Al Mn System Research Articles

Suppression of anti-phase boundary defects in Mn-Al-Ti permanent magnets

Permanent magnets (PMs) based on manganese show significant potential for applications in electric motors and devices as an alternative to Rare-earth PMs (REPMs). The metastable ferromagnetic τ phase of the Mn-Al system has magnetic performance between the REPM Nd-Fe-B magnets and the lower performance ferrite magnets. However, the maximum performance in Mn-Al PMs has not reached its theoretical limit, in part due to challenges in controlling crystalline defects such as anti-phase boundaries (APBs). APBs act as nucleation sites for domain reversal in Mn-Al and negatively affect magnetization by interrupting the L10 ordering, placing Mn atoms into AFM-coupled Mn-Mn configurations. In this study, Ab-initio modeling was used to screen ternary elements based on their affinity to segregate to the APB and on their preference for FM configuration. The ternary element addition of 1 at.% Ti lowered the density of APBs as observed in a transmission electron microscope. The 1 at.% Ti addition was observed to improve (BH)max over the base alloy, by preserving Hci and improving Mr. It also significantly increased the fraction of twin boundaries in the τ phase. AFM behavior that was observed in the base alloy during TC heating experiments (Néel behavior) and high-field VSM measurements (spin-flop behavior) was effectively suppressed with the addition of Ti. Additionally, the Ti addition thermally stabilized Hci at 550 °C, improving τ phase processability. Other candidate elements, Cr, V, and Zr, were modeled to have similar potential for minimizing APBs when added to Mn-Al.

The phase transformation behavior of Mn-Al rare-earth-free permanent magnets

Rare-earth-free permanent magnet materials based on Mn show great promise for applications in electric motors and devices. The metastable ferromagnetic τ phase of the Mn-Al system has magnetic properties between those of the high-performance Nd-Fe-B magnets and the lower-performance ferrite magnets. However, the hybrid displacive-diffusional pathway of τ formation, from the parent ε phase through the intermediary ε’ phase, is still not fully understood. This phase transformation progression was studied in-situ using diffractive, calorimetric, and magnetometric techniques to show that the progression from ε to τ in Mn54Al46 at <450 °C involves the ordering of ε into ε’. Density functional theory calculations were performed on each phase and confirmed the experimental observation that the ε to ε’ to τ pathway is energetically favorable. Isothermal annealing of quenched-in ε at 350 °C demonstrated that ε’ is ferromagnetic, also in agreement with theoretical results, with a moderate coercivity of at least 50 kA/m. The τ phase was observed to nucleate along the prior ε phase grain boundaries and grow into the ε’ phase regions. A boundary front of ε’ was observed between the τ and ε phases. Both Kissinger and Flynn-Wall-Ozawa methods were used to determine the activation energies for the ε’ and τ phase transformations with values of ∼140 kJ/mol obtained for both phases. Therefore, the ordering transformation to ε’ and the hybrid displacive-diffusional transformation to τ were shown to overcome the same magnitude energy barrier. Both activation energies were less than previous τ phase activation energies measured on Mn55Al45 in the absence of a significant ε’ ordering exotherm, providing a kinetic benefit to the ε to ε’ to τ pathway at 350 °C. The results of this study give insight into the phase transformation of L10 binary materials as well as materials that undergo a disorder–order transformation followed by displacive shear.

Additive Manufacturing of MnAl(C)-Magnets

Permanent magnets are becoming more and more relevant for modern society. As the most widely used permanent magnets contain rare-earth elements, the increased dependence on these strategic elements is worrisome, and the pursuit for rare-earth free alternatives has become a strategic goal in many countries. The metastable and ferromagnetic τ-phase that forms in the MnAl(C) system is one of the most promising alternatives, and since its discovery, major efforts have been made to improve its performance and realize its full potential. One major factor that has prevented a widespread commercialization of MnAl(C) permanent magnets is their relatively low coercivity. Here, we demonstrate that additive manufacturing, using laser powder bed fusion, can be used to produce MnAl in its high-temperature polymorph (ε, hcp), which can be subsequently transformed, through post-heat treatments to the ferromagnetic τ-phase. Although we successfully obtained a preferential orientation of the ε-phase with &lt;001&gt; parallel to the build direction, this did not translate into a strong preferential orientation in the τ-phase, thus indicating that the phase transformation occurs by the migration of incoherent interfaces. The MnAl(C) samples are characterized by a density of ≈4.4 g/cm3, a saturation magnetization of 39.3 Am2/kg, a coercivity of 168 kA/m, and a remanence of 17.5 Am2/kg.

The Effect of Y Content on Structural and Sorption Properties of A2B7-Type Phase in the La-Y-Ni-Al-Mn System.

Metal hydrides are an interesting group of chemical compounds, able to store hydrogen in a reversible, compact and safe manner. Among them, A2B7-type intermetallic alloys based on La-Mg-Ni have attracted particular attention due to their high electrochemical hydrogen storage capacity (∼400 mAh/g) and extended cycle life. However, the presence of Mg makes their synthesis via conventional metallurgical routes challenging. Replacing Mg with Y is a viable approach. Herein, we present a systematic study for a series of compounds with a nominal composition of La2-xYxNi6.50Mn0.33Al0.17, x = 0.33, 0.67, 1.00, 1.33, 1.67, focusing on the relationship between the material structural properties and hydrogen sorption performances. The results show that while the hydrogen-induced phase amorphization occurs in the Y-poor samples (x < 1.00) already during the first hydrogen absorption, a higher Y content helps to maintain the material crystallinity during the hydrogenation cycles and increases its H-storage capacity (1.37 wt.% for x = 1.00 vs. 1.60 wt.% for x = 1.67 at 50 °C). Thermal conductivity experiments on the studied compositions indicate the importance of thermal transfer between powder individual particles and/or a measuring instrument.

Self-Propagiating High-Temperature Synthesis in Ti–Al–Mn System

Self-Propagiating High-Temperature Synthesis in Ti–Al–Mn System

Changes in the physical and mechanical properties of aluminum depending on the composition of the alloying elements

Subject of research: the influence of the concentration and composition of alloying elements Mn, Ti, Cr, Y, Mo, W, V on the change in the aluminum recrystallization temperature.&#x0D; Purpose of research: to find the optimal concentration of alloying additives, at which the recrystallization temperature reaches its maximum value.&#x0D; Methods and objects of research: using the methods of thermodynamic analysis of binary state diagrams of aluminum with alloying additives, it has been established that the nature of the change in the recrystallization temperature depends on what type of eutectic or peritectic reaction the formation of intermetallic compounds belongs to. It is shown that aluminides act as alloy modifiers and impart high mechanical properties to products.&#x0D; Main results of research: it was found that for the AlMn system, the optimal content of Mn should be considered 0.2%, for the AlCr system, the maximum increase in the Al recrystallization temperature is observed at 0.6% Cr, for the AlY system, the mechanical properties of Al at elevated temperatures maximum at 1% Y.

Effect of Cu addition on phase fraction, mechanical properties and corrosion properties of Fe–Cr–Mn–Al duplex stainless steel

In recent years, Cu has been regarded as an important element to improve the corrosion resistance of stainless steels. For duplex stainless steels, especially those obtained by cold rolling and annealing, at present, little is known about the role mechanism of Cu addition. Therefore, on the basis of a new type of Fe–Cr–Mn–Al duplex stainless steel designed by the author, the effects of Cu on phase fraction, mechanical properties and corrosion resistance were studied in detail through tensile tests, electron backscattering diffraction (EBSD), polarization curve test and laser scanning confocal microscopy. The results show that the addition of 0.5% Cu to Fe–Cr–Mn–Al system increases the volume fraction of austenite and its stability, greatly improving the strength and ductility of steels due to the TRIP effect occurring in a wider strain range. In addition, the addition of Cu increases the content of Cr in austenite, improving the pitting resistance of duplex stainless steels. After annealing at 860 °C, the Cu-added duplex stainless steel exhibits superior mechanical and corrosive properties, i.e. the yield strength, tensile strength, elongation and pitting potential are 520 MPa, 760 MPa, 42.5% and 260 mV, respectively. In view of obvious advantages in mechanical properties and corrosion resistance, the present developed Cu-added Fe–Cr–Mn–Al duplex stainless steel is expected to replace the conventional 304 stainless steel for some applications.

SHS in the Ni–Al–Mn System: Influence of Mechanical Activation

SHS in the Ni–Al–Mn System: Influence of Mechanical Activation

Influence of annealing on the microstructure and magnetic properties of the τ-MnAl alloy deformed by high pressure torsion

Ferromagnetic alloys of the Mn-Al system are promising materials for permanent magnets and details of electric motors. Deformation methods of processing these alloys allow obtaining high magnetic properties, however, they are still not well researched. In the current study the effect of the τ-MnAl alloy structure obtained by severe plastic deformation on the phase composition, structure, and magnetic properties gained during subsequent annealing is investigated. It was shown that a twinned structure is preferable for recrystallization (in terms of recrystallized volume) than a dislocation one. The largest coercive force of 3.7 kOe was reached in the current investigation after deformation by 20 revolutions (ε ≈ 6.83). Subsequent annealing led to a drastic fall in coercive force due to vanishing of defects (dislocations and nanotwins) acting as sites of domain wall pinning.

Influence of Ga on the formation of phases in cast Al–Mn-based alloys

This work deals with the influence of gallium addition on the constitution and formation of the phases in the Al-rich corner of the Al–Mn system during casting. Al-rich binary Al–Mn and ternary Al–Mn–Ga alloys were cast into a copper mould with a cavity diameter of 5 mm. The microstructures of the produced alloys were characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy, electron backscatter diffraction and X-ray diffraction. The characterization revealed the presence of αAl, Al6Mn, λ-Al4Mn, L-Al4Mn, icosahedral quasicrystals (IQCs) and decagonal quasicrystals (DQCs). As the amount of gallium in the synthesized alloys increased, the proportion of the phases varied and IQCs and DQCs were formed. Microanalysis revealed that IQCs contained more gallium and less manganese than DQCs.

Ti-bearing lightweight steel with large high temperature ductility via thermally stable multi-phase microstructure

Abstract The global demand for lightweight design is increasing to provide sustainable solutions to counteract climate change. We developed a novel Ti-bearing lightweight steel (8% lower mass density than general steels), which exhibits an excellent combination of strength (491 MPa ultimate tensile strength) and tensile ductility (31%) at elevated temperature (600 °C). The developed steel is suitable for parts subjected to high temperature at reduced dynamical load. The composition of the developed steel (Fe–20Mn–6Ti–3Al–0.06C–NbNi (wt%)) lends the alloy a multiphase structure with austenite matrix, partially ordered ferrite, Fe2Ti Laves phase, and fine MC carbides. At elevated temperature (600 °C), the ductility of the new material is at least 2.5 times higher than that of conventional lightweight steels based on the Fe–Mn–Al system, which become brittle at elevated temperatures due to the inter/intragranular precipitation of κ-carbides. This is achieved by the high thermal stability of its microstructure and the avoidance of brittle κ-carbides in this temperature range.

Alloy Production from High-Silica Manganese Ore and High-Ash Kazakhstan Coal

Engineering principles are outlined for the production of silicon–aluminum–manganese alloy from high-silica manganese ore and high-ash Kazakhstan coal (from the Borly and Saryadyr fields in the Karaganda and Teniz-Korzhunkol coal basins), Tekturmas quartzite, and Shubarkol long-flame coal. By thermodynamic diagram analysis of the four-component Fe–Si–Al–Mn system on the basis of handbook data (and calculated thermodynamic data where no handbook data are available), a mathematical model of the phase structure may be developed. The aluminum–silicon–manganese composition obtained from the Karaganda and Teniz-Korzhunkol coal, in contrast to the aluminum–silicon–manganese alloy from Ekibastuz coal, is shifted on the thermodynamic diagrams toward tetrahedra with relatively large volume. This indicates increased stability and technological predictability. The results of tests in an ore furnace show that aluminum–silicon–manganese alloy of regular composition may be obtained by a continuous slag-free method from high-ash Borly and Saryadyr coal and unconditioned high-silica manganese ore from the Western Kamys field if Shubarkol long-flame coal and Tekturmas quartzite are added to the batch. The alloy composition may be regulated by adding manganese ore to the weighed batch materials. An alloy with the following composition is obtained: 32–53 wt % Si, 15.5–25.0 wt % Al, 12–32 wt % Mn, 8–20 wt % Fe, 0.02–0.05 wt % P, and 0.2–0.5 wt % C. The resulting alloy does not crumble to powder on storage, thanks to the low phosphorus content and high aluminum content (>10%). The phase components of the experimental alloy are determined. The cost of the alloy is low, since it is produced from high-ash tailings coal and unconditioned high-silica manganese ore, with absolutely no coke. The alloy may be used for the reduction and alloying of steel and also as a reducing agent in the production of refined ferromanganese.

Properties of Fe–Mn–Al alloys with different Mn contents using density functional theory

The chemical stability, electronic structures, mechanical properties and Debye temperature of Fe–Mn–Al alloys were investigated using first-principles calculations. The formation enthalpy and cohesive energy are negative for Fe–Mn–Al alloys, showing that they are thermodynamically stable. FeAl has the lowest formation enthalpy, indicating that FeAl is the most stable alloy in the Fe–Mn–Al system. The partial density of states, total density of states and electron density distribution maps were used to analyze the physical properties of the Fe–Mn–Al alloys. A combination of mainly covalent and metallic bonds exists in these Fe–Mn–Al alloys, resulting in good electronic conductivity, high melting points, and high hardness. These alloys display disparate anisotropy due to the calculated different shapes of the 3D curved surface of the Young’s modulus and anisotropic index. FeAl has the highest bulk modulus, shear modulus and Yong’s modulus of 187.1, 119.8 and 296.2 GPa, respectively. Further, the Debye temperatures and sound velocity of these Fe–Mn–Al compounds were explored.

МОДЕЛЮВАННЯ ТЕРМОХІМІЧНИХ ВЛАСТИВОСТЕЙ ТА СХИЛЬНОСТІ ДО АМОРФІЗАЦІЇ РОЗПЛАВІВ ПОТРІЙНОЇ СИСТЕМИ Mn–Al–Gd

In the present work, the enthalpies of mixing of liquid alloys of the ternary Mn-Al-Gd system have been calculated using the regular solution model by the Redlich-Kister-Muggianu formula. Also a comparison was made of calculated values of enthalpies of mixing in this system with the experimentally determined thermochemical properties of liquid alloys of the Mn-In-Gd ternary system obtained previously. In general, we estimate that the values of the enthalpies of mixing in the Mn-Al-Gd ternary system should be more exothermic than in the Mn–In-Gd one. This fact can be explained taking into consideration the main features of the component interaction in the boundary binary systems, namely, such important characteristics as electronegativity of the components, their electron work functions and a large difference in size of atoms. It can be concluded that it is the binary Mn–Al system that makes a significant contribution to the formation energy of ternary alloys. An imaginary line drawn through the points of maximum curvature of the isoenthalpic lines is considerably shifted towards the binary Mn–Al boundary, thus expanding significantly the region of rather exothermic enthalpies of mixing in the corresponding ternary system. For the two indicated ternary systems the size mismatch entropy has been calculated within the framework of hard spheres model and the Sσ/kB parameter has been determined. On the basis of the comprehensive analysis carried out, the criteria for the probability of occurrence of regions of easy amorphization in these ternary systems are proposed. The determination of the topology of the mixing enthalpy surface and the Sσ/kB parameter for the melts of studied ternary systems together with the data on binary and ternary compounds existing in these systems allowed to reasonably assume the concentration regions where the investigated ternary alloys have tendency for easy amorphization while rapid cooling of the melt. The simultaneous realization of the following three conditions was taken as a criterion for the possible existence of a region of easy amorphization: the absolute value of the enthalpies of mixing is at least 6 kJ/mol, the Sσ/kB parameter is not less than 0.3–0.4 and a certain distance from the concentration region corresponding to the exact composition of binary or ternary compounds.

Intermetallic Aluminide Coatings by Magnetron Sputtering

It was studied the ways of obtaining the aluminide intermetallic coatings of Al-Ag, Al-Ti, Al-Cr, Al-V and Al-Mn systems by method of simultaneous magnetron sputtering of the reagents. It was produced the synthesis of coatings from stable phases AlAg2 +Ag3Al, AlCr2, Al8Cr5, AlCr2 + Al8Cr5, AlTi, AlTi3, Al8Mn5. The coatings with thickness of 2 μm were carried out on the aluminum and the carbon fiber plates. The study of the coatings was carried out on X-ray diffractometer, the microhardness and electrical conductivity were measured. It was shown that after sputtering of the reagents on the substrate the amorphous, glassy phase is formed except for intermetallic phases Al8V5 and Al3V which were formed during sputtering. It is necessary the heat treatment in a vacuum at 400°C during 1 hour for the synthesis of the intermetallic compound from the amorphous phase. The amorphous phase had a microhardness in the range of 2237-8219 MPa, intermetallic – 1929-8181 MPa. For comparison, the microhardness of high quality steel is about 5500 MPa. The coatings were electroconductive. The coatings are of interest as protective for soft metals, carbon fiber reinforced plastic (CFRP), and plastic materials.

Exploring the pathways for enhancing the hard magnetic properties of binary Al-55at.%Mn Heusler alloy through mechanical alloying

This work reports enhancing the hard magnetic properties of a binary ferromagnetic Heusler alloy based on Mn-Al system through mechanical milling. We report the processing induced evolution of magnetic properties for two sets of alloys, both having the same stoichiometric composition of Al-55at.%Mn with one of them containing high temperature ε phase while the other consisting of only metastable ferromagnetic τ phase. No effect of milling on the magnetic properties of ε phase could be detected due to its nonmagnetic nature. However, subsequent annealing at 350°C for 30min after milling results in structural change and exhibits magnetic response. The phase transitions were found to depend on prior milling history. The highest saturation magnetization and coercivity were obtained for 4h milled sample that is annealed at 350°C for 30min with values of 23emu/g and 5.2 KOe, respectively. In the case of samples with initial microstructure consisting of grains of only metastable τ phase, no decomposition could be observed when milled for a period up to 9h. Additionally, it was observed that after 3h of milling, the saturation magnetization value reduces to 24emu/g and coercivity increases to 5.2 KOe from an initial values of 116emu/g and 0.98KOe respectively. Further milling causes a decrease in both the values. Annealing of the 3h milled powder at 350°C for 30min, resulted in a slight decrease in coercivity (Hc=4.9 KOe) while a significant increase in saturation magnetization (34emu/g) value could be observed. Experimental results suggest that magnetization reversal is domain nucleation controlled and that the nonmagnetic phases (β+γ2) present can act as the pinning sites.

Stability, electronic structures, and mechanical properties of Fe–Mn–Al system from first-principles calculations**Project supported by the National Natural Science Foundation of China (Grant No. 51261013).

The stability, electronic structures, and mechanical properties of the Fe–Mn–Al system were determined by first-principles calculations. The formation enthalpy and cohesive energy of these Fe–Mn–Al alloys are negative and show that the alloys are thermodynamically stable. Fe3Al, with the lowest formation enthalpy, is the most stable compound in the Fe–Mn–Al system. The partial density of states, total density of states, and electron density distribution maps of the Fe– Mn–Al alloys were analyzed. The bonding characteristics of these Fe–Mn–Al alloys are mainly combinations of covalent bonding and metallic bonds. The stress-strain method and Voigt–Reuss–Hill approximation were used to calculate the elastic constants and moduli, respectively. Fe2.5Mn0.5Al has the highest bulk modulus, 234.5 GPa. Fe1.5Mn1.5Al has the highest shear modulus and Young’s modulus, with values of 98.8 GPa and 259.2 GPa, respectively. These Fe–Mn–Al alloys display disparate anisotropies due to the calculated different shape of the three-dimensional curved surface of the Young’s modulus and anisotropic index. Moreover, the anisotropic sound velocities and Debye temperatures of these Fe–Mn–Al alloys were explored.

Thermodynamic Modeling of the Al-Cr-Mn Ternary System

The phase diagram information available in the literature on the Al-Cr-Mn system was comprehensively evaluated and optimized for the first time to obtain a set of Gibbs energies of all the solid and liquid phases in the Al-Cr-Mn system. The Modified Quasi-chemical Model (MQM) was utilized to describe the Gibbs energy of the liquid phase of the Al-Cr-Mn system. The Compound Energy Formalism (CEF) was used to model the solid solution phases. A revision of the Al-Mn system was simultaneously conducted to consider the γ_H (Al8Mn5) phase. The liquid Cr-Mn phase was also remodeled using the Modified Quasi-chemical Model (MQM) to obtain a consistent description of the ternary Al-Cr-Mn liquid phase. Accurate description of the phase diagram of the entire Al-Cr-Mn system was obtained from the thermodynamic models with optimized parameters in the present study, and the model parameters can be used to predict the thermodynamic properties of the ternary system.

High-temperature transformation pathways for metastable ferromagnetic binary Heusler (Al–55 at.%Mn) alloy

The present manuscript probes the decomposition behaviour of the ferromagnetic binary metastable Heusler alloy in the Al-Mn system. The ferromagnetic ordered tetragonal phase (L1(0), popularly known as tau phase), which is metastable in nature, was synthesised from the melt through a copper mould chill casting process using 10-mm diameter mould. Isothermal and non-isothermal heat treatments were carried out to understand the decomposition sequence of tau phase at high temperatures. The metastable phase undergoes, on heating, a eutectoid-like decomposition of , where is the intermetallic phase Al8Mn5. Both the phases are present in the equilibrium diagram. The two phases at higher temperature further transform to a single phase epsilon having a hexagonal structure. We show through in situ X-ray diffraction studies that transforms to a disordered bcc phase () prior to the transformation to the epsilon-phase. The overall sequence of phase decomposition during heating can be given as . The high-temperature phase cannot be retained through quenching experiment and its existence can only be established by in situ studies.

Structural, electronic and magnetic properties of the Mn54−xAl46Tix (x = 2; 4) alloys

The structural, electronic and magnetic behavior of the as-cast and annealed Mn52Al46Ti2 and Mn50Al46Ti4 alloys have been studied through electronic band structure calculations, X-ray diffraction and magnetic measurements in the temperature range 4–850 K and magnetic field up to 7 T. Band structure calculations show a preference for Ti atoms to occupy the Mn sites in the plane of Al atoms with their magnetic moments (−0.68 μB/Ti) coupled antiparallel relative to the Mn magnetic moments in the plane of Mn atoms (2.33 μB/Mn). The as-cast and annealed samples were phase mixtures with different values of the hard ferromagnetic τ phase content. Except the as-cast and annealed at 1050 °C Mn52Al46Ti2 alloys, all the analyzed samples include, along with the τ and γ2 phases, a soft κ phase (CsCl - structure type) with TC around 530 K. The best magnetic characteristics were obtained for Mn52Al46Ti2 alloy annealed at 470 °C for 6 h: MS = 116 A m2/Kg at 4 K and TC = 668 K, in good agreement with the values reported in the literature for the τ phase of the MnAl system. The effects of the composition and of the preparation route on the electronic and magnetic properties are discussed in comparison with the properties of Mn54Al46 parent alloy.