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Discovered in the early 2000s, giant magnetostriction prompted many experimental and theoretical studies. However, the physical mechanism underlying this important functional property has not been fully understood, despite 20 years of continuous effort. The models currently under discussion are based on the concept of specifically ordered microscopic regions that emerge in a disordered crystal matrix. Of special importance in detecting suchlike structural states are techniques that involve the scattering of X-ray (synchrotron), electron, and neutron radiation. The current state of structural studies of Fe–Ga and Fe–Al alloys is reviewed, with the focus on neutron diffraction.

Ferromagnetic high damping (FHA) alloys with a wide temperature range from -150 °C to 300 °C have unique application value in extreme environments. In the present work, the damping behaviors of Fe-21Ga-xLa (x = 0.12 wt.%, 0.24 wt.%, 0.47 wt.%, 1.18 wt.%, and 2.33 wt.%La) alloys have been studied in detail, and a new phenomenological model has been proposed. With the increase of La content, the Laves phase (LaGa2) in the matrix increases gradually, and the resistance opposing the domain movement increases as well. Combined with the results of synchrotron radiation X-ray diffraction, neutron diffraction, and magnetic domain observation, the resistance mainly comes from three parts: the average stress related to the lattice distortion of the matrix, the average stress related to the increasing area energy of domain walls (DWs), and the average stress related to the increasing demagnetization energy induced by the Laves phase. Different from the traditional method of reducing internal stress through annealing to improve the damping capacity, the proper internal stress barriers are necessary to Barkhausen jumps to dissipate energy. Therefore, proper doping to balance resistance and mobility of DWs is a reliable way to improve damping capacity. Meanwhile, for Fe-Al and Fe-Cr based Alloys, the new model also has a good fitting effect. This study provides a theoretical and experimental reference for improving the functional properties of ferromagnetic alloys.

A (Fe83.4Ga16.6)99.9(NbC)0.1 alloy was used to investigate the effect of thermomechanical treatment on the texture formation and magnetostriction. The main idea was to develop the Goss and cube texture after rolling and primary recrystallization, without secondary one, in order to enhance the magnetostriction strain. Rolling at elevated temperature was used to produce thin sheets; total degree of deformation was 83%. As a result, heterogeneous texture of deformation with a significant amount of orientations with 〈100〉 directions along the rolling direction was created. Subsequent primary recrystallization was initialized by annealing at different temperatures: 900, 950, and 1000°C. The texture evolution was studied by EBSD technique. The texture, residual stress level, and parallel magnetostriction were studied in the samples after recrystallization. By applying high temperature annealing, the magnetostriction is increased. The maximal magnetostriction strain is obtained after annealing for 2 h at 1000°C. An increase in magnetostriction caused by the texture change and a decrease in the internal stresses were shown.

The microstructure of several Fe–xGa alloys with phase-separated structure have been studied by neutron diffraction with high Δ d/d resolution. Analysis of diffraction data shows that the microstructure of these alloys is organized as nano-sized clusters with a better-ordered atomic structure coherently embedded in a disordered or less-ordered matrix. The characteristic size of the clusters depends on the Ga content and ranges from 100–2000 A.

Comparative in situ X-ray and neutron diffraction studies of the phase transitions in a high magnetostriction Fe–27Ga alloy sample have been performed, with heating up to 850°C and subsequent cooling to room temperature. Different structural information (phase content, phase-transition temperatures, unit-cell behaviour) is obtained for the bulk sample and its surface, and this fact is discussed here in terms of the difference between the scattering properties of X-rays and neutrons. In particular, a gallium-deficient phase with A2-type structure was found on the surface of the sample. The results demonstrate that conventional X-ray diffraction methods are insufficient for precise structural analysis of bulk samples of galfenols and cannot be used alone to build their phase diagrams.

This review article is devoted to studies of the structure and properties of Fe–Ga alloys that serve as functional materials with high magnetostriction. Particular attention is paid to diffraction methods that allow one both to monitor phase transformations in real time and identify phase structures and microheterogeneities in their structure. Based on the studies published in recent decades, the existing equilibrium diagrams and mechanisms of formation of elastic and anelastic properties, including magnetostriction and internal friction, are critically analyzed.

Thermoelastic martensitic transformation of Ti29.7Ni50.3Hf20 alloy was studied by high-resolution and in situ real-time neutron diffraction in the temperature range from 25 °C to 250 °C upon heating and cooling. It was shown that B19′ martensite phase is characterized by strong anisotropy of thermal expansion, lattice parameters of aB19′ and bB19′ increase while cB19′ and β angle decrease with increasing of temperature. Coefficients of thermal expansion for martensite and austenite were determined. The volume effect of transformation in Ti29.7Ni50.3Hf20 alloy is 0.75% which is six times larger than that of binary TiNi alloy.

Structural features and kinetics of the transition between ordered metastable b.c.c.-derived D03 and equilibrium f.c.c.-derived L12 phases of Fe–xGa alloys (x = 27.2% and 28.0%) have been analyzed by in situ real-time neutron diffraction during isothermal annealing in the temperature range 405–470°C. It has been revealed that the transition proceeds with alternation of the first- and second-order phase transformations according to a D03 → A2 → A1 → L12 scheme, where A2 and A1 are disordered b.c.c. and f.c.c. structures. Deformations of the crystal lattice that arise due to these transitions are determined. The kinetics of the L12 phase nucleation and growth were analyzed in the frame of the Johnson–Mehl–Avrami–Kolmogorov (JMAK) model; however, only the early stage of the D03 → L12 transition is well described by the JMAK equation. The value of the Avrami exponent corresponds to the constant growth rate of the new L12 phase and decreasing nucleation rate in the Fe–27.2Ga alloy and indicates the presence of pre-existing nucleation centres of the L12 phase in the Fe–28.0Ga alloy.

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

Phase transitions and related anelastic effects are examined in Fe-xGa alloys (x = 19 and 27 at.%) by means of in-situ neutron diffraction, vibrating sample magnetometry, dilatometry, and three different mechanical spectroscopy techniques: torsion forced pendulum, vibrating reed, and commercial DMA Q800. Anelastic transient effects due to ordering-disordering (D03 ↔ A2) in Fe-19Ga, and first order phase transitions (D03 → L12 → D019 → B2) in Fe-27Ga compositions, are discussed with respect to phase and magnetic transitions.

The paper studies amplitude-independent thermally-activated and transient effects in as-cast Fe-(8–33)%Ga alloys in a temperature range from 0 to 600 °C and frequencies from 0.1 to 30 Hz using a dynamic mechanical analyser. The origin of the recorded anelastic effects is discussed based on both earlier publications and new, most systematic, data obtained in this paper. Activation energies and characteristic relaxation time are evaluated and analysed to conclude about the influence of Ga content on Zener relaxation, possible overlapping of Snoek-type relaxation with another, still not well defined, mechanism. The transient effect along with a sharp increase in the modulus is a sensitive tool to detect transition from metastable to stable structure in the Fe-Ga alloys.

Structure of binary Fe-19Ga and ternary Fe-19Ga-Tb alloys at room temperature are investigated by TEM and high-resolution neutron diffraction (ND). In contrast with as cast or water quenched samples with A2 structure, the D03 ordering was detected in slowly cooled or annealed samples by ND. According to TEM, the D03 ordering takes place in the form of ordered clusters with the size of about 5 nm embedded into an A2 matrix. Disordering of the D03 clusters at heating and ordering at cooling were investigated by three in situ techniques: ND, vibrating sample magnetometry (VSM), and internal friction (IF). Temperatures of ordering-disordering were estimated by VSM and IF to be close to 500 °C. The effect of Fe-Ga alloys doping with Tb is also analyzed.

The thermal and mechanical relaxation spectra of a Zr-Cu-Fe-Al bulk metallic glass were obtained before and after room-temperature cyclic loading up to 0.4% of elastic strain. The loading was performed using a dynamic mechanical analyzer at an oscillation frequency of 3 Hz to induce the structural changes within the glassy phase at room temperature. A double-stage structure relaxation behavior was monitored using the same dynamic mechanical analyzer at a lower strain on heating. These structure changes within the glassy phase were studied with X-ray diffractometry and high-resolution transmission electron microscopy. The cycling loading at room temperature lead to drastic changes in the atomic structure of the bulk metallic glassy samples. In particular, it caused partial nanocrystallization after 10,000 elastic cycles, which in turn influenced the relaxation behavior. The structural relaxation process of the Zr-Cu-Fe-Al bulk metallic glass monitored by thermal measurements is different from that observed by the dynamic mechanical analysis.

The structural, electronic and magnetic properties of Fe100−xGax alloys are studied computationally in the composition range up to x≤ 31.25 at.% and experimentally about 27 at.%. Ga content. Using ...

A significant difference in properties and structure of Fe-Ga alloys in their equilibrium and metastable states limits their application. This necessitates an immediate understanding of the importance of cooling rate in the formation of alloy metastable and equilibrium structures. In this paper, we experimentally studied the structure of the Fe-(23−24) Ga alloys after both (i) cooling with different cooling rates and (ii) isothermal annealing between 300 and 575 °C up to 1800 h to report the alloy structure and present the Time-Temperature-Transformation (TTT) diagrams for the metastable to equilibrium transition in these alloys. The critical cooling rates were defined with respect to the formation of the equilibrium state. A theoretical model along with corresponding Monte Carlo simulations for modeling phase transitions and construction of TTT diagram for the same alloys were developed: simulated phase diagrams were analyzed with respect to our the experimental findings.

The evolution of structural phases and the morphology of the microstructure of several Fe-xAl and Fe-xGa compositions were studied by neutron diffraction with high Δd/d resolution and with high-intensity continuous scanning in a wide temperature range. It was found that the formation of an ordered structure upon a change in the Al or Ga content or during a phase transition upon a change in temperature leads to a decrease in the unit-cell parameter with a “jump” of the order of Δa/a ~ 0.001. A specific microstructure in the form of mesoscopic clusters (L ~ 200–1000 A) with an ordered atomic structure dispersedly incorporated into a disordered or less ordered matrix can be formed in the ranges of 23 at%

Enhancement of the magneto-mechanical properties in directional solidified Fe80Al20 alloys by doping Tb is demonstrated. The ΔE effect of 9.1%, large magnetostriction of 144 ppm, magnetostriction sensitivity of 0.28 ppm/Oe, ΔG effect of 5.4%, and magneto-mechanical coupling of 29.74% reached for Fe79.9Al20Tb0.1 alloy are beneficial for applications. The increased magnetostriction with increasing the Tb content x from 0 to 0.1 is related to the increased degree of (110) texture with Tb doping. Notably, the increased magnetostriction sensitivity, resulted from the increased magnetostriction with Tb-doping, leads to the enhancement of ΔE and ΔG effects. Nevertheless, the degraded (110) texture for higher Tb content (x = 0.15) results in the reduction of magneto-mechanical properties. Summarized with the experimental measured and theoretically estimated results, the micro eddy-current mechanism mainly governs the change of damping capacity with H for frequency of vibrations ~ 2.0 kHz resulting from the magnetic domain wall motion. Moreover, the amplitude and temperature dependences of internal friction and elastic modulus data, measured by DMA, including damping capacity and Young’s modulus, at a frequency of 0.1–30 Hz could characterize hysteretic damping and anelastic effects at heating. The result of this study suggests a cost-effective and simple method to obtain Fe80Al20 based alloy with excellent magneto-mechanical properties via proper Tb-doping.

This paper investigates the influence of substitution of 18 at.% of Fe by Co in Fe-27Ga alloy as an effort to improve magneto-mechanical coupling. Study of phase transitions by neutron diffraction reveals that the formation of close packed phases is suppressed in the as-cast Fe-18Co-27Ga alloy. The degree of D03 ordering in the as-cast state for the Fe-18Co-27Ga alloy is lower than that for the Fe-27Ga alloy as estimated by intensities of super-lattice reflections of neutron diffraction spectra in these alloys. Investigation of magnetic properties by vibrating sample magnetometry and magnetic thermal gravimetry proved that the high-temperature B2 phase in the Fe-18Co-27Ga is ferromagnetic, whereas that of the Fe-27Ga is non-ferromagnetic. The Curie temperature (TC) here and later in the text in slowly-cooled Fe-18Co-27Ga is 726 °C, which is higher than that (650 °C) of Fe-27Ga. The mechanical and magneto-mechanical properties samples were studied through impulse excitation of vibration (IEV) method by the Resonance Frequency and Damping Analysis (RFDA) device. The results demonstrate that substitution of 18 at.%Fe by Co in Fe-27Ga alloy could enhance both the elastic, E0, and shear moduli, G0, at zero filed and the total (flexure mode) damping capacity, (ΔW/W)F0, under the measuring conditions.

The effect of Zr addition to the novel Al-Er-Y alloy on microstructure, phase composition, recrystallization behavior, mechanical properties and electrical conductivity is studied. Formation of the Al3Y, Al3Er and Al3(Er,Y) intermetallic phases in the Al-Er-Y alloy is proved by SEM. Zirconium leads to the formation of the Al3(Er,Y,Zr) eutectic phase. We demonstrate the formation of nanosized Al3(Er,Y) and Al3(Er,Y,Zr) dispersoids in the Al-Er-Y and Al-Er-Y-Zr alloys, respectively. The recrystallization temperature for the Al-Er-Y alloy at about 365 °C is recorded by dynamic mechanical analyzer. Zirconium addition to the Al-Er-Y alloy increases the recrystallization temperature to above 400 °C. The YS and UTS of the Al-Er-Y alloy are decreased after annealing of the rolled sheets from 130 to 115 MPa and from 142 to 125 MPa, respectively. The average tensile properties of the Al-Er-Y-Zr alloy in the deformed and annealed conditions are YS = 144 ± 3 MPa and UTS = 156 ± 3 MPa with 11 ± 1% elongation. The Al-Er-Y alloy demonstrates a good electrical conductivity of 64–64.7% IACS. Zirconium addition decreases electrical conductivity to 57% IACS.

Several aspects of the formation of functional Fe-Ga alloys are considered in this paper: (i) the mechanism of phase transition from a metastable ordered bcc-derivative phase to an equilibrium fcc-derivative ordered phase, (ii) the nature of corresponding anelastic effects, (iii) the usage of isothermal annealing for the formation of an intrinsic composite microstructure with a different ratio between the bcc-derivative metastable and fcc-derivative equilibrium phases that have different magnetic properties, and (iv) the effect of an additional doping by Tb to stabilize bcc-derivative phases with high positive values of magnetostriction. In situ neutron diffraction, measurements of magnetostriction and magnetization, mechanical spectroscopy were applied to achieve the goals of this study using Fe-27Ga type alloys.

The dependence of magnetostriction and magnetic properties in Fe-19Ga-xTb (x = 0–0.37 at. %) and Fe-27.4Ga-xTb (x = 0–0.5 at. %) alloys on the concentration of Tb has been analyzed. A phase enriched in Ga and Tb (up to 7 at. % Tb and 41 at. % Ga) was observed at the grain boundaries and inside the interdendritic regions after direct solidification. Microstructure analysis shows a two-phase (D03 and Tb + Ga-rich phase) structure in Fe-19Ga-Tb and a three-phase (D03, L12 and Tb + Ga-rich phase) structure in Fe-27Ga-Tb-type alloys. The chemical compositions of all phases have been analysed quantitatively and the solubility limit of Tb in Fe-Ga was evaluated to be less than 0.15 at. %. The addition of Tb increases the saturation magnetostriction in the Fe-19Ga-xTb and Fe-27.4Ga-xTb alloys (up to ≈235 ppm for the Fe-19Ga-0.37 Tb and ≈240 ppm for the Fe-27.4Ga-0.3 Tb samples). These values are considerably higher than those of the binary counterparts. The magnetic permeability, μ, and magnetocrystalline anisotropy constant, K1, are increased by the addition of Tb, too, from 3.94 × 10−4 H/m and 1.28 × 104 J/m3 for the Fe-19 Ga alloy to 4.62 × 10−4 H/m and 1.316 × 104 J/m3 for the alloy containing 0.37 at. % Tb. The reversible order – disorder phase transition of the type D03 ↔ A2 leads to a transient anelastic effect at about 555 °C and 520 °C respectively upon heating and cooling of the Fe-19 Ga-0.15 Tb alloy. Vibrating sample magnetometry results are in a good agreement with the internal friction measurements, demonstrating the occurrence of an ordering reaction at 510 °C during cooling.

The accumulation of defects and internal stresses and related changes of the direct and reverse martensitic transition (MT) on thermocycling over the phase transition in different Fe–Mn–Si alloys are investigated by in situ neutron diffraction, TEM, SEM-EBSD, DSC and mechanical spectroscopy. The temperature of direct MT in Fe-22Mn-3Si, Fe-26Mn-4Si and Fe-26Mn-7Si alloys decreases during thermal cycling, while that of the inverse MT increases, which causes a widening of the transformation hysteresis. Transmission electron microscopy shows that a large number of dislocations and stacking faults are formed in both martensitic and austenitic phases in the Fe-22Mn-3Si annealed alloy submitted to γ ↔ e thermocycling. From in situ neutron diffraction tests on Fe-22Mn-3Si annealed alloy and classical Williamson-Hall analysis, we found that the microstrains in the e-martensite after 1 and 12 thermocycles are roughly twice higher as compared with the austenite phase.

A combination of high-resolution and in situ real-time neutron diffraction was used to collect the experimental data concerning coherent atomic ordering in Fe3Al-type alloys in a wide temperature range. The analysis of the obtained data was carried out within the framework of two models: antiphase domains and dispersed clusters embedded in matrix. The second model, for which the atomic ordering is organized in the form of clusters of mesoscopic sizes (from ∼200 to ∼400 A) randomly distributed inside a less ordered matrix, provides a better fit of the data. For two chemically identical Fe3Al samples - the first was in the as-cast polycrystalline bulk state, and the second was grown as a single crystal - the initial state can be described as a partially ordered B2 structure (matrix) with dispersed clusters of the D03 ordered phase. The initial (quenched) state of the (Fe0.88Cr0.12)3Al polycrystalline sample is the disordered A2 phase with clusters of the partially ordered B2 phase. After heating and subsequent slow cooling, the structure of both binary and ternary alloys is B2 matrix with dispersed D03 clusters, whose dimensions are increased up to ∼900 A.

Isothermal annealing treatment was used to form a natural two-phase ferromagnetic composite structure with a different ratio between the bcc-derivative metastable D03 and fcc-derivative equilibrium L12 phases. Depending on the ratio of these phases, magnetostriction values of the alloy can be varied considerably between +100 and −50 ppm, while magnetic field dependence of the magnetostriction depends on dispersion of the L12 phase. Microalloying of Fe-27Ga type alloy with Tb significantly stabilizes the metastable D03 phase and leads to the formation of a new phase enriched of Tb and Ga at the grain boundaries of as cast alloy. A competition between the precipitation of the Tb-enriched phase and the nucleation of the L12 phase at the grain boundaries of the D03 phase can reasonably explain the decelerating effect of Tb on the kinetics of the phase transitions in Fe-27Ga alloys. The Tb-enriched phase precipitates during casting, and therefore, at subsequent annealing these precipitations prevent the nucleation of the L12 phase on the grain boundaries of the as cast (D03) structure.

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.

Neutron diffraction studies of a α → γ structural phase transition (Tc ≈ 911°C) in iron samples at different initial states have been performed. The anomalous disappearance of a diffraction pattern is observed in iron in the region of the α → γ phase transition. At repeated heating processes of an as cast sample, this effect becomes less pronounced and it is absent at the heating of iron powder. The observed effects have been assumingly attributed to the formation of small paracrystalline clusters with a large dispersion of the cell parameters in the process of phase transition. The kinetics of formation of clusters is slowed in as cast samples, which leads to the temporal disappearance of the diffraction pattern. These results make it possible to reconsider the atomic processes in the α → γ phase transition in iron.

Diffusion couple technique is an efficient tool for the estimating the chemical diffusion coefficients. Typical experimental uncertainties of the composition profile measurements complicate a correct determination of the interdiffusion coefficients via the standard Boltzmann-Matano, Sauer-Freise or the den Broeder methods, especially for systems with a strong compositional dependence of the interdiffusion coefficient. A new approach for reliable fitting of the experimental profiles with an improved behavior at both ends of the diffusion couple is proposed and tested against the experimental data on chemical diffusion in the system Fe-Ga. An extension of the approach for reliable description of the up-hill diffusion phenomenon in multicomponent systems is presented.

Effect of microalloying by Tb on the microstructure, phase transitions, and functional properties of the Fe-19Ga-xTb and Fe-27.4Ga-xTb (where x = 0, 0.15, 0.3, 0.4, or 0.5 at.%) alloys was investigated by several techniques including in-situ neutron diffraction, X-ray diffraction (XRD), SEM-EBSD, magnetic measurements, and mechanical spectroscopy (internal friction). We could establish a microstructural understanding to figure out why doping with the trace amounts of Tb leads to an enhanced magnetostriction in the Fe-27.4Ga alloy up to 242 ppm. Our results demonstrate that the microalloying of Fe-27.4Ga with Tb significantly suppresses the formation of the phases with close-packed L12 and D019 structures and stabilizes the dominant phase with D03 structure. The L12 has negative magnetostriction compared to positive magnetostriction of the D03 matrix; therefore, the lower the volume fraction of the L12 is the higher the saturation magnetostriction at room temperature is. The influence of Tb on decelerating the kinetics of the phase transitions in the Fe-27Ga alloys can be reasonably explained by considering a possible competition between precipitation of the Tb-enriched phase and the nucleation of the L12 at the grain boundaries. Both Tb-enriched and the L12 prefer D03 grain boundaries for their nucleation as demonstrated by EBSD analysis. Nevertheless, the Tb-enriched phase already precipitates during casting, and therefore, at subsequent annealing, these precipitations prevent the nucleation of the L12 on the grain boundaries of the as-cast (D03) structure.

The effect of partial substitution of Cu by Cr on the spinodal decomposition of face-centered cubic (f.c.c.) austenite in the as-quenched Mn-10Cu-4Cr alloy is studied after different ageing treatments by small-angle neutron scattering (SANS) and in situ neutron diffraction. Under the same quenching conditions, additional α-Mn phase with A12 structure in the Mn-10Cu-4Cr alloy is observed as compared with Mn-13Cu alloy at room temperature (RT). The replacement of Cu atoms by Cr atoms retards the spinodal decomposition of austenite during ageing compared to the binary Mn-13Cu alloy according to SANS and Differential scanning calorimetry (DSC) results. The reason is that Cr enriches in the α-Mn phase, and thus its addition leads to the formation of the α-Mn phase. Compared to the Mn-13Cu alloy, there is an increase in the tetragonality of the face-centered tetragonal (f.c.t.) martensite, which may be attributed to changes in magnetic interaction owing to partial substitution of Cu by Cr. The higher tetragonality value leads to a higher volume effect during martensitic transition (MT) of Mn-10Cu-4Cr alloy than that of Mn-13Cu alloy (around 1.5 times). The lattice parameters of the f.c.t.-martensite do not converge exactly to the parameter of the f.c.c.-austenite at the MT temperature due to replacement of Cu by Cr. Instead, there is a jump of the lattice parameters during phase transition.

In order to improve the understanding of the sensibility of the internal friction phenomena to different stages of precipitation in Al-Mg alloys, the ageing effect of a supersaturated solid solution on the Temperature Dependent Internal Friction (TDIF) spectra has been studied. The research showed that the dissolution of the β phase and the transfer of Mg atoms to a solid solution and the formation of β′ metastable phase have an effect on internal friction. Thus, it was proved that the precipitation or the dissolution of β phase plays an important role in the anelasticity of Al-Mg alloys. A detailed TDIF analysis revealed the sensibility of the internal friction technique to the formation of semi-coherent and non-coherent phases (β′ and β) but it is not sensitive enough to the formation of coherent phases (GP zones). Several observations on the nature and the shape of the precipitates are also discussed.

Anelastic effects in Fe-(23–38)Ga binary and ternary alloys doped with rare-earth (RE) elements, RE = Pr, Sm, Tb, Er, and Yb, are studied in a sub-resonance frequency through heating and cooling in the range from 0 to 600 °C. In situ neutron diffraction, vibrating sample magnetometry (VSM), and differential scanning calorimetry (DSC) are used to trace phase transitions during heating and cooling and to interpret anelastic effects due to phase transitions. Besides the thermally activated effects, two transient effects due to the first-order transitions D03 → L12 and B2/D03 → Fe13Ga9 (later in alloys with Ga content>29 at%) are studied. In most cases, the RE elements decrease the rate of phase transitions. The obtained results demonstrate an excellent correlation between temperature-dependent internal friction, in situ neutron diffraction, and vibrating sample magnetometry tests.

Modelling of the deformation process of Al85Y8Ni5Co2 amorphous alloys was carried out under simultaneous application of cyclic mechanical load (at 0.3 or 3 Hz frequencies) and continuously increasing temperature (heating rate 5 K/min). It is shown that deformation of the amorphous specimens occurs by the hyperbolic temporal dependence. It is analytically determined and experimentally proved that for non-isothermal cyclic deformation, the wave effects take place as a result of the superposition of thermal-activated and mechanical components. The behaviour of the material under thermo-mechanical action was described qualitatively within the framework of Spaepen’s model. The dependencies for the reaction force of the samples were obtained as two-parameter functions of the frequency and temperature. A reaction force surface of a specimen, as a function of the different forcing frequencies and time, has been plotted.

Anelasticity of Fe-(16−21)at% Ga-RE (rare earth RE = La, Tb, Dy, Er, Yb elements) alloys at room and elevated temperatures is studied in a sub-resonance mechanical spectroscopy. Two thermally-activated and two transient effects are recorded in most of the studied alloys. To explain these phenomena, structure and phase transitions in several binary and ternary Fe-Ga alloys are investigated. The D03 ordering of rapidly cooled alloys with the A2 structure at heating at around 300 °C and the disordering at heating and the D03 ordering at cooling around 500 °C for annealed samples are proved using three in situ techniques: neutron diffraction, vibrating sample magnetometry, and internal friction and supported by positron annihilation experiments. Thermally activated transitory effects are tentatively explained by stress-induced reorientation of Ga-Ga, vacancy-vacancy pairs, and carbon atoms jumps.

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 D0 3 → L1 2 → D0 19 → B2 → A2 in binary Fe-27Ga is changed for D0 3 → B2 → B2 + L1 2 → B2 + D0 19 → 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 D0 3 + L1 2 is recorded in the Tb-containing sample instead of dominating L1 2 (∼90%) and a very limited amount of D0 19 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 L1 2 phase in subsequent heating and cooling cycles. Thus, we conclude that the additions of Tb stabilize bcc-born phases (A2, B2 and D0 3 ) and prevents the appearance of closed packed (fcc ordered L1 2 and hcp ordered D0 19 ) phases, which contributes to the functional properties of that alloys.

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 D03 and L12 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 D03 and L12 phases, the magnetostriction values of the alloy, λS, vary from +100 to −50 ppm, including the value of λS = 0 for the alloy with L12:D03 = 2:1 achieved after 600 min annealing at 400 °C, thus demonstrating the controlled adjustment of magnetostriction in these advanced alloys.

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.

Neutron diffraction and mechanical spectroscopy techniques were combined in one study in order to interpret structure induced anelasticity of Fe-(25–27)Me alloys where Me is Al, Ga or Ge. The following sequences of phase transitions at continuous heating in the 20–850 °C temperature range were recorded: (i) in Fe-27Al the B2 (only in water quenched state) → D0 3 → B2 → A2, (ii) in Fe-27Ga: D0 3 → L1 2 → D0 19 → A2(B2), and (iii) in Fe-25Ge: D0 19 (+A2 very limited amount) → A3 (+A2 very limited amount). At continuous cooling from 850 °C, we recorded the following transitions: (i) in Fe-27Al A2 → B2 → D0 3 , (ii) in Fe-27Ga: A2 → B2 → L1 2 (+ very limited amount of D0 19 and remaining A2 phases which underwent to D0 3 ordering), and (iii) in Fe-25Ge A3 (+A2 very limited amount) → D0 19 (+A2 very limited amount). These transition sequences determine different temperature dependencies of magnetic and anelastic properties in the studied alloys. In Fe-27Al and Fe-27Ga water quenched samples the bcc-born phases (A2, B2, D0 3 ) dominate at room temperature and a Snoek-type anelastic relaxation is recorded in both alloys. The Snoek relaxation is not recorded in Fe-25Ge alloy which has a close-packed D0 19 structure. Zener relaxation was recorded in all three systems Fe-Al, Fe-Ga and Fe-Ge both at heating and cooling. The first order irreversible D0 3 → L1 2 transition (in Fe-27Ga) at continuous heating generates internal stresses due to a huge jump-like increase of atomic volume with temperature and leads to a well-pronounced transient internal friction effect. The reversible D0 3 ↔ B2 transition (in Fe-27Al) also leads to a transient but much smaller anelastic effect. Much slower phase transition in Fe-25Ge alloy does not influence temperature dependent anelasticity in this alloy.

Nano-SiCp/AZ91 magnesium matrix composite was fabricated by stir casting. The as-cast ingots were extruded at 350 °C, then processed by equal channel angular pressing (ECAP) at various temperatures (250 °C, 300 °C and 350 °C). Grains are significantly refined after the extrusion and the ECAP. A basal fibre texture was detected by neutron diffraction after the extrusion, which inclines about 45° to the extrusion direction (ED) after the ECAP. Nano-scaled SiC particles agglomerate in the as-cast composite. After the extrusion, the agglomeration tends to form continuous or discontinuous strips along the extrusion direction. By application of the ECAP, the agglomerated SiC particles are partly dispersed and the strips formed during the extrusion tend to be thinner and broken with the increasing pass number. The yield tensile strength (YTS) and the ultimate tensile strength (UTS) of the composite are dramatically increased after the extrusion. ECAP for one pass at various temperatures further increases the strength, however, the YTS decreases with the increasing ECAP temperature and the pass number. The Orowan equations predict the maximum YTS of the composite may be up to 400 MPa providing SiC particles are homogenously distributed in the matrix.

The influence of homogenisation regimes on precipitations of fine Mn-bearing dispersoids, recrystallisation kinetics, grain structure, mechanical properties and superplasticity of cold worked sheets of Al-3Mg alloys with Mn, Cr and Zr is studied. Precipitates of coherent compact and plate-like particles of Mn-bearing phase are found after homogenisation annealing. Activation parameters of the low-temperature internal friction, internal friction solute grain boundaries peak and dislocation nature thermally activated relaxation peak in the samples treated by different regimes are compared. High-temperature homogenisation at 460 °C provides a higher volume fraction and finer particles of Mn-containing phases after thermomechanical processing compared to low temperature treatment at 380 °C. Consequently, finer grains and higher superplasticity indicators are achieved in a recrystallised state. Polygonisation is observed during heating of the cold worked samples pre-homogenised at 380 °C: recrystallisation temperature is increased and mechanical strength at room temperature is improved. Keywords: Aluminium alloys, Precipitations, Recrystallisation, Internal friction, Superplasticity