L12 Crystal Structure Research Articles

Corrosion studies of Al-Mg-Sc-Zr Alloy with Low Sc/Zr ratio fabricated by laser powder bed fusion for marine environments

This study investigates the corrosion behavior of a laser powder bed fusion (LPBF) Al-Mg-Sc-Zr alloy with a Sc/Zr ratio of less than 1 in 3.5wt% NaCl solution. X-ray diffraction (XRD) analysis revealed the presence of an Al matrix with face-centered cubic (FCC) structure and the secondary phase Al3(Sc,Zr) with L12 crystal structure. Microstructural analysis indicated a bimodal grain size distribution with fine equiaxed and columnar grains influenced by thermal gradients and secondary phase Al3(Sc,Zr). Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) tests in 3.5wt% NaCl solution demonstrated that the alloy exhibits a less negative corrosion potential (Ecorr) and lower corrosion current density (icorr) compared to other Al-Mg-Sc-Zr alloys with higher Sc/Zr ratios, indicating superior corrosion resistance. The enhanced performance is attributed to the fine grain structure and the formation of a stable protective oxide layer facilitated by the higher Zr content.

Effect of Precipitation on Residual Stresses in Alloy 693

Alloy 693 is a precipitation hardenable nickel base superalloy containing about 30% Cr, 4% Fe, 4% Al, 1.5% Nb and 0.3% Ti (in wt.%). At elevated temperatures, alloy precipitates out particles of an ordered γ′ phase (L12 crystal structure) with Ni3(Al,Ti,Nb) stoichiometry. These particles remain coherent and maintain a cube-to-cube orientation relationship with the face-centered cubic matrix. The alloy also has a tendency to form chromium-rich α phase (body-centered cubic crystal structure) particles at temperatures above 800 °C. The α phase particles maintain a Kurdjumov–Sachs orientation relationship with the matrix. This paper reports the effect of the precipitation of γ′ and α phases on the residual stresses developed in the alloy, and correlates them with the misfit strains due to the precipitation of the two phases. Residual stresses have been measured using the blind hole drilling method, while the misfit strains have been calculated based on the lattice parameters of matrix, γ′ and α phases determined using neutron diffraction. The precipitation of the γ′ phase introduces tensile nature of stresses in the matrix, while that of the α phase introduces compressive stresses. The overall nature of the residual stresses in the alloy is governed by the volume fraction of the two precipitates.

Superelastic Properties of Aged FeNiCoAlTaB Cold-Rolled Shape Memory Alloys

In the present study, microstructure and cyclic tensile tests were used to measure the superelastic responses of Fe40.95Ni28Co17Al11.5Ta2.5B0.05 (at.%) shape memory alloys after 97% cold rolling. Cold-rolled samples underwent annealing heat treatment (1250 °C/1 h) followed by quenching in water or aging heat treatment (700 °C/6 h and 700 °C/12 h) followed by quenching in water. The microstructure results showed that the average grain size increased from 210 μm to 1570 μm as annealing times increased from 0.5 h to 1 h. X-ray diffraction (XRD) spectra for FeNiCoAlTaB (NCATB) showed that in cold-rolled alloys after solution, the strong peak was in the face-centered cubic (γ, FCC) <111> structure. In aged samples, a new peak (γ’, FCC) emerged, the intensity of which increased as aging times rose from 6 to 12 h. Transmission electron microscope (TEM) images showed that the average precipitate size was around 10 nm in 700 °C/6 h specimens and 18 nm in 700 °C/12 h specimens. The precipitate was enriched in Ni, Al, and Ta elements and exhibited an L12 crystal structure. Tensile samples aged at 700 °C for 6 and 12 h exhibited recoverable strains of 1% and 2.6%, respectively, at room temperature. Digital image correlation (DIC) results for the sample aged at 700 °C for 12 h showed that two martensite variants were activated during the superelastic test. Such variants can form corresponding variant pairs (CVPs), which promote tensile deformation. The tensile sample exhibited a gradual cyclic degradation, and a large irrecoverable strain was observed after the test. This irrecoverable strain was the result of residual martensite, which was pinned by dislocations.

Ab initio study of structural, electronic and magnetic properties of the new full Heusler alloys Co2ZrZ (Z = Pb, Bi, As)

In this paper, the calculations of the structural, electronic, and magnetic properties of new full Heusler Co2ZrZ (Z = Pb, Bi, As) alloys were investigated within the framework of the density functional theory (DFT). Calculations were performed using the Quantum-Espresso package and ultrasoft pseudopotential, based on generalized-gradient approximation (GGA) as the exchange–correlation potential. Using ab initio calculations, properties such as equilibrium lattice constants (a0), bulk modulus (B), electronic band structures, majority and minority of density of states (DOS), as well as the total and atomic magnetic moments of these new compounds were calculated. The results show that the most stable structure of these compounds is the Cu2MnAl phase with a L21 crystal structure. The calculation of the electronic band structure and the majority and minority of DOS show that the Co2ZrPb compound has half-metallic nature with a band gap of 0.33eV. However, based on the band structure and total and partial DOS, the Co2ZrBi and Co2ZrAs compounds exhibit ferromagnetic metallic nature. In addition, the calculation of the magnetic properties indicates that the Co2ZrPb has a total magnetic moment of 2µB, which follows the Slater-Pauling (SP) rule.

The Equilibrium α (Al-Li Solid Solution) and Metastable δ′ (Al3Li) Phase Boundaries in Aluminum–Lithium Alloys

Data on the equilibrium solubilities of the α Al-Li solid solution phase and the ordered metastable δ′ Al3Li (L12 crystal structure) precipitate phase are critically reviewed, and a new binary alloy phase diagram is proposed. The δ′ solvus, describing the equilibrium solubility of Li in the α phase, Xαe, in atom fraction Li, is given by the equation X_{alpha e} , = ,0.{6}00{text{86 exp}}left{ {{-}{8669}.{55}/{text{R}}T} right}, where R is the gas constant, and the temperature T is in K. The α solvus, i.e. the equilibrium solubility of Li in the δ′ phase, Xδ′e, is given by the equation X_{delta prime e} , = ,0.{18}0{9}, + ,{6}.{413}, times ,{1}0^{{{-}{4}}} {{T}}{-}{1}.{861}, times ,{1}0^{{{-}{6}}} T^{{2}} , + ,{1}.{4684}, times ,{1}0^{{{-}{9}}} T^{{3}} , which represents a compromise between previously published theoretical curves that predict retrograde behavior. It is emphasized that that all the data cited and re-analyzed exclusively involve binary Al-Li alloys. The new phase diagram eliminates data that were previously mis-attributed. Most importantly, it is informed by considerable re-analysis of previously published data, supplemented by the inclusion of data that were not previously considered, and eschews data on both Xαe and Xδ′e that are indubitably non-equilibrium in nature.

Realization of Enhanced Refrigeration Capacity with Non-Hysteretic Behavior in Ni40Gd5Co5Mn37In12Si1 Alloy Near Room Temperature at 2T

Ni–Co–Mn–In–Si-based Heusler alloys have recently attracted a lot of attention because of their superior magnetocaloric properties around the second-order magnetic transformation near room temperature. In this paper, the effects of Gd substitution (Ni45–xGdxCo5Mn37In12Si1; x = 0 and 5) and Gd addition (Ni45Co5Mn37In12Si1 + Gdx; x = 0 and 5) on thermal and magnetic hysteretic behavior of temperature- and field-dependent magnetization of Ni45Co5Mn37In12Si1 Heusler alloy were investigated. The as-prepared Ni45–xGdxCo5Mn37In12Si1 Heusler alloys crystalize into a high-temperature austenite cubic L21 crystal structure, confirmed by powder X-ray diffraction. Microstructural and elemental composition analyses from field emission scanning electron microscopy reveal that parent Ni45Co5Mn37In12Si1 alloy shows single phase with larger grains in its as-cast form, whereas the Gd-doped Ni45Co5Mn37In12Si1 sample possess some dendritic well-distinguishable Gd-rich and deficient regions. Thermomagnetic measurements show that substitution of Gd at the Ni site in Ni45Co5Mn37In12Si1 notably reduces the Curie temperature, TC, from 333 to 317 K. Thermodynamic analyses of isothermal field-dependent magnetization result in significantly large magnetic entropy change, ΔSM = −0.842 J kg–1 K–1 under an applied field change, ΔH = 2 T at 305 K across the austenite regime for Ni40Gd5Co5Mn37In12Si1. Furthermore, the maximum refrigeration capacity of ∼47 J kg–1 was achieved for the composition of Ni40Gd5Co5Mn37In12Si1 at 305 K.

The Effect of Cr Substitution on the Anomalous Hall Effect of Co3−xCrxAl (x = 0, 1, 2, 3) Heusler Compounds: An Ab Initio Study

Based on density functional theory, we studied the electronic, magnetic, and mechanical properties of Co3−xCrxAl (x = 0, 1, 2, 3) Heusler compounds with the generalized gradient approximation (GGA) for the exchange-correlation potential. In this study, we report two principal spin-related phenomena, namely, the anomalous Hall effect and current spin polarization of the Co3−xCrxAl Heusler compounds in the L21 crystal structure. Heusler compounds, both ideally and inversely ordered, were considered. We found that the calculated magnetic moment of Co3−xCrxAl decreased with an increase in the Cr concentration for both ideally and inversely ordered structures, except for Cr3Al. We also found that the spin polarization for all Co3−xCrxAl was larger than 50%, except for Cr2CoAl in the inverse structure. All the considered Heusler compounds were mechanically stable except for the regular Cr2CoAl. The Hall current spin polarization was also calculated. We found that Co2CrAl in the XA structure had the largest spin Hall conductivity of 370 (ℏS/e cm), and the spin polarization of the induced Hall current was high.

Experimental Investigation on Isothermal Sections at 1273 and 1473 K in the Co–Ti–W System

The microstructures of 25 annealed alloys and XRD patterns of partial critical alloys in the Co–Ti–W system were investigated by using scanning electron microscopy (SEM) with energy dispersive spectrometer (EDS) and X-ray diffraction (XRD) methods. The isothermal sections at 1273 and 1473 K of the Co–Ti–W system were established. Five three-phase regions and five two-phase regions at 1273 K and eight three-phase regions and two two-phase regions at 1473 K were experimentally determined. The maximum solubilities of W in Co3Ti, αCo2Ti, βCo2Ti and CoTi were determined to be ∼7.9 at%, ∼1.5 at.%, ∼5.9 at.% and ∼1.8 at.% at 1273 K, respectively. The maximum solubilities of Ti in Co7W6 and Co3W were determined to be ∼11.9 at.% and ∼15.2 at.% at 1273 K, respectively. The compound Co3Ti with L12 crystal structure was found to be stable at 1473 K in the Co–Ti–W system owing to the addition of W element, which confirmed that W can improve the stability of γ′ with L12 crystal structure in the Co-based superalloys. The composition range of W in Co3Ti was measured to be ∼7.4–10.4 at.% at 1473 K. In addition, the maximum solubilities of Ti in Co7W6 and W in βCo2Ti and CoTi were ∼15.4 at.%, ∼7.6 at.% and ∼3.1 at.% at 1473 K, respectively. No ternary compounds were found in the Co–Ti–W system at 1273 and 1473 K.

Mechanical Properties of Co-Al-Mo-Nb Intermetallic Alloys

The results of the experimental study of the mechanical properties and structure of the Co-9.5Al-2.9Mo-4Nb, Co-9.1Al-5.2Mo-4.7Nb, and Co-8.9Al-6.5Mo-9.3Nb alloys were presented. The Young’s moduli in the studied alloy samples were found to be smaller than those of Ni3Al-based and Co3(Al,W)-based alloys. The eutectic structure was observed in all studied alloys. Cuboids of the Co3(Al,Nb,Mo) intermetallic compound with L12 crystal structure were found by TEM study.

Criteria for developing castable, creep-resistant aluminum-based alloys – A review

AbstractWe describe four criteria for the selection of alloying elements capable of producing castable, precipitation-strengthened Al alloys with high-temperature stability and strength: these alloying elements must (i) be capable of forming a suitable strengthening phase, (ii) show low solid solubility in Al, (iii) low diffusivity in Al, and (iv) retain the ability for the alloy to be conventionally solidified.With regard to criterion (i), we consider those systems forming Al3M trialuminide compounds with a cubic L12crystal structure, which are chemically and structurally analogous to Ni3Al in the Ni-based superalloys. Eight elements, clustered in the same region of the periodic table, fulfill criterion (i): the first Group 3 transition metal (Sc), the three Group 4 transition metals (Ti, Zr, Hf) and the four latest lanthanide elements (Er, Tm, Yb, Lu). Based on a review of the existing literature, these elements are assessed in terms of criteria (ii) and (iii), which satisfy the need for a dispersion in Al with slow coarsening kinetics, and criterion (iv), which is discussed based on the binary phase diagrams.

Ripening of L12 Ni3Ti precipitates in the framework of the trans-interface diffusion-controlled theory of particle coarsening

Abstract Data are presented on the kinetics of coarsening of γ′-type Ni3Ti precipitates (L12 crystal structure) in three binary Ni –Ti alloys containing 10.31, 11.84, and 13.72 at.% Ti aged at 720 °C for times up to 64 h. Data on the distributions of particle sizes (PSDs) are also presented. These data, as well as previously published data, are analyzed in light of a new theory of coarsening in which diffusion is controlled by transport through the non-sharp interface between the matrix and precipitate phases. The new theory, called the trans-interface diffusion-controlled (TIDC) theory of coarsening, predicts time (t)-dependent behavior of the type 〈r〉 n ∝ t for the growth of precipitates of average radius 〈r〉 and X Ti ∝ t–1/n for the depletion of the solute concentration of the matrix, X Ti. The exponent n is intimately related to the width of the interface between the precipitate and matrix phases, δ, which is assumed to depend on the particle radius as δ ∝ rm , where n = m + 2. The shape of the scaled distribution of particle sizes (PSD) depends on n and the thermo-physical kinetic constants are independent of volume fraction. The data on kinetics are evaluated and compared for n = 2.375, determined from analyses of the PSDs, and for n = 3, which is the traditionally accepted value. The agreement between the data on kinetics and predictions of the TIDC theory is acceptable, and the TIDC theory is the only one capable of explaining the experimentally observed absence of an effect of volume fraction on the kinetics at larger volume fractions, and the shapes of the PSDs.

Assessment of Local Observation of Atomic Ordering in Alloys via the Radial Distribution Function: A Computational and Experimental Approach

As a powerful analytical technique, atom probe tomography (APT) has the capacity to acquire the spatial distribution of millions of atoms from a complex sample. However, extracting information at the Ångstrom-scale on atomic ordering remains a challenge due to the limits of the APT experiment and data analysis algorithms. The development of new computational tools enable visualization of the data and aid understanding of the physical phenomena such as disorder of complex crystalline structures. Here, we report progress towards this goal using two steps. We describe a computational approach to evaluate atomic ordering in the crystal structure by generating radial distribution functions (RDF). Atomic ordering is rendered as the Fractional Cumulative Radial Distribution Function (FCRDF) which allows for greater visibility of local compositions at short range in the structure. Further, we accommodate in the analysis additional parameters such as uncertainty in the atomic coordinates and the atomic abundance to ascertain short-range ordering in APT data sets. We applied the FCRDF analysis to synthetic and experimental APT data sets for Ni3Al. The ability to observe a signal of atomic ordering consistent with the known L12 crystal structure is heavily dependent on spatial uncertainty, irrespective of abundance. Detection of atomic ordering is subject to an upper limit of spatial uncertainty of atoms described with Gaussian distributions with a standard deviation of 1.3 Å. The FCRDF analysis was also applied to the APT data set for a six-component alloy, Al1.3CoCrCuFeNi. In this case, we are currently able to visualize elemental segregation at the nanoscale, though unambiguous identification of atomic ordering at the Ångstrom (nearest-neighbor) scale remains a goal.

Exchange Bias Effect in NiMnSbB Ferromagnetic Shape Memory Alloys Depending on Mn Content

In this study, exchange bias effect was investigated in boron added NiMnSb Heusler alloys. The samples were fabricated by arc melting method with Ni49Mn37,5Sb13,5+Bx, Ni49Mn37,7Sb13,3+Bx and Ni49Mn37,9Sb13,1+Bx nominal compositions. XRD analyzes showed that the samples were in L21 crystal structure at room temperature. While the martensitic phase transition temperatures increased, the magnetic moment value decreased with the increase in Mn content. The decrease in magnetization is owing to the increase in antiferromagnetic interactions with the increase of Mn content. Under low field and zero field cooling M-T measurements revealed that antiferromagnetic interactions were more dominant at low temperature but ferromagnetic behavior was more effective in the system at high temperature region. The coexistence of ferromagnetism and antiferromagnetism in a magnetic material can cause the exchange bias effect. Therefore, the hysteresis loops were examined at 5 K of the samples cooled under 50 kOe magnetic field. The shift at the origin of the magnetization curve, which is attributed to the exchange bias effect, increased with increasing Mn amount.

Effect of hydrostatic pressure on magneto-crystalline anisotropy of Heusler Ni2MnSn-based alloy

ABSTRACT Single crystal of the stoichiometric Ni2MnSn alloy (cubic L21 crystal structure) was prepared by the Czochralski method. The values of the magneto-crystalline anisotropy constant K 1 have been determined at temperature 10 K under ambient and high hydrostatic pressures, K 1 = + 0.17 × 104 and +1.96 × 104 J/m3 (0.7 GPa), respectively. The pressure-induced decrease of magnetization was confirmed and hence the significant non-trivial increase of uniaxial anisotropy with increasing pressure points to a possible distortion of the cubic structure of the single crystal under hydrostatic pressure. Simultaneously, the more pronounced and pressure almost insensitive magneto-crystalline anisotropy, K 1 = + 9.1 × 104 J/m3, has been observed in the martensite phase (orthorhombic structure) of the off-stoichiometric Ni2Mn1.43Sn0.57 alloy. The effect of a directional dependence of the Young modulus that was theoretically derived in the case of the Ni2MnSn-based alloys is discussed.

Structural, electronic, magnetic, transport and mechanical properties of the half-metal-type quaternary Heusler alloy [formula omitted][formula omitted][formula omitted]Ge

We report on the bulk properties of the Heusler alloy system Co2Fe1-xVxGe with 0⩽x⩽1 in steps of 0.125. We find single-phase alloys only for x=0.25 and x=0.375, both of which exhibit an L21 crystal structure. The alloys are found to be soft ferromagnets with high Curie temperatures (∼800K). Magnetization measurement shows the saturation magnetization to be 5.21 μB/f.u. and 4.78 μB/f.u. for Co2Fe0.75V0.25Ge and Co2Fe0.625V0.375Ge respectively, in good agreement with the values expected from a Slater-Pauling rule for half metals. In zero applied magnetic field, the resistivity versus temperature of these alloys does not display the usual T2 dependence at low temperatures indicative of electron-magnon scattering, another indirect suggestion of half metallicity. Our ab initio calculations also predict half-metallic character in the alloys after V substitution. The large exchange splitting between the occupied majority- and unoccupied minority-spin states leads to the Fermi level almost intersecting a peak in the V majority density of states. This leads to a markedly higher spin polarization upon V doping, making V an ideal dopant for achieving half-metallic behavior in Co2FeGe. Relatively high mechanical hardness values are also observed.

Control of Structural and Magnetic Properties of Polycrystalline Co2FeGe Films via Deposition and Annealing Temperatures.

Thin polycrystalline Co2FeGe films with composition close to stoichiometry have been fabricated using magnetron co-sputtering technique. Effects of substrate temperature (TS) and post-deposition annealing (Ta) on structure, static and dynamic magnetic properties were systematically studied. It is shown that elevated TS (Ta) promote formation of ordered L21 crystal structure. Variation of TS (Ta) allow modification of magnetic properties in a broad range. Saturation magnetization ~920 emu/cm3 and low magnetization damping parameter α ~ 0.004 were achieved for TS = 573 K. This in combination with soft ferromagnetic properties (coercivity below 6 Oe) makes the films attractive candidates for spin-transfer torque and magnonic devices.

Structural and magnetic characterisation of Co substituted Ni2MnSb Heusler alloy: effect of cobalt substitution on magnetism and Curie temperature

ABSTRACT In this study, Ni2-x Co x MnSb full-Heusler alloys (1.00 ≤ x ≤ 1.75) were prepared by arc melting process, and examined by X-ray diffraction (XRD), scanning electron microscopy (SEM), and SQUID. The L21 crystal structure of the synthesised Heusler alloy was confirmed by XRD patterns, and it was observed that the use of Co instead of Ni caused a decrease in the interatomic distance. The magnetisation results revealed that all samples show ferromagnetic (FM) behaviour, and substitution Co for Ni leads to increasing FM interactions in the samples. The calculated magnetic moment per formula unit increase from 4.38 µB(x = 1) to 5.17 µB (x = 1.75). On the other hand, the increase in FM interaction caused an increase in ferromagnetic-paramagnetic (PM) phase transition (T C) temperatures from 513 (x = 1) to 568 K (x = 1.75). The ability to control the Curie temperature with Co substitution makes these alloys suitable candidates for future spintronics and magnetoelectronic applications.

Effect of Ga substitution on structural and magnetic properties of Fe50Mn25Al25-xGax Heusler alloys

Heusler alloys possess the structure of an ordered compound while displaying most of the properties of metals. Numerous magnetic exchange mechanisms may be operating in such systems. Herein, the structural and magnetic properties have been investigated as a function of substitution of Al by Ga in Fe50Mn25Al25-xGax (x = 0, 2.5, 5.0, 7.5, 10.0) quaternary (pseudo-ternary) full Heusler alloys. The X-ray diffraction analysis confirms the substituting Al by Ga promoting the lattice expansion in the L21 crystal structure in Fe50Mn25Al25-xGax alloys. The line scanning profile using energy dispersive X-ray analysis investigations suggests the homogeneous distribution of Ga in all the alloys. The magnetic moment of the alloys was found to be affected by Ga as the antiferromagnetic counterpart increases with Ga. A decrease in the value of Curie temperature was found with increase in Ga content. A second-order magnetic phase transition was observed in the alloys above room temperature.

Anomalous Hall Effect and Magnetoresistance in Sputter‐Deposited Magnetic Weyl Semimetal Co2TiGe Thin Films

Herein, sputter‐deposited ferromagnetic Weyl semimetal (WSM) and full‐Heusler compound Co2TiGe is investigated. Crystal quality is analyzed using X‐ray diffraction and reflectivity. In addition, temperature‐dependent transport and magnetization measurements are carried out. The sample shows indications on the formation of L21 crystal structure. Magnetization measurements show a saturation magnetization of 1.98 μB (f.u.)−1 and 1.45 μB (f.u.)−1 at 50 and 300 K, respectively. This is in close agreement to the calculated value of 2 μB (f.u.)−1 at 0 K using the Slater–Pauling rule. The obtained Curie temperature is 378.5 K, which is close to prior results for bulk samples. The residual resistivity of 142.7 μΩ cm is mainly dominated by disorder scattering. At temperatures above 60 K, the Coulomb interaction dominates the resistance. The residual resistance ratio is around 1.49. Hall measurements show positive ordinary Hall and anomalous Hall constants and a positive dependence on temperature. Skew scattering and side jumps or intrinsic mechanisms contribute in similar amounts to the anomalous Hall resistivity, which indicates a higher than usual intrinsic contribution, which is expected for WSMs. The expected relation between the longitudinal and the anomalous Hall conductivity of is not met.

Lattice dynamics of novel Heusler alloys MnY2Z (Z=Al and Si)

Mn-based Heusler alloys ‘MnY2Z (Z= (Al and Si)) have ‘L21’ crystal structure at the ambient condition of temperature and pressure. MnY2Z have a high melting temperature, shows half-metallic character and shape memory effects where numerous of its applications takes place. In this report, theoretical investigations of the phonon properties of MnY2Z in the cubic phase has been investigated by using density functional theory followed by density functional perturbation theory to comprehend the role of phonons in these alloys. In these calculations, zone center phonon frequency, phonon modes in symmetric directions and phonon density of states are investigated for these alloys. The phonon modes are found to be positive in all symmetric directions indicate the stability of the present alloys in the L21 crystal structure. Additionally, Raman and infrared phonon modes have also been identified for each alloy. The investigated results are interpreted with other existing similar type of Heusler alloys.