Formation Of Bcc Research Articles

High-Temperature Oxidation and Phase Stability of AlCrCoFeNi High Entropy Alloy: Insights from In Situ HT-XRD and Thermodynamic Calculations.

The high-temperature oxidation behaviour and phase stability of equi-atomic high entropy AlCrCoFeNi alloy (HEA) were studied using in situ high-temperature X-ray diffraction (HTXRD) combined with ThermoCalc thermodynamic calculation. HTXRD analyses reveal the formation of B2, BCC, Sigma and FCC, phases at different temperatures, with significant phase transitions observed at intermediate temperatures from 600 °C-100 °C. ThermoCalc predicted phase diagram closely matched with in situ HTXRD findings highlighting minor differences in phase transformation temperature. ThermoCalc predictions of oxides provide insights into the formation of stable oxide phases, predominantly spinel-type oxides, at high p(O2), while a lower volume of halite was predicted, and minor increase observed with increasing temperature. The oxidation behaviour was strongly dependent on the environment, with the vacuum condition favouring the formation of a thin, Al2O3 protective layer, while in atmospheric conditions a thick, double-layered oxide scale of Al2O3 and Cr2O3 formed. The formation of oxide scale was determined by selective oxidation of Al and Cr, as further confirmed by EDX analysis. The formation of thick oxide in air environment resulted in a thick layer of Al-depleted FFC phase. This comprehensive study explains the high-temperature phase stability and time-temperature-dependent oxidation mechanisms of AlCrCoFeNi HEA. The interplay between surface phase transformation beneath oxide scale and oxides is also detailed herein, contributing to further development and optimisation of HEA for high temperature applications.

Mechanical properties and wear behaviors of FeCoNiCrMnTix high-entropy alloys manufactured by vacuum arc melting

FeCoNiCrMnTix (x = 0, 2, 4, 6 wt%) high-entropy alloys (HEAs) were prepared using vacuum arc melting. The microstructure, mechanical and wear properties of the HEAs were investigated using XRD, OM, SEM, Vickers hardness, tensile tests and friction tests. The crystal structure of the FeCoNiCrMnTix HEAs consists of FCC and BCC, and the precipitation of the strengthening phase Ni3Ti inhibits the FCC to promote the formation of BCC. The dendrites (DR) of the FCC phase enriched with Fe, Co, and Cr. Ni, Mn, and Ti aggregated between the inter-dendrites (IR) of BCC phase. The addition of Ti to FeCoNiCrMn HEA decreased the grain size. FeCoNiCrMnTi6 reaches a maximum microhardness of approximately 293 HV higher than the equiatomic FeCoNiCrMn HEA (∼151 HV). The significant increase in hardness and wear resistance is attributed to solid solution strengthening, grain refinement, and precipitation hardening. With increasing Ti content, the yield strength of FeCoNiCrMnTix HEAs increased from 296 to 601 MPa and the average coefficient of friction (COF) gradually decreased. Tensile fracture is characterized by ductile and brittle fracture. The generated oxide layer protects the alloy matrix during friction, and the wear mechanism gradually transforms from adhesive wear to abrasive wear.

Investigation of hydrogen storage properties for high entropy alloys (Ti30V30Cr30Fe10 and Ti40V30Cr10Fe10Al10)

The broad compositional space of high entropy alloys (HEAs) presents an opportunity to research new hydrogen storage materials, with improved hydrogen storage properties under ambient temperature and pressure. The properties of these materials are influenced by several factors including composition, operating pressure, and temperature, as well as the fabrication techniques employed. As such this study investigated two HEAs, namely Ti30V30Cr30Fe10 and Ti40V30Cr10Fe10Al10 using empirical and thermodynamic modelling methods, where Ti30V30Cr30Fe10 was successfully synthesized using LENS. The phase prediction criterion showed formation of a single solid BCC structure with VEC ≤ 5.4 and XRD confirmed formation of BCC and Laves phase structure. The investigated HEAs demonstrated excellent performance for hydrogen storage with maximum hydrogen storage capacities of about 3.8 and 4 wt% respectively at 25 and 100 0C, exceeding the previously reported HEAs for hydrogen storage.

The mechanism of hcp-bcc phase transformation in Mg single crystal under high pressure

The mechanism of phase transformation from hexagonal close-packed (hcp) to body-centered-cubic (bcc) structure in Mg single crystal under high pressure is studied by molecular dynamics (MD) simulations. The hcp-bcc phase transformation is achieved by a shear-shuffle mechanism, through the formation of bcc nanotwinned structure and the subsequent detwinning. The nanotwinned structure can effectively accommodate the shear caused by the hcp-bcc phase transformation, which facilities the growth of bcc phase under hydrostatic pressure. The detwinning turns the bcc nanotwinned structure into bcc nano-polycrystalline. Two twinning modes with the opposite twinning shear occur during the detwinning, which can accommodate the shear in different directions. The mechanism of hcp-bcc phase transformation revealed in this work brings out a comprehensive understanding of the plastic mechanism under high pressure, which is helpful for the further materials design under high pressure.

3D characterization of magnetic phases through neutron polarization contrast tomography

The advancement of laser-based metal additive manufacturing has enabled the production of near net shape complex geometries. Understanding the microstructural features of materials is crucial for accurate modeling of their mechanical behavior, particularly with regard to strain- or thermal-induced martensitic phase transformations in ferrous alloys and steels. For example, the formation of BCC α′-martensite can strengthen materials while preserving ductility of the dominating austenitic phase. However, in components where the shape memory effect is attributed to the reversible formation of ε-martensite, the accumulation of deformation-induced α′-martensite is an undesired, irreversible degradation mechanism. This study presents a novel tomographic approach utilizing polarization contrast neutron imaging for the 3D volumetric characterization of magnetic crystallographic phases, especially those present in low phase fractions that are typically undetectable with traditional techniques. The technique is applied to the study of strain-induced martensitic phase transformations in additively manufactured lattice structures made of high-Mn steels, which form small fractions of α′-martensite upon deformation. The results demonstrate the value of this technique for characterizing entire components and complex geometries found in numerous technological applications.

Hybrid molecular dynamic Monte Carlo simulation and experimental production of a multi-component Cu–Fe–Ni–Mo–W alloy

High-entropy alloys are a class of materials intensely studied in the last years due to their innovative properties. Their unconventional compositions and chemical structures hold promise for achieving unprecedented combinations of mechanical properties. The Cu–Fe–Ni–Mo–W multicomponent alloy was studied using a combination of simulation and experimental production to test the possibility of formation of a simple solid solution. Therefore, Molecular Dynamics and hybrid Molecular Dynamic/Monte Carlo simulations from 10K up to the melting point of the alloy were analyzed together with the experimental production by arc furnace and powder milling. The Molecular Dynamics simulations starting with a bcc type-structure show the formation of a single-phase bcc solid solution type-structure, whereas using Monte Carlo one, generally produced a two-phase mixture. Moreover, the lowest potential energy was obtained when starting from a fcc type-structure and using Monte Carlo simulation giving rise to the formation of a bcc Fe–Mo–W phase and a Cu–Ni fcc type-structure. Dendritic and interdendritic phases were observed in the sample produced by arc furnace while the milled powder evidence an separation of two phases Cu–Fe–Ni phase and W–Mo type-structures. Samples produced by both methods show the formation of bcc and a fcc type-structures. Therefore, the Monte Carlo simulation seems to be closer with the experimental results, which points to a two-phase mixture formation for the Cu–Fe–Ni–Mo–W multicomponent system.

Correlation between the nanomechanical characteristic and the phase transformation of BCC-based high entropy alloys produced via powder metallurgy

ABSTRACT In this study, the effects of Cu addition on AlFeMnTiSi0.75Cu x (x = 0, 0.25, 0.5, 0.75, 1.00; in molar ratios) high entropy alloys (HEAs) prepared via mechanical alloying and spark plasma sintering were investigated. The structure, phase, morphology and composition of HEA powders were analysed and the results revealed that the AlFeMnTiSi0.75Cu x HEAs exhibited a multiphase structure. Additionally, after sintering at 900 °C, the formation of BCC, µ and L21 phases in the densified HEAs was enhanced. The investigation of the hardness, nanoindentation and compressive properties revealed that the microstructural and mechanical properties of AlFeMnTiSi0.75Cu x HEAs were improved at the optimal Cu fraction (0.25 molar ratio). The nanoindentation results revealed that the AlFeMnTiSi0.75Cu x HEAs exhibited the highest hardness and elastic modulus (HIT = 19.2 GPa, EIT = 336 GPa). These results improve the current understanding of multiphase HEAs and may pave way for the development of advanced HEAs with superior mechanical properties.

Effect of Vanadium Addition On Structure And Soft Magnetic Properties of Nanocrystalline FeCoZrBCu Melt Spun Alloys

In this report, glass forming ability, structure and soft magnetic properties of melt spun ribbons of (Fe1-xCox) 88-yVyZr7B4Cu1alloys with compositions x0.1y2, x0.1y4 and x0.1y6 & x0.35y2, x0.35y4 and x0.35y6 have been investigated. All alloys were found to be fully amorphous after melt spinning. Annealing of amorphous ribbons of x0.1 series alloys leads to the formation of bcc α-Fe(Co) phase and Fe2Zr phase in the amorphous matrix, while annealing of amorphous ribbons of x0.35 series alloys, leads to the formation of only bcc α-Fe(Co) phase in the amorphous matrix. High precision lattice parameter calculation revealed that V addition influences the phase formation in low Co containing x0.1 alloys. It leads to low volume fraction of bcc α-Fe(Co) phase and promotes Fe2Zr phase. A higher Co content increases the Curie temperature of amorphous phase, while V addition decreases the TC of amorphous phase in both x0.1 and x0.35 series of alloys. Saturation magnetization (Ms) of x0.35 alloys are higher than of x0.1 alloy due to higher Co content and the Ms decreases with increasing V content due to its non-magnetic nature. Coercivity was found to be increased with annealing in x0.35 alloys due to the low volume fraction formation of bcc α-Fe(Co) phase and Fe2Zr phase. The coercivity decreases with increasing V addition in x0.35 alloys as spun ribbons and a lowest coercivity of 0.13 Oe has been obtained in x0.35y6 alloy which is one of the lowest among FeCoZrBCu alloys reported.

Synergistic effect of Ti, B, Si, and C on microstructure and mechanical properties of as-cast Al0.4Co0.9Cr1.2Fe0.9Ni1.2(Si, Ti, C, B)0.375 complex concentrated alloy

The synergistic effect of Ti, B, Si, and C on microstructure and mechanical properties of as-cast Al0.4Co0.9Cr1.2Fe0.9Ni1.2(Si, Ti, C, B)0.375 complex concentrated alloy (CCA) was studied. The as-cast alloy was prepared by vacuum induction melting in a ceramic crucible followed by a tilt casting to a graphite mould. The effect of alloying elements on the primary solidification phase, solidification path, and phase transformation temperatures is evaluated. The solidification of the alloy starts with the growth of columnar FCC(A1) (face-centred cubic crystal structure A1) dendrites and is finalised by the formation of lamellar FCC(A1) + (Ni,Co,Fe)16(Ti,Cr)6(Si,Al)7 eutectic in the interdendritic region. During solidification, Al, Ti, B, Si, and C segregate preferentially to liquid, which leads to the formation of BCC(B2) (ordered body-centred cubic crystal structure B2), BCC(A2) (body-centred cubic crystal structure A2), FCC(A1), (Ni,Co,Fe)16(Ti,Cr)6(Si,Al)7, Cr2B, and TiC phases in the interdendritic region. The highly anisotropic microstructure of tensile specimens prepared from the as-cast alloy consists of columnar FCC(A1) dendrites (89 vol%) oriented at an angle ranging from 75 to 90 degrees to the longitudinal axis of specimens and multiphase interdendritic region (11 vol%). The tensile deformation curves show only the strain hardening stage at test temperatures up to 700 °C. The strain hardening coefficient decreases from 0.20 to 0.17 by increasing the test temperature from 20° to 700°C. At temperatures ranging from 725° to 900°C, the tensile curves show the strain hardening stage, which is followed by the strain-softening stage up to a fracture. The strain softening stage results from dynamic recrystallisation of FCC(A1) dendrites and fracture of brittle high elastic modulus phases in the interdendritic region.

Effect of B-Si ratio and laser remelting on the microstructure and properties of Fe10Co10Ni10Cr4Mo6BxSi10-x coating by laser cladding

High-entropy alloy coating has huge potential application values in improving the service life of the friction parts. The effects of the B-Si ratio and laser remelting on the microstructure, phases, mechanical and wear properties of the laser cladding Fe10Co10Ni10Cr4Mo6BxSi10-x coatings were investigated. When x equals 10, the coating crystalizes in a FCC structure together with lots of MxB phases. Si element adding promotes the formation of BCC phase of Fe10Co10Ni10Cr4Mo6BxSi10-x coatings with the appearance of new MxSi and MxBSiy phases, but prevents the formation of MxB and MxBSiy with the decrease of B-Si ratio. When x drops to zero, the microstructure of the coating transforms into a BCC with tiny amounts of FCC and MxSi phase. With the increase of Si element content, Mx(B, Si) standing for any combination of MxB, MxSi and MxBSiy phases decrease. The lowest friction coefficient (0.3786) and wear volume loss (2.46 × 106 μm3) show that Fe10Co10Ni10Cr4Mo6B5Si5 coating has the best wear resistance because of a higher toughness and values of H/E and H3/E2. Laser remelting once reduces the component segregation of the coating, and promotes the formation of BCC and Mx(B, Si) phases. The wear resistance of the coating increases with the improvement of its wear characteristics (H/E, H3/E2 and η). However, when the coating is remelted twice, the wear resistance decreases due to the drop of the hardness and wear characteristics attributed to the dominant position of FCC structure. Fine and uniform microstructure, and proper proportion of hard phases (BCC and Mx(B, Si)) and soft phase (FCC) can increase the mechanical properties and wear resistance of Fe10Co10Ni10Cr4Mo6BxSi10-x coatings.

Structure-property relations of lightweight Ti-Sc-Zr-Nb-V high-entropy alloys

Recently, it has been a hot topic to explore lightweight high entropy alloys (HEAs) for their future potential application as engineering materials. In this work, novel lightweight Ti 22 Sc 22 Zr 22 Nb 17 V 17 , Ti 24 Sc 20 Zr 22 Nb 17 V 17 , Ti 24 Sc 22 Zr 20 Nb 17 V 17 , and Ti 26 Sc 20 Zr 20 Nb 17 V 17 HEAs were fabricated by rapid solidification. The phase constituents and microstructures of the HEAs in the cast and annealed states were characterized by X-ray diffraction spectrum (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), and energy dispersive spectrum (EDS), while their mechanical properties were also investigated in detail. The microstructures of the cast samples consist of the coarse equiaxed BCC dendrites with extremely heterogeneous chemical distributions and the intergranular structures that are made up of BCC and HCP precipitates. Both precipitates inside the intergranular structures exhibit slightly large worm-shaped and fine lamellar morphology features. After annealing at temperatures below 1273 K, the desolvation reaction occurs due to the strong solute redistribution, leading to the disappearance of the lamellar structures, the coarsening of the large worm-shaped BCC particles, and the solid phase separation of the equiaxed BCC dendrites. At 1273 K, the combined interaction from the eutectoid transformation and phase separation leads to the formation of the TiNbV-rich BCC, ScZr-rich HCP, and transitional BCC+HCP structures. Compared with reported lightweight HEAs (density ≤ 6.5 g/cm 3 ), the present HEAs in the cast and annealed states exhibit excellent comprehensive mechanical properties, which are attributed to the combined effect from the solid-solution strengthening, second phase strengthening, and fine-grained strengthening. The present studies provide potential candidates as lightweight high-temperature structural materials in the future. • Compositional variations and heat treatments on structure and properties of as-cast lightweight HEAs were investigated. • Phase types are well consistent with the calculation prediction. • Dendritic intergranular regions contain some worm-shaped and fine lamellar BCC particles and HCP precipitates. • Low-temperature annealing induces strong solute redistribution within BCC and HCP phases. • Annealing at 1273 K induces the eutectoid transformation and phase separation.

Wear and Corrosion Resistance of FeCoCrxNiAl High-Entropy Alloy Coatings Fabricated by Laser Cladding on Q345 Welded Joint

High-entropy alloy (HEA) coatings on the surface of low-alloy steel by laser cladding can improve the corrosion and wear resistance, and the performance can be further improved by adding the Cr element. However, the effect of Cr content on the microstructure, hardness, wear and corrosion resistance of the coatings on the welded joint has not been completely understood in the literature. This paper aims at revealing the influence of Cr content on the microstructure and properties of laser-cladded FeCoCrxNiAl HEA on different regions of Q345 welded structure. The results indicate that FeCoCrxNiAl HEA coating has good metallurgical bonding with the Q345 welded surface. The increase of Cr element content in the powder plays an important role in energy absorption of powder and substrate, affecting the dilution rate and diffusion of Fe from the substrate to HEA coating. The HEA coating is mainly composed of the face-centered cubic phase (FCC) and body-centered cubic phase (BCC). When x = 1.5, the actual Cr element content of coating is the highest, which promotes the formation of hard brittle phase BCC, and subsequently affects the hardness and wear resistance of the sample. Meanwhile, the corrosion resistance increases and then decreases, and reaches the highest when x = 1.5. Due to the existence of Cr and other elements with good corrosion resistance in the HEA coating, a dense oxide film can be formed in 3.5 wt.% NaCl solution and neutral salt spray environment to prevent the corrosion from continuing, which can effectively improve the corrosion resistance of each region of the welded joint, and the protective efficiencies on the weld bead (WB), heat-affected zone (HAZ) and base metal (BM) are 99.1, 98.4 and 96.6%, respectively.

Effects of Nb Additions and Heat Treatments on the Microstructure, Hardness and Wear Resistance of CuNiCrSiCoTiNbx High-Entropy Alloys.

In this research, a set of CuNiCrSiCoTi (H-0Nb), CuNiCrSiCoTiNb0.5 (H-0.5Nb) and CuNiCrSiCoTiNb1 (H-1Nb) high-entropy alloys (HEAs) were melted in a vacuum induction furnace. The effects of Nb additions on the microstructure, hardness, and wear behavior of these HEAs (compared with a CuBe commercial alloy) in the as-cast (AC) condition, and after solution (SHT) and aging (AT) heat treatments, were investigated using X-ray diffraction, optical microscopy, and electron microscopy. A ball-on-disc configuration tribometer was used to study wear behavior. XRD and SEM results showed that an increase in Nb additions and modification by heat treatment (HT) favored the formation of BCC and FCC crystal structures (CS), dendritic regions, and the precipitation of phases that promoted microstructure refinement during solidification. Increases in hardness of HEA systems were recorded after heat treatment and Nb additions. Maximum hardness values were recorded for the H-1Nb alloy with measured increases from 107.53 HRB (AC) to 112.98 HRB, and from 1104 HV to 1230 HV (aged for 60 min). However, the increase in hardness caused by Nb additions did not contribute to wear resistance response. This can be attributed to a high distribution of precipitated phases rich in high-hardness NiSiTi and CrSi. Finally, the H-0Nb alloy exhibited the best wear resistance behavior in the aged condition of 30 min, with a material loss of 0.92 mm3.

Effect of Al content on microstructure and mechanical properties of atmosphere plasma sprayed AlxCoCrFeNi high-entropy alloy coatings under post-annealing

In this work, AlxCoCrFeNi (x = 0.2, 0.5, 1.0) high-entropy alloy (HEA) coatings were fabricated by atmosphere plasma spraying (APS) and then annealed at 600, 800, 1000 °C under Ar atmosphere. The as-sprayed HEAs exhibited lamellar microstructure of alloy phase with oxide strips. The Al content showed a positive and negative correlation with the formation of BCC (A2/B2) and FCC (A1) in the coatings, respectively. A symbiotic relationship between FCC and oxides was first proposed. During annealing, the transformation from mixed BCC to A2/B2 in HEA coatings was dominated by Al content, thus leading to unique microstructure at different temperatures. The hardness of as-annealed HEAs was determined by the morphology and distribution of Al-rich BCC phase. The HEA coating with higher Al content (x = 1.0) could keep high hardness under elevated annealing temperatures. While the coating with lower Al content (x = 0.2) showed stability both in microstructure and mechanical properties.

Analysis of structure formation processes features in high-entropy alloys of Al-Co-Cr-Fe-Ni system during laser alloying

Using the time dependent nucleation theory, the temperature dependences of the heterogeneous nucleation time for multicomponent substitution solid solutions, the formation of which is typical for high-entropy alloys in Al–Co–Cr–Fe–Ni systems obtained by laser alloying, were calculated. It is established that taking into account the melt cooling rate leads to an increase in the minimum nucleation time. The cooling rates at which the BCC (B2) and FCC phases critical radius nucleus not formed are estimated. The intervals of melt cooling rates in which the formation of single-phase BCC (B2) - or two-phase (BCC (B2) + FCC) - alloys is estimated. The influence of chemical composition on the change of these cooling rates is analyzed.

Formation of hypoeutectic structure and strengthening mechanism of Co4Cr1.5Fe1.5Ni5 high entropy alloy alloyed by Al

To reveal the phase formation mechanism and the strengthening mechanism, the AlxCo4Cr1.5Fe1.5Ni5 alloys (x = 1.0, 1.2, 1.4, 1.6, 1.8, 2.0) were prepared by arc melting. Phase formation and prediction, tensile properties, strengthening mechanism and deformation mechanism were researched in detail. Results show that the microstructure of AlxCo4Cr1.5Fe1.5Ni5 alloys changes from single FCC phases (x ≤ 1.4)) to FCC and BCC phases (x＞1.4), which was in good agreement with the calculated phase diagram (CALPHAD) prediction. The lower mixing enthalpy of Ni-Al leads to the segregation of Al element at the inter-dendritic region, which promotes the formation of BCC and FCC lamellar structure in hypoeutectic Al2Co4Cr1.5Fe1.5Ni5 alloy. The ultimate tensile strength of Al2Co4Cr1.5Fe1.5Ni5 alloy is 835 MPa, meanwhile the fracture strain is 31.8 %. The tensile strength of Al2Co4Cr1.5Fe1.5Ni5 alloy is attributed to the interface strengthening and the solid solution strengthening. The massive cross slip of dislocations in primary FCC phases and the dense dislocations blocked by the FCC-BCC interface increase the tensile strength. The interface barrier strength of the BCC-FCC interface in Al2Co4Cr1.5Fe1.5Ni5 alloy was estimated to be 3.9 GPa, which shows the higher barrier strength than conventional BCC-FCC interfaces. Coupled effects of the primary FCC and the lamellar structure of FCC and BCC phases will maintain good mechanical properties.

Learning phase selection and assemblages in High-Entropy Alloys through a stochastic ensemble-averaging model

Efficient alloy design requires a knowledge of phase selection, phase-fractions and microstructure of the material. Prediction of the phase equilibria, though well-established for traditional alloys, is still an open challenge for novel materials and concentrated multicomponent systems such as the High-Entropy Alloys (HEAs). In this paper, we present a novel data-driven approach for learning the phase-equilibria in HEAs through the use of a stochastic ensemble averaging method. The proposed model employs a model-averaging technique on an ensemble of 150 artificial neural networks that have been trained on a 323 alloy dataset. A seven-label classification is presented using a three-element vector description of phases. This allows us to fit the classification boundaries to a relatively larger number of phase combination labels while using only three target parameters for training thereby improving accuracy. The phase prediction capabilities (i.e., formation of FCC, BCC, intermetallics or different combinations of these phases) were tested on 320 alloys outside of the training dataset. Additionally, quantitative estimate of the phase equilibria, i.e., relative phase-fractions, were estimated and compared with experimental measurements and CALPHAD predictions in three different high-entropy systems, viz., Fex-Niy-(AlCoCr0.5)1-x-y, Alx-Tiy-(CrFeNi)1-x-y and Crx-Moy-(VNbTi)1-x-y. The model’s capability of going a step beyond current state-of-the-art model allows greater insights into target composition spaces for the alloy designer and establishes the first such approach for HEAs.

Microstructural, magnetic, and geometrical thermodynamic investigation of FeCoNi(MnSi)x (0.0, 0.1, 0.25, 0.5, 0.75, 1.0) high entropy alloys

In the current investigation, FeCoNi(MnSi)x (x=0.0,0.1,0.25,0.5,0.75,1.0) high entropy alloys (HEAs) were effectively processed by mechanical alloying (MA) route. The impact of Mn and Si on the FeCoNi system was further analyzed based on structural, morphological, and magnetic properties utilizing X-ray diffraction (XRD), scanning electron microscopy (SEM), and vibrating sample magnetometer (VSM) at various processing stages. The results showed the formation of the Fe-rich BCC (major) + Ni-rich FCC (minor) phase in FeCoNi(MnSi)x (x=0.0,0.1,0.25) alloys however the Ni-rich FCC phase was significantly more recognizable in the case of FeCoNi(MnSi)x (x=0.5,0.75,1.0) HEAs. Furthermore, different symmetrical and asymmetrical geometrical thermodynamic models such as Muggianu, Lück chou, Kohler, Colinet, Hillert, Toop, and General solution model (GSM) were modeled using the Redlich-Kister formalism and then correlated the enthalpy value with the developed phases during MA. In the case of the GSM model, the enthalpy of mixing (ΔHmixGSM) was found to be negative in a whole concentration range of (MnSi)x at 1237 K and exhibited solid solution criteria confirmed from the enthalpy of mixing (ΔHmixMiedema) according to the Miedema model. Moreover, the associated activity coefficient (γa) revealed a negative deviation as Mn-Si content increased. Additionally, the magnetic properties showed a ferromagnetic nature, and its parameters were calculated from the "law of approach to saturation."

Solidification microstructure and phase transition of La-Nd-Fe alloys

The solidification microstructure and phase transition of ten La-Nd-Fe alloys were studied experimentally by scanning electron microscopy (SEM) with energy dispersive x-ray spectroscopy (EDS) and differential thermal analysis (DTA). Phase compositions and phase transition temperatures of La-Nd-Fe alloys were measured and the formed phases were identified. The solidification behavior of La-Nd-Fe alloys was analyzed based on the experimental results of both solidification microstructure and phase transitions with the reported Nd-Fe, La-Fe and La-Nd sub-binary phase diagrams. The results indicated that the solidification processes of all La-Nd-Fe alloys begin with the precipitation of primary phase fcc(γ-Fe) and then follow by the formation of bcc(α-Fe) and/or Fe17Nd2 phases through different peritectic reactions. The solidification microstructure of three Fe65La29Nd6, Fe65La25Nd10 and Fe65La22Nd13 alloys presents three-phase microstructure with bcc(α-Fe), Fe17Nd2 and fcc(La,Nd) phases, while that of three Fe65La19Nd16, Fe65La9Nd26 and Fe65La15.5Nd19.5 alloys shows three-phase microstructure with bcc(α-Fe), Fe17Nd2 and dhcp(La,Nd) phases. The two-phase micorstructure with Fe17Nd2 and dhcp(La,Nd) ohases was formed in the solidification microstructure of four Fe65La12Nd23, Fe65La6.5Nd28.5, Fe65La4Nd31 and Fe65La1.5Nd33.5 alloys. Moreover, no stable ternary intermetallic compound was found in the present experiments. The solidification microstructure and phase transition of La-Nd-Fe alloys would provide a basis for the design of La-Nd-Fe-B magnetic alloys.

Novel phase decomposition, good soft-magnetic and mechanical properties for high-entropy (Fe0.25Co0.25Ni0.25Cr0.125Mn0.125)100–B (x = 9–13) amorphous alloys

Abstract As-spun (Fe0.25Co0.25Ni0.25Cr0.125Mn0.125)100–xBx (x = 9–13 at%) alloys are fully amorphous with bending plasticity and good soft-magnetic properties. Manganese addition favors amorphous phase formation at lower B content than in comparable alloys. On heating, the alloys transform: [am] → [am’ + bcc + fcc] → [fcc] at 9–11% B; and [am] → [am’ + bcc + fcc] → [bcc + fcc + borides] → [fcc + borides] at 12–13% B. Novel observations are the formation of metastable bcc + fcc phases, and an endotherm due to the [bcc + fcc] → [fcc] transition. The Vickers hardness of 9–11% B alloys is ∼650 in the as-spun state, shows a maximum of 1010 for [bcc + fcc] state and then decreases to 750 upon transition to [fcc]. As-cast 9–11% B 2-mm-diameter rods, mainly [bcc + fcc], exhibit compressive strength of 1520–1705 MPa and plastic strain >25%. These high-strength alloys, and the as-spun amorphous alloys with soft-magnetic properties, are encouraging for the further development of structural and functional materials.