Cubic Crystal Research Articles

Designing Quaternary and Quinary Refractory-Based High-Entropy Alloys: Statistical Analysis of Their Lattice Distortion, Mechanical, and Thermal Properties

The rapid evolution in materials science has resulted in a significant interest in high-entropy alloys (HEAs) for their unique properties. This study focuses on understanding both quaternary and quinary body-centered cubic (BCC) of 12 refractory-based HEAs, and on analysis of their electronic structures, lattice distortions, mechanical, and thermal properties. A comprehensive assessment is undertaken by means of density functional theory (DFT)-based first principles calculations. It is well known that multiple constituents lead to notable lattice distortions, especially in quinary HEAs. This distortion, in turn, has significant implications on the electronic structure that ultimately affect mechanical and thermal behaviors of these alloys such as ductility, lattice thermal conductivity, and toughness. Our in-depth analysis of their electronic structures revealed the role of valence electron concentration and its correlation with bond order and mechanical properties. Local lattice distortion (LD) was investigated for these 12 HEA models. M1 (WTiVZrHf), M7 (TiZrHfW), and M12 (TiZrHfVNb) have the highest LD whereas the models M3 (MoTaTiV), M5 (WTaCrV), M6 (MoNbTaW), and M9 (NbTaTiV) have the less LD. Furthermore, we investigated the thermal properties focusing on Debye temperature (ΘD), thermal conductivity (κ), Grüneisen parameter (γα), and dominant phonon wavelength (λdom). The NbTaTiV(M9) and TiVNbHf(M10) models have significantly reduced lattice thermal conductivities (κL). This reduction is due to the mass increase and strain fluctuations, which in turn signify lattice distortion. The findings not only provide an understanding of these promising materials but also offer guidance for the design of next-generation HEAs with properties tailored for potential specific applications.

Effect of Mo content on the microstructure and mechanical properties of CoCrFeNiMox HEA coatings deposited by high power impulse magnetron sputtering

In this work, CoCrFeNiMox high entropy alloy (HEA) films were deposited by High Power Impulse Magnetron Sputtering (HiPIMS) using pure Mo and equiatomic CoCrFeNi targets. The effect of Mo content on the microstructure, residual stress state, and mechanical properties of the films was investigated in the range of 0–20 at.%. All films exhibited a columnar growth morphology and a high density of planar defects. Increasing the Mo content promoted the formation of a fine-grained structure and induced the transformation from a single face-centered cubic (FCC) phase to a mixture of FCC and body-centered cubic (BCC) phases. All produced films displayed a compressive residual stress state regardless of the Mo concentration. In terms of mechanical properties, the hardness of the films increased with increasing Mo content due to solid solution and grain boundary strengthening, along with the formation of a hard BCC phase. On the other hand, the elastic modulus decreased, likely due to the formation of an amorphous phase at higher Mo concentrations.

Additively Manufactured Foot Insoles Using Body-Centered Cubic (BCC) and Triply Periodic Minimal Surface (TPMS) Cellular Structures

This study presents the development of insoles using 3D scanning and additive manufacturing; additionally, the feasibility of implementing cellular structures in their design was evaluated. Using finite element models, the displacements and Von Mises stresses in the insoles were obtained considering the exerted pressures of a person during walking. The insoles developed in this work presented a decrease of 91.48% in deformation while the maximum Von Mises stress increased by 32.62%, compared with what other authors reported. The Von Mises stresses and displacements in the insole were calculated when two cellular topologies, triply periodic minimal surfaces (TPMS) and body-centered cubic (BCC), and different relative densities (10.33%, 14.67%, and 20.19%) were implemented. When compared to solid insoles, the Von Mises stresses and displacements for the models with cellular structures increased. The maximum Von Mises stresses and displacements resulted for the insoles with a relative density of 10.33%; for the insole with the BCC cellular structure, the displacement was 2.06 mm, and the Von Mises stress was 22.17 MPa, while for the TPMS structure, these were 2.7 mm and 23.84 MPa, respectively. The designs were additively manufactured, and the printing defects were visually characterized.

TWIP-assisted Zr alloys for medical applications: Design strategy, mechanical properties and first biocompatibility assessment

This study proposes a novel strategy for the design of a new family of metastable Zr alloys. These alloys offer improved mechanical properties for implants, particularly in applications where conventional stainless steels and Co-Cr alloys are currently used but lack suitability. The design approach is based on the controlled twinning-induced plasticity (TWIP) effect, significantly enhancing the ductility and strain-hardenability of the Zr alloys. In order to draw a “blueprint” for the compositional design of biomedical TWIP (Bio-TWIP) Zr alloys—using only non-toxic elements, the study combines d-electron phase stability calculations (specifically bond order (Bo) and mean d-orbital energy (Md)) with a systematic experimental screening of active deformation mechanisms within the Zr-Nb-Sn alloy system. This research aids in accurately identifying the TWIP line, which signifies the mechanism shift between TWIP and classic slip as the primary deformation mechanism. To demonstrate the efficacy of the TWIP mechanism in enhancing mechanical properties, Zr-12Nb-2Sn, Zr-13Nb-1Sn, and Zr-14Nb-3Sn alloys are selected. Results indicate that the TWIP mechanism leads to a significant improvement of strain-hardening rate and a uniform elongation of ∼20% in Zr-12Nb-2Sn, which displays both {332}<113> mechanical twinning and dislocation slip as the primary deformation mechanisms. Conversely, Zr-14Nb-3Sn exhibits the typical mechanical properties found in stable body-centered cubic (BCC) alloys, characterized by the sole occurrence of dislocation slip. Cell viability tests confirm the superior biocompatibility of Zr-Nb-based alloys with deformation twins on the surface, in line with existing literature. Based on the whole set of results, a comprehensive design diagram is proposed.

The effect of the volume fraction of nanocrystals on the brittleness of Fe-based amorphous/nanocrystalline alloys simulated by molecular dynamics

The effect of the volume fraction of body-centered cubic (BCC) crystal in Fe-based amorphous nanocrystalline alloys on room temperature brittleness was investigated via molecular dynamics simulations. Seven model samples with embedded BCC nanocrystal contents ranging from 0 to 33.4 vol.% were obtained. The indentation tests were carried out by spherical rigid indenter to investigate the microstructural evolution and the mechanical properties of those Fe-based amorphous/nanocrystalline alloys in terms of the indentation force, hardness, von Mises shear strain, atomic displacement vector as well as surface morphology. It is found virtually that the plasticity shows a gradient decrease tendency for the three types of samples with 0, less than 16, and more than 20 vol.% nanocrystal, respectively, which is caused by the free volume decreases via monitoring the Voronoi polyhedra.

Mechanical Properties and Deformation Behaviors of Layered‐Hybrid Lattice Structure Fabricated by Selective Laser Melting

Three types of layered‐hybrid lattice structures (LHLSs) with different layer thicknesses composed of body‐centered‐cubic (BCC) and face‐centered‐cubic (FCC) unit cells are designed and manufactured by selective laser melting using Ti–6Al–4V powder. The microstructure and surface morphologies of the three types of the selective laser melting‐formed LHLSs are examined by an optical microscope and scanning electron microscope (SEM), respectively. Quasistatic compression experiments are carried out to investigate the mechanical properties. The results show that the layer thickness has a significant effect on the mechanical properties and deformation behaviors. The elastic modulus, yield strength, and ultimate compressive strength of LHLS increase with the increasing BCC and FCC layer thickness, respectively. Based on the observations of deformation process, a 45° shear band and axial fracture are observed in LHLS‐8, and step‐like deformation bands are observed in both LHLS‐4 and LHLS‐2 samples. Besides, the influence of different loading directions on mechanical properties is also investigated; it is found that the ultimate compressive strength loaded in the transverse direction is independent of the layer thickness in LHLSs.

Processing and characterization of TiNbMoTaW refractory high entropy alloy by mechanical alloying

Refractory High Entropy Alloys (RHEAs) are a new class of alloys that have attractive properties suited for high-temperature applications. An equiatomic combination of the elements Ti, Nb, Mo, Ta, and W has been processed by mechanical alloying (MA) route to yield TiNbMoTaW RHEA powder. Structural analysis of RHEA powder obtained after 100 h of mechanical milling, indicated the formation of a single-phase solid solution with a body-centered cubic (BCC) structure and has a lattice constant of 3.1645 Å. CALPHAD modeling of TiNbMoTaW RHEA was carried out to understand the effect of phase changes with respect to temperature. RHEA was found to be thermally stable at elevated temperatures with a dominant BCC structure, which highlights its potential in high-temperature engineering applications.

Composition optimization and hydrogen storage properties of Ti–V–Mn–Fe alloys

Ti–V-based hydrogen storage alloys have garnered interest owing to their salient advantages of reversible hydrogen absorption/desorption at room temperature and excellent kinetic properties. However, the complicated smelting technology of high-purity V metal renders expensive prices, hampering their large-scale production and application. Herein, to overcome this hurdle, abundant and inexpensive Mn and Fe are added to obtain Ti–V–Mn–Fe hydrogen storage alloys. The novel alloy compositions were obtained using a uniform design method. The hydrogen absorption/desorption behaviors of alloys prepared using arc melting technology were analyzed in detail. Systematic investigations show that the activation, kinetics, and thermodynamic properties of alloys are closely correlated with the Ti/(Mn + Fe) ratios. The designed alloy compositions have a multiphase structure with a body-centered cubic (BCC) main phase. The lattice parameters of the BCC phase increase with increasing Ti/(Mn + Fe) ratio, and the large lattice parameters of alloys are beneficial to facilitate the diffusion of hydrogen atoms, resulting in fast kinetics. A reasonable Ti/(Mn + Fe) ratio positively affects the hydrogen storage properties. Among them, the Ti40V40Mn2Fe18 alloy with Ti/(Mn + Fe) = 2 achieved a hydrogen absorption capacity of 3.472 wt% at 298 K and an effective reversible hydrogen storage capacity of 1.485 wt% above 0.1 MPa at 363 K. This study provides a novel insight for designing Ti–V-based alloy compositions via the uniform design method.

The nanocrystalline and high density dislocation-Enabled ultrahigh strength and ductility of Al0.4Co0.5V0.2FeNi high entropy alloy

The evolution of the microstructure and mechanical properties of a vacuum arc melted non-equiatomic Al0.4Co0.5V0.2FeNi high-entropy alloy (HEA) subjected to severe plastic deformation was investigated experimentally and by simulations. The present work explored duplex HEAs, comprising a face-centered cubic (FCC) matrix and a body-centered cubic (BCC) phase, towards outstanding their mechanical responses. The Al0.4Co0.5V0.2FeNi alloys had a duplex structure, i.e., with dispersed B2-phase islands (with sizes of dozens of microns) in several hundred micron-, even millimeter-sized FCC grains. The mechanical properties of this HEA were strongly deformation dependent, i.e., when deformation increased from 30 % up to 60 %, the yield strength and ultimate strength tensile increased from ∼0.9 GPa and 1.0 GPa to ∼1.2 GPa and 1.3 GPa, respectively. During tensile deformation, initial fractures occurred in the FCC phase located close to the interface between the FCC and BCC phases. With an increase of deformation, the fracture degree in the FCC phase got larger, and fractures also appeared in the BCC phase. Combined with the geometric dislocation density calculation results from an electron backscatter diffraction (EBSD) analysis, it can be seen that the dislocation density near the phase interface of FCC was higher, making it more likely to produce defects.

Plastic deformation capacity obtained by the process of strain delocalization in Hf0.5Nb0.5Ta0.5Ti1.5Zr multi-principal-element alloy

Multi-principal element alloys (MPEAs) with body-centered-cubic (BCC) structures composed of elements of IVB, VB, and VIB usually exhibit high compressive strength and superior high-temperature performance. However, premature necking under tensile loading at ambient temperature limits their applications. Herein, we report the Hf0.5Nb0.5Ta0.5Ti1.5Zr MPEA with a single BCC phase, which performs considerable tensile plasticity by the process of strain delocalization. The formation of dispersed slip bands and two major strain localized regions suppress premature necking. The strain-localized region with a larger strain gradient realized strain delocalization during non-uniform deformation, resulting in considerable tensile plasticity (∼20%) with a yield strength of 922 MPa. Two dominated work hardening mechanisms were revealed. One is the geometrically necessary dislocations (GNDs) produced by non-uniform deformation which can coordinate deformation incompatibility, thus enhancing plastic deformation capability. The other is the lattice distortion which can provide an easy path for the cross slip of dislocations and realize strain delocalization. These two kinds of work-hardening mechanisms jointly contribute to the significant plastic deformation capacity of the Hf0.5Nb0.5Ta0.5Ti1.5Zr MPEA.

Structure and mechanical properties of novel lightweight refractory high entropy alloys NbMoTiZr-(Al/V): a combined first principles and experimental study

NbMoTaW refractory high entropy alloy (RHEA) has excellent high temperature mechanical properties, but low room temperature ductility and high density severely limit its practical applications. In the present work, to overcome this deficiency, the composition was adjusted, and the mechanical properties of four novel as-cast NbMoTiZr-(Al/V) lightweight refractory high entropy alloys (LRHEAs) were investigated by theoretical calculations combined with experimental methods. The first-principle calculations approach based on density functional theory predicts the mechanical properties of LRHEAs and explains the alloying effects at the atomic and electronic levels. The body-centered-cubic (BCC) phase structure of the alloys were predicted on the formation enthalpy and cohesive energy, as well as empirical parameters such as ΔSmix, ΔHmix, VEC, and the atomic size difference, in conjunction with CALPHAD and XRD. The microstructure of the LRHEAs were also analyzed by SEM. The experimental results, along with the calculated elastic constants and moduli, show significant improvement in the strength and ductility of NbMoTiZr-(Al/V) LRHEAs compared to NbMoTaW RHEA. LRHEAs exhibit elastic anisotropy and are therefore more suitable for use in engineering applications. The strengthening mechanisms of the alloys were analyzed in terms of total and partial densities of states, overlapping Mulliken population, charge density contour and atomic distances. The increased plasticity of LRHEAs is mainly due to the formation of Ti-Ti, Zr-Zr and Zr-Al metallic bonds in the alloys. The calculated results agree with the experimental results, indicating that first-principles calculations are an effective method for predicting the improved properties of lightweight refractory high-entropy alloys. The present work provides a good guideline for the design and research of lightweight refractory high entropy alloys.

Experimental and numerical investigation to elucidate the fluid flow through packed beds with structured particle packings

The present paper presents an experimental and numerical investigation of the dispersion of the gaseous jet flow and co-flow for the simple unit cell (SUC) and body-centred cubic (BCC) configuration of particles in packed beds. The experimental setup is built in such a way that suitable and simplified boundary conditions are imposed for the corresponding numerical framework, so the simulations can be done under very similar conditions as the experiments. Accordingly, a porous plate is used for the co-flow to achieve the uniform velocity and the fully developed flow is ensured for the jet flow. The SUC and BCC particle beds consist of 3D-printed spheres, and the non-isotropy near the walls is mostly eliminated by placing half-spheres at the channel walls. The flow velocities are analysed directly at the exit of the particle bed for both beds over 36 pores for the SUC configuration and 60 pores for the BCC configuration, for particle Reynolds numbers of 200, 300, and 400. Stereo particle image velocimetry is experimentally arranged in such a way that the velocities over the entire region at the exit of the packed bed are obtained instantaneously. The numerical method consists of a state-of-the-art immersed boundary method with adaptive mesh refinement. The paper presents the pore jet structure and velocity field exiting from each pore for the SUC and BCC packed particle beds. The numerical and experimental studies show a good agreement for the SUC configuration for all flow velocities. For the BCC configuration, some differences can be observed in the pore jet flow structure between the simulations and the experiments, but the general flow velocity distribution shows a good overall agreement. The axial velocity is generally higher for the pores located near the centre of the packed bed than for the pores near the wall. In addition, the axial velocities are observed to increase near the peripheral pores of the packed bed. This behaviour is predominant for the BCC configuration as compared to the SUC configuration. The velocities near the peripheral pores can become even higher than those at the central pores for the BCC configuration. It is shown that both the experiments as well as the simulations can be used to study the complex fluid structures inside a packed bed reactor.

Fracture behaviour of laser powder bed fusion AlSi10Mg microlattice structures under uniaxial compression

Microlattice structures produced by laser powder bed fusion (LPBF) have been tested in compression extensively. Yet, their failure modes remain unexplained. This study bridges this research gap by accurately predicting the crack initiation process in LPBF body centred cubic (BCC) microlattices and their failure mode. In this study, LPBF AlSi10Mg BCC microlattice structures were tested in uniaxial compression and their detailed response modelled using a finite element (FE) modelling methodology on microlattices with idealised struts which was validated experimentally. Crack initiation in BCC microlattices with 2 × 1 × 2 unit cells loaded in compression was observed in situ via a scanning electron microscope (SEM). The force–displacement response of the microlattice was studied with respect to crack initiation and propagation. It was found that the locations of crack initiation could be predicted by considering the equivalent plastic strain and stress triaxiality fields obtained by an FE analysis and assuming a monotonically decreasing fracture locus. Subsequently, microlattices with 4 × 4 × 4.5 unit cells were similarly subjected to compression. Using a monotonically decreasing fracture locus extrapolated from uniaxial tension testing of the bulk LPBF AlSi10Mg, an FE simulation successfully predicted the commonly reported diagonal shear band failure mode of the microlattice on a model with idealised struts.

Stability and growth kinetics of {112} twin embryos in [formula omitted]-Ti alloys

{112}〈111̄〉 deformation twin, shortened as {112} twin, is usually the dominant twinning mode in transition metal alloys in a body-centered cubic (BCC) lattice except for many BCC β titanium (Ti) alloys. To understand this twin-mode variation, we investigate stability and early-stage growth kinetics of {112} twin embryos with multiple atomic layers in a series of β-Ti alloys by applying density functional theory (DFT) and classical atomistic simulations. Both simulation methods demonstrate that, as average valence electron concentration (VEC measured in a unit of e/a) of Ti alloys decreases, β→ω phase transformations at {112} twin boundaries, which are confirmed by our transmission electron microscopy characterizations, increase the critical thickness of {112} layers as stable twin embryos, possibly raising {112} twin nucleation energy barriers. In simulations of twin embryo growths under applied shear stress on {112} planes, when VEC (or temperature) values are low (∼4.25e/a at 300 K), the applied shear stress results in β twin →α’/α” phase →β matrix phase transformations through an anti-twinning mechanism inside the existing twin embryos; concurrently, ω phases strongly impede the twin boundary migration; these combined effects result in eliminations of {112} twin embryos. However, when VEC increases slightly (∼4.34e/a at 300 K), ω phases at twin boundaries reduce the required stress for {112} twin embryo growth compared with the cases with high VEC values (e.g., ∼4.50e/a at 300 K). These changes of ω effects on {112} twin embryo growth kinetics could originate from free energy landscape variations of β matrix →ω phase →β twin phase transformations.

Structure and magnetism of AlCoCrCuFeNi high-entropy alloy

We report on the investigation of magnetic and structural properties of AlCoCrCuFeNi, which is known to crystallize in a dual phase solid solution: the face-centred cubic (FCC) or the body-centred cubic (BCC). The results of neutron (NPD) and synchrotron powder diffraction (SXRD) allow to partially resolve magnetic information coming from BCC and FCC phases, which is impossible in the bulk magnetic measurements. Electron diffraction (PED) revealed that AlCoCrCuFeNi forms dendritic microstructure with the Cu-rich FCC phase and the Ni-rich BCC phase. Lattice parameters obtained from PED method are in good agreement with parameters obtained after refinement on the basis of powder X-ray diffraction measurements. The local crystal and electronic structure around Co was studied using Co K X-ray Absorption Spectroscopy (XAS). The magnetic measurements show that AlCoCrCuFeNi reveal a ferromagnetic transition at about 330 K and displays magnetic hysteresis loop at the room temperature. Results from NPD suggest that the magnetic moment is mostly located in the BCC subsystem. The alloy shows soft magnetic properties. Saturated magnetizations (Ms), remanence ratio (Mr/Ms) and coercivity (Hc) of the cast are estimated to be 45.10 emu/g, 5.1 % and 56 Oe at 300 K, respectively. Finally, the BCC-FCC phase transformation up to 673 K (400 °C) was investigated using temperature dependent NPD, where a possible second BCC phase was identified.

Optimization of growth conditions to obtain highly anisotropic FeCo nanowires prepared through magnetic-field-assisted chemical route

In this study, we synthesized one-dimensional α-FeCo nanowires using the magnetic-field-assisted hydrazine reduction method. The amount of hydrazine, NaOH, synthesis temperature and strength of the magnetic field were optimized to obtain high aspect ratio nanowires with good quality. Two samples, obtained at 90 °C (S12) and 60 °C (S34) with improved morphologies and aspect ratios, while keeping the other optimized conditions (Hydrazine - 1 mL; NaOH - 1.5 g and strength of the magnetic field - 4000 Gauss (G)) same, were characterized using various techniques viz. X-ray diffraction (XRD), High-resolution transmission electron microscopy (HR-TEM), selected area electron diffraction (SAED), X-ray photoemission spectroscopy (XPS) and dc-magnetization to investigate structural, electronic structural and magnetic properties. Both the samples revealed single-phase α-FeCo formation with body centered cubic (BCC) geometry with space group: Im-3m indicating decrease in the lattice parameter and crystallite dimensions at 60 °C (S34). The influence of synthesis temperature was notably observed on the magnetic properties as well. The saturation magnetization was found to be enhanced from 233 emu/g for S12 to 247 emu/g for S34 along with the enhancement in coercivity. The effective magnetic anisotropy also enhanced to be 2.3× 106 erg/cm3 in S34. In brief, the improvement in aspect ratio and morphology of the wires resulted in the enhancement of saturation magnetization and effective magnetic anisotropy. The enhanced value of magnetocrystalline anisotropy and shape magnetic anisotropy is attributable to the external magnetic field applied during growth and curling of spins due to the reduced diameter of the wires.

The synergistic effect of Ni and C14 Laves phase on the hydrogen storage properties of TiVZrNbNi high entropy hydrogen storage alloy

As a hydrogen storage alloy, the body-centered cubic (BCC) structure has been well studied due to its large hydrogen storage capacity. On this basis, the introduction of catalytic elements and an appropriate amount of C14 Laves phase can further improve the comprehensive hydrogen storage properties of hydrogen storage alloys. Based on this theory, (Ti32.5V27.5Zr7.5Nb32.5) 1-xNix (x = 0.03, 0.06, 0.09) high entropy hydrogen storage alloys with an appropriate amount of catalytic element Ni are prepared in this study. The raise in Ni content is accompanied by grain refinement of the dendritic structure, an increase in the number of grains and grain boundaries, and a gradual increase in the proportion of C14 Laves phase. The introduction of catalytic element Ni reduces the dissociation energy of hydrogen molecules. The increasing grain and grain boundaries increase more hydrogen absorption sites with lower activation energy. The diffusion channel provided by the appropriate amount of C14 Laves phase makes it easier for hydrogen atoms to diffuse into the main phase BCC phase with strong hydrogen absorption capacity, and the hydrogen atoms are trapped by vacancy defects with large hydrogen binding energy. The synergistic effect of the three factors ensures the improvement of hydrogen absorption performance of high entropy hydrogen storage alloys. (Ti32.5V27.5Zr7.5Nb32.5) 0.94Ni0.09 high entropy hydrogen storage alloy achieves excellent saturated hydrogen storage capacity of 2.78 wt % and 2.99 wt % at room temperature and 150 °C under 3 MPa hydrogen pressure, respectively. In addition, the introduction of Ni element reduces the thermal stability of metal hydrides, thereby improving the dehydrogenation performance of high entropy hydrogen storage alloys. The reversible phase transition occurs during the whole hydrogen absorption and desorption cycle.

Tailoring microstructure and tensile properties of low-cost AlCrFeNi-based high-entropy alloys via Co and/or Ti addition

Al-Cr-Fe-Ni high-entropy alloys (HEAs) have low cost but suffer from intrinsic brittleness, leading existing research to concentrate on compressive properties. This study explores alloying strategies to improve tensile properties for these HEAs. Minor elements including 5 at.% Co, 5 at.% Co + 3 at.% Ti, and 5 at.% Co + 5 at.% Ti are added to investigate their impact on microstructure, tensile properties, and solidification behavior for Fe30Ni35Cr21.25Al13.75 HEA. The addition of both Co and Ti has a synergistic effect on the alloys; however, it does not alter the types of phases present, as the face-centered cubic (FCC), body-centered cubic (BCC), and B2 phases are maintained. Specifically, the increase of Ti content promotes the transformation of the primary phase from FCC to BCC and causes the BCC phase to undergo spinodal decomposition. The addition of Co alone decreases the strength, whereas the synergistic combination of Co and Ti enhances the yield strength (from ∼571 MPa to ∼625 MPa) and ultimate tensile strength (from ∼1112 MPa to ∼1288 MPa). Nonetheless, the total elongation is only reduced by 1.5% with this combination. Specially, introducing 5% Ti into the alloy instantly renders it brittle. These results provide valuable insights into improving the mechanical properties and understanding the solidification behavior of low-cost Al-Cr-Fe-Ni HEAs through synergistic alloying.

Evolution in microstructure and tribological behavior of laser cladded MoxNbTiZr high-entropy refractory alloy coatings with varying Mo content

The effect of the Mo element on the Ni-Ti-Zr refractory high-entropy alloy (RHEA) coatings synthesized by laser cladding were explored in terms of microstructural evolution and tribological behavior assessed by material characterization techniques and drying sliding wear tests. The findings reveal that MoxNbTiZr RHEA coatings, comprising of body center cubic (BCC) matrix phase and several hexagonal close packed (HCP) phases, have a dendrite microstructure with Mo, Nb-rich dendritic region (DR) and Zr-rich interdendritic region (IR), affected by Mo-induced thermodynamic instability. The micro-segregation between DR and IR becomes serious by the synergy effect of melting point difference, diffusion rate, and mixing enthalpy. The microhardness of the RHEA coating has a linear relationship with Mo content, with the highest value of 732.67 HV at x = 1.0. Nanotwins induced by residual stress, high cooling rate, solid-solution strengthening, fine-grain strengthening, and second-phase strengthening, cause microhardness improvement. Due to the generation of the destructive oxide layer and rising coating brittleness, the wear rate rises from 1.66 × 10−4 mm3/(N·m) to 3.75 × 10−4 mm3/(N·m). The wear mechanism of the MoxNbTiZr coatings shifts from oxidation wear to abrasive wear and eventually to three-body abrasion and severe brittle micro-peeling. Among these coatings, Mo0.6NbTiZr exhibits the optimal performance with excellent comprehensive characteristics.

Microstructural Characterization of Al0.5CrFeNiTi High Entropy Alloy Produced by Powder Metallurgy Route.

Alloys with superior properties represent the main topic of recent studies due to their effectiveness in reducing the cost of equipment maintenance and enhancing usage time, in addition to other benefits in domains such as geothermal, marine, and airspace. Al0.5CrFeNiTi was produced by solid state processing in a planetary ball mill, with the objective of obtaining a high alloying degree and a homogenous composition that could be further processed by pressing and sintering. The metallic powder was technologically characterized, indicating a particle size reduction following mechanical alloying processing when compared to the elemental raw powder materials. The microstructural analysis presented the evolution of the alloying degree during milling but also a compact structure with no major defects in the pressed and sintered bulk samples. The X-ray diffraction results confirmed the presence of face-centered cubic (FCC) and body-centered cubic (BCC) phases, predicted by the theoretical calculations, along with a hexagonal close-packed (HCP) phase, where the Al, Cr, Fe, Ni, and Ti phase was identified in both the alloyed powder material and sintered sample.