Mn Ni System Research Articles

Thermodynamic stability and diffusivity of near-equiatomic Ni–Mn alloys

The equilibrium phase diagram of the nickel-manganese system is determined between 500 and 850 °C, in the composition range between 25 and 70 at. % Ni. A combination of electron probe microanalysis, x-ray diffraction, and optical microscopy was employed to analyze 47 samples that were annealed anywhere from three to seven months. The equiatomic, antiferromagnetic, L10-NiMn phase that is of considerable technological interest was found to exist continuously between 500 and 700 °C. No other intermediate phases were found in this study at low temperatures. These results are in contrast to the currently accepted phase diagram published in most handbooks. A hot-isobaric-pressing method was used to initially bond samples that were subsequently used to determine interdiffusion coefficients in the Ni–Mn system at 650 °C. The Boltzmann–Matano method [T. Heumann, Z. Phys. Chem. 201, 168 (1952)] allowed the calculation of these interdiffusion coefficients across the α-Mn, β-Mn, γ-Mn, L10-NiMn, and γ-Ni phases.

Thermodynamic calculations for precipitation in maraging steels

In the present work, thermodynamic calculations for several maraging systems have been carried out, and the results are compared with experimental data. The calculations were conducted using ThermoCalc. Excellent agreement is obtained between calculation and experimental measurements using mainly the atom probe. As a highlight, calculated equilibrium phases and their mole fractions in 1RK91 steel recently developed by Sandvik compare extremely well with atom probe microchemistry data, which showed the presence of copper rich particles, mixed Ni3Al and Ni3Ti, and molybdenum rich precipitates. Calculations also indicate the thermodynamic stability of μphase in the Fe–Ni–Mo and Fe–Ni–Co–Mo systems, Ni3Al and Ni3Ti in a chromium containing steel, and NiMn in a Fe–Ni–Mn system. However, it should be noted that thermodynamic calculations may only be used as a guideline for systems not in equilibrium.

Advanced nanocrystalline Zr-based AB2 hydrogen storage electrode materials for NiMH EV batteries

Abstract The metallurgical microstructure, crystal-structure and electrochemical properties of Laves phase Zr–V–Mn–Ni system alloys (modified with Ti, Co, Sn, etc.) were investigated systematically in the present paper. Conventional polycrystalline Zr-based alloys, which consist of cubic C15 Laves phase, hexagonal C14 Laves phase and non-Laves phase (such as Zr7Ni10, Zr9Ni11, Zr(NiMn)Sn0.35), show the highest discharge capacity of 342 mAh g−1 (at 60 mA g−1 charge–discharge current), which decreases by 7.8% after 300 cycles. Amorphous phase alloys in melt-spun alloys exhibit poor electrochemical properties. Advanced nanocrystalline C15-Laves single-phase alloys were prepared by completely crystallizing the melt-spun amorphous Zr1−xTix[(NiVMnCo)1−ySny]2+α alloys. These alloys have a special microstructure composed of high-density interface phase and random-oriented grains varying from several nanometres to several dozens of nanometres. It was found that these materials had high discharge capacity (the maximum capacity is up to 379 mAh g−1) and long cycle life (the capacity only decreases 3% after 300 cycles). The maximum discharge capacities were found in the metallurgical microstructure and crystal-structure in Zr-based AB2 alloys. The maximum discharge capacity increases in regular nanocrystalline/C15-Laves single-phase>polycrystalline/multi-phase (Laves and non-Laves)>comorphous state/C15-Laves single-phase. It was shown that the complete crystallization method from amorphous solids is an effective way to greatly improve the electrochemical performance of Zr-based AB2 hydrogen storage electrode materials, which is not only significant for academic research but also valuable for practical applications in the NiMH battery system for pure electric vehicles (PEV) and hybrid electric vehicles (HEV).

Effect of antiferromagnetic grain size on exchange anisotropy in Ni-Fe/25 at% Ni-Mn films

The correlation between the antiferromagnetic (AF) grain volume, νAF and the exchange anisotropy is discussed for Ni-Fe/25 at% Ni-Mn system. In spite of various thickness combination of ferromagnetic (F) and AF layers, the unidirectional anisotropy constant, Jk commonly became large and saturated with increasing νAF. The substantial coercivity originated from the AF layer decreased and became constant with increasing νAF. These experimental results were well explained by a simple model based on Meiklejohn's single spin model. We concluded that increasing νAF is key to induce the exchange anisotropy effectively in F/AF bilayers.

Texture Development in Electrodeposited Nanocrystalline Ni-Mn-Fe Alloys

SUMMARYNi-Mn-Fe alloys were electrodeposited from three compositionally altered Ni-Mn electrolytes containing a small amount of FeSO4.(NH4)2SO4.6H2O (10gl−1) Texture development in the resultant codeposits was investigated with opticical colour polarisation microscopy. Addition of Fe in the electrodeposited Ni-Mn system results in the development of additional textures. Most of the samples show three different types of textures though the texture types are characteristic of the bath composition and deposition CD.

The STRUCTURE OF THE c(2×2) Mn/Ni(001) SURFACE ALLOY BY PHOTOELECTRON DIFFRACTION

Surface alloys are two-dimensional metallic systems that can have structures that are unique to the surface, and have no counterpart in the bulk binary phase diagram. A very unusual structure was reported for the Mn–Ni system, based on a quantitative LEED structure determination, which showed that the Mn atoms were displaced out of the surface by a substantial amount. This displacement was attributed to a large magnetic moment on the Mn atoms. The structure of the Mn–Ni surface alloy was proposed to be based on a bulk termination model. Magnetic measurements on Mn–Ni, however, showed conclusively that the magnetic structure of these surface alloys is distinct from the bulk alloy analogs. For example, bulk MnNi is an antiferromagnet, whereas the surface alloy is ferromagnetic. This suggests that the proposed structure, based on bulk termination, is not complete. Photoelectron diffraction techniques were used to investigate this structure, using both a comparison to multiple scattering calculations and photoelectron holography.

Liquid equilibria in the Fe–Ni–Mn system

New literature results on the liquid equilibria in the three edge binary systems make necessary a reconsideration and correction of liquidus surfaces of the γ and δ solid solutions hitherto outlined in the literature. Therefore, with respect to the critically reinterpreted edge binary systems, the shape of the stable liquidus surface of the γ and δ solid solutions has been newly outlined.

The role of Pt impurities on both bulk and surface anisotropies in amorphous NiMn films

Electron spin resonance (ESR) measurements have been carried out on amorphous Ni76Mn24 and Ni74Mn24Pt2 films in the temperature range 4–300 K. The spectra at each temperature have been taken for both parallel geometry, where the applied magnetic field is in the surface of the films and perpendicular geometry with the magnetic field perpendicular to the surface. Using computer simulations, the bulk (K) and surface anisotropy constants (Q and ks), the exchange stiffness constants (D) and the induced exchange fields (Hexc) were obtained for both films as a function of temperature. At lower temperatures, we were not able to analyse the ESR spectra due to very broad lines, which are associated with the frustration of spins. The frustration manifests itself at higher temperatures for Ni74Mn24Pt2 than for Ni76Mn24 and becomes more severe with Pt impurities. The induced exchange anisotropy, Hexc, which is created during cooling of the sample rotates freely towards the applied field. The temperature behaviour of this anisotropy is in agreement with the exponential law (exp(-α/T) for both samples. The exchange stiffness constants, D, of both samples show similar behaviour, D increases with decreasing temperature, slowly at first above certain temperature values (100 K for Ni76Mn24 and ∼ 150 K for Ni74Mn24Pt2) and then more rapidly at lower temperatures, being related to the frustration of the system. Furthermore, the deduced bulk and surface anisotropy coefficients from the ESR data analysis revealed that Pt impurities have a considerable influence on the domain structure and, accordingly, the surface anisotropies of the NiMn system.

Erratum to: The equiatomic region of the Mn-Ni system

Whereas the JPE editorial and production staff make every effort to preserve the integrity of each author’s work, the occasional error occurs. In Vol. 16, No. 2, p. 108 of the Short Communication “The Equiatomic Region of the Mn-Ni System” by B.R. Coles, an incorrect diagram was printed as Fig. 1. The diagram that was printed shows the situation prior to Prof. Coles’ work. Fig. 1 should have been the diagram from Constitution of Binary Alloys, 2nd ed. (by Max Hansen and Kurt Andrenko, Genium Publishing Corp., Schenectady, N.Y.), which is reprinted here with permission from Genium Publishing Corp., and draws mainly on the information given in Ref. 1 of the short communication as published. The entire staff extends sincere apologies to the author.

The Ti-based metal hydride electrode for NiMH rechargeable batteries

The pressure-composition isotherms and electrochemical characteristics of titanium-based hydrogen storage alloys have been studied for various compositions. In the TiZrVMnNi system, Ti0.2Zr0.05V0.4Mn0.35 − xNix (x = 0.1–0.25) alloys were found to have a large hydrogen storage capacity (greater than 1.75 wt.% g−1 alloy) and high discharge capacity (350–440 mA h g−1). Their structure was confirmed to be multi-phase and composed of an AB2-type C14 Laves phase matrix and V-rich b.c.c. second phase by using X-ray diffraction, scanning electron microscope and electron microprobe analyses. In order to identify the contribution of each phase to the high discharge capacity of multi-phase alloys, these two phases were prepared separately and their hydrogen storage capacities were investigated. It was found that the V-rich b.c.c. second phase was hardly hydrogenated in KOH electrolyte, though its theoretical hydrogen storage capacity was as high as 1.93 wt.% H g−1 alloy as determined from the pressure-composition isotherms in the solid-gas reaction. Its potential hydrogen storage capacity was able to be utilized by the presence of a C14 matrix phase which had a catalytic activity for the charge-transfer reaction in KOH electrolyte.

The equiatomic region of the Mn-Ni system

The equiatomic region of the Mn-Ni system

The selective corrosion of type 316 stainless steel in molten lead

Molten lead is a potential electrodynamic fluid for magneto-hydrodynamics (MHD) liquid metal (LM) generators in a project developed in the Center for MHD studies at Be n-Gurion University [1]. Obviously, the structural materials of the generator have to be corrosion-proof in liquid lead turbulent flow, and the material of the wall close to the electrode zone should not be ferromagnetic. Austenitic type 316 stainless steel (SS316) is a promising structural material which meets these requirements. To our knowledge, no data are yet available about the behaviour of SS316 in liquid lead turbulent flow. There is very little information about the behaviour of SS316 in contact with static or low speed flow molten lead in the literature [2]. The interaction of SS316 with Pb-17Li liquid alloy is described in a larger number of works, perhaps because this melt is a potential breeder in fusion reactors [3-5]. As a rule, selective nickel dissolution (leaching) from steel is mentioned. The selective process is related to higher nickel solubility in the liquid eutectic Pb-Li as compared with iron and chromium. In this letter the results of an investigation of the corrosion of SS316 samples in turbulent liquid lead flow are described. The experimental conditions determining either selective or uniform types of SS316 corrosion are discussed and the role of oxygen impurities is discussed in greater detail. An analysis of the equilibrium states in the P b P b O F e C r Ni-Mn system was also performed to estimate the characteristics of steel-liquid interaction under our experimental conditions. The samples under investigation were in the form of discs 40 mm in diameter and 8 m thick. The samples were polished and degreased with acetone. Tests were carried out by the rotating disc method described previously [6]. The test conditions were: temperature 500 °C, sample rotation rate 2400 rpm. The test container for the molten lead (99.97%) was made of carbon steel and the melt volume was approximately 1 I. Nitrogen (99.7%) was padded through the container above the melt surface at a flow rate of 4 1 min -1. The duration of the experiment was 800h. Every 200h the sample was removed from the container for X-ray diffraction (XRD) and scanning electron microscopy (SEM)/electron probe X-ray microanalysis (EPMA) [6]. According to EPMA, the steel composition was (wt %): Cr 17.9, Ni 10.5, Mo 2.5, Mn 1.8, Si 2.0, Fe remainder. The steel in the initial state proved to be two-phase: the main phase was 7 austenite (a = 0.3602 nm) and the second phase was oL-ferrite (a = 0.2870 nm). This corresponds to the equilibrium phase diagram of Fe -Ni -Cr [7]. It should be noted that the steel retained its phase composition during the entire test. The y phase cell parameter did not change during the test, but the parameter of the o~ phase increased to 0.2890 nm after 800 h. The concentrations of iron, nickel and chromium near the sample surface, according to EPMA data, did not change during the test period (Fig. 1). The presence of 7 and ol phases, complex oxide phase FeCr204 and small quantities of Fe2SiO4 (faylite) and o~-MnSiO3 was determined by XRD analysis of the sample surfaces. As follows from the above data, the composition of the subsurface zone remained unchanged for a long time. The dimensions of the samples also remained constant to within + 10 #m. An obvious question arises as to why there is no selective dissolution of nickel and, as a result, no build-up of o~-phase on the surface of the sample tested, despite the large solubility difference of Ni, on the one hand, and iron and chromium, on the other, in liquid lead (this difference amounts to four or five orders of magnitude at 800 K [8-10]). Firstly, the rate of nickel leaching from SS316 by liquid lead turbulent flow under the rotating disc regime was estimated. The rate of pure nickel dissolution, Jr~i, under our experimental conditions is expressed by [11]:

Field-induced anisotropy in the NiMn system with Pt impurities

We have carried out ferromagnetic resonance (FMR) and magnetization measurements on Ni 76− x Mn 24Pt x ( x = 0, 1, 1.5, 2, 3) alloys. After cooling the samples down to 4.2 K in a magnetic field of 10 kG, the FMR and dc magnetization measurements have been done in the applied field either parallel (n-FC case) or antiparallel (r-FC case) to the cooling field direction for parallel geometry (static magnetization parallel to the surface of samples). It has been observed from the FMR and dc magnetization data that both the unidirectional and uniaxial anisotropies are significantly induced with increasing platinum impurity atoms. The ratio of the intensity of the resonance line for the r-FC case to that for the n-FC case increases with platinum as well. Furthermore, the line shapes are highly correlated with platinum. This asymmetric behaviour relative to the applied field direction has been discussed by taking into account the surface induced mode and introducing a directional character to the surface anisotropy in the Rado-Weertman (R-W) general surface boundary conditions.

Use of metastable equilibria for determination of Gibbs energy of solids

Attempts are made to measure activities of both components of a binary alloy (A–B) at 650 K using a solid-state galvanic cell incorporating a new composite solid electrolyte. Since the ionic conductivity of the composite solid electrolyte is three orders of magnitude higher than that of pure CaF2, the cell can be operated at lower temperatures. The alloy phase is equilibrated in separate experiments with flourides of each component and fluorine potential is measured. The mixture of the alloy (A–B) and the fluoride of the more reactive component (BF2) is stable, while (A–B) + AF2 mixture is metastable, Factors governing the possible use of metastable equilibria have been elucidated in this study. In the Co–Ni system, where the difference in Gibbs energies of formation of the fluorides is 21.4 kJ/mol, emf of the cell with metastable phases at the electrode is constant for periods ranging from 90 to 160 ks depending on alloy composition. Subsequently, the emf decreases because of the onset of the displacement reaction. In the Ni–Mn system, measurement of the activity of Ni using metastable equilibria is not fully successful at 650 K because of the large driving force for the displacement reaction (208.8 kJ/mol). Critical factors in the application of metastable equilibria are the driving force for displacement reaction and diffusion coefficients in both the alloy and fluoride solid solution.

Spin-orientation phase transitions in itinerant multiple spin-density-wave systems

Using a simple Landau model the authors have found six different magnetic phases: one cubic (TSDW), three tetragonal (SSDW, DSDW, ASDW) and two orthorhombic (OSDW and GSDW) phases. The above phases may be categorised by the number of order parameters and the number of non-zero magnetic moments. It is found that second-order transitions between states with different numbers of magnetic components have discontinuities in the elastic constants, whereas those maintaining the number of components have vanishing shear components. For a specific parametrisation of the authors' model they find a sequence of ground states that have identical symmetries to those found in the Mn-Ni system. The authors predict the vanishing of a shear elastic constant at one of the tetragonal-to-orthorhombic phase transitions but not the other. They also discuss an alternative microscopic model for determining the onset of the various phases. This involves the calculation of the n-point static Green functions in the long-wavelength limit for a simple one-band model.

Spin-glass behavior as a function of concentration and local order by NMR in nearly random NiMn systems

Unidirectional anisotropy fields ( H A) in disordered Ni 100 − x Mn x (25 ⪕ x ⪕ 32) systems after field cooling are found by NMR (spin echo) to be very sensitive to the Mn concentration and to local order. The H A increases by roughly a factor of 10 when the concentration increases 5%. The Mn NMR spectra show that all Mn have several first nearest Mn neighbours. For a given concentration, in the above range, the H A are very sensitive to the annealing-quenching temperatures ( T AQ) and vanish when the sample is cooled down from 900°C in 2 h. The NiMn system can be tuned by heat treatments from spin-glass to a ferromagnet. The Mn NMR spectra with decreasing T AQ show a clear metallurgical evolution tending to states where a Mn atom sees fewer first nearest Mn neighbours. We find evidence that the anisotropy has its roots in atomic randomness.

Activity of manganese in liquid Ni-Mn alloys

Manganese is usually present as a minor component in alloys designed for high temperature oxidation resistance, and promotes the formation of protective spinel layers. Although thermodynamic data on liquid Fe-Mn alloys are well established, 1 there is a lack of corresponding experimental information regarding Ni-Mn alloys. Available data on solid Ni-Mn alloys have been evaluated by Hultgren et al.1 A solid state emf cell, with yttria doped thoria as the electrolyte and a mixture of Cr + Cr203 as the reference electrode, is employed in this study for measurement of the activity of manganese in the Ni-Mn system at 1683 K, for 0.4 > Xun > 0.05. The liquid alloy is contained in an alumina crucible and saturated with MnA12+2,O4+3x. The cell can be represented as:

Abstract: Spin glass-ferromagnetic transition in disordered Ni-Mn

The magnetization M of a disordered Ni-Mn alloy of ∼22 at. % Mn was measured as a detailed function of field H and temperature. For the alloy cooled to 4 K in zero H, M increases slowly as H is raised to a critical value (Hc∼200 Oe), where M increases rapidly and then slowly approaches ferromagnetic saturation as H is raised to 5 kOe. As H is subsequently lowered, M undergoes a similarly rapid drop at the same Hc and then slowly reaches zero at zero H. Since the isothermal remanence is zero, the low-M state below Hc cannot derive from simple ferromagnetic domain effects. That this is a spin-glass state is evidenced by field-cooling experiments which result in displaced hysteresis loops at 4 K. At higher temperatures after cooling in zero H, the field-induced transition to ferromagnetism is seen to occur at a progressively lower Hc. Hc reaches zero at ∼40 K, above which the spontaneous M varies like that of a ferromagnet with a Curie point of ∼350 K. However, the low-temperature values of the spontaneous M are well below the values expected from a ferromagnetic alignment of all the atomic moments. Similar experiments on a Ni-Mn alloy of ∼26 at. % Mn reveal it to be a typical spin glass with a susceptibility cusp at ∼80 K.1 A detailed determination of the magnetic phase diagram of the disordered Ni-Mn system is currently in progress. a) Work supported by NSF Grant. No. DMR78-12777. b) Presently at University of Colorado, Colorado Springs, CO 80907. c) Presently at Queens College-CUNY, Flushing, NY 11367. 1 ESR results for this alloy are reported at this conference by Hurdequint, Kouvel, and Monrod.

Structures and phase transformations in the MnNi system near equiatomic concentration

The crystal and magnetic structures and their transformations have been investigated by X-ray and neutron diffraction as well as electrical resistivity measurements on samples of Mn 0·91Ni 1·09, MnNi and Mn 1·07Ni 0·93 composition. In the tetragonal Θ phase all samples exhibit the same simple antiferromagnetic structure between liquid helium temperature and the Néel point. Ordered structure of CsCl type has been established for the high temperature β phase. Magnetic order is not observable in this phase. The transformation between the ordered Θ and β phases is found to be of the diffusionless martensitic type. The observed time dependence of the resistivity in Mn 1·07Ni 1·07 is attributed to the precipitation of the γ phase from the Θ phase. A temperature dependence of the rate of the β ⇌ γ, transformation is observed. The temperatures T N, T θ and T γ of the antiferromagnetic-paramagnetic, Θ ⇌ β and β ⇌ γ transformations respectively, have been determined.

Structures and phase transformations in the Mn-Ni system near equiatomic concentration

Medium/high-entropy alloys (MEAs/HEAs) have become one of the primary research highlights in the material field due to their superior microstructure and mechanical properties. By means of molecular dynamic (MD) simulation, the tensile behavior of polycrystalline Fe80-xMnxCo10Cr10 (x=20, 30, 40, 50) MEAs was investigated under uniaxial stretching. The effects of various strain rates (1 × 108 s−1, 1 × 109 s−1, 1 × 1010 s−1) and deformation temperatures (77 K, 300 K, 600 K, 800 K) on tensile properties and deformation mechanisms of Fe80-xMnxCo10Cr10 (x=30, 40) MEAs were explored, and the interaction of dislocation defects with stacking fault including intrinsic and extrinsic stacking fault (ISF/ESF) as well as the evolution of dislocation and cluster defects were further discussed. Moreover, the relationship between grain size and flow stress of polycrystalline Fe50Mn30Co10Cr10 MEAs was discussed. Results indicated that Fe40Mn40Co10Cr10 and Fe50Mn30Co10Cr10 alloys exhibited higher yield stresses and Young's moduli. The yield stresses, Young's moduli and average flow stresses of Fe40Mn40Co10Cr10 and Fe50Mn30Co10Cr10 MEAs increased with an increase in strain rates from 1 × 108 to 1 × 1010 s−1. Besides, the deformation temperature produced a considerable influence on its mechanical properties. The phase transformation, grain boundary glide, dislocation slip and twinning formation together accounted for the plastic deformation behavior of Fe80-xMnxCo10Cr10 MEAs under uniaxial stretching on an atomic scale.