Structure Induced Anelasticity in Iron Intermetallic Compounds and Alloys
Abstract
eBook PDF / eBook PDF
Different anelastic phenomena are discussed in this book with respect to
iron-based binary and ternary alloys and intermetallic compounds of
Fe3Me type, where Me are α-stabilizing elements Al, Ga, or Ge. An
introduction into anelastic behavior of metallic materials is given, and
methods of mechanical spectroscopy and neutron diffraction are
introduced for the better understanding of structure-related relaxation and
hysteretic phenomena.
Keyword: Anelasticity, Damping Capacity, Magnetostricition, Structure
Transitions, Phase Transitions, Fe-Based Alloys, Intermetallic
Compounds, Mechanical Spectroscopy, In Situ Neutron Diffraction
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This article reviews original work and important new developments in the field of deformation behavior of high manganese face-centered cubic γ-Fe alloys. Owing to their exceptional mechanical properties, these alloys, referred to as twinning-induced plasticity, or TWIP, steels, have come to the fore as prime candidate materials for light-weight applications, notably in automotive, shipbuilding, and oil and gas industries. It is established that a superior combination of strength and ductility exhibited by TWIP steels is associated with a specific character of the variation of the dislocation density. The defining feature of TWIP steels is the small magnitude of the intrinsic stacking fault energy. In addition to limiting the dynamic recovery rate, the low stacking fault energy of TWIP steels results in the formation of isolated stacking faults and deformation twins, which reduces the dislocation mean free path. Both effects lead to an increased strain hardening rate. Despite the progress made, there are still considerable differences between the models proposed for the microstructural evolution during the deformation of TWIP steels and the concomitant strain hardening behavior. The review surveys the experimental literature, summarizes the current modeling concepts, and identifies the outstanding issues with TWIP steels that require the attention of the materials science community. Suggestions for the direction of future research on twinning-induced plasticity steels are offered.
Phase transformations in an iron–gallium alloy have been analyzed by in situ real-time neutron diffraction in the temperature range from 293 to 1223 K. Two compositionally identical samples were studied: the first was in the as-cast bulk state, and the second was ground into a powdered state. In both samples, the same sequence of structural transitions was recorded on heating with a constant heating rate (D03 → A2 → L12 → D019 → A2), and the same structural state (D03 + L12) was recorded after slow cooling to room temperature. Owing to strong texture in the bulk sample, only diffraction patterns of the powdered sample were treated with the Rietveld method to determine the volume fractions of the coexisting phases, the coefficients of thermal expansion, and the thermal and static atomic disorder parameters. The occupancy of Ga positions and the ordered iron magnetic moment were refined at selected temperatures. The level of microstrain in the crystallites in the initial as-quenched state is small, but it sharply increases in the course of phase transitions when the alloy is heated. The microstrains are high and strongly anisotropic after slow cooling. Generally, phase transformations occur similarly in the powdered and bulk samples, but with a noticeable difference in details. The fulfilled analysis of the bulk and powdered samples allowed the real possibilities of the quantitative neutron diffraction analyses of phase transitions in ferromagnetic ordered alloys to be assessed.
All ferromagnetic materials show deterioration of magnetism-related properties such as magnetization and magnetostriction with increasing temperature, as the result of gradual loss of magnetic order with approaching Curie temperature TC. However, technologically, it is highly desired to find a magnetic material that can resist such magnetism deterioration and maintain stable magnetism up to its TC, but this seems against the conventional wisdom about ferromagnetism. Here we show that a Fe–Ga alloy exhibits highly thermal-stable magnetization up to the vicinity of its TC, 880 K. Also, the magnetostriction shows nearly no deterioration over a very wide temperature range. Such unusual behaviour stems from dual-magnetic-phase nature of this alloy, in which a gradual structural-magnetic transformation occurs between two magnetic phases so that the magnetism deterioration is compensated by the growth of the ferromagnetic phase with larger magnetization. Our finding may help to develop highly thermal-stable ferromagnetic and magnetostrictive materials.
Dual-phase (Fe83Ga17)100−xTbx alloys with 0 ≤ x ≤ 1 were synthesized by arc melting and homogenization treatment. The microstructures and the corresponding mechanical properties were systematically investigated. The chemical composition of the body centered cubic matrix is Fe83Ga17. The monoclinic second phase was composed of meltable precipitates with approximate composition Fe57Ga33Tb10. The nano-hardness of matrix and precipitates were 2.55 ± 0.17 GPa and 6.81 ± 1.03 GPa, respectively. Both the ultimate tensile strength (UTS) and fracture strain (ε) of the alloys were improved by the precipitates for x ≤ 0.2 alloys, but the strain decreases significantly at higher values of x. As potential structural-functional materials, the best mechanical properties obtained were a UTS of 595 ± 10 MPa and an ε of 3.5 ± 0.1%, four-fold and seven-fold improvements compared with the un-doped alloy. The mechanism for these anomalous changes of mechanical properties was attributed to the dispersed precipitates and semi-coherent interfaces, which serve as strong obstacles to dislocation motion and reduce the stress concentration at the grain boundaries. A sizeable improvement of magnetostriction induced by the precipitates in the range 0 ≤ x ≤ 0.2 was discovered and an optimal value of 150 ± 5 ppm is found, over three times higher than that of the un-doped alloy.
The analysis of line profiles in Powder Diffraction patterns is a topic nearly as old as diffraction itself. However, despite the long time that has passed since the pioneering studies of Scherrer (1918),1 and the rich literature and textbooks2–5 produced over many decades, line profile analysis is ...
This is a reference to a pair of software packages, GSAS & EXPGUI, which are no longer supported or updated. The two packages are The correct citations are: described in Larson, A. C., and Von Dreele, R. B. (2004). Report LAUR 86-748. Los Alamos National Laboratory; and Toby, B. H. (2001). "EXPGUI, a Graphical User Interface for GSAS," J. Appl. Crystallogr. 34, 210.
This software has been replaced with GSAS-II: Toby, B. H., and Von Dreele, R. B. (2013). "GSAS-II: The Genesis of a Modern Open-Source All-Purpose Crystallography Software Package," J. Appl. Crystallogr. 46, 544-549. (available here: The correct citations are:
Larson, A. C., and Von Dreele, R. B. (2004). Report LAUR 86-748. Los Alamos National Laboratory.
Toby, B. H. (2001). "EXPGUI, a Graphical User Interface for GSAS," J. Appl. Crystallogr. 34, 210.
but I'd really like to encourage people to switch to using GSAS-II: Toby, B. H., and Von Dreele, R. B. (2013). "GSAS-II: The Genesis of a Modern Open-Source All-Purpose Crystallography Software Package," J. Appl. Crystallogr. 46, 544-549. See
Article GSAS-II: The Genesis of a Modern Open-Source All-Purpose Cry...
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Neutron diffraction and mechanical spectroscopy studies were performed in Fe-Al-Cr, Fe-Al-Si and Fe-Si alloys. Results show that in ordered alloys independently of the type of order, D03 or B2, the mobility of dislocations and grain boundaries is markedly reduced. It is revealed through small values both of damping and of the strength of the amplitude dependent damping (S). Moreover, the behaviour of S as a function of temperature is a suitable tool for determining the order changes as a function of temperature.
We studied the crystalline structure of Fe - 8at.%Al - 4at.%Ge alloy between 300 and 1300 K and its relation to the mechanical response by means of neutron diffraction and mechanical spectroscopy. At room temperature we observe a Fe3Al-type ordered structure with a deficiency of Al in the 8c sites. The Ge atoms are distributed in the 4a and Al atoms in 8c sites. At high temperature we observe an order-disorder transformation when the crystal structure becomes Fe-α type. This loss of order gives rise to the hysteresis behavior of damping between the heating and cooling runs.
Legierungen aus Eisen und Aluminium finden in vielen industriellen Bereichen Verwendung, da sie ein niedriges Gewicht, eine höhere Festigkeit und eine bessere Korrosionsbeständigkeit gegenüber reinem Eisen oder vielen Stählen aufweisen. Das mechanische und thermische Verhalten solcher Legierungen zu kennen und zu verstehen ist entsprechend wichtig; hierfür bietet die Messung der inneren Reibung mittels Vibrating-Reed-Technik mit Biege- und Torsionsschwingungen eines dünnen Blättchens, einem Teilbereich der so genannten Mechanischen Spektroskopie, eine gute Möglichkeit, weil sie dynamische Prozesse bei atomaren Umordnungen bei zunehmender Temperatur zu detektieren und quantitativ zu analysieren gestattet.
In dieser Arbeit wird die Mechanische Spektroskopie an einer Reihe von verschiedenen Fe-Al Legierungen vorgenommen. Die untersuchten Konzentrationen variieren von reinem Eisen bis zu FeAl Legierungen mit 50 at.%Al Anteil, wobei die Variationsschritte bei Erhöhung des Al-Anteils unter 5 at%.Al liegen. Der untersuchte Temperaturbereich reicht von ca. 93 bis 923 K. In diesem Intervall lassen sich vier Maxima im Dämpfungsspektrum finden, der D-, S-, X- und Z-Peak. Den gefundenen Peaks werden mittels Variation unterschiedlicher Parameter, wie z.B. der thermischen und mechanischen Vorbehandlung oder des Kohlenstoffanteils, bestimmten Mechanismen zugeordnet. Der D-Peak wird mit Versetzungen (linienhaften Defekten) in Verbindung gebracht, während der S-Peak durch einen Snoek-artigen Mechanismus (Sprünge von Kohlenstoff-Atomen zwischen benachbarten Zwischengitterplätzen) gedeutet wird. Der X-Peak wird auf eine Relaxation kombinierter Kohlenstoff-Leerstellen-Paare zurückgeführt. Der Z-Peak kann dem Zener-Mechanismus (Reorientierung von Substitutionsatom-Paaren entlang der Spannungsrichtung) zugeordnet werden. Die gefunden Mechanismen werden mit Literaturangaben verglichen und verifiziert. Eine Gegenüberstellung der ermittelten Aktivierungsenergien illustriert die gefundenen Zusammenhänge. Eine eingehende quantitative Analyse des S-Peaks bei variierter Al-Konzentration erlaubt eine Abschätzung der Wechselwirkungsweite zwischen Al- und C-Atomen in der Legierung Fe-Al(-C).
Als zusätzliche Ergänzung werden bestimmte binäre Legierungskonzentrationen um ein drittes Element erweitert, um so Aussagen, die bei der Fe-Al Legierung gefunden wurden, zu verifizieren, aber auch um sie auf die ternären Legierungen zu übertragen.
Anelastic relaxations by point defects and dislocations in Fe-Al alloys
Iron-Aluminium alloys are applied in different industrial areas owing to their superior properties, like lower weight, higher stiffness and better corrosion resistance than for pure iron or many kinds of steels. Accordingly it is important to know and to understand the mechanical and thermal behaviour of such alloys. Measurements of internal friction using the vibrating-reed-technique with flexural and torsional vibrations, which is part of the so called mechanical spectroscopy, provide a good choice with the possibility to detect and to analyse qualitatively the dynamical processes during atomic reorientation when the temperature is increased.
In this work mechanical spectroscopy is conduced with a series of different Fe-Al-alloys. The Al concentrations vary from pure iron up to FeAl with 50 at.%Al, with concentration steps less than 5 at.%. The measured temperature range varies from approximately 93 K to 923 K. In this interval four maxima in the damping spectra are detected, the D-, S-, X- and Z-Peak. Via variation of different parameters, like the thermal and mechanical pre-treatments or the carbon ratio, it is possible to assign each peak to a specific mechanism. The D-peak is connected to dislocations (line defects), while the S-peak is interpreted as a Snoek-like mechanism (jumps of carbon interstitial atoms). The X-peak is ascribed to a relaxation of combined carbon and vacancy pairs. The Z-peak is related to a Zener-mechanism (reorientation of substitional atom pairs according to the direction of strain). The proposed mechanisms are compared and verified with data from literature. A comparison of the determined activation energies illustrates the found coherences. A detailed quantitative analysis of the S-peak with varying Al concentrations permits to estimate the interaction range between Al- and C-atoms in the alloy Fe-Al-(C).
For an additional development certain binary alloy concentrations are extended by a third element, in order to verify the achieved statements, as well as to transfer them to the ternary alloys.
In this book basic and some more advanced thermodynamics and phase as well as stability diagrams relevant for diffusion studies are introduced. Following, Fick's laws of diffusion, atomic mechanisms, interdiffusion, intrinsic diffusion, tracer diffusion and the Kirkendall effect are discussed. Short circuit diffusion is explained in detail with an emphasis on grain boundary diffusion. Recent advances in the area of interdiffusion will be introduced. Interdiffusion in multi-component systems is also explained. Many practical examples will be given, such that researches working in this area can learn the practical evaluation of various diffusion parameters from experimental results. Large number of illustrations and experimental results are used to explain the subject. This book will be appealing for students, academicians, engineers and researchers in academic institutions, industry research and development laboratories. © 2014 Springer International Publishing Switzerland. All rights are reserved.
Effect of thermal cycling(γ↔ε) on γ→ε martensitic transformation kinetics and damping capacity of Fe-17mass%Mn alloy has been studied. The amount of ε martensite increases with thermal cycling in spite of decrease in Ms temperature. The increase in ε martensite content with thermal cycling is attributable to an increase in the density of martensite nucleation sites by introduction of dislocations during thermal cycling. The γ→ε martensitic transformation kinetics shows a burst mode in the non-cycled specimen, while the kinetics exhibits a sigmoidal mode in the cycled specimens. The damping capacity of the alloy increases with increasing the ε martensite content in the non-cycled specimen. On the contrary, the damping capacity of the alloy decreases with increasing the ε martensite content in the cycled specimens. The reason is that the dislocations introduced during thermal cycling, which obstruct the movement of the damping sources, become more with thermal cycling.
Mechanical spectroscopy and in situ neutron diffraction techniques were employed to study and interpret anelasticity in Fe-27 at.%Al single crystal (SC) and polycrystal (PC) alloys from room temperature to 600 °C. Thermally activated Zener relaxation was recorded in the temperature dependent internal friction (IF) curves for both SC and PC alloys upon heating and cooling. The reversible second-order D03 ↔ B2 phase transition studied by in situ neutron diffraction leads to a transient anelastic effect at ∼550 °C both upon heating and cooling. The transient peak temperature does not depend on measurement frequency, whereas the peak height is roughly proportional to the inverse frequency of measurements according to Landau's theory for the second order transitions. Calorimetry and magnetometry techniques recorded the same temperature range for the D03 ↔ B2 phase transition as mechanical spectroscopy and in situ neutron diffraction. The study of amplitude dependent internal friction (ADIF) revealed that the absolute value of maximum damping Qm−1 in the SC sample is about five times higher than that of in the PC sample at room temperature. The calculated value of internal stresses opposing magnetic domain wall motions for the PC sample is ∼1.5 times larger than that of for the SC sample, which corresponds to the detrimental influence of grain boundaries to magnetomechanical damping. By increasing the tightening force of torque wrench, a higher level of localized stress is induced to the sample, and the damping capacity (Qm−1) in single cantilever configuration of forced bending vibrations reduces monotonously.
The Fe-Mn-Si alloys are promising materials for biodegradable metallic implants for temporary healing process in the human body. In this study, three different compositions are considered (Fe23Mn5Si, Fe26Mn5Si, and Fe30Mn5Si, all in wt pct). The phase composition analysis by XRD reveals ε-martensite, α-martensite, and γ-austenite in various proportions depending on the manganese amount. The DSC study shows that the starting temperature of the martensitic transformation (Ms) of the alloys decreases when the manganese content increases (416 K, 401 K, and 323 K (143 °C, 128 °C, and 50 °C) for the Fe23Mn5Si, Fe26Mn5Si, and Fe30Mn5Si alloys, respectively). Moreover, mechanical compression tests indicate that these alloys have a much lower Young’s modulus (E) than pure iron (220 GPa), i.e., 145, 133, and 118 GPa for the Fe23Mn5Si, Fe26Mn5Si, and Fe30Mn5Si alloys, respectively. The corrosion behavior of the alloys is studied in Hank’s solution at 310 K (37 °C) using electrochemical experiments and weight loss measurements. The corrosion kinetics of the Fe-Mn-Si increases with the manganese content (0.48, 0.59, and 0.80 mm/year for the Fe23Mn5Si, Fe26Mn5Si, and Fe30Mn5Si alloys, respectively). The alloy with the highest manganese content shows the most promising properties for biomedical applications as a biodegradable and biomechanically compatible implant material.
Zener type relaxation in Fe-Ga based alloys with Ga content from ∼8 to ∼28 at.% were identified and studied using the Dynamical Mechanical Analyser (DMA) and a Forced Torsion Pendulum (FTP). The Zener relaxation caused by reorientation of pairs of Ga atoms in Fe was used to evaluate the activation parameters of Ga atom jumps in Fe. An increase in the relaxation strength occurred with an increase in the Ga content up to 19 at.% according to an increase in the number of Ga-Ga atom pairs (Δ∼CGa²(1-CGa)²), whereas a decrease in the relaxation strength from 19 to 28 at.% Ga was assigned to D03 and L12 ordering of Ga atoms in Fe-Ga alloys. Ordering and phase transitions in these alloys affected the Zener relaxation parameters and led to the appearance of transient anelastic effects. A study of several ternary Fe-Ga-Al alloys using both temperature dependent and isothermal mechanical spectroscopy (frequency variations from 10⁻⁴–10² Hz) was conducted to avoid transient effects which take place at heating or cooling, and to measure anelasticity of alloys in the equilibrium state for the chosen temperatures. The Arrhenius treatment of relaxation effects in single- and poly-crystals allows identifying the Zener effects in ternary alloys and to analyse them with respect to alloy structures.
Kinetische Besonderheiten der α-γ-Umwandlung in Eisen-Nickel-Legierungen. Ermittlung der Dämpfung und des elektrischen Widerstandes an Eisen-Nickel-Legierungen mit 10, 15 und 20% Ni. Der bei Dämpfungsmessungen auftretende Vorbereitungseffekt. Das Fehlen des Vorbereitungseffektes nach einer Stoßglühung unterhalb der Temperatur der α-γ-Umwandlung. Zeitabhängigkeit der Dämpfung. Verhältnisgleichheit zwischen Dämpfung und Umwandlungsgeschwindigkeit. Unterschiede zwischen Umwandlungsdämpfung und Relaxationsdämpfung.
A technique of fabricating ultrafine grained Fe-based shape memory alloys with high strength via differential speed rolling with high speed ratios of 2–3.8 and subsequent annealing was proposed. The processed alloy exhibited a markedly higher recovery stress compared to the same alloy with a coarse grain size.
Decent magnetostriction of ~ 255 ppm and giant tensile strain of ~ 6.6% is obtained through trace Tb addition and directional solidification method in (Fe0.83Ga0.17)100 − xTbx (x = 0–0.5) alloys. The particle-shaped Tb-rich precipitates are formed and dispersively distributed in the matrix along the (sub-) grain boundaries; preferred 〈100〉 orientation is achieved in the alloys by appropriate directional solidification process, which makes contribution to improve the magnetostriction. The formation of Tb-rich precipitates induces the transition of the fracture mechanism from brittleness to ductility. The maximal room-temperature tensile strain is obtained in x = 0.05 specimen, which is superior to existing literatures about the mechanical properties of Fe-Ga based alloys. The regular columnar grain morphologies and certain distribution pattern of granular precipitates are considered to be responsible for the excellent ductility in Fe-Ga-Tb alloys. This work may provide a new thinking to design high ductility Fe-Ga magnetostrictive alloys and significantly broaden the application of these materials in industry field.
Fe-Ga alloys exhibit unique functional properties such as magnetostriction that can be varied from the highest positive values among iron-based alloys to negative values including zero magnetostriction, if proper compositions and heat treatments are chosen. This remarkable behavior is related to rather complex phase transformation sequences in this alloy family that are still unresolved. In earlier studies, the phase transformations in Fe-Ga alloys were studied by X-ray diffraction, which provides structural information limited to the near-surface sample area. In this paper, we use electron back-scatter diffraction and in situ neutron diffraction to characterize the D0 3 and L1 2 phases that originate from the fcc and bcc phases in the Fe-27Ga type bulk alloy, respectively. Different ratios between these phases, characterized by magnetostriction values of different signs, were achieved using an isothermal annealing treatment that produces an intrinsic composite in the alloy. Depending on the relative fraction of the D0 3 and L1 2 phases, the magnetostriction values of the alloy, l S , vary from þ100 to À50 ppm, including the value of l S ¼ 0 for the alloy with L1 2 :D0 3 ¼ 2:1 achieved after 600 min annealing at 400 C, thus demonstrating the controlled adjustment of magnetostriction in these advanced alloys.
Application spectrum of shape memory alloys (SMA) is expanding rapidly and proportionately so is the engineering demand for superior materials. An essential prerequisite to developing novel SMAs is a clear perception of the deformation physics underlying their extraordinary shape recoverability. To that end, modern atomistic simulation tools have proffered state-of-the-art models, which usher in new clarifications for SMA deformation properties. It was found, for example, that ab initio energy pathways are at the core of dictating the extent of shear and shuffle for both phase transformation and variant formation at atomic lengthscale. These important revelations are accomplished by addressing inherent solid-state effects, which underpin the natural tendency to seek the energetic ground state. Moreover, empirical potential based models, benefitting from ab initio calculations, have allowed an atomic-resolution view into the phase evolution and the concurrent twinning phenomena relating directly to constitutive properties. Here, we revisit salient examples of these cutting-edge theoretical discoveries regarding SMA deformation along with discussions on pertinent experimental evidences.
Elastic modulus of magnetic materials tends to increase with temperature rising, as the result of gradual loss of magnetic order with approaching Curie point. In this work, the similar behavior was also observed in the directional solidified Fe73Ga27 alloy along the <100> preferred orientation. However, unlike the previous theory, results of magnetic-temperature and thermal expansion measurements show the absence of magneto-volume effect. Such unusual behavior of Young's modulus could be attributed to the enrichment of diffusing atoms along the direction of lowest modulus during the phase transition of A2 → D03. According to the analysis of in situ heating XRD and TEM, the structure transitions of A2 → D03 → A1 → L12 were identified in the temperature range 20–500 °C, which correspond exactly to the changes of Young's modulus in both as-cast and directional solidified samples.
Neutron diffraction studies of the Fe Al compound are performed in a wide temperature range (20– 900°C) in order to determine its structural states and the mechanism of ordering of atoms. The combination of high-resolution diffraction and the real-time detection of diffraction spectra makes it possible to establish that, in contrast to traditional notions, the structure of this compound at room temperature is a phase with only a partially ordered arrangement of Fe and Al in a unit cell. A completely ordered phase (such as Fe Al) is present in the form of mesoscopic (Å) clusters coherently incorporated into the disordered matrix of the main phase. After the transition of the sample to a disordered state (С) and slow cooling to room temperature, the size of structurally ordered clusters increases to Å. A high contrast in the coherent neutron scattering lengths of iron and gallium nuclei allows the accurate determination of the temperature dependence of the occupancy factors of sites by Fe and Al atoms up to a phase transition to the disordered state.
Untersuchung des Einflusses von Aluminium auf die Kohlenstoffdämpfung und die Kohlenstofflöslichkeit von α-Eisen an elf Reineisen-Aluminium-Kohlenstoff-Legierungen mit 0,007 bis 0,019% C, ≦ 0,01% Si, 0,01 bis 0,05% Mn, ≦ 0,003% P, 0,004 bis 0,012% S, ≦ 0,0010% N und 0,003 bis 8,0% Al. Zerlegung der ermittelten Dämpfungskurven in Einzelkurven mit Hilfe eines graphischen Verfahrens, Zuordnung dieser Einzelkurven zu Platzwechselvorgängen. Ermittlung einer Beziehung zwischen Dämpfungskurve und Gehalt an gelöstem Kohlenstoff. Investigation of the effect of aluminium on the damping (internal friction) curve and carbon solubility of α-iron as determined on eleven pure iron-aluminium-carbon alloys with 0.007% to 0.019% C, ≦ 0.01% Si, 0.01 to 0.05% Mn, ≦ 0.003% P, 0.004 to 0.012% S, ≦ 0.0010% N and 0.003 to 8.0% Al. Splitting-up of the damping curves obtained into individual curves by means of a graphical method, allocating of these individual curves to phenomena of site changes. Determination of a relationship between damping curve and content of carbon dissolved. Etude de l'influence de l'aluminium sur l'amortissement et la solubilité du carbone du fer α sur onze alliages fer pur-aluminium-carbone tenant 0,007 à 0,019% C, ≦ 0,01% Si, 0,01à 0,05% Mn, ≦ 0,003% P, 0,004 à 0,012% S, ≦ 0,0010% N et 0,003 à 8,0% Al. Dissociation des courbes d'amortissement obtenues en courbes séparées, par un procédé graphique; rattachement des courbes séparées aux processus de migration. Détermination d'une relation entre la courbe d'amortissement et la teneur en carbone dissous.
Influence of microalloying by Tb on structure and some properties of Fe-19%Ga and Fe-27%Ga type alloys is studied. 0.1%Tb increases magnetostriction of water quenched Fe-19%Ga alloy with A2 structure from 120 to 210 ppm (1.75-fold). Slow cooling decreases magnetostriction in both Tb-free and Tb-doped alloys. Microalloying by Tb increases magnetostriction and influences on phase transitions in the Fe-27Ga type alloys in the range of 20–750 °C as observed by in situ neutron diffraction and vibrating sample magnetometry. The conventional transition sequence of phase transitions at heating D03 → L12 → D019 → B2 → A2 in binary Fe-27Ga is changed for D03 → B2 → B2 + L12 → B2 + D019 → B2 → A2 transitions in the Tb-containing alloy. The increase in Tb content from 0.15% to 0.3% decreases the amount of closed packed phases. At slow cooling (2 K/min), the mixture of D03 + L12 is recorded in the Tb-containing sample instead of dominating L12(∼90%) and a very limited amount of D019 and A2 phases in the binary Fe-27Ga alloy. This influence of Tb on the phase transition kinetics explains temperature dependent magnetization curves with step by step accumulation of the L12 phase in subsequent heating and cooling cycles. Thus, we conclude that the additions of Tb stabilize bcc-born phases (A2, B2 and D03) and prevents the appearance of closed packed (fcc ordered L12 and hcp ordered D019) phases, which contributes to the functional properties of that alloys.
The unitary deformation of single-phase ferromagnets by a magnetic field, i.e., either positive or negative linear magnetostriction, allows only monotonous control. Here we report a proof-of-principle ferromagnetic composite Fe73Ga27, for which the magnetostriction sign changes from positive to negative by increasing the magnetic field strength. Based on the transformation from body-centered-cubic (BCC) to face-centered-cubic (FCC) phases in this binary system, Fe73Ga27 composite is prepared by aging the BCC averaged precursor for 3 days at 803 K. Magnetic measurements indicate that the BCC phase exhibits smaller magnetocrystalline anisotropy constant than the FCC phase. The offset effect between BCC and FCC phases produces positive net magnetostriction at low magnetic fields but negative net magnetostriction at high magnetic fields. By tuning the field strength, such composites can mediate compressive and tensile strains to other functional materials, e.g., piezoelectric material or optic-fibers, which is beneficial to design multifunctional devices.
Fe55Co19Ga26 alloy was made in an induction furnace, and then slowly cooled to room temperature (RT). The structural property of the as-cast alloy was examined by an x-ray diffractometer. From the diffraction pattern, we conclude that the alloy contains the A2 and D03 phases at room temperature. The magnetic hysteresis loop was measured by the vibration sample magnetometer: saturation magnetization MS = 123 emu/g, and coercivity HC = 22 Oe. The mechanical properties, such as Young's modulus (E) and shear modulus (G), were measured as a function of magnetic field (H) up to H = 3 KOe, respectively, by the impulse excitation of vibration (IEV) method. The ΔE or ΔG effect is defined as ΔE/E = [ES – E0]/E0, or ΔG/G = [GS – G0]/G0, where subscript “s” means the saturation state, and the subscript “0” means the zero-field state. Moreover, the flexural magneto-mechanical coupling coefficient (KE) and the torsional magneto-mechanical coupling coefficient (KG) were calculated from: (KE)2/[1 – (KE)2] = ΔE/E0 and (KG)2/[1 – (KG)2] = ΔG/G0. Thus, KE = 22% and KG = 19% for the slowly-cooled Fe55Co17Ga28 alloy.
Enhanced magnetostriction in iron-rich Fe–Ga alloys has been attributed to a heterogeneous nanostructure with tetragonal inclusions, although direct experimental evidence for their structure was lacking. Here we use transmission electron microscopy to show that melt-spun, (001) textured Fe83Ga17 ribbons contain 3 nm inclusions with c-axis Ga–Ga pairs aligned in a tetragonal L60-type structure; the induced tetragonality of the entire A2 matrix is observed directly by synchrotron X-ray diffraction. Trace doping with 0.2 atomic % nonmagnetic elements such as La or Pb increases the magnetocrystalline anisotropy and greatly enhances the magnetostriction. Rare-earth dopants from La to Lu produce a quarter-shell variation of the magnetic anisotropy; the crystal field parameter A20 is determined to be −15 Ka0−2. The best trace dopants are the light rare earths Ce and Pr that give a transverse magnetostriction of up to −800 ppm, as these elements soften the tetragonal modulus via their crystal field interaction. A new model is proposed to explain nanoheterogeneous magnetostriction, where the Ga–Ga pairs remain fixed, but the tetragonal axis of the matrix can be realigned in a magnetic field by a series of small deformations of the A2 matrix. These results signal a new approach to creating highly-magnetostrictive materials.
An integral investigation into the crystalline and magnetic structure, damping properties and magnetic characteristics of Fe-Cr and Fe-Al alloys with a magnetomechanical mechanism for elastic vibration energy dissipation has been carried out. General regularities for the implementation of the high-damping state in these materials have been revealed, that allows to control effectively the formation of their properties.
The anelasticity of binary Fe-Al and ternary Fe-Al-Me (Me = Co, Cr, Ge, Mn, Mb, Si, Ta, Ti, Zr) alloys has been studied by mechanical spectroscopy in the Hz and kHz ranges. Relaxation peaks due to point defects - Snoek effect (S) with carbon interstitial jumps, carbon-vacancy complexes (X peak), Zener effect (Z), dislocations (D), and grain boundaries (GB) - are observed and their changes with addition of the third element are used to corroborate the respective proposed relaxation mechanisms, taking account of the changes of structure and order in the alloys which contain up to 5Co, 25Cr, 25Ge, 5Mn, 0.3Nb, 25Si, 6Ta, 4Ti, and 15Zr (all in at.%), respectively. In addition, some data of ordering temperatures, Curie temperatures, and hardness are provided for several alloys.
Isothermal sections at 800, 1000, and 1150°C as well as a tentative partial liquidus surface of the ternary Fe-Al-Zr system were established by means of electron-probe microanalysis, X-ray diffraction, differential thermal analysis, and light-optical as well as scanning electron microscopy. The most prominent features of the ternary phase diagram are the extended homogeneity ranges of the Laves phases. By continuous substitution of Fe by Al, the structure changes three times starting from the cubic C15 structure of Fe 2Zr to hexagonal C14 (λ1) back to cubic C15 (λ2) and again to hexagonal C14 (Al2Zr). The various Laves phase fields are separated by very small two-phase fields. Besides the Laves phases λ1 and λ2, three more ternary intermetallic phases were found, whose homogeneity ranges have been determined for the first time. In addition, new results concerning the homogeneity ranges of intermetallic phases in the binary subsystems Fe-Al and Al-Zr are reported. The solubilities of the third components in the binary phases are found to be generally very low with the exception of the Laves phases. As a consequence, extended two-phase fields between the Fe(Al) solid solution and Laves phase or between Fe(Al) solid solution and the ternary ThMn12type phase 1 are formed.
In this study, we discussed the structural, magneto-mechanical, and damping properties of slowly-cooled polycrystalline Fe81Ga19 alloy. From the X-ray diffraction, transmission electron microscopy, and optical microscopy studies, we conclude that the alloy contains the disordered A2 and ordered D03 phases. Due to the D03 precipitation hardening effect, the yield strength (Y) of slowly-cooled Fe81Ga19 is about 950 MPa, much higher than that (about 500 MPa) of [100] single crystal Fe81Ga19. For the first time, both Young's modulus (E) and shear modulus (G) were measured vs. magnetic field (H) up to 3 kOe by the impulse excitation of vibration method successfully: the ΔE and ΔG effects. The magneto-mechanical (flexure) coupling factor (KE) of the alloy, estimated from the ΔE effect, is 11.7%, and the (torsion) coupling factor (KG), from the ΔG effect, is 19.1%. The damping capacity, estimated by considering the magneto-elastic hysteresis mechanism alone, is 0.0076 only. The experimentally found total damping capacity is about 0.01-0.03. The latter should be larger than the former, because there are additional micro- and macro-eddy-current contributions to the total damping capacity.
The present study focuses on the effect of constant prestress on damping capacity of Fe-15Cr-2.5Mo-1.0Ni casting ferromagnetic alloy by using dynamic mechanical analyzer (DMA). The stable magnetic fluid was used to observe the magnetic domain structure, a self-regulating apparatus was adopted to obtain the domain structure change under constant prestress. The result shows that the constant prestress exhibits significant effect on damping capacity of the alloy, the internal friction decreases as the prestress increases. It is ascribed to the magnetic domain walls movement of 90°or angled domains caused by domain walls redistribution in responding to the applied constant prestress. Under the constant prestress, the domain structure shows apparent modification. The angle between the domain wall sides dwindles and the domain walls tend to assemble themselves towards the prestress direction. As a result, new 180°domains generate with the domain walls paralleling to the prestress direction and they contribute zero to energy dissipation under following periodic vibration stress, thus causing damping capacity decrease. However, the damping capacity does not decrease when the prestress is small as it is not enough to provide the fluctuating energy of domain wall movement, and the magnetic domain structure remains the initial condition. With the amounts of 90°or angled domain walls and tangle-like sub-domains which devote to a relatively high magnetostriction coefficient λs, the alloy obtains high damping behavior.
The effect of silicon on the damping capacity of Fe-Cr-Al alloy has been investigated with the inverted torsion pendulum techniques. The results indicate that, small amount silicon (app. 1% mass fraction) addition to Fe-Cr-Al or substitution of silicon for aluminum in Fe-Cr-Al alloy can make the damping capacity of the alloys higher than that of Fe-Cr-Al alloy when annealed below 1273 K; substituting silicon for small amount aluminum in Fe-Cr-Al the damping capacity of the alloy is much higher than that of Fe-Cr-Al alloy when annealed above 1373 K followed by air cooling. The curves of logarithmic decrement versus strain amplitude reveal the damping of the alloys resulting mainly from magonetomechanical hystereses.
Three methods, casting, melt-quenching and melt-spinning were applied for preparing Tb-doped (Fe0.83Ga0.17)(100-x)Tb-x (0 <= x <= 0.47). The magnetostriction improved drastically by Tb solid dissolved in Fe83Ga17 alloys. A giant perpendicular magnetostrictions lambda(perpendicular to) up to -886 ppm was achieved in the (Fe0.83Ga0.17)(99.77)Tb-0.23 melt-spun ribbons. The enhanced magnetostriction was thought to be associated with the strong local magnetocrystalline anisotropy caused by the Tb doping into Fe83Ga17 alloys.
In order to improve magnetostriction of the polycrystalline Fe-Ga alloy, the rare earth element Ce was firstly doped into Fe83Ga17 and the melt-spinning method was subsequently applied. The as-cast Fe83Ga17 and Ce-doped Fe83Ga17 alloys were prepared by arc melting. Then the as-cast Ce-doped Fe83Ga17 alloy was melt-spun by the melt-spinning technique. The microstructures and magnetostrictions of all these three alloys were investigated by X-ray diffractometer (XRD), scanning electron microscopy and energy dispersive spectroscopy (SEM/EDS), differential scanning calorimeter (DSC) and magnetostriction measurements. The results indicated that the CeGa2 phase and asymmetrical DO3 phase are formed caused by Ce-doping and melt-spinning, respectively. The magnetostrictions of three alloys are ranked in sequence the melt-spun Fe83Ga17Ce0.8 alloy > as-cast Fe83Ga17Ce0.8 alloy > as-cast Fe83Ga17 alloy. The enhanced magnetostriction is attributed to the fact that the formation of new phases and the preferred orientation along (100) direction.
Soluting rare earth atoms Tb or Dy into body centered cubic (BCC) Fe-Ga through rapid cooling significantly enhances the magnetostriction due to strong localized magnetocrystalline
anisotropy. Origin of the local strong anisotropy, however, awaits comprehensive microstructural investigation. In this letter, formation of tetragonal nanoparticles with c/a ∼ 0.979 has been found in the giant magnetostrictive ribbons Fe82.89Ga16.88Tb0.23 due to local symmetry breaking of the BCC lattice using high resolution transmission electronic microscopy. First principal calculations suggest that random replacement of Tb atoms for Fe or Ga in the ordered DO3
superlattice is beneficial in the formation of such tetragonal symmetry. Exchange couplings between the nearest Tb-Fe or Tb-Tb pairs of the tetragonal nanoparticles might generate strong localized magnetocrystalline
anisotropy, leading to extraordinary magnetostriction enhancement.
A substitutional relaxation peak has been investigated in an iron–15% germanium alloy by free-decay internal-friction technique in an evacuated inverted torsion pendulum. The parameters Q R , ∆ M , τ 0 , and β for the Zener peak are calculated. The presence of a grain-boundary peak at a temperature higher than the Zener peak is also reported.
In order to get more information about the Zener relaxation than ever reported and, furthermore, to elucidate the interrelation between the relaxation effect and diffusion phenomena, the Zener peak which appears around 500°C has been investigated in the range of 11.1 to 30.0 at% Al by means of the internal friction technique. The activation energy, H, and the term D0 of the diffusion coefficient deduced from the relaxation time are roughly given byH=73.4−71.8c(kcal/mol),and lnD0=5.35×10−4H−27.8(cm2⁄sec)where c is the atomic fraction of Al, respectively. Referring to the result of inter-diffusion, it has been argued that the diffusion of Al atom is possibly responsible for the relaxation effect in Fe–Al system. A definite correspondence has been found to exist between the changes of the half-width and of the relaxation strength of the Zener peak against Al concentration.
Zener damping peaks which appear in Fe-(6.4∼11.8)at%Si and Fe-(10.5∼24.2)at%Cr poly-crystalline alloys have been investigated in detail. The magnitudes of the relaxation strength ΔM of these alloys, combined with those of the Fe–Al alloys investigated previously, have been compared with both Zener’s solute pair reorientation theory and LeClaire and Lomer’s directional short-range order theory. It has been shown that ΔM is closely related with the deviation of lattice parameter from Vegard’s law on alloying rather than with the size factor, as predicted by Nowick and Seraphim on the basis of Zener’s theory. The difference of the relaxation strength among the ferrous alloys appears to be reasonably explained by their model. The validity of LeClaire and Lomer’s theory has also been examined briefly. Using the interatomic potentials given by Leamy, the theory accounts for ΔM in Fe–Al alloys to some extent.
Dynamical mechanical and positron annihilation spectroscopies were applied to study the structure of two Fe-Ga alloys with 18 and 21 at. pct Ga after quenching and subsequent annealing. It was found that the alloy with 18 pct Ga has much better damping capacity (psi = 30 pct) than the alloy with 21 pct Ga (psi = 5 pct). The reason for that is the ordering of the Ga atoms in Fe-21Ga alloy. Ordering processes in both alloys are studied at heating by differential scanning calorimetry, dilatometry, and internal friction or by step-by-step annealing using positron annihilation spectroscopy and hardness tests. Experimental results are explained by sequence of ordering transitions: A2 - D03 - L12.
Interdiffusion in Fe-Al alloys was studied by electron-microprobe analysis of the interdiffusion profiles for three series of FexAl 1-x/FeyAl1-y diffusion couples. Temperatures between 997 and 1447 K and Al contents between 18.0 and 49.5 at.% Al were investigated. Interdiffusion coefficients were obtained from the diffusion profiles by a modified Boltzmann-Matano method taking into account the composition dependence of the molar volume. Al tracer diffusivities for concentrations of 25.5, 33.0, and 48.0 at.% Al were deduced from the interdiffusion coefficients with the help of the Darken-Manning equation using Fe tracer diffusivities available from a previous study in our laboratory and thermodynamic factors calculated on the basis of theoretical models, the latter being verified by an analysis of the Kirkendall effect of the interdiffusion couples. Al self-diffusion is found to be slightly faster than Fe self-diffusion and is comparable to the diffusion of the 65Zn and 114mIn radiotracers, which substitute Al on the Al-sublattice of B2 Fe-Al and were used in the previous study from our laboratory to approximate Al self-diffusion.