Difference In Atomic Radii Research Articles

Effect of carbon on microstructure and mechanical properties of TiZrNb0.5V0.5 lightweight refractory high entropy alloy

The single-phase body-centered cubic TiZrNb0.5V0.5 lightweight refractory high entropy alloy exhibits good plasticity but poor strength. Therefore, C is added to this alloy to enhance its strength and improve its mechanical properties in this paper. The influence of varying C content on the microstructure, phase composition, and mechanical behavior of TiZrNb0.5V0.5C x RHEAs is investigated in detail. The results indicate that C addition leads to the dissolution of alloying dendrites and induces the formation of the FCC – MC carbides phase. The carbide volume fraction increases in proportion to the carbon content, thereby enhancing the alloy's yield strength and hardness. The yield strength increases by 36%, while the hardness increases by 39%. The physical parameters of the alloy are analyzed, which reveals that the introduction of C increases the alloy's electronegativity and atomic radius difference, thus promoting the formation of carbides.

Solute Segregation and Pinning Effect on Lateral Twin Boundary in Magnesium

Deformation twinning creates a three-dimensional twin domain via the migration of forward, normal and lateral twin boundaries (TBs) with respect to twin shear direction, normal to twin plane and twin lateral direction. Solute segregation and pinning effect on the forward and normal TBs have been experimentally observed and demonstrated via atomistic simulations. Here, we conducted a comprehensive study of solute segregation and the pinning effect on the lateral TBs in Mg. First-principles density functional theory calculations were used to obtain the segregation and formation energies of 19 alloying elements in coherent regions of lateral TBs. Alloying elements with greater difference in atomic radius from Mg generally show more negative segregation energy. Moreover, alloying elements with good solubility are selected to demonstrate the pinning effect on a coherent interface. Ge, Ga, Y, Gd, La and Ca show negative segregation energy and solubility energy, indicating that these elements can form stable segregation and have a strong pinning effect at the lateral boundary. Molecular dynamics simulations revealed that solutes in coherent regions are more effective in pinning lateral TBs than those in misfit regions. The results provide insight into the selection of solute atoms for tailoring twinning behavior.

Enhancing elastocaloric performance: Ti-doped Co–V-Ga bulk polycrystalline alloys with minimal stress hysteresis

Currently, practical applications of shape memory alloy (SMA) solid elastocaloric refrigeration materials are limited by low elastocaloric effect (eCE), high applied stress, and large stress hysteresis (Δσhys). Here, we introduce a composition design strategy using Ti-doped Co–V-Ga SMAs to address these challenges. We combine first-principles calculations and experiments to verify this strategy. Our results show that the lattice distortion caused by the significant difference in atomic radius after Ti doping produces a solid solution strengthening effect inside the alloy, which significantly improves the superelasticity of the alloy, delays the plastic deformation of the austenite phase, and the volume fraction of martensitic transformation increases significantly. The newly developed Co51.7V31.3Ga16Ti1 bulk polycrystalline alloy exhibits a remarkable adiabatic temperature change (ΔTad) of −10 K at room temperature under a low stress of 400 MPa, a minimum Δσhys of 18 MPa, and a high coefficient of performance COPmat of 31.9. Importantly, the 100-cycle loading-unloading test at 350 MPa is done, and it reveals that the ΔTad for the Ti0 alloy was only 3.9 K, while it reached 6.2 K for the Ti1 alloy, marking a noteworthy 59 % performance enhancement. From the simplicity of the fabrication process to the comprehensive performance of the material, it exhibits a promising advantage for practical cooling applications This study presents a feasible design strategy for large-scale production of high-performance bulk polycrystalline alloys with high eCE, low stress, and Δσhys.

In-situ deformation mechanisms of a novel Ti-5Mo-4Cr-1V-1Zr metastable β titanium alloy

To overcome the strength-plasticity trade-off in the structural titanium alloys, a novel metastable β titanium alloy Ti-5Mo-4Cr-1V-1Zr (Ti-5411) with high strength and high plasticity was designed by the d-electrons theory, average electron-to-atom ratio (e/α‾) and atomic radius difference (Δr‾) theory. Combined in-situ scanning electron microscope (SEM) and electron backscatter diffraction (EBSD), the deformation mechanisms of the novel Ti-5411 metastable β titanium alloy were systematically investigated. The results show that the Ti-5411 alloy exhibits excellent yield strength (∼689 MPa), tensile strength (∼930 MPa) and total elongation (∼39%). The in-situ tension indicates that slip activities, crystal rotation, stress induced martensite (SIM) α″ transformation and {332}<113> deformation twin are the major deformation mechanisms of Ti-5411 alloy. Besides, with the increase of strain degree (0–0.5 mm displacement), deformation twins increase, widen and interlace. At 0.35 mm tensile displacement, the orientation of the β grains rotates ∼6.65° to accommodate the increased macrostrain. Additionally, martensite α″ also assists the nucleation of twins. Some {332}<113> twins grow and merge by consuming martensite α″ during deformation, and the residual martensite α″ remains in the merged twins.

Exploring NiCrAlYSiTa multicomponent coatings: Combining high-throughput synthesis and CALPHAD modeling

Multicomponent alloys pose great challenges for efficiently screening desired composition. Here, we combined high-throughput magnetron-sputtering experiments and CALculation of PHAse Diagrams (CALPHAD) methods to screen NiCrAlYSiTa coatings. The compositionally graded coatings showed increased amorphization with higher Si content, indicated by the steepen T0 curves and enlarged amorphous formation region. For the crystallized coatings, the phase structure transformed from Al- and Cr-rich bcc region to Ni-rich fcc, consistent with our calculated phase diagrams. Owing to the high cohesion energy and strong atomic bonding induced by large atomic radius difference and negative mixing enthalpy, the amorphous coatings exhibited superior hardness (25.8 GPa) and elastic modulus (415.8 GPa) compared to the reported multicomponent coatings. By combining high-throughput experimental and theoretical methods, this work pioneers an integrated framework for rapid development of new multicomponent alloy coatings.

Room temperature properties of microstructure and resistivity of alkaline earth – doped on lanthanide manganite

Microstructure of material has a strong relation with resistivity property. Here we report our interesting sample of La0.7(Sr1-xBax)0.3MnO3 (x = 0, 0.3, 0.6, and 0.9) material that has been synthesized by using sol-gel method successfully. All pattern of X-ray diffractometer (XRD) on the successful samples show that all samples are single phase confirmed without significant crystal disorder. The XRD pattern refinement yield that all samples formed R-3c space group with a rhombohedral structure. Although the substitution of Ba2+ to Sr2+ ions have significant difference in atomic radius; it does not change the crystal structure. However, the alkaline earth – doped on lanthanide manganite causes a change in lattice parameters which is followed by shifted of average crystal size, bond length, cell unit volume and bond angle at Mn-O-Mn. The microstructure results by means of scanning electron microscope (SEM) characterization shows that substitution of Ba2+ ions decrease the grain size and yield agglomeration. The relation on the microscopic result resistively confirmed by cryogenic magnetometer characterization in the concentration x = 0 has minimum resistivity of 1.28.10-3 Ωm and the maximum resistivity in the concentration x = 0.9 is 1.85.10-1 Ωm. The Ba2+ doped into Sr2+ in lanthanum manganite may cause a wider resistivity range.

Effect of elemental substitution on transition threshold behaviours of Ge-As(Sb)-Se glasses

In this paper, We prepare two groups of glasses: one is Ge&lt;sub&gt;&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt;As&lt;sub&gt;20&lt;/sub&gt;Se&lt;sub&gt;80–&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt; with x ranging from 5% to 32.5%, the other is Ge&lt;sub&gt;&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt;Sb&lt;sub&gt;20&lt;/sub&gt;Se&lt;sub&gt;80–&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt; with x spanning from 5% to 25%, by using the conventional melt-quench method, and investigate the effect of the elemental substitution of Sb for As on the threshold behaviors in Ge&lt;sub&gt;&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt;As(Sb)&lt;sub&gt;20&lt;/sub&gt;Se&lt;sub&gt;80–&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt; glasses. We are to understand to what extent the topological model and chemical order model can explain the correlation between physical properties and glass compositions, and how the chemical composition can affect the glass transition threshold. Glass transition temperature is measured by the differential scanning calorimeter (Mettler-Toledo, DSC1) with different scanning rates ranging from 5 K/min to 30 K/min under a uniform nitrogen gas flow of 50 mL/min, the glass density is measured by a Mettler H20 balance with a MgO crystal used as a reference. Samples of each glass composition are weighed five times and the average density is recorded. The refractive index of the glass at 1.5 um is measured by a Metricon Model 2010 prism coupler. Raman spectra are measured by a T64000 Jobin-Yvon-Horiba micro-Raman spectrometer equipped with a liquid-nitrogen-cooled CCD detector. The 830 nm laser line is used as an excitation source, and the laser power is kept as small as possible to avoid any photo-induced effects. The resolution of the spectrometer is about 0.5 cm&lt;sup&gt;–1&lt;/sup&gt;. The systematic measurements of these physical parameters show that while the transition thresholds at MCN = 2.4 and 2.67 are verified in the Ge-As-Se glasses with ideal covalent network, these two transitions represent the covalent network structure inside the glass from an under-constrained “floppy” network to an over-constrained “rigid” phase and from the two-dimensional to the three-dimensional “stressed rigid” phase respectively. However, when As is substituted by Sb, the the resulting Ge&lt;sub&gt;&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt;Sb&lt;sub&gt;20&lt;/sub&gt;Se&lt;sub&gt;80–&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt; glass with non-ideal covalent network will change its transition threshold, changing into the chemically stoichiometric composition. We further deconvolve Raman scattering spectra into different structural units and the change of their respective intensity shows the same behavior, which is ascribed to the chemical effect induced by a large difference in atomic radius between As and Sb, and a relatively strong ionic feature of element Sb.

Nickel content-dependent microstructure and mechanical properties of TiZrNbHfNi high entropy alloy thin films

Alloying is known as an effective strategy to improve the mechanical properties of metallic materials. Here we show that the microstructure and mechanical behavior of a TiZrNbHf1.6 high entropy alloy film can be highly tuned by Ni addition. The newly designed TiZrNbHf1.6Nix (x = 0, 0.4, 1.2, 1.8, 2.5, 3.0, 4.6) alloy films are synthesized by co-sputtering Ti, Zr, Nb, Hf and Ni elemental targets. The microstructure and mechanical behavior of the alloy films are investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), and nano/micro-indentations. The microstructural analysis indicates that the TiZrNbHf1.6 film has a single body-centered cubic with columnar-nanograined structure. As Ni content increases to 0.4 or above, the films show a complete amorphous structure. Our theoretical analysis shows that the transition from the crystalline to the amorphous structure can be attributed to the large atomic radius difference and the change of the thermodynamic parameters (e.g., mixing entropy and mixing enthalpy) due to the Ni addition. Compared to the TiZrNbHf1.6 film with a hardness of 4.8 GPa, a hardness increase of 8–35% is achieved in the Ni-doped alloy films (5.2–6.5 GPa) as measured by nanoindentation. The elevated hardness may be attributed to the severe lattice distortion and the amorphous structure induced by the Ni addition. Furthermore, microindentation reveals a diversity of deformation behavior in those films with different Ni content. A homogeneous deformation (slight plastic pileup) occurred in the films with Ni content of 1.2 and 4.6, which is close to the deformation behavior of the crystal TiZrNbHf1.6 film. While the film with a Ni content of 1.8 exhibits a catastrophic cracking deformation. Finally, multiple shear banding dominates the deformation of these films with Ni content of 0.4, 2.5 and 3.0. Our findings demonstrate that ultrastrong and highly deformable amorphous high entropy alloy thin films can be developed by appropriate element addition, making them promising materials for corrosion and wear-resistant coatings.

Mechanical analysis of the incorporation of vanadium atoms into the TiCN system for the conformation of the TiVCN system

Hard coatings are in constant development and evolution, so the generation of new quaternary systems is of great importance. Thus, this research studies the influence of the incorporation of Vanadium atoms into the FCC structure of TiCN, to conform to a quaternary system (TiVCN), which there is very little information so far. The structural analysis evidenced that this quaternary system maintains the same FCC crystal structure as TiCN, and that this structural configuration is in agreement with the models proposed by Hume-Rothery, in which the Titanium and Vanadium atoms randomly occupy the Wyckoff 4a positions and the Carbon and Nitrogen atoms occupy the Wyckoff 4b position. Since Ti and V atoms have a difference in atomic radius, they cause a distortion of the crystal lattice, which will modify the mechanical properties. Experimental results determined a 60 % decrease in roughness, and a 26 % increase in hardness for the TiVCN system compared to TiCN. Thus, this new quaternary system will be a better option to be implemented as protective coatings compared to conventional systems such as TiCN.

Excellent elastocaloric and mechanical performance in Mn-doped Co–V-Ga as-cast polycrystalline alloy with simple preparation

With the rapid development of solid-state refrigeration technology, elastocaloric materials face higher requirements, such as a higher elastocaloric effect (eCE), better mechanical properties, and simpler and faster large-scale preparation. In this work, we propose a composition design strategy for Mn-doped Co–V-Ga shape memory alloys, which can enhance both the eCE and the mechanical properties. We combine first-principles calculations and experiments to demonstrate this strategy. Our results reveal that the lattice distortion caused by the difference in atomic radii produces a solid-solution-strengthening effect within the alloy, impeding dislocation motion and significantly improving the mechanical properties. Through composition optimization, the low-cost Co51.7V31.3Ga14.75Mn2.25 as-cast polycrystalline alloy exhibits a large adiabatic temperature change (ΔTad) of −11.2 K at room temperature, while its maximum compressive strength and strain can reach up to 1859 MPa and 26% at room temperature, respectively. Importantly, the alloy exhibits excellent cycle stability, and its ΔTad does not decay after 100 loading and unloading cycles, indicating that it has the potential for practical application. Further comparison with the annealed sample shows that the secondary defects deteriorate the ΔTad of the alloy. Our research provides an effective strategy for the simple, rapid and large-scale production of as-cast eCE alloys.

An atomic size criterion for stabilizing and strengthening multicomponent nanocrystalline engineering alloy

Previous studies have been focused on stabilizing a nanocrystalline (NC) metallic element by doping a solute element. This study aims to explore the stabilization of a NC engineering alloy, Fe-based Fe-Cr-Ni-X stainless steels (SSs) with 1 at% doped element X (X = Y, La, W, Mo, Nb, Ta Zr, Hf). We find that the larger the atomic radius difference between doped X and matrix Fe elements, the smaller the grain boundary (GB) energy. The smaller GB energy lowers the thermodynamic driving force for grain growth and results in a smaller grain size, which in turn makes the NC engineering alloy harder and stronger. The Y- and La-doped NC SSs are ten times stronger than coarse-grained SSs. The present work provides a simple criterion to select doped alloying element that can effectively stabilize and strengthen multicomponent engineering NC alloys.

Formation of single-phase multicomponent zirconate with colossal atomic radius difference via reactive flash sintering

In this study, multicomponent rare-earth zirconate ceramics (Sm0.2Eu0.2Tb0.2Dy0.2Lu0.2)2Zr2O7 and (La0.2Eu0.2Gd0.2Yb0.2Y0.2)2Zr2O7 were synthesized via conventional sintering and reactive flash sintering, respectively. Single-phase (Sm0.2Eu0.2Tb0.2Dy0.2Lu0.2)2Zr2O7 ceramics, with the defect fluorite structure, were successfully obtained via conventional sintering and reactive flash sintering, while secondary phase segregation and precipitation were observed only in conventionally-sintered (La0.2Eu0.2Gd0.2Yb0.2Y0.2)2Zr2O7 ceramics. This study proposes that the critical electric field of reactive flash sintering introduces defects to soften the lattice, which not only improves the mass transportation, but also relieves the lattice stress induced by the atomic radius difference, resulting in the single-phase defect fluorite structure of (La0.2Eu0.2Gd0.2Yb0.2Y0.2)2Zr2O7. Thus, reactive flash sintering is an efficient route for synthesizing and developing novel multicomponent oxides that cannot be synthesized via conventional sintering due to pronounced lattice stress.

The gradient high entropy alloy coating prepared in-situ by bidirectional diffusion of Mo/Nb and FeCoCrNi

Based on the influence of Mo and Nb content on the eutectic degree of FeCoCrNi high-entropy alloy (HEA), this study prepared in-situ HEA composite coatings with a gradient eutectic degree using the principle of element diffusion in the molten pool under a laser beam, namely Mo-CC and Nb-CC. Both of the two coatings were composed of the face-centered cubic (FCC) phase and Laves phase. Within the coating, there was a gradual decrease in the Laves phase and an increase in the FCC phase from top to bottom. The Laves phase in Mo-CC was rich in Mo (21.36 at.%) element and exhibited an orientation relationship with the FCC phase of [01¯1]Laves//[01¯1]FCC. The phase interface was a non-coherent crystal plane. The Laves phase in Nb-CC is enriched with Nb (36.15 at.%) element and demonstrated an orientation relationship with the FCC phase of [1¯2¯1]Laves//[001]FCC. The phase interface was a semi-coherent crystal plane. Furthermore, the process and mechanism of FCC phase transformation into FCC + Laves phase were elucidated by examining the mixing enthalpy, lattice distortion, and atomic radius difference. In terms of properties, the hardness of Mo-CC and Nb-CC from the top to the bottom section gradually decreased from the outer to inner section. Nb-CC possessed a higher surface average hardness (773.66 HV0.3) and superior tribological properties compared to Mo-CC. The gradient control method for HEA and the phase structure formation mechanism presented in this study provided valuable insights for the research and development of new HEA coatings.

A novel strategy for promoting corrosion and wear resistance of Mg-Li alloys: Gradient eutectic high-entropy alloy coating induced by in-situ bidirectional diffusion

In this work, a novel surface strengthening strategy for Mg-Li alloys was proposed, called cold spraying assisted high-speed laser cladding. CuAl9 aluminum bronze coating was firstly deposited on Mg-Li alloy by cold spraying, and then CoCrFe0.5Ni1.5Mo0.1Nb0.68 eutectic high-entropy alloy (EHEA) coating was prepared on the CuAl9 coating utilizing high-speed laser cladding. A gradient coating consisted of in-situ transition region and EHEA layer formed by bidirectional diffusion. The in-situ transition region was composed of β-Li, Cu2Mg and Cu3Al2 phases. TEM analysis indicated that Cu2Mg and Cu3Al2 phases were well matched with the β-Li matrix phase. The EHEA coating had a nano-lamellar eutectic microstructure with relatively small lamellar-spacing (< 100 nm). Metallurgical bonding interfaces formed between the EHEA coating, transition region and Mg-Li substrate. The evolution mechanism of the coating was revealed from the perspectives of mixing enthalpy, atomic radius difference and laser energy distribution. In 3.5 wt.% NaCl solution, the corrosion potential of the EHEA coating (-24 mVSHE) was 1345 mVSHE higher than that of Mg-Li alloy (-1369 mVSHE), while the corrosion current density of the EHEA coating (3.13 × 10−7 A·cm−2) was almost three orders of magnitude lower than that of Mg-Li alloy (1.25 × 10−4 A·cm−2). The wear rate of Mg-Li alloy (1.11 × 10−3 mm3/N·m) was about 36 times higher than that of the EHEA coating (3.05 × 10−5 mm3/N·m).

Revealing the influence of solute segregation on the stability and strength of Cu Σ11 [110](113) symmetrical tilt grain boundary via first-principles investigation

The stability and strength of the grain boundary (GB) structure are critical for the practical application of nanocrystals. This study systematically calculates the impact of the segregation of 26 transitional alloy elements on Cu Σ11 [110](113) GB using the first-principle theoretical calculation method. The research findings demonstrate that there is a parabolic connection between atomic number and segregation energy of TM elements in the same period. In addition to Fe, Co, and Ni, all other 23 elements have the potential to segregate to Cu GB, with Zr exhibiting the strongest segregation tendency. The difference in atomic radius and electronegativity between solute atoms and copper atoms strongly affects the segregation tendency, the greater the difference, the greater the tendency for segregation. The segregation energy of solute segregation has strong linear correlation with its GB energy, and the stronger the segregation ability, the more stable the GB. Except for Zn, Ag, Cd, and Au, other 19 alloying elements can increase the strength of GB. Electronic analysis indicates that the strengthening and embrittlement of solutes are primarily related to the accumulation and consumption of electrons near GB and the bonding between atoms.

From dolomite waste to katoite-based binder: Synthesis, performance and characterization

Calcium aluminate cement, in which katoite (KT) is the main binder, has garnered significant attention for its resistivity against aggressive environments. Despite its impressive durability, the production of this cement is costly and generates a substantial CO2 emission. Therefore, the objective of this study was to develop an eco-friendly KT-based binder using exchange reaction between sodium aluminate (NaAlO2) solution and dolomite waste powder. The performance of KT-binder was evaluated by measuring compressive strength, drying shrinkage, bulk density, and porosity. The phase composition and microstructural changes were also investigated by XRD, TG/DTG, FT-IR, and SEM/EDS techniques. The resulting hardened materials exhibited 28-day compressive strengths ranging from 5 MPa to 50 MPa and contained primarily katoite Ca3Al2(OH)12, along with pirssonite Na2CO3·CaCO3·2H2O, thermonatrite Na2CO3·H2O, and aluminum hydroxide Al(OH)3 phases. EDS mapping indicated that only a small amount of Mg2+ was present in the katoite phase, suggesting that the alkalinity and atomic radius difference between Ca2+ and Mg2+ were the main factors. Altering the content of concrete waste (CoW) in the cementitious system within the range from 10 to 50 wt% leads to an improvement in compressive strength and a reduction in both pore volume and drying shrinkage of NaAlO2-DW mixture. Conversely, perlite waste (PW) shows an opposite trend despite its high amorphicity. The presence of highly water-soluble thermonatrite, which is a byproduct of the cationic exchange reaction, is responsible for the low water resistivity of the prepared binder. As a result, more research is needed to tackle this problem.

Predicting phases and hardness of high entropy alloys based on machine learning

The mechanical properties of high entropy alloys are highly dependent on phase structure. Therefore, accurate prediction of the phase structure is a guide to composition selection and performance enhancement, and it saves both experimental and financial expenditure. In this study, seven classification models were selected to predict the phase structure of high-entropy alloys and six regression models were selected to predict the hardness, and it was found that the XGB model performed best in both classification and regression predictions, where in the prediction phase structure, the XGB model has an error rate of 4.5% in the 10% prediction set, 11.6% in the 20% prediction set and 6.25% in the 30% prediction set. In predicting the hardness, the RMSE and MAE evaluation indexes of the XGB model are 52.66, 26.49. The δ (atomic radius difference) feature parameter having the strongest contribution to the phase formation in the high-entropy alloys. In addition, valence electron concentration(VEC), y/n BCC (The presence or absence of BCC) and y/n lm (The presence or absence of other phases) were key features affecting the hardness. Predictive analysis of two high-entropy alloys, AlCoCrFeNi and AlCoCrFeNiTi0.5, and a characterization effect map based on the Shapley additive explanations (SHAP) framework were developed to provide decision support for hardness assessment.

CoFeNiTix and CrFeNiTix high entropy alloy thin films microstructure formation

High entropy alloys (HEA) composition-structure relationships are crucial for guiding their design and applications. Here, we use a combined experimental and molecular dynamics (MD) approach to investigate phase formation during physical vapor deposition (PVD) of CoFeNiTix and CrFeNiTix HEA thin films. We vary titanium molar ratio from 0 to 1 to understand the role of a larger element in the alloy mixture. The experiments show that a high titanium content favors amorphous phase formation in the samples produced by magnetron co-sputtering. In contrast, a low titanium content results in the formation of a face-centered cubic (FCC) structure in both HEA families. This effect of titanium content on the stability of the amorphous and FCC phases is reproduced in PVD MD simulations. The threshold titanium molar ratio is identified to be ∼0.53 and ∼0.16 for the CoFeNiTix and CrFeNiTix films in the experiments, and ∼0.53 and ∼0.53 in the MD simulations. In addition, the atomistic modeling allows for energy versus volume calculations with increasing titanium content, which demonstrate the stabilization of the amorphous phase with respect to crystalline structures. To isolate the effect of atomic sizes, additional simulations are performed using an average-atom model, which disregards differences in atomic radii while preserving the average properties of the alloy. In these simulations, the energetic stability of the amorphous phase disappears. The combined experimental and simulation results demonstrate that the formation of the amorphous phase in HEA thin films generated by PVD is directly caused by the atomic size difference.

Evolution of the Phase and Hydrogen Storage Properties of New-Type VTiCrFeMn High-Entropy Alloy Prepared via Mechanical Alloying

High-entropy alloys (HEAs) have ample space for composition design, so finding an ideal hydrogen storage material is a great challenge. This work used the atomic radius difference, valence electron concentration, entropy, enthalpy, and new design parameters to develop a new-type alloy with a BCC structure. The V35Ti25Cr20Fe10Mn10 alloy was selected by semi-empirical formula calculation, subsequently, the alloy was successfully synthesized by mechanical alloying, and hydrogen storage properties were evaluated. The activated sample shows an excellent kinetic performance of hydrogen absorption, but its maximum hydrogen storage capacity is only about 0.34 wt.%. The results of the PCI test show that the hydrogen absorption way may be composed of the H-solid solution in the alloy and the formation of a few hydrides, which determines the hydrogen storage capacity. Significantly, the design method reported in this paper can meet the composition design of most HEAs, which has a broad application prospect.

Microstructure, hardness and wear performance of quaternary CrNbTiZr refractory medium-entropy alloy coating fabricated on a commercial Zr alloy by pulsed laser cladding

To attain enhanced surface hardness and wear resistance, a quaternary CrNbTiZr refractory medium-entropy alloy (RMEA) coating was fabricated on a commercial Zr alloy (Zr-702) by a pulsed laser cladding technique. Phase constitution, microstructural feature, hardness and wear performance of the RMEA coating were systematically investigated. The specific influence of Zr diluted from the substrate on the coating was explored. The results reveal that the cladding zone is mainly featured by a BCC solid-solution phase and net-like Cr2Zr intermetallics. Such microstructural features agree with those predicted based on atomic radius difference, Allen electronegativity and valence electron concentration. Allotropic solid phase transformation occurs in the heat-affected zone, resulting in a mixed microstructure of blocky grains (α-Zr) and martensitic laths. The hardness of the RMEA coating (637 ± 46 HV) is ∼3.3 times that of the Zr-702 substrate, which results from joint contribution from solid-solution, low-angle grain boundary and second-phase strengthening. The RMEA coating exhibits a wear rate ∼56% lower than the substrate, demonstrating significantly improved wear resistance. Both oxidation and adhesive wear are determined to be dominant wear mechanisms of the RMEA coating, accounting for its enhanced wear performance.