between these two phases decreases. At a certain time during solidification, compared with the low-entropy alloy, the high-entropy alloy in the solid phase has an atomic arrangement close to that in the liquid, and it is more likely to form the amorphous phase.In the aspect of kinetics, the increase of entropy results in the decrease of the viscosity of the system according to the Adam-Gibbs equation. As a result, atoms diffuse easily in the system and the ordered-phase is more likely to form, which means that the glass-formation ability decreases with the increase of entropy. Furthermore, in the aspect of atomic structure, the increase of mismatch entropy relates to the big misfit degree between atoms, i. e., the large atomic size difference. Atoms in the high-entropy alloy tend to distribute disorderly in the system, and therefore the stress between atoms increases. As a result, with the increase of the entropy, the ordered-phase becomes unstable and the GFA will be enhanced.Furthermore, the high-entropy-glass is briefly reviewed and analyzed, which is a new system between high-entropy alloy and amorphous alloy. There have been many high-performance high-entropy-glass systems reported up to now. Researches about this unique system will contribute to developing some new amorphous alloys with excellent performances, and more importantly, to exploring the complex relationship between GFA and multicomponent alloys.