Multicomponent Alloys Research Articles

The impact of vacancy formation energies on the nucleation and growth of helium (He) bubbles in low-activation multicomponent vanadium-based alloys

Generally, the complexity of concentrated solid solution alloys (CSAs) can effectively enhance their radiation tolerance. We studied the effect of helium (He) ion irradiation on body centered cubic (BCC) V, VCr, VCrFe and VCrFeMn alloys with the increase of complexity. The comparison shows the void swelling in terms of the size and density of bubbles in V, VCrFe and VCrFeMn decreases with the increase of the complexity after the same He ion irradiation. However, binary VCr alloy has the smallest void swelling although it has only two types of elements, that is less complexity, which is significantly different from VCrFe and VCrFeMn subjected to the same He ion irradiation. Meanwhile, the irradiated VCr lattice exhibits almost no shrinkage. First-principles calculations reveal that the high vacancy formation energy (VFE) of VCr could prevent He-vacancy clusters from absorbing vacancies to grow. The results suggest that the VFE could play a more important role in enhancing the radiation tolerance under He ion irradiation in addition to the compositional complexity.

Rapid acquisition of liquid thermophysical properties from pure metals to quaternary alloys by proposing a machine learning strategy

The establishment of reliable materials genome databases involving the thermophysical properties of liquid metals and alloys promotes the progress of materials research and development, whereas acquiring these properties imposes great challenges on experimental investigation. Here, we proposed a deep learning method and achieved a deep neural network (DNN) interatomic potential for the entire Ti–Ni–Cr–Al system from pure metals to quaternary alloys. This DNN potential exhibited sufficient temperature and compositional transformability which extended beyond the training and provided the prediction of the liquid structure and thermophysical properties for metallic materials with both density functional theory accuracy and classic molecular dynamics efficiency. The predicted results agreed well with the reported experimental data. This work opens a feasible way to address the challenges of rapidly and accurately acquiring thermophysical properties data for liquid pure metals and multicomponent alloys, covering a broad temperature range from superheated to undercooled state.

A precipitation strengthened high entropy alloy with high (Al+Ti) content for laser powder bed fusion: Synergizing in trinsic hot cracking resistance and ultrahigh strength

Additive manufacturing (AM) is a highly promising technique for producing near-net-shape high-value aerospace components with intricate geometries. However, due to the susceptibility to hot cracking, high-volume-fraction Ni3(Al,Ti)-type precipitation-strengthened Ni-base superalloys typically used for these applications are usually difficult or even infeasible to manufacture via AM. Previous metallurgical methods to mitigate hot-cracking in AM usually compromise strength, resulting in a trade-off between hot-cracking resistance and strength. Here, we overcome this trade-off in AM of a multicomponent Ni-rich precipitation-strengthened high-entropy alloy (MNiHEA) Ni46.23Co23Cr10Fe5Al8.5Ti4W2Mo1C0.15B0.1Zr0.02 (at%): synergizing remarkable hot-cracking resistance and ultrahigh strength. Crack-free MNiHEA is successfully fabricated via laser powder bed fusion (LPBF) without preheating, despite its high (Al+Ti) content of ∼7.4 wt%. This remarkable resistance to hot cracking arises from the comparatively low critical solidification range, the small average solidification cracking index, the suppression of the intermetallic phases in solidification, and the moderate hardening rate induced by the nanoprecipitates in aging, which are intrinsically imparted by thermodynamic and mechanical characteristics. The yield strength of the as-built-to-aged MNiHEA reaches ∼1.2 gigapascal, together with acceptable ductility. This ultrahigh strength outperforms its cast-to-aged counterpart by more than one-third and existing commercial superalloys CM247 and IN738LC. Such pronounced enhancement in strength is attained through multiple strengthening mechanisms, including solid-solution hardening, dislocation hardening, precipitation-hardening and grain-boundary strengthening. Our results demonstrate that intrinsic hot-cracking resistance can be utilized as a new metallurgical concept for mitigating hot-cracking without compromising strength in AM of high-temperature materials such as HEAs and superalloys.

Formation and ultrahigh mechanical strength of multicomponent Co-based bulk glassy alloys

A glassy phase with glass transition (GT) was formed in a wide B content range of 12–31 at% for (Co0.75Cr0.125Mo0.125)100-xBx alloys. The appearance of GT at the low metalloid content of 12%B among Co-, Fe- and Ni-based alloys is the first, in contrast to the absence of GT for (Fe0.75Cr0.125Mo0.125)88B12 and (Ni0.75Cr0.125Mo0.125)88B12 alloys. The Co-based 12%B glassy alloy crystallized through unique three stages, i.e., glass (G) → [G + hcp + fcc] → [G + fcc] → [fcc + M23B6]. The appearance of GT is due to the necessity of long-range rearrangement of constituent elements for the simultaneous precipitation of hcp and fcc phases from glassy phase. The glass transition temperature, crystallization temperature, Vickers hardness (Hv) and Young's modulus for the Co-based glassy alloys increase linearly with increasing B content and reach 904 K, 946 K, 1566 and 188 GPa, respectively, at 31%B. The good bending plasticity is retained up to 29%B. The crystallization of the 27–29%B alloy occurs through G → [G + M23B6] → [M23B6 + M2B] and the ultrahigh Hv above 2000 is attained for the metastable [G + M23B6] phase state. The glassy alloy rod with a diameter of 1 mm was prepared for the 27%B alloy and exhibited ultrahigh yield strength of 4700 MPa, plastic strain of 1% and high oxidation resistance up to about 1200 K. The Co-based bulk glassy alloy with simultaneously high strength, ultrahigh hardness and high oxidation resistance, is promising for the future high hardness and heat-resistance materials.

Efficient thermodynamic modelling with uncertainty quantification of the Ag–Cu–Co system from its sub-binary systems

Thermodynamic modelling of the multi-component system from the low-order subsystems in a self-consistent way and a quantitative description of the uncertainty in the modelling are critical to multicomponent alloy design. The Ag–Cu, Ag–Co, and Co–Cu binary systems are the subsystems to build the Ag–Cu–Co ternary system. They are important for the Ag–Cu-based lead-free solders and represent typical eutectic, monotectic, and peritectic systems. In this work, we present a case study of modelling and uncertainty quantification with the recently developed Extensible Self-optimizing Phase Equilibria Infrastructure (ESPEI). Enthalpies of mixing at 0 K were calculated by density functional theory (DFT)-based first-principles method using the special quasi-random structures (SQS) to compensate for the lack of thermochemical solid solution data. Incorporating the collected experimental data, the three sub-binary systems were successfully assessed, and the Ag–Cu–Co ternary system was subsequently modelled. The calculated phase diagrams of the ternary system and the sub-binary system agree with the experiments well. The reliability of the obtained models was further validated by the “residual driving force” approach. The probability distribution of the mono-variant points reside within composition-temperature space is also determined by the Phase Diagram Uncertainty Quantification (PDUQ) tool, providing confidence measures in the design of solder alloys.

Efficient medium entropy alloy thin films as bifunctional electrodes for electrocatalytic water splitting

The development of high-performance, robust, and economical bifunctional electrode materials for efficient H2 and O2 evolution reactions (HER and OER) in water splitting is one of the fundamental aspects of the ever-growing H2 research. In this regard, high and medium entropy alloy systems exhibit great potential in cost-to-performance trade-off as bifunctional electrodes. In particular, the richness in mixing various elements with different hydrogen bonding abilities brings the possibility to tune the catalytic properties that aim for high HER/OER efficiency. In this regard, CoNiCr and CoNiV systems are highly promising model systems with only 3 elements and low hydrogen diffusivity. Also, excellent corrosion resistance in acidic/alkaline environments and high conductivity, and simple crystal structure make these materials very auspicious candidates for HER/OER studies. Here, we have evaluated the electrocatalytic performance of the medium entropy alloy system NiCo(Cr/V) for water splitting. For our investigations, thin films of three compositions namely, NiCoCr, NiCoV, and NiCo(Cr/V) were fabricated using magnetron sputtering. In particular, the NiCo(CrV) (thickness: 1 μm) demonstrates excellent performance with overpotentials of 87 and 320 mV at 10 mA/cm2 and Tafel slopes of 96 and 69 mV/dec towards HER and OER, respectively in 1 M KOH solution. Our findings suggest that the higher HER catalytic activity originates from the synergistic effects of the multicomponent alloy system in single-phase, while the higher OER activity comes from the multicomponent functional oxides of NiCo(CrV) generated on the surface during CV activation. An alkaline electrolysis cell with NiCo(CrV) as bifunctional electrode requires only 1.58 V to maintain 10 mA/cm2, with outstanding electrochemical stability with no compositional reorganization after long-term durability tests.

Design of amorphous-nanocrystalline films of TiAlCrNbZrx multi-component alloy: The effect of Zr on the corrosion resistance and mechanical properties

In this study, amorphous/nanocrystalline TiAlCrNbZrx (x = 0, 0.3, 0.7, 1) multi-component alloy films have been successfully prepared on the surface of 316L stainless steel using direct current magnetron sputtering technique. The composition, microstructure, corrosion and mechanical properties, especially the effect of Zr content and structure on the properties, are discussed in detail. X-ray diffraction (XRD) and transmission electron microscopy (TEM) data revealed the presence of nanocrystalline phases among the amorphous phase. The results showed that the amorphous phase can effectively mitigate corrosion, while the nanocrystals can improve the mechanical properties and adhesion of the films as the Zr content increased. The lattice distortion caused by the incorporation of large atomic Zr contributed to a significant change in the film structure. TiAlCrNbZr films with the most nanocrystals showed better plastic deformation ability, while TiAlCrNbZr0.3 has a suitable amorphous/nanocrystal ratio, good corrosion resistance, and excellent mechanical properties.

Electrodeposited Co–Mn–Sn multicomponent alloy as an efficient electrocatalyst for hydrogen evolution reaction

Despite having exciting material characteristics, the potential of multi-component alloys (MCAs) as electrocatalysts has not been fully realized. In this work, efficient binary and ternary MCA electrocatalysts containing inexpensive metals like Co, Mn and Sn have been prepared via the electrodeposition process. When tested for hydrogen evolution reaction (HER) in an alkaline medium, ternary Co–Mn–Sn alloy displayed enhanced activity with the lowest overpotential of 136 mV, a Tafel slope of 111 mV dec−1 and a very low charge transfer resistance, making it superior to the binary alloys (Co–Mn and Co–Sn), or the single metal catalysts (Co, Mn and Sn). The ternary alloy also displayed high electrochemical and structural stability, making it a viable electrocatalyst for the hydrogen economy.

Quantitative phase-field model for the isothermal solidification of a stoichiometric compound in a ternary liquid

The phase-field (PF) model is one of the most powerful mathematical models to simulate the solidification of multicomponent alloys. A major challenge faced by the PF model is the treatment of stoichiometric compounds (SCs). In the PF model, compositional derivatives of the free energies of phases need to be treated; however, those of SCs are thermodynamically defined only at a certain composition with respect to the stoichiometric components. Therefore, conventional studies used parabolic functions to provide a pseudo-compositional dependence to free energies. In this paper, we propose a methodology to treat SCs without using the parabolic free energy function. Time-evolution equations were rederived assuming that the free energy of the SC is independent of the composition of its stoichiometric component. We performed numerical calculations for a ternary system comprising two phases, olivine (stoichiometric solid phase) in a basaltic melt (liquid phase), whose free energies were gathered from a thermodynamic database, and we confirmed that the model represents the stoichiometry of the solid phase with high accuracy. This model provides a simple and straightforward methodology to handle SCs in the quantitative PF model.

Experimental study platform for electrocatalysis of atomic-level controlled high-entropy alloy surfaces

High-entropy alloys (HEAs) have attracted considerable attention to improve performance of various electrocatalyst materials. A comprehensive understanding of the relationship between surface atomic-level structures and catalytic properties is essential to boost the development of novel catalysts. In this study, we propose an experimental study platform that enables the vacuum synthesis of atomic-level-controlled single-crystal high-entropy alloy surfaces and evaluates their catalytic properties. The platform provides essential information that is crucial for the microstructural fundamentals of electrocatalysis, i.e., the detailed relationship between multi-component alloy surface microstructures and their catalytic properties. Nanometre-thick epitaxially stacking layers of Pt and equi-atomic-ratio Cr-Mn-Fe-Co-Ni, the so-called Cantor alloy, were synthesised on low-index single-crystal Pt substrates (Pt/Cr-Mn-Fe-Co-Ni/Pt(hkl)) as a Pt-based single-crystal alloy surface model for oxygen reduction reaction (ORR) electrocatalysis. The usefulness of the platform was demonstrated by showing the outperforming oxygen reduction reaction properties of high-entropy alloy surfaces when compared to Pt-Co binary surfaces.

Utilising physics-informed neural networks for optimisation of diffusion coefficients in pseudo-binary diffusion couples

ABSTRACT We propose a numerical inverse method based on physics-informed neural networks (PINN) for calculating composition-dependent diffusion coefficients in pseudo-binary (PB) diffusion couples in multicomponent alloys. Traditional methods rely solely on experimental diffusion profiles as design targets, which can lead to unreliable estimates. In contrast, PINN uses a combination of available data and physics-based constraints to obtain optimised design parameters and exact solutions for constrained governing differential equations. The constraints in PINN include governing partial differential equations, initial and boundary conditions, and any other equality/inequality relations obeyed by physical parameters. Our study shows the necessity of experimentally estimated intrinsic diffusion coefficients for the prediction of reliable composition-dependent mobility data. In the absence of such data, different combinations of unknown intrinsic diffusion coefficients can also produce reasonable approximations of diffusion profiles and interdiffusion coefficients while wrongly predicting more fundamental quantities (i.e. intrinsic diffusivities). Our method utilises PINN to simultaneously obtain optimised design parameters (diffusion coefficients) and exact solutions for governing diffusion equations. The implementation of PINN uses experimentally estimated diffusion coefficients obtained by the PB diffusion couple method, in addition to diffusion profiles, as design targets. The method is extended to non-ideal PB diffusion profiles, such as conventional diffusion couples in which all the components develop diffusion profiles, by incorporating additional constraints such as zero composition gradient of certain component(s) and experimentally estimated interdiffusion coefficients at extrema in the composition profiles. PINN is found to be a promising approach for obtaining reliable estimates of diffusion coefficients in multicomponent alloys.

Performance of two complementary machine-learned potentials in modelling chemically complex systems

Chemically complex multicomponent alloys possess exceptional properties derived from an inexhaustible compositional space. The complexity however makes interatomic potential development challenging. We explore two complementary machine-learned potentials—the moment tensor potential (MTP) and the Gaussian moment neural network (GM-NN)—in simultaneously describing configurational and vibrational degrees of freedom in the Ta-V-Cr-W alloy family. Both models are equally accurate with excellent performance evaluated against density-functional-theory. They achieve root-mean-square-errors (RMSEs) in energies of less than a few meV/atom across 0 K ordered and high-temperature disordered configurations included in the training. Even for compositions not in training, relative energy RMSEs at high temperatures are within a few meV/atom. High-temperature molecular dynamics forces have similarly small RMSEs of about 0.15 eV/Å for the disordered quaternary included in, and ternaries not part of training. MTPs achieve faster convergence with training size; GM-NNs are faster in execution. Active learning is partially beneficial and should be complemented with conventional human-based training set generation.

Combinatorial design of partial ordered Al–Cr–Mn–Co medium-entropy alloys for room temperature magnetic refrigeration applications

Multi-component alloys have received increasing interest for functional applications in recent years. Here, we explore the magnetocaloric response for Al–Cr–Mn–Co medium-entropy alloys by integrated theoretical and experimental methods. Under the guidance of thermodynamic and ab initio calculations, a dual-phase system with large magnetic moment, i.e., Al50Cr19Mn19Co12, is synthesized, and the structural and magnetocaloric properties are confirmed via characterization. The obtained results indicate that the selected alloy exhibits a co-continuous mixture of a disordered body-centered cubic and an ordered B2 phase. The ab initio and Monte Carlo calculations indicate that the presence of the ordered B2 phase is responsible for the substantial magnetocaloric effect. The magnetization measurements demonstrated that this alloy undergoes a second-order magnetic transition with the Curie temperature of ∼300 K. The magnetocaloric properties are examined using magnetic entropy change, refrigeration capacity, and adiabatic temperature change. The property-directed strategy explored here is intended to contribute to the study of potential multi-component alloys in magnetocaloric applications.

Temperature and composition dependence of thermophysical properties within a wide temperature range for ternary Si–Ge–Ag alloys

The thermophysical properties of Si–Ge–Ag alloys in a broad temperature range are essential for the design of electronic devices. In this work, relationships between specific heat, thermal expansion, thermal conductivity and temperature, as well as chemical composition of Si–Ge–Ag alloys were clarified. Moreover, various thermophysical properties’ prediction strategies of multicomponent alloys from pure elements were evaluated. The specific heat of Ag–Si, Ag–Ge, Si–Ge, and Si–Ge–Ag alloys was determined by the differential scanning method. The results showed a significant increase with rising temperature at low temperatures followed by a gradual rise at high temperatures. The specific heat reached the maximum value when a small amount of Si/Ge was introduced to Ag. The coefficient of thermal expansion was obtained by a dilatometric method and increased slightly with the increasing temperature, while decreased linearly with the increase in the Si/Ge content. Furthermore, the thermal conductivity was investigated via a laser flash apparatus. It decreased with rising temperature when the Ag content is smaller than 50%, whereas it increased with rising temperature when the Ag content exceeds 50%. The thermal conductivity of Si–Ge alloys decreased with rising temperature and reached the local minimum for Si–Ge alloys with an equiatomic ratio of Si and Ge. More importantly, the experimental results reveal that the thermal expansion that is related to volume can be estimated approximately by pure metals in Si–Ge–Ag alloys. However, this rule cannot be applied to specific heat and thermal conductivity, which is due to the influence of lattice vibration, electronic scattering, and microstructure.

Design of a Multicomponent Alloy for Application in Electronic Components Solder.

Design of a Multicomponent Alloy for Application in Electronic Components Solder.

Phase Selection and Mechanical Properties of CoCrFexNiMn Multicomponent Alloys With Equivalent Electron Concentrations

Phase Selection and Mechanical Properties of CoCrFexNiMn Multicomponent Alloys With Equivalent Electron Concentrations

Elastic Field Evolution in Al–X (X = Sc, Zr, Er) Alloy During Heat Treatment, Insights From 3D-Multiphase Field Study

Abstract Microstructural evolution and resulting stress, strain, and concentration field distribution during Al3X (X = Sc, Zr, Er) precipitation in Al matrix are investigated in this work using the 3D-multiphase field method. Depending on the heat treatment, modulus mismatch, lattice parameter mismatch, and interfacial free energy, precipitate developed to rhombicuboctahedron, and near cuboidal morphologies. The composition distribution and Al–Al3X transformation driving force map identified a difference in precipitation kinetics for each alloy. The precipitation mechanism in the three systems is analyzed in detail with temporal evolution plots of energy components during phase transformation. Al3Er precipitate exhibits the highest growth rate due to Er's high diffusivity and significant lattice parameter mismatch in the Al–Er system. The system has a high chemical and elastic driving force for particle growth, thus attaining quasi-static equilibrium at a relatively lower temperature and time. Therefore, this system observes high magnitude stress, strain, and strain energy field around the Al matrix. The theoretical simulation results obtained from the present study will benefit aluminum multicomponent alloy design for high-strength applications.

Effect of Ti and Cu addition on microstructure, mechanical property and strengthening mechanism of nanocrystalline FeCrV-based MCAs

Nanocrystalline and nano-precipitation are two effective factors to improve comprehensive mechanical properties and irradiation tolerance. Motivated by creating the two important structural features, multi-component alloys (MCAs) FeCrVTix (x = 0.07,0.2,0.3,0.4) and FeCrVCuy (y = 0, 0.05, 0.08, 0.2, 0.3) were designed and fabricated by mechanical alloying and spark plasma sintering. The results showed that FeCrVTix was mainly composed of BCC matrix phase and tens of nanometers of Ti(C,N) precipitation, while BCC solid solution with nanoscale Cu precipitates was primarily present in Cu-containing MCA. Nanocrystalline is the prominent characteristic of the two MCAs, in which the average grain size is about 193 nm and 360 nm for FeCrVTi0.2 and FeCrVCu0.05, respectively. The coexistence of FCC Cu precipitates with about 13 nm and ultrafine BCC Cu of only ∼3 nm was observed within the gains of FeCrVCu0.05. The relationship between Cu nanoparticles and BCC matrix was determined. FeCrVTi0.2 and FeCrVCu0.05 demonstrate excellent mechanical properties with compressive yield strength of more than 1.90 Gpa, ultimate strength of above 3.0 GPa, plasticity of over 32 % and more than 590 HV microhardness at room temperature. The strengthening effects were qualitatively analyzed in detail to reveal the different influences of Ti and Cu addition on microstructure and the strengthening.

Compositional Dependence of the Recrystallization and Grain Growth in Strongly-distorted Pd-containing Multi-Component Equiatomic Alloys

Compositional Dependence of the Recrystallization and Grain Growth in Strongly-distorted Pd-containing Multi-Component Equiatomic Alloys

Structural and mechanical properties of multi-component TiVTaNbZrHf and (TiVTaNbZrHf)N coatings for biomedical applications

Multicomponent TiVTaNbZrHf alloy and (TiVTaNbZrHf)N coatings were deposited on Ti6Al4V alloy by High Target Utilization Sputtering. Sputtering was carried out by reactive sputtering from a TiVTaNbZrHf target with a different nitrogen addition. The microstructures, mechanical properties, and cytotoxicity tests were studied. It was found that the (TiVTaNbZrHf)N coatings showed a dense columnar structure with a face-centered-cubic solid solution phase. The (ZrTaNbVHfTi)N with 4 sccm nitrogen addition exhibited the highest hardness of 34 ± 0.33 GPa and high Indentation modulus of 408.47 ± 24.97 GPa. The mechanical properties greatly depended on the amount of added nitrogen in reactive plasma Physical vapor deposition sputtering. Cytotoxicity tests proved that a very high percentage of live cells were observed after 7 days of incubation time on (TiVTaNbZrHf)N coating.