Γ2 Phase Research Articles

Grain characteristics and mechanical properties of as-cast Cu-10%Al alloy: Effects of alloying additions

In this research, a study between the microstructure and mechanical properties of Cu–10%Al alloy with the single addition of V, Ni, Mn, Nb and Cr at 5 wt% was carried out. This work aims to analyse the grain size criterion of Cu-10% Al alloy with various alloying elements. Six synthetic alloys of Cu%10Al were produced by sand casting using a bailout crucible furnace. Mechanical properties such as ultimate tensile strength, percentage elongation, hardness, and impact strength were determined on the alloys. The structural properties were examined by an optical metallurgical microscope and scanning electron microscopy (SEM). The average grain size, profile plot and grain size distribution were also determined using ImageJ software. The results indicated that Cu10%Al alloys with alloying elements had improved mechanical properties compared to Cu–10%Al alloy without alloying elements. Cu–10%Al–5%Nb alloy showed the optimum performance in terms of ultimate tensile strength and percentage elongation, while Cu–10%Al–5%Mn alloy gave peak value of hardness and impact strength. From structural observation, α-phase, β-phase, and intermetallic phases such as fine stable reinforcing kappa phase and coarse α+γ2 phase were detected and allied to the properties enhancement. The properties improvement is directly dependent on the grain refinement of the microstructures as the average grain size of the parent alloy decreased from ≈16.54 μm to ≈11.08 μm after the adding of alloying elements.

Effect of powder processing and alloying additions (Al/ZrB2) on the microstructure, mechanical and electrical properties of Cu

The present work elucidates the effect of powder processing conditions (milling/mixing) and conductive alloying element (Al: aluminium) and ceramic (ZrB2: zirconium diboride) reinforcement addition on the densification, microstructure and electrical conductivity of copper (Cu) processed via hot pressing route. Disregard of alloying element/reinforcement/content or powders preparation method, the density of Cu materials varied between 92.16 and 99.76% ρth (theoretical density) after hot pressing at a low temperature of 500 °C. In case of Cu-Al alloys, the powder processing method significantly influenced its microstructure and conductivity. Particularly the Cu-Al alloys processed using mixed powders consisted of various phases Cu, α-Cu, γ1 (Cu9Al4), δ (Cu3Al2), ζ1 (Cu4Al3), η2 (CuAl) and θ (CuAl2) and the Cu alloys prepared using milled powders composed of either only α-Cu or α-Cu and γ1 (Cu9Al4) phases (depending on the Al content). Whereas, only Cu and ZrB2 phases were observed with the Cu-ZrB2 composites processed using either milled or mixed powers. In case of Cu-Al alloys, the hardness (0.88–3.41 GPa) and strength (540.30–1120.18 MPa) of Cu increased with the addition of Al. Interestingly, the hardness (0.88–2.55 GPa) and strength (508.50–970.60 MPa) of Cu increased upto 5 wt% ZrB2 and then they lowered with further addition of ZrB2. In particular, the hardness and strength of Cu-ZrB2 composites are lower than Cu-Al alloys reflecting the effectiveness of solid solution strengthening in the Cu alloys as compared to dispersion strengthening mechanism in Cu composite. The pure Cu prepared using milled powders exhibited low conductivity (75.70% IACS) than Cu processed using as-received/un-milled powders (97.00% IACS). Also, the Cu-ZrB2 composites measured with better electrical conductivity than Cu-Al alloys. Depending on the milling conditions and alloying/reinforcement amount, the conductivity of Cu-ZrB2 composites varied between 44.10 and 88.70% IACS.

Study on diffusion characteristics of Al-Cu systems and mechanical properties of intermetallics

The kinetics of reaction diffusion in Al-Cu binary systems at solid-state temperatures was experimentally investigated. The Al-Cu diffusion couples were heat treated in the temperature rang of 673–813 K for different period of time, respectively. A layer of intermetallic compounds (IMCs) consisting of θ(Al2Cu), η2(Al0.939Cu0.987), ζ2(Al9Cu11.5) and γ1(Al4Cu9) phases was formed in the diffusion region. The thickening of all four IMCs follows a parabolic growth pattern, which can be used to estimate the growth constants of the IMCs. The composition of IMC was quantitatively analyzed by electron probe microanalysis (EPMA), and the interdiffusion coefficients and activation energies were evaluated for each phase. The nanoindentation technique was employed to obtain the hardness, Young's modulus and creep stress index of the IMCs. It was demonstrated that the ζ2(Al9Cu11.5) phase has the greatest hardness of 11.94 GPa, while γ1(Al4Cu9) has the largest Young's modulus of 254.69 GPa and the minimum creep stress index of 10.75.

Structure and magnetic properties of spinodal decomposed Cu60Ni20Fe10Co10 ribbons with hard magnetism

The spinodal decomposed Cu-Ni-Fe alloy can possess both hard magnetic properties and excellent plastic toughness, corrosion resistance, and cold workability. Cu60Ni20Fe10Co10 ribbons are prepared by melt-spinning and annealing methods, and their phase composition, microstructure, and magnetic properties are studied. The results show that the as-spun ribbons are composed of equiaxed grains. Through the decomposition of γ → γ1 + γ2 inside the grains, the spinodal structure is formed, which endows the ribbons with the hard-magnetic properties. Also, the maximum coercivity of 679.3 ± 149.1 Oe and saturation magnetization of 72.0 ± 2.7 emu/g are obtained in the ribbons annealed at 435 °C for 30 min and 835 °C for 30 min, respectively. The shape anisotropy of γ1 and γ2, the concentration of Fe, Co, Ni in the γ2 phase, and the content of the α phase are the main factors to determine the magnetic properties. At the same time, the corresponding microstructure evolution models are proposed.

Phase Equilibria in the Al-Cr-Co System in the Range of Compositions 0-70 at.% Al

Phase equilibria during solidification in the Al-Cr-Co system in the range of compositions 0-70 at.% Al were studied using optical microscopy, scanning electron microscopy, electron probe microanalysis, differential thermal analysis and x-ray diffraction. Solidus and liquidus surfaces, a melting diagram as their superposition, a Scheil diagram for solidification, as well as series of isopleths were constructed for the first time. Solid solutions based on Cr, αCo, Cr5Al8 (γ3 and γ1 phases), CoAl, Co2Al5 binary compounds and the ternary compound τ5 take part in phase equilibria. The monoclinic ternary compound τ5 forms by peritectic reaction L + γ1 + Co2Al5 ↔ τ5 at 1065 °C. Four invariant four–phase reactions and one invariant three–phase reaction involving liquid take place at 1280, 1175, 1110, 1065 and about 1480 °C, respectively. Isopleths 10, 20, 30 and 40 at.% Al as well as 40 at.% Cr demonstrate peculiarities of the phase diagram.

The Microstructure and the Phase Stability of a Cu–30at.%Al Alloy Obtained by Reactive Milling and Quenching

The phase stability of a Cu–30at.%Al milled and quenched is studied by differential scanning calorimetry and in situ high-temperature X-ray diffraction (HT-XRD). This analysis was performed from room temperature to 700 °C. The grain growth at fixed temperatures was analyzed by HT-XRD. The size of the γ2 phase grains do not change at a constant temperature with the time at temperatures below 600 °C. This behavior was attributed to the pulling force resulting from the presence of nanometric grains. The presence of nanometric grains was confirmed by TEM. The lack of grain size growth at a constant temperature is a promising result for the technological application of the Cu–30at.%Al milled and quenched as a shape memory alloy.

Microstructure evolution in U-10Zr alloy irradiated by swift Xe ions at 700 ∘C

The post-irradiation examination (PIE) results of U-10Zr binary metallic fuel that was irradiated by 84 MeV Xe ions at 700 ∘C are reported. The U-10Zr specimen was synthesized by homogenizing elemental U and Zr powders through arc-melting. The as-fabricated U-10Zr was dominated by the sub-micron acicular α+δ phase. After being irradiated by 84 MeV Xe ions at 700 ∘C up to 2.19 × 1017 ions/cm2 fluence, the U-10Zr was speculated to evolve into micro-scale γ1+γ2 phases as predicted by the U-Zr phase diagram. During post-irradiation cooling, the U-rich γ1 phase was mainly transformed to the α phase, while the Zr-rich γ2 phase was partially retained along with formation of hexagonal structure phase (δ or ω). Xe bubbles formed in the γ1 and γ2 phases have salient different morphologies, implying faster Xe diffusion in the γ1 phase than the γ2 phase. The quantitative bubble morphology data collected in this study can provide valuable references for the development and validation of fuel performance models for this fuel.

Influence of copper precipitates on clustering behavior of alloying elements observed in Japanese reactor pressure vessel surveillance materials using atom probe tomography

In a highly irradiated reactor pressure vessel (RPV), solute Mn, Ni, and Si (MNS) atoms gather to form nanometer-sized microstructures, generally called MNS clusters. MNS often gather with Cu-rich precipitates, which can form in RPVs following lower dose irradiation. In this study, surveillance specimens provided from four nuclear power plants in Japan were analyzed using three-dimensional atom probe tomography (APT), and the nature of the solute enrichment was carefully compared. When analyzing the chemical composition of each cluster, a clear negative correlation was found between Si and Cu in all materials, but conversely, Mn was likely present in clusters with a high Cu concentration. Moreover, in a boiling water reactor material with high Cu, the ratio of MNS was shown to be similar to that of the Γ2 phase [Mn (Ni, Si)2]. In pressurized water reactor materials with medium and low Cu, however, Ni and Si enrichment was demonstrated to be higher than the ratio of the expected intermetallic compounds; such as a Γ2 phase and a G phase [Mn6 Ni16 Si7]. Ni and Mn atoms, once enriched in a copper-rich region, may elute out, and form an intermetallic compound with Si atoms within the vicinity. Particularly in highly irradiated RPV materials, such a structure may tend to be decorated by irradiation-induced lattice defects with Si segregation.

Thermodynamic modelling of the Al–Co–Mn system

In the present work, the Al–Co–Mn ternary system is thermodynamically modelled using the Calphad approach. In the modelling, experimental data such as liquidus, solidus, tie lines, and phase boundaries are included. An order–disorder model is used to describe the bcc and B2 phases. The bcc/B2 description was modified in the binary Al–Co system to improve the fit of bcc/B2 equilibria in the ternary system. The thermodynamic models of Al5Co2, M-Al13Co4, γ1, and γ2 intermetallic phases were modified to include the third element to reflect the solubility of this element in the ternary system. The ternary phase T-AlCoMn is described as a stoichimetric compound. Ternary interaction parameters for liquid, bcc, β-Mn, and hcp were optimized, using all the relevant experimental data in the literature. Calculated isothermal and isoplethal sections are compared with experimental data. A comparison between modelling and experimental measurements showed a good agreement between the present results and experiments.

Effect of Co additions on the damping properties of Cu–Al–Ni shape memory alloys

This study investigates the effect of Co additions on the damping properties of Cu-13.5Al–4Ni-xCo and Cu-14.0Al–4Ni-xCo (x = 0–2 wt%) shape memory alloys (SMAs). The Cu-14.0Al–4Ni SMA exhibits a higher inherent and intrinsic internal friction (IFPT + IFI) peak than the Cu-13.5Al–4Ni SMA, but its (IFPT + IFI) peak temperature is below 0 °C. Adding Co into the Cu-14.0Al–4Ni SMA can effectively increase the (IFPT + IFI) peak temperature and reduce the grain size of the alloys. The grain size of the Cu-14.0Al–4Ni-xCo SMAs decreases from approximately 300 μm to below 50 μm when the Co content increases from 0 to 2 wt%. The (IFPT + IFI) peak temperature for the Cu-14.0Al–4Ni-xCo SMAs increases from −0.1 °C to 77.7 °C when the Co content increases from 0 to 1 wt%, but their tan δ values decrease from 0.0402 to 0.0090 simultaneously. The Cu-14.0Al–4Ni–2Co SMA does not exhibit an observable (IFPT + IFI) peak. The tan δ values of the (IFPT + IFI) peaks decrease with increasing Co content because the movements of the parent/martensite phase interfaces and twin boundaries are impeded by the increased amounts of grain boundaries and γ2 phase precipitates. Among these Cu–Al–Ni–Co SMAs, the Cu-14.0Al–4Ni-0.5Co SMA is more suitable for high-damping applications as it possesses an (IFPT + IFI) peak with tan δ close to 0.02 at approximately 50 °C.

Advanced thermal stability investigations of the Mn–Al-Ga system

A ternary Mn–Al-Ga alloy with the nominal composition Mn55Al38.57Ga6.43 was produced by arc melting. After homogenisation, the alloy consisted of the ε and γ2 phases. Appropriate heat treatments were used to transform each of these into a phase with the L10 structure. These two L10 phases had different compositions, lattice parameters and magnetic properties. In order to test the stability of the L10 phases against decomposition, heat treatments were carried out at 700 ​°C for durations of up to 14 days. The results showed that the decomposition started with formation of the β-Mn phase and subsequent appearance of the γ2 phase. The resulting diffusion gradients resulted in composition changes in the L10 phases and after 7 days, only a single, intermediate composition remained. After 14 days, the decomposition was almost complete. The decomposition of the L10 phases in the ternary Mn–Al-Ga alloy was significantly slower than in binary Mn–Al alloys.

Near room temperature spin reorientation and temperature evolution of magnetic structure in Mn substituted HoFeO3

Magnetic structure and spin reorientation transition of 45% Mn substituted HoFeO3 have been investigated using bulk magnetization, neutron powder diffraction and specific heat capacity techniques. These studies confirm the presence of antiferromagnetic ordering of Fe/Mn sublattice below 336 K. The spin reorientation (SR) transition (TSR ~ 290 K) where the magnetic structure changes from Γ4(Ax, Fy, Gz) to Γ1(Gx, Cy, Az) is confirmed by Rietveld analysis of neutron diffraction patterns taken at various temperatures. Though the spin reorientation (SR) transition is happening at 290 K, the system is found to be in mixed Γ4(Ax, Fy, Gz) + Γ1(Gx, Cy, Az) phase from room temperature to 275 K. Below 275 K, the sample exhibits a pure Γ1(Gx, Cy, Az) structure in which the weak ferromagnetic component is absent. Bulk magnetization and specific heat capacity measurements also confirm the Néel temperature and spin reorientation transitions and support the neutron diffraction analysis.

PHASE EQUILIBRIA IN THE Cu2Se – Ga2Se3 – In2Se3 QUASI-TERNARY SYSTEM

Isothermal section of the quasi-ternary system Cu2Se – Ga2Se3 – In2Se3 at 820 K has been built according to the X-ray analysis results of 100 samples. The system is characterized by the formation of the region of α-solid solutions with the chalcopyrite structure, S.G. I-42d. δ'-Solid solutions based on CuIn3Se5 and δ-solid solutions based on CuGa3Se5 are formed at 820 K. The first one have tetragonal structure and crystallize in S.G. I-42m with changing of the cell parameters from a = 0.57540(1) nm, c = 1.1520(2) nm for CuIn3Se5 to a = 0.56207(9) nm, c = 1.1286(6) nm for the composition 48 mol.% CuIn3Se5 – 52 mol.% CuGa3Se5. δ-Solid solutions crystallize in tetragonal system, S.G. I-42m. The cell parameters change from a = 0.55092(3) nm, c = 1.0973(2) nm for CuGa3Se5 to a = 0.56040(7) nm, c = 1.1179(9) nm for the composition 28 mol.% CuIn3Se5 – 72 mol.% CuGa3Se5. The mechanism of the formation of solid solutions, namely the substitution In3+ « Ga3+, was established. In addition to these solid solutions, the system is characterized by the formation of ε-solid solutions based on HTM Ga2Se3 with cubic structure, S.G. F-43m. The unit cell parameters vary from a = 0.5430(2) nm for Ga2Se3 to a = 0.5512(3) nm for the sample 4 mol.% Cu2Se – 83 mol.% Ga2Se3 – 13 mol.% In2Se3. There are also γ2 and γ1 phases, which areas of existence extend into the quasiternary system till 1-2 mol.% and streach along the Ga2Se3 – In2Se3 system (γ1 – up to 10 mol.% In2Se3, γ2 – up to 30 mol.% In2Se3). There are small regions of homogeneity based on HTM Cu2Se, CuIn5Se8, CuIn7Se11, CuIn11Se17, 1-HTM In2Se3. These one-phase regions are separated by two- and three-phase equilibria.The liquidus surface projection has been built based on the results of investigations of the quasi-binary CuInSe2 – Ga2In8Se15 system and 6 polythermal sections. The liquidus surface projection of the Cu2Se – Ga2Se3 – In2Se3 system consists of 11 fields of the primary crystallization: μ-solid solutions based on HTM-Cu2Se, Cu3InSe3 compound, α-solid solutions with the chalcopyrite structure, β-solid solutions based on HTM-CuInSe2, quaternary high-temperature γ-phase formed in the Cu2Se – Ga2Se3 system, δ-solid solutions based on CuGa3Se5, ε-solid solutions based on HТМ-Ga2Se3, γ1-phase based on the Ga0.4In1.6Se3 composition, compounds CuIn5Se8 and CuIn11Se17, and 3-HТМ In2Se3. These fields are separated by 21 monovariant curves and 22 nonvariant points which lie on the corresponding planes of nonvariant four-phase processes. There is one quasibinary section CuInSe2 – Ga2In8Se15 (γ1) in the system. The compounds CuGaSe2, CuGa3Se5, CuIn5Se8, CuIn11Se17 have a peritectic type of formation. The CuIn3Se5, CuIn7Se11, Ga6In4Se15 compounds have a solid-phase type of formation, therefore, they do not have areas of primary crystallization on the liquidus surface projection.

Microstructure and Corrosion Resistance of Zn-Al Diffusion Layer on 45 Steel Aided by Mechanical Energy.

In harsh environments, the corrosion damage of steel structures and equipment is a serious threat to the operational safety of service. In this paper, a Zn-Al diffusion layer was fabricated on 45 steel by the Mechanical Energy Aided Diffusion Method (MEADM) at 450 °C. The microstructure and composition, the surface topography, and the electrochemical performance of the Zn-Al diffusion layer were analyzed before and after corrosion. The results show that the Zn-Al diffusion layer are composed of Al2O3 and Γ1 phase (Fe11Zn40) and δ1 phase (FeZn6.67, FeZn8.87, and FeZn10.98) Zn-Fe alloy. There is a transition zone with the thickness of about 5 μm at the interface between the Zn-Al diffusion layer and the substrate, and a carbon-rich layer exists in this zone. The full immersion test and electrochemical test show that the compact corrosion products produced by the initial corrosion of the Zn-Al diffusion layer will firmly bond to the Zn-Al diffusion layer surface and fill the crack, which plays a role in preventing corrosion of the corrosive medium and reducing the corrosion rate of the Zn-Al diffusion layer. The salt spray test reveals that the initial corrosion products of the Zn-Al diffusion layer are mainly ZnO and Zn5(OH)8Cl2H2O. New corrosion products such as ZnAl2O4, FeOCl appear at the middle corrosion stage. The corrosion product ZnAl2O4 disappears, and the corrosion products Zn(OH)2 and Al(OH)3 appear at the later corrosion stage.

Effect of Aging on the Structure and Transformation Behavior of Cu–12Al–3.5Ni–0.7Ti–0.05RE High Temperature Shape Memory Alloy

In this study, the effect of isothermal aging on the thermoelastic martensitic transformation and microstructure of the as-quenched Cu–12Al–3.5Ni–0.7Ti–0.05RE (RE = Ce, La) high temperature shape memory alloy was studied. The results showed that the alloy microstructure and martensitic transformation are strongly influenced by the aging temperature rather than aging time. During aging at 350 °C the alloy was prone to both the precipitation of the γ2 phase and the bainitic transformation, resulting in a loss of martensitic transformation and damping capacity. The prolonged aging at 350 °C caused a decomposition of parent phase into the equilibrium γ2 phase alongside the α phase which produced a significant hardness increment. On the other hand, aging at 250 °C affected the microstructure only slightly producing insignificant shift in the transformation temperatures. It was found that, the secondary phases including Ti-rich X-phase and the RE-rich phase were not influenced by the aging process. The results prescribe a high temperature order of the stability of martensitic transformation for this new alloy which is important for its high temperature shape memory applications.

Dealuminification of heat exchanger tubes

This paper presents a failure analysis of heat exchanger tubes manufactured from aluminum bronze. The equipment operates as an intercooler after the first stage compression. The cooling medium was seawater that passed inside the tubes. The investigation involved visual inspection, chemical analysis, metallography, hardness test, scanning electron microscope analysis, and thermal-hydraulic evaluation.The aluminum content of the analyzed tube was higher than the maximum value defined by the design specification ASTM B111 C61400. The high aluminum content promoted γ2 phase formation that was preferentially attacked from the tube inner surface. The tubes failed due to dealloying (dealuminification) associated with under-deposit corrosion in regions of higher temperatures and lower seawater velocities.

On the Elevated Temperature Thermal Stability of Nanoscale Mn-Ni-Si Precipitates Formed at Lower Temperature in Highly Irradiated Reactor Pressure Vessel Steels

Atom probe tomography (APT) and scanning transmission electron microscopy (STEM) techniques were used to probe the long-time thermal stability of nm-scale Mn-Ni-Si precipitates (MNSPs) formed in intermediate and high Ni reactor pressure vessel steels under high fluence neutron irradiation at ≈320 °C. Post irradiation annealing (PIA) at 425 °C for up to 57 weeks was used to determine if the MNSPs are: (a) non-equilibrium solute clusters formed and sustained by radiation induced segregation (RIS); or, (b) equilibrium G or Γ2 phases, that precipitate at accelerated rates due to radiation enhanced diffusion (RED). Note the latter is consistent with both thermodynamic models and x-ray diffraction (XRD) measurements. Both the experimental and an independently calibrated cluster dynamics (CD) model results show that the stability of the MNSPs is very sensitive to the alloy Ni and, to a lesser extent, Mn content. Thus, a small fraction of the largest MNSPs in the high Ni steel persist, and begin to coarsen at long times. These results suggest that the MNSPs remain a stable phase, even at 105 °C higher than they formed at, thus are most certainly equilibrium phases at much lower service relevant temperatures of ≈290 °C.

Microstructure and mechanical properties of Cu–12Al–xNi alloy prepared using powder metallurgy

The study investigated the effect of nickel content on the microstructure and mechanical properties of Cu–12Al-xNi alloys prepared using powder metallurgy. The results indicated that the alloys investigated consisted of α-Cu and γ2 (Al4Cu9), containing less than 4 wt% Ni content. The α-Cu phase gradually increased, while the γ2 (Al4Cu9) phase gradually decreased as the sintering temperature increased. Both the strength and hardness of the alloy thus reduced. When the Ni content increased above 4 wt%, the NiAl phase precipitated at the grain boundaries, which resulted in an increase in the strength of the alloy. Additionally, the tensile strength reached a maximum of 390 MPa when the Ni content reached 6 wt%. The decrease in the tensile strength for higher Ni content was attributed to the formation of a NiAl phase network. And the addition of nickel did not significantly alter the sintering density of the alloy. The mechanisms of microstructure evolution and strengthening mechanisms were investigated and discussed.

In Situ Time-Resolved Phase Evolution and Phase Transformations in U-6 Wt Pct Nb

In situ time-resolved synchrotron X-ray diffraction experiments were conducted to study the fine-scale phase evolution of U-6Nb. Upon rapid heating from 125 °C to 400 °C, a reverse martensitic transformation sequence, α″ → γo → γs, was observed in less than 4 seconds, which represents the first direct observation of the γo → γs transformation in diffraction-based measurements. Consistent with previous ex situ metallography experiments, our isothermal hold experiments at 526 °C, 530 °C and 565 °C reveal two distinct reactions for the phase separation, γs → α-U + γ1 (general precipitation) followed by (α-U + γ1) → α-U + γ1-2 (discontinuous precipitation). For the first-stage precipitation, the incubation time is determined to be ~ 50 and 100 seconds, respectively, for the isothermal aging at 526-530 °C and 565 °C. At this stage, the phase transformation is characterized by the simultaneous growth of α-U and γ1 at the expense of γs. As expected from the Arrhenius equation for the reaction rate, the determined times (~ 23 minutes) for the completion of the first-stage reaction at 526 ± 3 °C and 530 ± 3 °C are nearly twice longer than that at 565 ± 4 °C (~ 13 minutes). Over these periods of time, the Nb contents derived from a Vegard’s-type relationship for γ1 are in the 30.2 to 32.1 and 29.2 to 30.6 at. pct ranges, and the kinetics of the precipitation at 565 ± 4 °C can be described by the classic Avrami rate equation and one-dimensional growth of a surface or grain-boundary nucleation. During the second-stage precipitation, the γ1 phase continues to enrich in Nb as it gradually evolves toward the α + γ1-2 metastable state (up to 47 at. pct over a period of 172 minutes at 530 °C). These new and time-resolved measurements can be used to better constrain the time–temperature–transformation diagram, solute (Nb) redistribution, and transformation kinetics during the early stages of the diffusional phase transformation.

Large easy-plane anisotropy induced spin reorientation in magnetoelectric materials (Co4−xMnx)Nb2O9

Neutron powder diffraction experiments were carried out on the magnetoelectric compound series (Co4−xMnx)Nb2O9 (x = 0, 1, 2, 3, 3.5, 3.9, 3.95 and 4) from base temperature to above their Néel temperatures. Their magnetic structures were analysed by using the irreducible representation analysis and Rietveld refinement method. Similar to Co4Nb2O9, the compounds with x ⩽ 3.9 have noncollinear in-plane magnetic structures (Γ6) with magnetic moments lying purely in the ab plane with certain canting angles. Mn4Nb2O9 has a collinear antiferromagnetic structure (Γ2) with magnetic moments aligning along the c axis. The compound of x = 3.95 shows two magnetic phases in the magnetization, which was confirmed to have the Γ2 magnetic structure above 60 K and develop a second Γ6 local phase in addition to the main Γ2 phase due to doping. This study indicates 2.5 at% Co2+ doping is sufficient to alter the collinear easy-axis magnetic structure of Mn4Nb2O9 into the noncollinear easy-plane magnetic structure, which is attributed to the large easy-plane anisotropy of Co2+ and relative small Ising-like anisotropy of Mn2+. The doping effects on the Néel temperature and occupancy are also discussed.