D03 Phase Research Articles

Computational Assessment of Novel Predicted Compounds in Ni-Re Alloy System

Ab initio high-throughput efforts are continuously identifying new intermetallic compounds in a wide range of alloy systems that were previously thought to be well-characterized. While such predictions are likely valid near absolute zero, they carry the risk that such phases become unstable at the higher temperature relevant to typical synthesis conditions. We illustrate how this possibility can be rapidly tested by integrating Calphad modeling into the high-throughput loop. As an example, we investigate the Ni-Re system, in which D019 and D1a phases were predicted as possible intermetallic compounds. We confirm that these phases are indeed stable at practical synthesis temperatures and explain how they could have been overlooked in prior assessments.

Electronic structures and properties of TiAl/Ti2AlNb heterogeneous interfaces: A comprehensive first-principles study

The electronic structures and properties of ten TiAl/Ti2AlNb heterogeneous interfaces with three Ti2AlNb phases (B2, D019, O) and different terminations/boundaries were comprehensively studied via first-principles calculations. Their interfacial bonding features, strength and relative stability are quantitatively and qualitatively revealed by the equilibrium energy, Fermi energy, interfacial energy (γint), electron localization function and bonding charge density (Δρ), respectively. Accordingly, it was revealed by the partial and total electron density of states that the decreasing tendency of the bond strength in the order of Ti-Nb > Ti-Al > Nb-Al at the interfaces was attributed to the electrons hybridization of Ti-d states, Nb-d states and Al-p states. Since the γint decreased in the order of TiAl/B2 > TiAl/O > TiAl/D019, the TiAl/D019 interfaces with the lowest energy was regarded as the most stable phase boundaries and was further validated by the electron back-scattered diffraction analysis. It is found that the D019 phase is dominated at the interface boundaries while the B2 serves as a transition phase distributed on its both sides. On the contrary, the metastable O phase can form in the bulk Ti2AlNb but not at the interface due to their largest distortion when precipitating at the phase boundary. This work provides an insight into the atomic and electronic basis for the bonding and strengthening mechanisms of TiAl/Ti2AlNb heterogeneous interfaces.

Formation and magnetic properties of spark plasma sintered Mn3−δGa (δ = 0, 1) Heusler alloys: Experiment and theory

In this study, we synthesized D022 Mn3−δGa (δ = 0, 1) alloys using the spark plasma sintering method. The m(T) results confirmed the formation of the D022 phase with Tc≃ 780 K (710 K) for Mn3Ga (Mn2Ga). The alloys exhibited hard magnetic behavior with large room temperature spontaneous magnetization of ms(80 kOe) = 1.63 (0.83) μB/f.u. and coercivity of Hc = 4.28 (3.35) kOe for Mn3Ga (Mn2Ga). The magnetic properties were investigated further up to Tc and Hc (T) analysis using the Stoner–Wohlfarth model demonstrated the nucleation mechanism for the magnetization reversal. Calculations of the electronic density of states confirmed the magnetic contribution from two symmetrically inequivalent Mn sites in a Heusler-like tetragonal phase. Density functional theory calculations also showed that the ground state of D022 Mn2Ga was achieved by the removal of Mn atoms from the full Heusler Mn3Ga structure in accordance with the half-Heusler alloy structure, which supported the experimental observations.

Влияние температуры продолжительного отжига на структуру и магнитные свойства нанокристаллического сплава FeSiNbCuB

A dependence of the soft magnetic properties of the Fe73.5Si13.5Nb3Cu1B9 alloy on the temperature of annealing (Tan) carried out in air for 2 hours at temperatures from 520 to 620°C was investigated. It was shown that with Tan increasing, the magnetic hysteresis loop broadens significantly and becomes more inclined, and the Curie temperature of the amorphous matrix surrounding the α-FeSi nanocrystals decreases. The atomic structure and phase composition of the alloy samples were investigated by X-ray diffraction in transmission geometry. After annealing at temperatures of up to 580°C, nanocrystals contain predominantly D03 phase (Fe3Si stoichiometry) and have average size of about 7 nm. Their relative fraction in the alloy increases as the temperature increases due to the additional diffusion of iron from the matrix into the nanocrystals. After annealing at Tan ≥ 600°C, the average size of the nanocrystals increases, and reflections of iron boride crystals appear in the diffractograms. The deterioration of the soft magnetic properties of the Fe73.5Si13.5Nb3Cu1B9 nanocrystalline alloy, when the annealing temperature rises from 520 to 580°C, is explained by a decrease in the silicon concentration in Fe-Si nanocrystals, which leads to a growth of the constant of the magnetocrystalline anisotropy.

Evolution of microstructures and properties of SLM-manufactured Cu–15Ni–8Sn alloy during heat treatment

Abstract Due to the aging hardening nature of Cu–15Ni–8Sn alloy, it is necessary to investigate the effect of aging on the properties of SLM-manufactured Cu–15Ni–8Sn alloy. In the present work, first, microstructural evolution of the alloys that underwent the direct aging treatment, solution treatment, and solution treatment plus aging are investigated in detail using scanning electron microscopy (SEM) and transmission electron microscopy (TEM); and second, mechanical properties and electrical conductivity of these samples were measured. After solution treatment, it’s found that fine Sn-enriched precipitates resolved in matrix, an abundance of dislocation diminished, the grain size increased and a number of annealing twins formed. Spinodal decomposition could happen during the cooling of solution-treatment. According to the comparison of the microstructure and performance of the printed sample and the solution treated sample after aging, it’s concluded that the strength and conductivity of the aged SLM-manufactured samples are higher than that of the aged solution-treatment samples for same aging duration, however, the plasticity and aging strengthening effect is inverted. The sharp decrement of plasticity is mainly ascribed to network discontinuous precipitations (DPs) in the grain boundary, but not the lamellar DPs. Annealing twin boundaries depressed the formation of DPs in the grain boundary, and improved the plasticity of aged solution-treatment samples. Lamellar DPs were also considered to be enhanced the strength of aged samples, besides modulated structures, D022 phase and L12 phase.

Distribution of transition metal elements in an Al-Si-Cu-based alloy

An Al-Si-Cu-based cast alloy was modified with transition metal elements Zr, V and Ti to achieve enhanced mechanical performance at elevated temperatures. Multiple microstructural characterization techniques were used to investigate the solidification segregation behavior of these transition metal elements and their partitioning to the primary intermetallic phases and secondary precipitates. Three transition metal elements were shown to segregate into the dendrite center to varying degrees. Two primary intermetallic phases enriched with different amounts of transition metal elements were identified as D022 and D023 phases. Zr was observed to concentrate much more than V and Ti in the nano-size secondary L12 precipitates, which formed in the matrix during post-solidification heat treatment.

Boron interaction with D03 phase in Fe-(27–29)Ga alloys

Two Fe–Ga alloys with 27 and 29% Ga additionally alloyed with boron (B) were studied using neutron diffraction, scanning electron microscopy with energy dispersive spectroscopy, and magnetostriction measurements. Neutron diffraction experiments demonstrated that the preponderant phase is the cubic Fe3Ga with structure D03. The lattice parameter of the Fe3Ga phase is much larger than the expected if the Ga composition of this phase is considered. The conclusion is that boron enters in the interstitial octahedral sites of the D03 lattice causing the lattice expansion, whose result is supported by ab initio calculations. Consequently, an increase on the magnetostriction is attributed to B located at the interstices that introduces local strains in the lattice. It is also suggested that the expansion of the lattice may increase Ga solubility in the D03 phase.

Magneto-mechanical properties of Fe100-xAlx alloys (x = 14-27) prepared by directional solidification

The magneto-mechanical properties, including ΔE and damping capacity, magnetic properties, magnetostriction, and phase constitutions of Fe100-xAlx alloys, prepared by directional solidification (DS) are systematically studied. The remarkable ΔE effect of 10.1%, magnetostriction (Δλ) of 141 ppm, dλ///dH of 0.43 ppm/Oe, magneto-mechanical coupling (K) of 48%, and damping capacity of 6.0% reached for Fe81Al19 alloy favor for applications. The increased Δλ with increasing x from 14 to 19, possibly related to increased amount of Al-Al pairs, largely improves dλ///dH and therefore ΔE and damping capacity. Nevertheless, the formation and growth of D03 phase for higher Al content (x = 23-27) results in the reduced Δλ and dλ///dH, and therefore K, ΔE effect, and damping capacity. The proportional relation between ΔEs/E0 and K2 suggests that the experimentally ΔEs/E0 is consistent with theoretically calculated K2. Additionally, the proportional relation between the experimentally measured ζ and theoretically estimated (ΔW/W)eth suggests the change of damping capacity with H is mainly governed by the micro eddy-current mechanism resulted from magnetic domain wall motion. Most importantly, the experimental result suggests a cost-effective method to attain remarkable magneto-mechanical properties for Fe81Al19 alloy.

Phase-field simulation on microstructure evolution of D019 phase in γ/γ′ structure of Co–Al–W superalloys

The morphological evolution and precipitation kinetics of γ′ and D019(Co3W) phase in Co–Al–W alloys at 900 °C have been studied by applying Phase-field method and experiment in order to understand the transformation process of γ′ phase and D019 phase. The growth processes of D019 phase and precipitation of γ′ phase under elastic fields were simulated through coupling with thermodynamics and dynamics databases. The simulation results indicate that the misfit δ ≥ 0.53% has a greater impact on γ′ particle morphology in γ/γ′ structure. Co–Al–W alloy with low Al and high W is one of the factors to promote the precipitation of D019 phase. Three stages during aging, namely the γ′ phase incubation stage, the γ′ phase fast nucleation and growth stage, and the transformation from γ′ phase to D019 phase stage can be observed with the non-constant coarsening rate that varying with the decrease of γ′ phase. The particle size distribution(PSD) during the precipitation of D019 phase is more in line with MLSW theory than LSW theory. This simulation results are in good agreement with the experiment results to help analyze microstructure evolution of Co–Al–W alloy.

Formation mechanism of tetragonal nanoprecipitates in Fe–Ga alloys that dominate the material's large magnetostriction

Up to now, the formation mechanism of tetragonal nanoprecipitates that may dominate the large magnetostriction of Fe–Ga alloys remains unclear. Here we found that both L60- and D022-type face-centered-tetragonal nanoprecipitates are precursors of the face-centered-cubic L12 equilibrium phase, as identified in the isothermally-aged Fe73Ga27 and Fe74Ga26 alloys, respectively. The L60 phase is formed due to Ga ordering along -A2 direction and simultaneous lattice distortion. The D022 phase is formed via diffusionless lattice distortion when the D03 ordering degree is sufficient high. These findings may provide a microstructural basis for the large magnetostriction induced by soluting nonmagnetic Ga into body-centered-cubic Fe.

Microstructural Instability and Precipitation Behaviors of Intermetallic Phases in a Nb-Containing CoNi-Based Superalloy

Exploring the alloying effect of various elements plays a crucial role in optimizing the alloy design for superalloys. In this study, the influence of Nb additions on a γ′-strengthening CoNi-based superalloy has been investigated. Undesirable intermetallic phases including the topologically close-packed D85 phase and the ordered D019 phase were observed to preferentially form in the dendritic and interdendritic regions of the investigated alloy, respectively. Precipitation behaviors of the D019 phase and the D85 phase including growth mechanisms and crystallographic orientation relationships have been characterized and analyzed in detail using advanced electron microscopy techniques. First-principle calculations using density function theory have been carried out to evaluate the effect of Nb additions on the thermodynamic stability of the L12-γ′ phase. It turns out that the supercell with L12 structure would be energetically destabilized when the Nb-substituted atom sits on the Co or Al sites, which could correspond to the microstructural instability of the Nb-containing CoNi-based superalloy.

Effects of Iron Addition on the Microstructures and Mechanical Properties of Two-Phase Ni3Al-Ni3V Intermetallic Alloys

Microstructures and mechanical properties of dual two-phase Ni3Al (L12)-Ni3V (D022) intermetallic alloys to which iron (Fe) was added in different substitution manners were investigated by scanning electron microscopy, transmission microscopy, Vickers hardness, and tensile tests. Primary Ni3Al precipitates were extremely fine in the alloys in which Fe was substituted for Al. The changes of the volume fraction in the Ni3Al precipitates by the addition of Fe were explained in association with the partition behavior of Fe into the constituent phases and the relative content of Al to V which was affected by the substitution manner of Fe. The microstructures in the channel region of the alloys in which Fe was substituted for Ni, Al, and V were suggested to be comprised of L12 and D022 phases, L12, D022 , and Ni slid solution (A1) phases, and A1 phase, respectively. From the partition coefficients of Fe estimated using the alloys constituted by L12, D022 , and A1 phases, it was shown that Fe evenly destabilizes the two intermetallic phases. For the alloys in which Fe was substituted for Al and V, the yield strength (or hardness) decreased and the tensile elongation conversely increased with increasing Fe content. For the alloys in which Fe was substituted for Ni, the tensile elongation as well as strength remained unchanged. The changes of the strength (hardness) as well as tensile elongation in the alloys in which Fe was substituted for Al and V were attributed to the imperfect ordering in the two intermetallic phases and/or the presence of the Ni solid solution (A1) phase.

Effects of Ordering in Fe-xAl Alloys

The evolution of the structurally different phases and of the microstructural state of Fe-xAl alloys is studied in neutron diffraction experiments performed in the high resolution and continuous temperature scanning modes. It is found that the D03 phase in a weakly nonequilibrium state of alloys occurring in the doping range from x ≈ 23 to x ≈ 31 at % has the form of nanoclusters (L ≈ 100–800 A) dispersed within a host material (matrix) such as the disordered (A2) or partially ordered (B2) phase. The B2 → D03 → B2 → A2 phase transitions are accompanied by a decrease or increase in the lattice parameters of these phases in the course of ordering or disordering of the atomic structure, respectively. In this situation, the lattice parameters of both the matrix and clusters change simultaneously and a high degree of coherence of the crystal lattices of the matrix and clusters is observed.

Finding a New B1-Type Phase in Single Crystals of Fe–Al and Fe–Ga Soft Magnetic Alloys

The atomic structure of Fe–Al (7 and 9 at % Al) and Fe–Ga (18 at % Ga) alloys is studied by X‑ray diffraction using a laboratory four-circle diffractometer. After refining annealing, single-crystal alloy samples were annealed in the ferromagnetic state (T TC), was quenched in room temperature water. Earlier, the authors reported on the peculiarities of the ordering of alloying atoms in B2 and D03 phase structures in quenched and annealed samples of these alloys. Here, we present and discuss the results of our observations in these alloys of a new phase with a face-centered cubic (fcc) lattice (B1-type structure with NaCl prototype and unit cell parameter ~5.2 nm). The fcc phase appears in the Fe–Al alloy as the aluminum concentration increases from 7 to 9 at %; it is observed in the Fe–18 at % Ga alloy, and its volume fraction increases after annealing in the ferromagnetic state in comparison with a quenched alloy sample. In these alloys (9 at % Al) and (18 at % Ga), different ways of embedding fcc crystals in the bcc phase of single crystals are realized; i.e., the axes of the fcc lattice are directed in four different ways relative to the axes of the bcc lattice.

Itinerant Semiconducting Antiferromagnetism in Metastable V3Ga

Herein, a metastable phase of β‐W type V3Ga is identified to exhibit an itinerant semiconducting antiferromagnetism. Density functional theory plus Hubbard U (DFT+U) calculations predict the β‐W type structure as a possible metastable phase, although energetically less favorable than the previously known D03 phase, which is successfully synthesized with good crystallinity by alternating evaporation method with postannealing process rather than traditional coevaporation method. Such a metastable β‐W phase results in an antiferromagnetic (AFM) order up to at least 500 K and highly conductive semiconducting behavior. The antiferromagnetism in the β‐W type V3Ga can be understood in terms of strong Coulomb repulsion and Hund's rule coupling between the nearest neighbor V 3d orbital states and their covalent bonding with the Ga 4p orbitals. These results are further verified by an exchange bias phenomenon revealed in antiferro/ferromagnet hybrid heterostructure of V3Ga and Fe films, where the strong hybridization between Fe 3d and V 3d orbital states at the interface gives rise to the robust perpendicular magnetic anisotropy therein. Herein, a novel route is used to prepare an AFM semiconductor material for antiferromagnet spintronics.

Thermodynamic and mechanical stability of Ni3X-type intermetallic compounds

Ni3X-type intermetallic compounds, also often referred to as γ′, γ″, and η precipitates in Ni-base alloys, have been investigated by first-principles methods. Thermodynamic and mechanical stability of Ni3X (X = Al, Ti, Nb, Mo, Fe, and Cr) compounds has been determined by density functional theory calculations of formation enthalpies and elastic properties of their L12, D022 and D024 phases. In addition, we have investigated the site preference behavior of Al, Ti, Nb, Mo, Fe, and Cr solutes in the L12-structure Ni3Al, Ni3Ti, and Ni3Nb intermetallic compounds and used this information to investigate the solubility of the aforementioned alloying elements. Our results show that the most stable structures of Ni3Al, Ni3Ti, Ni3Nb, Ni3Cr, Ni3Mo, and Ni3Fe at 0 K are L12, D024,D022, D024, D022, and L12 respectively.

Cooling rate as a tool of tailoring structure of Fe-(9–33%)Ga alloys

A huge difference between the structure and the properties of equilibrium and metastable Fe–Ga alloys along with an uncertain specification for their metastable state lead to urgent necessity of understanding the cooling rate role in the formation of the alloys structure. We studied structure of Fe-(9-33 at.%)Ga alloys after cooling with different cooling rates (furnace, air, water, as cast) and report structure and dependencies of lattice parameter for A2 and D03 phases on Ga content in Fe–Ga alloys. The first and second critical cooling rates are determined as the beginning and the end of formation of equilibrium L12 phase.

Synchronously enhanced mechanical and damping properties of Fe-18Ga alloy by mechanical treatment

High-damping Fe-18Ga alloy (HDA Fe-18Ga) with enhanced mechanical properties was developed by the treatment successively consisting of hot rolling, water quenching, and tempering. Microstructure characterizations were performed by means of EBSD, SEM, XRD, TEM, and Bitter method. Combining these results with macro-mechanical and damping tests, we systematically studied the effects of deformation and annealing temperature on the mechanical and damping properties of HDA Fe-18Ga, and the relationship between texture and damping was established. It was found with increasing the total deformation, the mechanical strength of the alloy increases, while the plasticity increases firstly and then decreases. This is mainly due to the fact that grain refinement and cracks reduction optimize the strength and ductility of HDA Fe-18Ga during the hot rolling process. As the total deformation reaches a certain level of ∼53%, it lead to dislocation pinning and work hardening resulting in the phenomenon of increased strength and decreased plasticity. When HDA Fe-18Ga plates annealed at 600 °C, the mechanical strength and plasticity were further improved owing to the precipitation of the nano-scale D03 phase. Meanwhile, during the tempering process, the dagger shaped domains decrease, and the 90° maze domains appear, resulting in an increase in the damping capacity of HDA Fe-18Ga.

Comparative study of structure and phase transitions in Fe-(25–27)%Ga alloys

A wide range of complementary research technique - XRD, SEM, TEM, MFM, HV, and low temperature heat capacity, in situ neutron diffraction, resistivity, vibrating sample magnetometry, internal friction, dilatometry, and differential scanning calorimetry - is applied to study structure and phase transitions at heating and cooling of two Fe–Ga functional alloys with 25 and 27 at.% Ga. Using high resolution neutron diffraction, it is unambiguously proven that the initial state of both as-cast samples at room temperature is the D03 phase which results from ordering of the high temperature A2 phase during cooling. Heating of as-cast samples and their subsequent cooling leads to a cascade of phase transitions which change the samples’ structural, mechanical and physical properties. These transitions and properties are discussed in the paper. Transition from metastable D03 to stable L12 phase at heating or isothermal annealing leads to significant changes in macro (grain size) and micro (ordering) structure, hardness and magnetic properties (magnetostriction, magnetization). According to our structural studies (ND, XRD), composition Fe-25.5 at.%Ga below ∼600 °C belongs to a single phase (L12) range of the equilibrium phase diagram, while in the Fe-26.9Ga alloy some amount of the D019 phase is also present.

Significant enhancement of ΔE effect in Fe87Ga13 alloy by doping 0.2 at% Dy

We present the effects of Dy additives on the ΔE and ΔG effects, magnetic properties, magnetostriction sensivity, magneto-mechanical coupling, and phase constitutions of Fe87Ga13Dyx alloys, prepared by vacuum induction-melting and then water-quenching. ΔE and ΔG effects, permeability (μR), dλ///dH, and magneto-mechanical coupling (K) are significantly enhanced by doping 0.2 at% Dy. The attractive ΔE/E0 of 5% at very small H = 0.10 kOe and a significant enhancement of about 100% from 6.1% to 12.0% in ΔE/E0 at H = 2.5 kOe (ΔEs/E0) achieved for Fe86.8Ga13Dy0.2 alloy favors for applications. The enhanced μR indicates magnetic softening. The increased amount of modified D03 phase and magnetic softening contribute to remarkable enhancements in dλ///dH, accordingly ΔE and ΔG effects, and K. Nevertheless, higher Dy content (x = 2.0) reduces the amount of modified D03 phase, μR, dλ///dH, and therefore K, ΔE, and ΔG effects. The proportional relation between ΔEs/E0 and K2 suggests that the experimentally ΔEs/E0 is consistent with theoretically calculated K2. This work provides an effective method for significantly enhancing the ΔE and ΔG effects and magnetostriction sensitivity for Galfenol alloys.