Pseudo-ternary Alloys Research Articles

The varying nature of the martensitic phase transition and associated entropy changes in a Co and Cr doped pseudo-ternary Heusler alloy system

We have investigated the magnetostructural phase transitions and the associated entropy changes in a system of three Heusler alloys, namely: Ni2Mn0.55Cr0.45Ga, Ni2Mn0.55Co0.10Cr0.35Ga, and Ni2.15Mn0.75Cr0.1Ga. All three alloys exhibited first-order martensitic phase transition. An inter-martensitic phase transition raised the magnetic and structural phase transition temperatures, and partially decoupled the said transitions. Furthermore, field magnetization measurements demonstrated that a significant reduction in magnetic hysteresis is achieved in the Ni2Mn0.55Co0.10Cr0.35Ga compound, resulting in improved effective refrigerant capacity values. The largest magnetic entropy change of −23.5 J/kg K and refrigeration capacity of 97.7 J/kg were observed in Ni2.15Mn0.75Cr0.1Ga. This observation of mitigated deficiencies in materials experiencing a first-order phase transition is relevant towards their application in magnetic refrigeration.

Enhanced Thermoelectric Properties of Nb-Doped Ti(FeCoNi)Sb Pseudo-Ternary Half-Heusler Alloys Prepared Using the Microwave Method.

Pseudo-ternary half-Heusler thermoelectric materials, which are formed by filling the B sites of traditional ternary half-Heusler thermoelectric materials of ABX with equal atomic proportions of various elements, have attracted more and more attention due to their lower intrinsic lattice thermal conductivity. High-purity and relatively dense Ti1-xNbx(FeCoNi)Sb (x = 0, 0.01, 0.03, 0.05, 0.07 and 0.1) alloys were prepared via microwave synthesis combined with rapid hot-pressing sintering, and their thermoelectric properties are investigated in this work. The Seebeck coefficient was markedly increased via Nb substitution at Ti sites, which resulted in the optimized power factor of 1.45 μWcm-1K-2 for n-type Ti0.93Nb0.07(FeCoNi)Sb at 750 K. In addition, the lattice thermal conductivity was largely decreased due to the increase in phonon scattering caused by point defects, mass fluctuation and strain fluctuation introduced by Nb-doping. At 750 K, the lattice thermal conductivity of Ti0.97Nb0.03(FeCoNi)Sb is 2.37 Wm-1K-1, which is 55% and 23% lower than that of TiCoSb and Ti(FeCoNi)Sb, respectively. Compared with TiCoSb, the ZT of the Ti1-xNbx(FeCoNi)Sb samples were significantly increased. The average ZT values of the Nb-doped pseudo-ternary half-Heusler samples were dozens of times that of the TiCoSb prepared using the same process.

Magnetic enhancement of ferroelectric polarization in a particulate multiferroic composite derived in situ via additive assisted sintering of a pseudo ternary alloy system BiFeO3–PbTiO3–DyFeO3

We report here the synthesis of a self-grown 0–3 particulate multiferroic composite by controlled precipitation of the ferrimagnetic garnet phase using additive (MnO2) assisted sintering of a multi-cation ferroelectric system (Bi, Pb, Dy)(Fe, Ti)O3. The particulate multiferroic composite derived in this manner exhibits a favorable microstructure, wherein, although the volume fraction of the garnet phase is kept low (6%), which helps in retaining the electrical insulating character of the specimen, the number fraction of the garnet grains vis-à-vis the ferroelectric grains is ∼1:1. The composite shows a nearly ∼50% increase in saturation polarization at room temperature under a modest magnetic field of 1 T, suggesting a considerable improvement in ferroelectric domain switching due to the efficient strain transfer from the minority garnet grains to the majority piezoelectric grains.

Development of Mischmetal-Fe-Co-B Permanent Magnet Alloys via High-Throughput Methods.

Additive manufacturing synthesis using laser engineered net shaping (LENS) is utilized to rapidly print libraries of mischmetal (MM = La, Ce, Nd, and Pr) containing R2TM14B alloys (R = MM + separated Nd and TM = Fe and Co) enabling robust evaluation of physical properties over a wide composition range. High-throughput characterization of the magnetic and thermal properties are used to identify compositions for potential high-temperature, high-performance permanent magnets with reduced critical rare-earth elements. Improved Curie temperature (Tc ∼ 450 °C) is obtained with substitution of Fe by Co in pseudoternary R2TM14B alloys. Furthermore, a 4-fold decrease in the Nd content can be achieved through substitution with less critical Ce- and La-rich MM, while retaining high Tc. Guided by the properties of the LENS printed samples, selected compositions with and without TiC additions are synthesized via melt-spinning techniques to produce nanostructured ribbons. The maximum room temperature coercivity (Hc) and energy product ((BH)max) without TiC are found to be 5.8 kOe, 8.5 MGOe, respectively, while TiC additions as a grain refiner gave Hc and (BH)max of 4.9 kOe, 9.8 MGOe, respectively. Structural characterization of the melt-spun ribbons shows homogeneous grain refinement with TiC additions, which leads to an increase in the energy product.

Electrostrain in excess of 1% in polycrystalline piezoelectrics.

Piezoelectric actuators transform electrical energy into mechanical energy, and because of their compactness, quick response time and accurate displacement, they are sought after in many applications. Polycrystalline piezoelectric ceramics are technologically more appealing than single crystals due to their simpler and less expensive processing, but have yet to display electrostrain values that exceed 1%. Here we report a material design strategy wherein the efficient switching of ferroelectric-ferroelastic domains by an electric field is exploited to achieve a high electrostrain value of 1.3% in a pseudo-ternary ferroelectric alloy system, BiFeO3-PbTiO3-LaFeO3. Detailed structural investigations reveal that this electrostrain is associated with a combination of several factors: a large spontaneous lattice strain of the piezoelectric phase, domain miniaturization, a low-symmetry ferroelectric phase and a very large reverse switching of the non-180° domains. This insight for the design of a new class of polycrystalline piezoceramics with high electrostrains may be useful to develop alternatives to costly single-crystal actuators.

A complex lead-free (Na, Bi, Ba)(Ti, Fe)O3 single phase perovskite ceramic with a high energy-density and high discharge-efficiency for solid state capacitor applications

We have investigated a series of compositions in the pseudo-ternary lead-free alloy system Na1/2Bi1/2TiO3-BaTiO3-BiFeO3 with regard to its energy storage density and discharge efficiency. A composition 0.4(Na0.5Bi0.5TiO3)-0.225BaTiO3-0.375BiFeO3 of this series was identified to give the best energy density and discharge efficiency. While conventional sintering gave energy density of 0.77J/cm3 and discharge efficiency of 67%, we achieved a remarkable increase in energy storage density (∼1.4J/cm3) and discharge efficiency (∼90%) by using spark plasma sintering of this composition. Our results suggest that this alloy system can be a potential lead-free candidate for high electric energy storage and discharge efficiency.

Theoretical investigations of Co2Mn1-xCrxSn and Co2MnSn1-ySiy pseudo-ternary alloys: First principles calculations

The electronic and magnetic properties of Co2Mn1−xCrxSn and Co2MnSn1−ySiy alloys are investigated using density functional theory (DFT) within a full-potential linearized augmented-plane-wave (FP-LAPW) method. Amongst the systems under investigation, Co2MnSn1−ySiy alloys show half metallicity with 100% spin polarization at the Fermi level, however Co2Mn1−xCrxSn are found to be pseudo-half metals with few minority states at the Fermi level and high spin polarization. The substitution of Si with Sn keeps the magnetic moment constant in Co2MnSn1−ySiy alloys, whereas the substitution of Mn with Cr decreases the magnetic moment and degrade the half-metallicity in Co2Mn1−xCrxSn alloys. The Curie temperature is calculated and it is found to be about 928K for all Co2MnSn1−ySiy alloys, whereas it decreases linearly with x for Co2Mn1−xCrxSn alloys. The lattices constants, bulk modulii, energy gaps, polarization ratio and density of states are calculated and their variation versus x or y are discussed.

Electrical and magnetic properties of the Kondo system [formula omitted

Measurements of electrical resistivity ρ ( T ) , magnetoresistivity MR and magnetic susceptibility χ ( T ) are reported for the pseudo-ternary alloys ( Ce 1 - x Y x ) Pt 2 Si 2 . ρ ( T ) results reveal coherent Kondo scattering above 80% Ce concentration and a rapid evolution to single-ion Kondo scattering with an increase in Y concentration x. MR measurements on Ce alloys in the single-ion Kondo region are analyzed on the basis of calculations by Schlottmann for the Bethe-ansatz solution in the context of the Coqblin–Schrieffer model. The analysis yields values of the Kondo temperature T K and the effective moment of the Kondo ion μ K . χ ( T ) data above 120 K follow the Curie-Weiss relation for all the investigated concentrations and give effective moment values μ eff in close agreement with μ eff = 2.54 μ B expected for the Ce 3 + -ion.

Microstructure and mechanical property in dual two-phase intermetallic alloys composed of geometrically close-packed Ni 3X (X: Al and V) containing Nb

Dual two-phase intermetallic alloy, which is composed of Ni 3Al (L1 2) and Ni solid solution (A1) phases at high temperature and is refined by a eutectoid reaction during low temperature aging, was prepared on the basis of the Ni 3Al–Ni 3Nb–Ni 3V pseudo-ternary alloy system. The eutectoid reaction decomposes the A1 phase to a mixture of geometrically close packed (GCP) structures of Ni 3Al (L1 2) and Ni 3V (D0 22). Dual two-phase intermetallic alloys were characterized by scanning electron and transmission electron microscopy. High-temperature compression and tensile tests, and compression creep test were conducted. It was found that the dual two-phase intermetallic alloys showed high yield and tensile strength with good temperature retention, accompanied with reasonable tensile ductility. The dual two-phase intermetallic alloys showed lower creep rate than conventional Ni-base superalloys. Also, the present two-phase intermetallic alloys are superior to the counterparts containing Ti, and they are promising for the development of a new-type of high-temperature structural material.

Effect of Co substitution for Ni on the Ti–Zr–(Ni, Co) pseudo-ternary quasicrystal formation

A series of alloys designed along a Ti 9(Ni,Co) 4–Zr e/ a-variant line in the Ti–Zr–(Ni, Co) pseudo-ternary alloy system, are investigated by XRD and TEM. Experimental results show that bulk icosahedral quasicrystals (IQC) prepared by copper mold suction casting, can be obtained in a large region from Ti 55Zr 20(Ni,Co) 25 to Ti 34.6Zr 50(Ni,Co) 15.4 with Ni/Co ratio equal to 3/1, and in a sharply diminished region from Ti 48Zr 30(Ni,Co) 22 to Ti 42Zr 40(Ni,Co) 18 with decreased Ni/Co ratio equal to 2/2 or 1/3. Ti 48Zr 30Ni 16.5Co 5.5 is the optimal quasicrystal-forming composition, where a nearly pure bulk IQC phase is achieved. The stepwise substitutions of Co for Ni in this pseudo-ternary system contribute to the formation of Ti 2Ni, fcc-Zr 2Ni, C14-type Laves and β-(Ti, Zr) solid solution phases. However, these substitutions greatly reduce the forming ability of the IQC phase. It is suggested that Co is essentially unfavorable to Ti/Zr-based quasicrystal formation.

Development of Thermodynamic Description of a Pseudo-Ternary System for Multicomponent Ti64 Alloy

A method is presented to obtain a thermodynamic description of a multicomponent alloy system in terms of a pseudo-ternary formalism. In the present study, this method was applied to multicomponent Ti64 alloys with the “6” and “4” denoting the nominal 6 wt.% of Al and 4 wt.% of V in this class of Ti alloys. However these alloys, in practice, contain many other alloying elements such as O, C N, Fe, and H which exhibit appreciable effect on the thermodynamic properties of Ti64. The essence of this approach is to treat the multicomponent alloys as a pseudo-ternary Ti-Al x -V y , in which the apparent composition of Al x is the weighted summation of that of Al and those of the α-stabilizers in minor quantities such as O, C and N and that of V y is the weighted summation of that of V and those of the β stabilizing minor elements such as Fe and H. Three Ti64 alloys with slightly different chemistries were treated as pseudo-ternary alloys, and the β transus and β (and α) approach curves were calculated using this pseudo-ternary thermodynamic description. The calculated results were found to compare favorably with those calculated from a multicomponent thermodynamic database for titanium alloys. This study demonstrates that such a simplified thermodynamic description, when available, can be readily coupled with kinetic models for engineering applications. One example is to predict microstructure evolution of a multicomponent alloy when subjected to a specific heat treatment condition.

Effect of Systematic Changes of Ti and Hf Si-oxynitride Alloys by Nitrogen Incorporation as a Bond Constraint on Electrical and Material Properties

AbstractWe have investigated the effect of Si3N4 content in (Ti(Hf)O2)x(Si3N4)y(SiO2)1-x-y pseudo-ternary alloys by tracking systematic changes of electrical properties, including electrically active defects. Results from Soft x-ray photoelectron spectroscopy (SXPS) studies indicate no detectable hole traps for Ti/Hf Si oxynitrides with Si3N4 content >35%; these alloys have equal concentrations of Ti(Hf)O2 and SiO2, ~30-32%, and additionally are stable for annealing in Ar ambients to temperatures of 1100°C. Derivative near edge x-ray absorption spectroscopy (NEXAS) comparisons for the O K1 edges of TiO2 and optimized Ti Si oxynitride alloys provides a significantly reduced average crystal field d-state splitting from 1.9 to 1.6eV, as well as decreased electron trapping, and is correlated with a four-fold coordination of Ti in the Ti Si oxynitride alloys. The flat band voltage shift with varying frequency from 10 kHz to 1MHz in these alloys is less than 12 mV and the compositional dependence of current-voltage characteristics on Si3N4 composition results in the lowest leakage current at a Si3N4 content of ~40 % with the smallest equivalent oxide thickness (EOT) as well. Based on these studies, Transition Metal (TM) Si oxynitride alloys are anticipated to yield EOT <1 nm for scaled CMOS devises.

Magnetic and electrical properties of the UCu 2T 3Al 7 alloys

The UCu 2T 3Al 7-type compounds with T = Cr, Mn and Fe crystallize in the tetragonal ThMn 12-type structure ( I4/ mmm space group). Magnetic properties have been examined in magnetic fields up to 50 kOe in the temperature range 1.9–400 K using a SQUID magnetometer. The Cr based pseudoternary alloy is paramagnetic with the linear field dependence of the magnetization at 1.9 K. The temperature dependence of the magnetic susceptibility is described by a modified Curie–Weiss (MCW) law. The Mn containing compound is ferrimagnetic and the field dependence of the magnetization does not reach saturation while the magnetic susceptibility follows the MCW law at high temperature. The Fe alloy is ferromagnetic and at higher temperature the MCW law is fulfilled. The temperature dependence of the electrical resistivity of all materials was examined between 4.2 and 300 K showing metallic character. The Mn and Fe based compounds demonstrate some anomalies in the ρ( T) plot at low temperature. The results are discussed in relation to the anomalies observed in magnetic measurements.

Magnetic properties of 3d impurities in GaAs

Electronic structure, thermodynamic, and magnetic properties of 3d-transition metal (TM) impurities in GaAs have been studied from first principles using Green's function approach. The studied TM impurities (V, Cr, Mn, and Fe) are found to form substitutional alloys on the Ga sublattice. The possibility of raising the Curie temperature T C in (GaMn)As by co-doping it with Cr impurities was examined on the basis of total energy difference between the disordered local moment (DLM) and the ferromagnetically ordered (FM) spin configurations. The calculated Curie temperature and magnetic moment have maxima for GaAs doped with Cr and Mn. The magnetic properties of Mn-doped GaAs are shown to be more sensitive to antisite As defects than those of Cr-doped GaAs. However, the Cr impurities are sensitive to the presence of acceptor defects, such as vacancies on the Ga sublattice. The investigation of the electronic structure of pseudo-ternary alloys (Ga (1− x − y )Mn x Cr y )As has shown a mutual compensation of Mn and Cr impurities. Therefore, in order to reach the highest critical temperature, GaAs has to be separately doped with Cr or Mn impurities. The GaAs doped with Fe is found to be non-ferromagnetic.

Strong composition-dependence on glass-forming ability in Ni–(Ti,Zr)–Si pseudo-ternary alloys

The glass formation in Ni–(Ti,Zr)–Si pseudo-ternary alloys was studied. For suction casting, by carefully adjusting the alloy composition and studying the microstructure changes, the best glass-forming alloy with a 2 mm diameter is pinpointed in a narrow composition region of 57.5–58.5 at.% Ni, 36.5–38.5 at.% (Ti + Zr) and 5–5.5 at.% Si. The main competing crystalline phases, identified by XRD and SEM, were Ni 10(Zr,Ti) 7, Ni(Ti,Zr) and an unidentified Si-containing phase. Our results indicate a clear need for monitoring the microstructure change in the cross section of the ingots to locate the best glass-forming alloys.

Development of Dual Multi-Phase Intermetallic Alloys Composed of Geometrically Close Packed Ni3X(X:Al and V) Structures

AbstractDual multi-phase intermetallic alloys composed of Ni3Al (L12)+Ni3V (D022) phases were developed, based on the Ni3Al-Ni3Ti-Ni3V pseudo-ternary alloy system. High-temperature tensile deformation, fracture behavior, and compression and tension creep were investigated using polycrystalline and single crystalline materials. The alloys with such a novel microstructure show extremely high yield and tensile strength with good temperature retention, and also reasonable tensile ductility. Also, creep test conducted at high temperature showed extremely low creep rate and long creep rupture time. The obtained results are promising for the development of a new-type of high-temperature structural material exceeding conventional superalloys.

Microstructure and Mechanical Properties of Dual Two-Phase Intermetallic Alloys Composed of GCP Ni3Al and Ni3V Phases containing Nb

AbstractDual multi-phase intermetallic alloys composed of Ni3X (X: Al and V) containing Nb were developed, on the basis of the Ni3Al-Ni3Nb-Ni3V pseudo-ternary alloy system. The dual multi-phase intermetallic alloys were characterized by scanning electron and transmission electron microscopies. High-temperature compression and tension tests, and compression creep test were conducted. It was found that the dual multi-phase intermetallic alloys show high yield and tensile strength with good temperature retention, accompanied with reasonable tensile ductility. The compression creep test conducted at high temperature showed lower creep rate in the dual multi-phase intermetallic alloys than in conventional Ni-base superalloys. The obtained results are superior to the dual multi-phase intermetallic alloys containing Ti.

Further investigation on phase relation and microstructures in Ni 3Si–Ni 3Ti–Ni 3Nb pseudo-ternary alloy system

The isothermal phase diagram at 1323 K in the Ni 3Si–Ni 3Ti–Ni 3Nb pseudo-ternary alloy system was re-investigated by scanning electron microscopy (attached with a wavelength dispersive spectroscope), X-ray diffraction and transmission electron microscopy (TEM), focusing on the phase relation among possible geometrically-close-packed (GCP) Ni 3 X phases. The prepared alloys exhibited widely different microstructures, depending on alloy compositions whether they exist in a single phase, a two- or a three-phase region, and also on the constituent GCP Ni 3 X phases. The L1 2(Ni 3Si), D0 24(Ni 3Ti) and D0 a(Ni 3Nb) phases were directly equilibrated one another or each other when keeping Ni content 79.5 at.%. On the other hand, the D0 19(Ni 3Ti 0.7Nb 0.3) phase was identified to exist when keeping Ni content 75 at.%. The phase stability and existing region of each GCP Ni 3 X phase identified in the Ni 3Si–Ni 3Ti–Ni 3Nb pseudo-ternary alloy system were discussed, based on the electron concentration ( e/a) and the atomic size factor ( R x / R Ni) of the constituent atoms.

Competition between superconductivity and charge-density-wave ordering in theLu5Ir4(Si1−xGex)10alloy system

We have performed bulk measurements such as dc magnetic susceptibility, electrical resistivity, and heat capacity on the pseudoternary alloys ${\mathrm{Lu}}_{5}{\mathrm{Ir}}_{4}{({\mathrm{Si}}_{1\ensuremath{-}x}{\mathrm{Ge}}_{x})}_{10}$ to study the interplay and competition between superconductivity and the charge-density-wave- (CDW) ordering transition. We track the evolution of the superconducting transition temperature ${T}_{\mathrm{SC}}$ and the CDW-ordering temperature ${T}_{\mathrm{CDW}}$ as a function of $x$ (concentration of Ge) $(0.0\ensuremath{\leqslant}\mathit{x}\ensuremath{\leqslant}\phantom{\rule{0.3em}{0ex}}1.0)$. We find that increasing $x$ (increasing disorder) suppresses the ${T}_{\mathrm{CDW}}$ rapidly with the concomitant increase in ${T}_{\mathrm{SC}}$. We present a temperature-concentration (or volume) phase diagram for this system and compare our results with earlier work on substitution at the Lu or Ir site to show how dilution at the Si site presents a different situation from these other works. The heat capacity data in the vicinity of the CDW transition has been analyzed using a model of critical fluctuations in addition to a mean-field contribution and a smooth lattice background. We find that the critical exponents change appreciably with increasing disorder. This analysis suggests that the strong-coupling and non-mean-field-like CDW transition in the parent compound ${\mathrm{Lu}}_{5}{\mathrm{Ir}}_{4}{\mathrm{Si}}_{10}$ changes to a mean-field-like transition with increasing Ge concentration.

Phase relation and microstructure in multi-phase intermetallic alloys based on Ni 3Al–Ni 3Nb–Ni 3V pseudo-ternary alloy system

The phase relation and microstructure of alloys based on the Ni 3Al–Ni 3Nb–Ni 3V pseudo-ternary alloy system at 1273 and 1373 K were investigated by optical microscopy, X-ray diffraction, and scanning electron microscopy (attached with a wavelength dispersive spectroscope). There was no other intermediate phase besides L1 2 (Ni 3Al), D0 a (Ni 3Nb) and D0 22 (Ni 3V). The phase fields of L1 2 (Ni 3Al), D0 a (Ni 3Nb) and D0 22 (Ni 3V) have been shown to primarily depend upon the free electron concentration ( e/ a) of the constituent atoms. Among the three constituent intermetallic phases, one kind of three-phase relation (i.e. L1 2–D0 a –D0 22) and three kinds of two-phase relations (i.e. L1 2–D0 a , D0 a –D0 22 and L1 2–D0 22) were found to exist at 1273 K. The prepared alloys exhibited widely different microstructures, depending on alloy composition and temperature. In the low Nb concentration region, dual multi-phase microstructures composed of L1 2+D0 a +A1(→L1 2+D0 22) were formed by a eutectic reaction.