Body-centered Cubic Structure Research Articles

Mechanical Properties of Lattice Structures with a Central Cube: Experiments and Simulations.

In this study, a new structure is proposed based on the body-centered cubic (BCC) lattice structure by adding a cubic truss in the center of the BCC structure and denoting it TLC (truss-lattice-cube). The different dimensions of the central cube can notably affect the mechanical properties of the lattice structure. With a fixed length (15 mm) of a unit cell, the optimal size for the central cube is determined to be 5 mm. Quasi-static compressive tests are performed on specimens made of polylactic acid (PLA) using additive manufacturing technology. The deformation characteristics of the new structure are analyzed in detail by experiments and numerical simulations. Compared to the BCC structure, the mechanical properties of the TLC structure were significantly improved. The initial flow stress of the TLC increased by 122% at a strain of 0.1; the specific strength enhanced by 293% at a strain of 0.5; and the specific energy absorption improved by 312% at a strain of 0.6. Printing defects in the lattice structure may remarkably damage its mechanical properties. In this work, incorporation of microcracks into the finite element model allows the simulation to capture the influence of printing defects and significantly improve the predictive accuracy of the simulation.

Magnetic Supramolecular Spherical Arrays: Direct Formation of Micellar Cubic Mesophase by Lanthanide Metallomesogens with 7-Coordination Geometry.

Here, an unprecedented phenomenon in which 7-coordinate lanthanide metallomesogens, which align via hydrogen bonds mediated by coordinated H2 O molecules, form micellar cubic mesophases at room temperature, creating body-centered cubic (BCC)-type supramolecular spherical arrays, is reported. The results of experiments and molecular dynamics simulations reveal that spherical assemblies of three complexes surrounded by an amorphous alkyl domain spontaneously align in an energetically stable orientation to form the BCC structure. This phenomenon differs greatly from the conventional self-assembling behavior of 6-coordinated metallomesogens, which form columnar assemblies due to strong intermolecular interactions. Since the magnetic and luminescent properties of different lanthanides vary, adding arbitrary functions to spherical arrays is possible by selecting suitable lanthanides to be used. The method developed in this study using 7-coordinate lanthanide metallomesogens as building blocks is expected to lead to the rational development of micellar cubic mesophases.

A partially hollow BCC lattice structure with capsule-shaped cavities for enhancing load-bearing and energy absorption properties

Lattice structures have gained larger design space and wider application in aerospace, automobile, civil and other engineering fields due to the advancements in additive manufacturing (AM) technology. Seeking the optimal lattice structure configuration for the purpose of enhancing mechanical performance holds paramount importance. The hollow lattice structure possesses high material utilization efficiency, but often suffers from premature failure at the node interconnections. In this paper we propose a partially hollow lattice structure (PHBCC) with solidified nodes and capsule-shaped cavities in the middle of truss components. Quasi-static compression tests were performed on the partially hollow body-centered cubic (BCC) lattices manufactured via selective laser melting technology (SLM). The effects of various geometric parameters were analyzed through finite element simulations. The findings demonstrate that the introduced PHBCC lattice exhibits enhanced mechanical properties. Specifically, there is an observed increase of 92%, 51.9%, and 22.8% in terms of specific stiffness, specific strength, and specific energy absorption, respectively, in comparison to the conventional BCC and hollow BCC (HBCC) structure. Notably, the proposed PHBCC lattice displays superior energy absorption capacity compared to a majority of existing lattice structures.

High-pressure phase transitions in a laser directed energy deposited Fe-33Cu Alloy

Additively manufactured Fe-Cu alloys contain both equilibrium face-centered cubic (FCC) and metastable body-centered cubic (BCC) crystal structure Cu precipitates depending on their size. However, the stability of these nanoscale precipitates under extreme conditions such as high pressures has not been reported. This study investigates the phase transformations and microstructural stability of laser directed energy deposition (DED-LB) made Fe67Cu33 alloy (nominal composition in at.%) under high static pressure deformation using in-situ synchrotron X-ray diffraction under pressure, postmortem high-resolution scanning transmission electron microscopy (HR-STEM), and molecular dynamics (MD) simulations. In-situ XRD results reveal a reversible phase transformation from BCC to the hexagonal close-packed (HCP) structure in the Fe grains at an onset pressure of 16.4 GPa, significantly higher than reported in the literature for pure Fe. Although no high-pressure phase transition was observed in the FCC Cu grains through XRD, HR-STEM analysis uncovers a phase transition to the HCP structure in nanoscale metastable BCC Cu precipitates within the BCC Fe matrix. After decompression, the Fe matrix reverted back to the BCC structure with periodic lath martensite, while regions of the nanoscale BCC Cu precipitates retained the metastable HCP structure. MD simulations support the BCC → HCP transition in the embedded nanoscale coherent Cu precipitates, consistent with the classical Burgers mechanism. Thus, by leveraging in-situ XRD observation, postmortem high-resolution S/TEM microscopy, and MD simulations, this study offers profound insights into the distinctive phase transformations induced by high pressure in DED-LB Fe67Cu33 alloy, which is distinguished by its hierarchical microstructure.

A combined EBSD and machine learning study of predicting deformation twinning in BCC Fe81Ga19 alloy

Compared to face-centered cubic (FCC) metals, body-centered cubic (BCC) metals demonstrate more intricate deformation behavior and microstructural characteristics because of the influence of intrinsic unstable stacking faults and defect structure. To investigate the unique phenomenon of deformation twinning in Fe81Ga19 alloy with BCC structure at moderate temperature and low strain rate, four twin nucleation models were constructed using a combination of electron backscatter diffraction (EBSD) technique and machine learning. These models are aimed to predict twin nucleation of grains and explore the relationship between twin nucleation and microstructural attributes. The study revealed that amongst the 235 grains analyzed during in-situ compressive deformation, 32 grains experienced twinning. Nine attributes influencing twin nucleation were selected and ranked according to their importance. Grain area, average image quality, neighboring grain count, and the Schmid factor of twinning systems exhibited significant influence on twin nucleation. Decision tree and tree ensemble (XGBoost) achieved 94% and 96% accuracy, respectively, on the test set, showcasing robust generalization capability. Due to the optimization of hyperparameters, support vector machine (SVM) and artificial neural network (ANN) exhibited outstanding performance. The ANN model achieved an accuracy of 97% and an F1 score of 0.91 on the test set, while the SVM model achieved an accuracy of 98% and an F1 score of 0.94, indicating superior performance. Furthermore, the study revealed that the twinning stress in Fe81Ga19 alloy exhibited weak responsiveness to temperature during deformation, and the intrinsic factors of grains were identified as crucial factors influencing twin nucleation.

Mechanical alloying of AlCoCrFe and AlCoCrFeNi: Design and experimental evaluation of medium- and high-entropy alloy particles for cold spraying

The manufacturability of equiatomic high-entropy alloy (HEA) particles with single- and dual-phase crystal structures using the high-energy mechanical alloying (HE-MA) method was explored in this study. Following a material design-of-experiment (DoE) curriculum, particles were synthesized in a planetary mill. Milling times varied while operating under two distinct HE-MA manufacturing regimes: the conventional approach (simultaneous milling of constituent elements) and the sequential method (progressive milling with the introduction of elements in a specific order). Within the conventional regime, equiatomic AlCoCrFe and AlCoCrFeNi blends were milled, focusing on the influence of incorporating nickel (Ni) as a transient element into the base composition. This led to an equivalent particle size distribution ranging from 5 to 100 μm. Notably, the presence of Ni resulted in an increased fraction of the face-centered cubic (FCC) phase, coupled with a simultaneous reduction in grain and crystallite sizes, thereby enhancing the overall material strength. This knowledge was applied to the design and synthesis of a target equiatomic FeNiCoCrAl HEA system. In this context, individual elements were added to the starting/milled Fe + Ni alloy at four-hour intervals, in line with the sequential milling regimen. The results showed an interesting evolution: the conventionally milled AlCoCrFeNi particles exhibited a dual-phase body-centered cubic (BCC) and FCC structure, with a composition of 55% BCC and 45% FCC phase fractions, while the sequentially milled FeNiCoCrAl particles demonstrated a single-phase BCC structure after 24 h of milling.

The microstructure, mechanical compression, and electrochemical behavior of novel equiatomic CoCrMoNiW and Co-rich Co50Cr12.5Mo12.5Ni12.5W12.5 high-entropy alloys fabricated by vacuum arc remelting

In this research, we developed and analyzed novel equiatomic CoCrMoNiW and Co-rich Co50Cr12.5Mo12.5Ni12.5W12.5 high-entropy alloys (HEAs). Using FactSage, we identified dual face-centered cubic (FCC) and body-centered cubic (BCC) phases in the equiatomic HEA and a predominant FCC phase in the Co-rich HEA. The results of an elemental analysis reveal the significant presence of W and Mo in the equiatomic HEA and Co, Cr, and Ni in the Co-rich HEA. X-ray diffraction revealed dual-phase FCC and BCC structures in both HEAs, with the presence of an intermetallic μ phase. The Co-rich HEA exhibited significant compressive strain due to the prevalence of the ductile FCC phase at the expense of corrosion resistance. On the other hand, the CoCrMoNiW HEA demonstrated superior corrosion resistance comparable to those of the L605 alloy and 316 L stainless steel.

Unraveling influence of entropy on thermal stability and glass-forming ability of (Fe, Co)–(Ta)–B amorphous alloys: Insights from local atomic structure simulated by ab initio molecular dynamics

The thermal stability, glass-forming ability (GFA), and local atomic structure of (Fe, Co)–(Ta)–B amorphous alloys with different entropy values were investigated by experiments and ab initio molecular dynamics simulations, and the effects of entropy were elaborated from the perspective of the local atomic structure. The experimental results show that crystallization temperature, activation energy for crystallization, and undercooling degree all rise with the increase of configurational entropy (ΔSconf) of the alloys, whereas the critical thickness for amorphous samples shows a weak correlation with the ΔSconf. The simulations indicate that the short-range orders of the amorphous alloys are all dominated by B-centered tri-capped trigonal prisms (TTPs) and bi-capped square Archimedean antiprisms, and Fe-/Co-centered deformed body-centered cubic structures (BCCs) and icosahedral-like structures (ICOs) mainly with covalent-like B–Fe/Co and metallic Fe/Co–Fe/Co bonds. The increase in the ΔSconf results in shortened bond lengths and strengthened interactions between the main atomic pairs and sluggish diffusion of the atoms, thereby leading to enhanced thermal stability of both the amorphous phases and alloy melts. The GFA of the alloys shows a strong correlation with the characteristics of the short-range orders but not the entropy. The alloy containing the lowest fractions of the TTPs and BCCs but considerable ICOs possesses the best GFA.

Effects of different cross-sections of Body Centered Cubic cells on pressure drop and heat transfer of additively manufactured heat sinks

In many industrial applications, heat loads management requires the design and production of compact heat exchangers which are expected to handle high thermal loads with acceptable pressure losses, while assuring good mechanical performances. These challenging targets can be achieved by filling the cavities where the cool/hot fluid circulates with lattice structures promoting the heat exchange between the fluid and the cavity boundaries. Such lattice structures can be only produced through Additive Manufacturing due to their high geometric complexity. Recent experimental investigations proved the effectiveness of some kinds of lattice structures having a circular cross section. Here the aerothermal behaviour of Body-Centred Cubic (BCC) lattice stagger arrays in a rectangular channel was experimentally investigated by considerably extending the previous studies to higher Reynolds numbers (up to 30′000) and to new types of lattice structures. Specifically, three new BCC structures having a cam-like, drop-like and elliptical cross section were explored in this work and compared against those having circular cross section. All the samples were manufactured by means of Laser Powder Bed Fusion and made from AlSi10Mg. At first, the heat exchangers were comprehensively characterized by means of optical non-destructive methods. Successively they were tested in a dedicated rig by imposing constant heat flux boundary conditions. The characteristics of the transitional or fully turbulent approaching flow to the test section are also reported thanks to dedicated flow field measurements performed by Particle Image Velocimetry. According to the obtained results, the BCC structure with the circular cross section of larger diameter is the most effective in terms of heat transfer, although it is largely penalized by the pressure losses. Similar heat transfer performances were achieved by the tapered cross section of elliptical shape with the advantage of a considerably lower friction factor. Pressure losses resulted almost identical for all the tapered cross sections but lower than those of the circular one having an equal frontal dimension. When considering the thermal performance factor the circular shape becomes unfavourable for Re>20′000, while the elliptical cross section is the best choice to efficiently promote heat transfer up to Re=30′000.

Dynamic magnetic field magnetorheological finishing with constant load and variable gap

Magnetorheological finishing is limited by weak polishing forces and small polishing areas, resulting in a low polishing efficiency. This study formulates a method for dynamic magnetic field magnetorheological finishing in compression-shear mode with a constant load and variable gap, which can remodel the magnetic particle string using a dynamic magnetic field and enhance the polishing force by a constant load and variable gap. To investigate the impact of process parameters on macro and micro machining processes, as well as their effects, a series of experiments were conducted to investigate the polishing force, machining clearance, and machining effect of single-crystal silicon wafers under four different conditions: static magnetic field magnetorheological finishing (T1), dynamic magnetic field magnetorheological finishing (T2) at a constant gap, static magnetic field magnetorheological finishing (T3), and dynamic magnetic field magnetorheological finishing (T4) with a constant load and variable gap. The results indicated that the shearing force and processing quality significantly improved in the constant-load and variable-gap modes, and the process of machining clearance reduction involved two stages: fast and slow compression. The shearing force of T3 increased by 35 % compared to T1, and T4 increased by 20 % compared to T2. The material removal rate of T3 and T4 increased over time, in contrast to those of T1 and T2. The key parameters of the T4 single-factor shear and machining gap testing experiments show that the constant load variable gap compression process adaptively adjusts the machining gap such that the chain string structure is in a body-centered cubic structure (BCT), increasing the number of abrasive contacts and the depth of pressure into the workpiece to achieve a significant increase in the polishing shear constant load.

Comprehensive understanding of the crystal structure of perovskite-type Ba3Y4O9 with Zr substitution: a theoretical and experimental study.

We previously reported that Zr substitution improves the chemical stability of Ba3Y4O9 and nominally 20 mol% Zr-substituted Ba3Y4O9 is an oxide-ion conductor at intermediate temperatures (500-700 °C). However, the influence of Zr substitution on the structural properties of Ba3Y4O9 was poorly understood. This paper aims to comprehensively understand the crystal structure of Ba3Y4O9 with Zr substitution by powder X-ray diffraction (XRD), extended X-ray absorption fine structure (EXAFS) measurements, and first-principles calculations. From the results, firstly we found that the hexagonal unit cell of Ba3Y4O9 reported in the database should be revised as doubled along the c-axis in terms of the periodicity of oxide-ion positions. The revised unit cell of Ba3Y4O9 consists of 18 layers of BaO3 and 24 layers of Y which periodically stack along the c-axis. In this work, we focused on the cationic lattice and noticed that the periodical stacking of Ba and Y layers comprises a similar sequence to that in the body-centered cubic (BCC) structure. There are two regions in the Ba3Y4O9 structure: one is a hetero-stacking region of Ba and Y layers (Ba-Y-Ba-Y-Ba) and the other is a homo-stacking region (Ba-Y-Y-Ba). It is noteworthy that the former region is similar to a cubic perovskite. In Zr-substituted Ba3Y4O9, Zr ions preferentially substitute for Y ions in the hetero-stacking region, and therefore the local environment of Zr ions in Ba3Y4O9 is quite similar to that in BaZrO3. Besides, the Zr substitution for Y in Ba3Y4O9 increases the fraction of the cubic-perovskite-like region in the stacking sequences. The structural change in the long-range order strongly affects the other material properties such as chemical stability and the ionic-conduction mechanism. Our adopted description of perovskite-related compounds based on the stacking sequence of the BCC structure should help in understanding the complex structure and developing new perovskite-related materials.

Transformations in crystals of DNA-functionalized nanoparticles by electrolytes.

Colloidal crystals have applications in water treatments, including water purification and desalination technologies. It is, therefore, important to understand the interactions between colloids as a function of electrolyte concentration. We study the assembly of DNA-grafted gold nanoparticles immersed in concentrated electrolyte solutions. Increasing the concentration of divalent Ca2+ ions leads to the condensation of nanoparticles into face-centered-cubic (FCC) crystals at low electrolyte concentrations. As the electrolyte concentration increases, the system undergoes a phase change to body-centered-cubic (BCC) crystals. This phase change occurs as the interparticle distance decreases. Molecular dynamics analysis suggests that the interparticle interactions change from strongly repulsive to short-range attractive as the divalent-electrolyte concentration increases. A thermodynamic analysis suggests that increasing the salt concentration leads to significant dehydration of the nanoparticle environment. We conjecture that the intercolloid attractive interactions and dehydrated states favour the BCC structure. Our results gain insight into salting out of colloids such as proteins as the concentration of salt increases in the solution.

Optimization of PdCu Alloys as Efficient and Durable HOR Electrocatalysts in Anion Exchange Membrane Fuel Cells

Anion-exchange membrane fuel cells (AEMFCs) allow for the use of Pt-free or precious group metal (PGM-free) catalysts and for a wider choice of cell and stack materials. Currently, there are still development challenges, such as the need to improve the efficiency of anode catalysts, due to the sluggish hydrogen oxidation reaction (HOR) in alkaline electrolytes. It has been demonstrated that the HOR rate can be improved using bifunctional materials, which have both an optimized hydrogen binding energy (HBE) and a favorable OHads binding energy (OHBE) [1,2]. In literature, experimental and theoretical studies demonstrate that HOR electrochemical activity of PdCu alloys strongly depends on their crystalline structure, which can be tuned through thermal treatment (300-600°C) modifying the Body-Centered Cubic (BCC) and Face-Centered Cubic (FCC) phase ratio [3-5]. On this basis, a FCC-phased PdCu(1:1) alloy supported on Vulcan XC-72 was synthesized via a metal-vapor method (MVS) and furtherly modified through thermal annealing (5 hours under N2 atmosphere) in order to obtain the appearance of an ordered BCC structure. The HOR performance and stability of these materials were tested for first time in a complete in AEMFC. The use of PdCu allows us to lower the effective Pd loading on the electrode to about 0.16 mg cm-2, obtaining in the case of PdCu/C-500°C (where FCC-BCC phases coexist) a maximum power density of 941 mW/cm2. The increased activity and stability of the PdCu/C-500°C was demonstrated through long stability test, where it exhibits an average of 685 mW/cm2 of power density over 15 hours of testing during 3 days in AEMFC fixed at a constant potential of 0.4 V and 80°C (H2 0.5 L/min, O2 1 L/min), 10% more of the FCC-phased PdCu. Moreover, acquiring a final scan of potential at the end of the experiments, it is clear that PdCu/C 500°C suffers of a minor drop of performances (only of 19%), respect with disordered FCC-phased PdCu which efficiency in terms of maximum power density drops of 30% (Figure 1). Figure 1

Effect of rare earth La2O3 on the microstructure and corrosion resistance of CoCrFeNiMoSi high entropy alloys

This study systematically investigated the effect of incorporating trace amounts of La2O3 into the CoCrFeNiMoSi high-entropy alloy (HEA) system on its corrosion resistance in neutral chloride ionic salt solutions. The CoCrFeNiMoSi HEA coatings and CoCrFeNiMoSi-0.5 % La2O3 HEA coatings were prepared using the laser melting technique. The microstructure, phase composition, and electrochemical corrosion performance were characterized using X-ray diffraction, scanning electron microscopy, electrochemical workstation, and X-ray photoelectron spectroscopy. The experimental results revealed that the microstructure primarily comprised face-centered cubic structure (FCC), body-centered cubic structure (BCC), and Si-rich intermetallic compounds. Notably, the addition of La2O3 facilitated the formation of the FCC phase. Electrochemical tests demonstrated that the CoCrFeNiMoSi-0.5 % La2O3 HEA coating exhibited an elevated corrosion potential and a reduced self-corrosion current density when compared to the CoCrFeNiMoSi HEA coating. The X-ray photoelectron spectroscopy (XPS) data revealed a notable increase in the Cr content and oxide content of the passive film when La2O3 was present in the HEA. This resulted in the formation of a more protective passivated film. Consequently, the potential utilization of rare earth lanthanum oxide to enhance the corrosion resistance of HEA coatings is promising.

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.

Work-hardening ability enhancement of lightweight high entropy alloys via adding yttrium

Lightweight high-entropy alloys (LHEAs) with body-centered-cubic (BCC) structure have attracted wide attention due to their considerable strength-ductility synergy. However, the lack of work hardening ability is a key weakness, limiting the engineering application. In this study, appropriate contents of rare-earth element yttrium (Y) were added to the as-cast Ti-Zr-V-Nb-Al LHEAs with single BCC structure, and the microstructure and work hardening behavior of these LHEAs were investigated. Benefiting from the addition of Y, these LHEAs generated slight of Y-rich and Y-O-rich phases both in the grains and on the grain boundaries. During plastic deformation, these precipitates can effectively prevent dislocation slip and promote the dislocation intersections and reactions, which can improve the work-hardening ability. Moreover, adding Y can promote the large constitutional supercooling of the LHEAs and refine the grain size of the LHEAs, which also improve the work-hardening ability. Finally, the work hardening of as-cast Ti-Zr-V-Nb-Al LHEAs were successfully turned from negative to positive with 0.2 at% Y addition, with only few ductility loss. Our work provides an effective means of optimizing the mechanical properties, especially the work hardening ability, of as-cast BCC LHEAs.

Vibration characteristics of additive manufactured IWP-type TPMS lattice structures

Several research has been done on the conventional strut-based lattice structures, which have the problem of stress concentration in the application. In recent years, a new lattice structure, the triply periodic minimal surface (TPMS) lattice structure is increasingly gaining attention, but its vibrational properties have been less studied. In this study, the IWP-type TPMS lattice structures and ordinary body-centered cubic (BCC) counterparts with similar topology were prepared by selective laser melting (SLM) additive manufacturing (AM) technique. The compression behavior of the structures and the energy absorption capacity were determined by uniaxial compression tests. The frequency response and the damping ratio of the structure were calculated by dynamic vibration transfer rate tests. The results show that the stiffness and inherent frequency of the lattice structure are proportional to the volume fraction and inversely proportional to the cell size. Decreasing the volume fraction and increasing the cell size can be more beneficial to achieve low-frequency vibration isolation. Moreover, the IWP-type triply periodic minimal surface lattice structures have better mechanical properties than BCC structures and have good vibration isolation properties. Insights from this paper provide a reference for improving the load-carrying and vibration isolation performance of lightweight lattice structures.

Novel candidate of metal-based thermal barrier coatings: High-entropy alloy

To obtain compatible properties of low thermal conductivity and high thermal stability, Al0.6CoCrFeNiTi high-entropy alloy was designed as a novel candidate of metal-based thermal barrier coatings (MBTBCs). The corresponding high-entropy alloy coatings were fabricated by both high-velocity oxygen-fuel spraying (HVOF) and atmospheric plasma spraying (APS), and then the dependence of thermal insulation properties on microstructure was investigated. The both coatings exhibit a simple body-centered cubic (BCC) structure, but present obvious difference in microstructure and defect characters which relates to the evolution of in-flight particles. Benefit from the extremely low thermal conductivity, the APS-deposited coating can increase 13.24 °C of the surface temperature of piston crown and yield a temperature reduction of 19.00 °C along the thickness direction, which mean a positivity on enhancing the power efficiency of vehicle engines without sacrificing the strength of aluminum alloy components. In virtue of a decoupling method, the crucial effect of microstructure on thermal conductivity is disclosed, thus interpreting the excellent thermal insulation property of APS-deposited coating dominated by grain refinement and disordered BCC structure. The present results demonstrate a great potential of high-entropy alloy coatings as thermal barrier application and provide an inspiration for future works aiming to design these coatings to meet specific engineering needs.

Effect of Aluminum Addition on the Microstructure, Magnetic, and Mechanical Properties of FeCrCoNiMn High-Entropy Alloy

High-entropy FeCoCrNiMn (C1) and FeCoCrNiMn10Al10 (C2) alloys (HEAs) were mechanically alloyed for 24 h and heated to 900 °C (C1_900 °C and C2_900 °C). The powders were also compacted into pellets (C1_pellet and C2_pellet) and sintered at 500 °C for 1 h. Crystal structure, microstructure, magnetic, and mechanical properties were investigated by X-ray diffraction, scanning electron microscopy, vibrating sample magnetometry, and microindentation. During the milling process, a mixture of body-centered-cubic (BCC) and face-centered-cubic (FCC) phases with a crystallite size in the range of 9–13 nm was formed in the C1 HEA alloy. The dual FCC + BCC solid solutions remain for the C1_pellet and transform to a single FCC for the C1_900 °C powders. Al addition stabilizes the BCC structure in the FeCoCrNiMn10Al10 HEA alloy, as revealed by the structural refinement. The structure exhibits a mixture of BCC + FCC solid solutions for the C2 powders and BCC + FCC + CrCo sigma phase for the C2_pellet and C2_900 °C powders. The crystallite sizes are in the range of 6-93 nm for all the samples. The saturation magnetization (Ms), coercivity (Hc), and squareness ratio (Mr/Ms) are estimated to be 24.2 emu/g, 153.62 Oe, and 0.165, respectively, for C1 and 28.45 emu/g, 188.48 Oe, and 0.172 for C2. The C1_900 °C and C2_900 °C powders exhibit, respectively, paramagnetic and soft magnetic behaviors and an exchange bias at room temperature. The C1_pellet and C2_pellet HEAs show high hardness values of 584.85 Hv and 522.52 Hv, respectively.

Preparation, characterization, and phase evolution of nanocrystalline Cu/Ti doped MoNbTa-based multi-principal element alloys

As multi-principal element alloys (MPEAs) continue to draw attention from researchers, there is a growing demand for MPEAs with a combination of body-centered cubic (BCC) and face-centered cubic (FCC) phases because of their intriguing properties. In the present study, we prepared MPEAs with BCC and FCC phases using composition optimization, mechanical alloying (MA), and powder sintering. Two alloys Mo25Nb25Ta25Cu25 and Mo28Nb28Ta28Cu8Ti8 (in at.%) were prepared from elemental powders. The phase evolution and composition were investigated from the powder processing stage to the annealing stage, using X-ray diffractometry and electron microscopy. As the milling times increase, the crystallite sizes were significantly refined. For the as-sintered Mo25Nb25Ta25Cu25, two different BCC structures were observed along with an FCC phase enriched in Cu. In contrast, the sintered Mo28Nb28Ta28Cu8Ti8 also exhibited the same dual-phase BCC structures but contained Ti-rich microprecipitates. The sintered Mo28Nb28Ta28Cu8Ti8 had a better balance of mechanical strength (1302 MPa) and plasticity (20%) compared to Mo25Nb25Ta25Cu25 alloy. Gibbs free energy calculations showed that the dual-phase BCC + FCC structure arose because of the miscibility gap between Cu and the refractory elements.