bluuebunny/crossref_metadata_2025_split huggingface dataset:
Materials Properties and Utilization of Fe3B/Nd2Fe14B-Type Nanocomposite Permanent Magnets Based on Nd-Fe-Cr-Co-B
Authors: Hirosawa S. , Kanekiyo H. , Shigemoto Y. 
Published: April 2011

ABSTRACTRecent progresses of materials development and their utilization of Cr-and-Co-doped Fe3B/Nd2Fe14B-type nanocomposite permanent magnets are reported. A practical balance between enhanced intrinsic coercivity and temperature stability of magnetic properties has been realized by simultaneous additions of Cr and Co. This type of magnets are less susceptible to oxidation because of the less rare-earth content. Consequently, even fine powders (e. g., under 38 micrometer sieve) are physically and chemically stable in contrast to the conventional Nd2Fe14B-type melt-spun materials. The stability in terms of the structural losses is also superior to that of the Nd2Fe14B-type melt-spun materials. Utilization of the Cr-and-Co-doped Fe3B/Nd2Fe14B nanocomposite permanent magnets as a hard magnetic component of injection-molded resin-bonded magnets seems promising because of the excellent stability of the magnetic properties of fine powders. Direct quenching of a melt into the nanocomposite structure has become possible recently in addition to the conventional processing route of crystallization of an amorphous precursor, opening up the possibility of less-expensive production of the material.
Magnetic Properties of Polymer Bonded Exchange-Spring NdFeB Magnets
Authors: Mokal B. , Smith N.A. , Williams A.J. , Harris I.R. 
Published: April 2011

ABSTRACTThe production of remanence enhanced powders, using a method of mechanical alloying of free iron to melt spun ribbon, has been studied. The final composition is Nd8. 1Fe77.1Co10.9B3.9 and both hard and soft materials possess an initial fine grain size; approximately 30nm for the Nd2Fe14B phase in the melt spun ribbon and 1µm for the α-Fe. The magnetic properties of resin bonded magnets fabricated using such material have been measured and found to exhibit exchangespring behaviour. The experiments performed in this work are described with respect to the volume fraction of the soft phase and subsequent annealing temperature of the as-milled material. Remanence enhancement has been observed and this can be attributed to the exchange interactions between the ferromagnetic soft and hard phases. For a 30% by volume addition of α-Fe, typical values of remanence were found to be ∼880mT with a coercivity of ∼250 kA/m. The reversible and irreversible components of the magnetisation have been determined, to demonstrate the exchange coupling and coercivity behaviours respectively.
Magnetic Properties of α Fe/NdFeB Nanocomposite Alloys Prepared by Two-Step Rapid Solidification
Authors: Yamasaki M. , Mizuguchi H. , Morioka H , Hamano M. , Inoue A. 
Published: April 2011

ABSTRACTIn order to obtain directly powders of nanocomposite a Fe/NdFeB alloys with the composition of NdxFebaICO8NbyB, where x: 8.0-8.5, y: 1.5-2.5, z: 6.0-6.5 in at%, have been prepared using the two-step rapid solidification apparatus, which is composed of a gas atomizing system at the upper side and a collision-and-solidificating rotor system at the lower side. It is found that the coercivity (HcJ) of flat-shaped powders obtained depends on powder sizes. The best HcJ in each sieved powder is 525 kA/m (6.60 kOe) for a size more than 500 p m, 449 kA/m (5.64 kOe) for 150-500 pm, and 391 kA/m (4.91 kOe) for 50-150 p m. These values are not so high compared to those of powders of ribbons prepared using a single-roller melt spinning apparatus. This should be attributed to the powder size distribution that causes fluctuation of the quenching rate. Thickness of the flat powder is found to be controllable up to 70/g m, which is useful to get compression molded bonded magnets with a high density and thus a high remanence (Br). An epoxy-bonded magnet with (BH)max: 61.8 kJ/m 3 (7.76 MGOe), Br: 0.732 T (7.32 kG), HcJ: 427 kA/m (5.36 kOe), and density of 6.20 Mg/m 3 is obtained.
Nd Rich Nd-Fe-B Tailored for Maximum Coercivity
Authors: Girt Er. , Krishnan Kannan M. , Thomas G. , Echer C. J. , Altounian Z. 
Published: April 2011

ABSTRACTThe coercive field, He, in rapidly quenched Nd-Fe-B was found to increase for samples with excess of Nd. In addition, Hc, strongly depends on the Fe/B ratio, increasing from 1.67 T for Fe/B = 1.07 to 2.05 T for Fe/B = 14.6 in Nd30(Fe,B)70. The increase in Hc seems to correlate with an increase of the γ-Nd phase in the sample. The initial magnetization curves of Nd30(Fe,B)70 show that the domain wall pinning plays a more important role as the Fe/B ratio increases. Thus, γ-Nd may play an important role in promoting a pinning mechanism. The excess of Nd in rapidly quenched Nd-Fe-B samples was also found to promote growth of Nd2Fe14B grains elongated in shape.
Hysteresis Loops and Coercivity Mechanisms in Sintered and Nanocrystalline Permanent Magnets
Authors: Kronmüller H. , Goll D. , Kleinschroth I. , Zern A. 
Published: April 2011

ABSTRACTThe hysteresis loops of nanocrystalline (nc) permanent magnets (pms) produced by the melt-spin technique have been investigated for compositions based on the intermetallic compounds R2Fe14B (R = Nd, Pr) and the carbides Sm2Fe17−xGaxCy. The following three types of pms have been studied: 1) High-coercivity pins with exchange decoupled grains. 2) High-remanence exchange-spring pms. 3) High-coercive-high-remanence composite pins with exchange coupled soft and hard magnetic grains. The temperature dependence of the coercive field μ0Hc for all three types ofpms obeys a relation for a modified nucleation field, Hc = (2K1/Js)α - Neff Ms (K1 = first anisotropy constant, Ms = spontaneous magnetization). For an analysis of the characteristic differences between the microstructural parameters a and Neff as obtained for the three types of pms, computational micromagnetism on the basis of the Finite Element Technique is applied. This powerful method allows a quantitative analysis of the role of grain size, grain boundaries (gbs), texture of easy directions and of soft magnetic phases in composite materials. In order to obtain satisfactory results, a self-adapting algorithm has been developed where the mesh size is adapted to the gradients of the direction cosines of the spontaneous magnetization. It turns out that excellent magnetic properties of composite pms can only be obtained if the gbs are as ideal as possible. Remanence and coercive field are found to decrease linearly with a corresponding reduction of both, the crystal anisotropy and the exchange constant within the gbs. In composite pins the diameters of the soft magnetic grains should be smaller than twice the domain wall width, of the hard magnetic phase in order to obtain a remarkable remanence enhancement. From these model calculations general rules for the development of optimized nc pms with large remanences and large coercivities are derived.
Thermal Plasma Synthesis of γ-FeN, Nanoparticles as Precursors for the Fe16N2 Synthesis by Annealing
Authors: Turgut Z. , Ferguson D. E. , Huang M. Q. , Wallace W. E. , Mchenry M. E. 
Published: April 2011

ABSTRACTAn ordered Fe16N2 phase has been reported with iron moments as high as 3.2 μB. It is precipitated from nitrogen martensite structures ideally containing 10.5 at.% nitrogen. Due to the highly distorted crystal structure and metastability of this phase non-equilibrium processing routes are sought to synthesize this phase. Here we report on radio frequency (RF) plasma torch synthesis which is used to produce FeN. nanoparticles quenched into a body centered tetragonal bct) structure as precursors for further annealing studies to form α“- Fe16N2 phase. We have employed a Tekna PL-50 type 50 kW, RF plasma torch. A plasma gas mixture containing 40 standard liters per minute (slpm) Ar and 8 slpm Hydrogen - 70 slpm Ar gas was used as a sheath gas. Iron powder ( < 10 μm) was injected into the plasma stream using Ar flowing 15 slpm as a carrier gas. Nitrogen and Ammonia were used as a nitrogenization sources. Relatively low injection rates were used in order to achieve smaller particle sizes and thus faster quenching rates. We were able to produce particles containing up to 45 % of the quenched γ-phase. Observations based on x-ray diffraction (XRD) determination of lattice expansion and phase transition temperatures observed by differential thermal analysis (DTA) indicated that the quenched phase contains 6.5 atomic % nitrogen. Scherrer analysis of the fine particle broadening indicated that the average particle size for γ- phase is 27 nm, whereas this value is found to be 55 nm. for α-Fe. Nitrogen is well known for its grain size refinement in Fe thin films. Saturation magnetizations were found to be as low as 123 emu/g due to the presence of the nonmagnetic γ-FeNx phase.
Polymer Coated Nanoparticulate Ferrite Powders: Properties and Application
Authors: Vollath D. , Szabó D. V. , Fuchs J. 
Published: April 2011

ABSTRACTSuperparamagnetic behavior is characterized by a thermally fluctuating vector of magnetization, leading to magnetization curves free of hysteresis: it is a property of isolated ferrite particles with sizes below ca. 10 nm. These particles fulfil the condition Kv < kT with K … energy of unisotropy, v … volume of the particle, kT has the usual meaning. To produce a superparamagnetic macroscopic part it is necessary to avoid the interaction of the particles. This can be achieved by coating the particles with a second non-magnetic phase. This special material can be synthesized using the microwave plasma process. Because of the specific interaction of charged particles with an oscillating electrical field, microwave plasmas excel in relatively low reaction temperatures. The low reaction temperature and the electrical charging of the particles in the plasma reduce the probability of agglomeration. Therefore, it is possible to pass the gas stream with the as produced particles through a second reaction zone, where the particles will be coated with a polymer. The thickness of the coating can be adjusted in the range from 1 to 5 nm. The composition of the ferrite kernel is selected either for maximum susceptibility or maximum frequency of application. They may consist either of maghemite, manganese-, manganese-zinc-, or magnesium iron spinell for maximum susceptibility or cobalt-iron spinelle type material for maximum frequency. Polymer coated ferrite nanoparticles can be consolidated by hot pressing with temperatures around 100 °C. Superparamagnetism is shown by static magnetic measurements and Moessbauer spectrometry. Dynamic measurements of the complex susceptibility show interesting properties up to frequencies in the gigahertz range.
Magnetic Properties of Hitperm (Fe,Co)88Zr7B4Cu1 Nanocrystalline Magnets (Invited)
Authors: Willard M. A. , Gingras M. , Lee M. J. , Harris V. G. , Laughlin D. E. , Mchenry M. E. 
Published: April 2011

ABSTRACTAlloys consisting of Fe-Co-M-B-Cu (with M = Zr, Hf, Nb), called HITPERM alloys, have been developed. Synchrotron X-radiation studies have been used to show that the ferromagnetic phase in an equiatomic FeCo-based alloy is the α'-FeCo phase. Since both the α'-FeCo phase and the FeCo-based amorphous phase of the nanocrystalline alloy have high Curie temperatures, a high magnetization persists up to the α -> γ structural phase transformation temperature of 980°C. Room temperature AC permeability measurements have shown that the alloys maintain a high permeability of ∼2000 up to a frequency of 20 kHz. The room temperature core loss has also been shown to be competitive with commercial high temperature magnetic alloys with a value of 1 W/g at Bs = 10 kG andf= 10 kHz. Analysis of extended X-ray absorption fine structure (EXAFS) data is consistent with a two-phase mixture of nanocrystalline body centered cubic derivative FeCo structure and an amorphous Zr-rich phase. A differential scanning calorimetry study of the primary crystallization reaction shows an activation energy of 323.3 kJ/mol. As a preliminary study of phase and grain stability, broadening of X-ray diffraction peaks indicates little grain growth after annealing at 600 °C for 3072 hours.
Surface Analysis Of The Nanocrystalline Fe-Based Alloys By Conversion Electron Mossbauer Spectroscopy
Authors: Grabias A. , Kopcewicz M. , Idzikowski B. 
Published: April 2011

ABSTRACTA combined conversion electron and γ-transmission Mössbauer spectroscopy is applied to investigate the differences in the surface and bulk crystallization of the amorphous Fe-M-B-Cu (M: Zr, Ti, Nb, Ta) alloys. It is shown that the surface crystallization occurs at an annealing temperature lower than in the bulk. The nanocrystalline bcc Fe phase is significantly more abundant at the surface than in the bulk in the entire annealing temperature range.
Crystallization and Nanocrystallization Kinetics of Fe-Based Amorphous Alloys
Authors: Hsiao A. , Turgut Z. , Willard M.A. , Selinger E. , Laughlin D.E. , Mchenry M.E. , Hasegawa R. 
Published: April 2011

ABSTRACTIn this work we describe crystallization kinetics as inferred from time-dependent magnetization studies and thermal analysis for an Allied Signal amorphous Fe-based METGLAS® 2605SA-1 alloy and a NANOPERM (Fe88Zr7B4Cu1) alloy. We illustrate and contrast several phenomena important to understanding crystallization kinetics in particular to the NANOPERM alloy system. In METGLAS® 2605SA-1 primary and secondary crystallization events are observed in differential scanning calorimetry data (DSC) at temperatures of 504 °C and 549 °C, respectively for data taken at a 10 °C/min scan rate. Both temperatures are greater than the Curie temperature of the amorphous alloy. For the NANOPERM alloy primary crystallization (as determined from differential thermal analysis (DTA)) occurs at 500 °C and secondary crystallization at 730 °C and M(t) at temperatures near the primary crystallization temperature is dominated (at short times < 1 hour) by the primary crystallization event. Using the Johnson-Mehl-Avrami equation for isothermal transformations and the Kissinger equation for constant heating transformations, we find corresponding models for the crystallization kinetics of the NANOPERM alloy.
Element-Specific Magnetization Reversal in Fe/Ce Multilayers
Authors: Munzenberg M. , Arend M. , Felsch W. , Pizzini S. , Fontaine A. , Neisius T. , Pascarelli S. 
Published: April 2011

ABSTRACTFe/Ce multilayers are magnetically soft with coercive fields of a few Oersteds. In these structures the Ce-5d states are magnetically polarized by hybridization with the 3d states of Fe. The element selectivity of X-ray magnetic circular dichroism (XMCD) is used to measure the magnetization reversal of the Ce-5d states at room temperature. Comparison with the macroscopic magnetization curves studied by the magnetooptical Kerr effect (MOKE) reveal that the ordered Ce-5d moment is not directly coupled to the overall Fe-layer magnetization: the coercitivity of the Ce hysteresis is reduced a factor of two. In view of previous 57Fe Mössbauer spectra this is attributed to an effect of the interface where nominally 1 atomic layer of Fe and Ce are intermixed. Magnetization reversal is initiated in this region due to a reduced magnetocrystalline anisotropy and then propagates into the Fe layers. This interpretation is supported by an experiment on a hydrided multilayer Fe/CeH2.6_6: In this case, there is no intermixing at the interfaces and the magnetization of the Ce-5d electrons follows the Fe-layer magnetization directly.
High Performance, Light weight Thermoplastic/Rare Earth Alloy Magnets
Authors: Xiao Jun , Otaigbe Joshua U. 
Published: April 2011

ABSTRACTWe report progress on our exploratory research on surface modification of magnetic NdFeB fillers, characterization of suitable magnetic rare earth alloy powders and high-performance polymer matrices, processability, and properties of novel thermoplastic/NdFeB magnets. The results suggest that blending liquid crystal polymer (LCP) with a high-thermoplastic polymer such as polyphenylene sulfide (PPS) provides the required balance of properties. These properties include superior magneto-mechanical performance, minimal melt viscosity at optimal NdFeB volume loading, enhanced thermal stability, high stiffness, high strength, improved dimensional stability, and excellent chemical resistance; making the thermoplastics magnets suitable for use in high temperature and aggressive environments where commercial polymer-bonded magnets are not useable.
Stochastic Mesoscale Modeling of Elastic-Plastic Deformation
Authors: Staroselsky A. , Bulatov V.V. 
Published: April 2011

AbstractPlastic response of a solid under stress depends on its crystallographic structure and morphology. Two of the major mechanisms of plasticity in metals are crystallographic slip and twinning. The purpose of this work is to analyze the influence of local stress distribution on slip and twin nucleation and propagation and to examine how this behavior depends on the interaction among slips, twins, and grain boundaries. We formulate a simple model in which slip and twin systems are defined at appropriate angles to each other. Plastic flow is treated as a Markovian stochastic process consisting of a series of local inelastic transformations (LITs) in the representative volume elements (RVE). The probabilities of LITs per unit time are defined in the framework of transition-state theory. By varying the types of allowed LITs and/or the scale of RVE, plastic deformation is modeled at different structural levels, from a small volume of single crystal to the aggregate response of an isotropic polycrystalline solid. An important feature of this model is that evolution of the internal stress distribution is traced explicitly throughout the simulation run. This allows us to examine conditions of slip and twinning in considerable detail. In particular, we observe that twinning occurs through a nucleation-and-growth mechanism whose rate is controlled by the size of the critical nucleus of the new phase.
Strain Tensors at the Atomic Scale
Authors: Horstemeyer M.F. , Baskes M.I. 
Published: April 2011

AbstractAlmansi and Green strain tensors are developed for use in large deformation molecular dynamics/statics simulations that employ Embedded Atom Method (EAM) potentials for metals. The strain tensors are formulated with respect to the deformation gradient. A scalar potential function is used with a weighting function that is dependent upon a cutoff radius for the deformation gradient. For a homogeneous or inhomogeneous deformation, a cutoff distance of one lattice parameter can be used to approximate local strain level. Inhomogeneous deformation reveals different results for Almansi and Green strain tensors indicating that the small strain assumption cannot be used to determine large atomic strains.
Single Crystal Elastic Moduli of Disordered Cubic Alloys
Authors: Hartley Craig S. 
Published: April 2011

AbstractA review of the relationship between elastic moduli and interatomic force constants precedes the description of a method for determining the composition dependence of single crystal elastic moduli of disordered alloys having the face-centered cubic structure. The method treats the alloy as a virtual crystal, characterized by an effective pair potential between atoms. Results of calculations are presented using experimental data on Cu-rich Cu-Al alloys.
The Structure of Defects Formed by Absorption of Crystal Dislocations in Interfaces in the HCP Metals
Authors: Bacon D.J. , Pond R.C. , Serra A. 
Published: April 2011

AbstractAtomic-scale computer simulation has been used to investigate the interaction of crystal dislocations with two interfaces in hexagonal-close-packed (HCP) metals, namely the {1012} twin boundary and a <1210>/90° tilt boundary that is incommensurate in the direction perpendicular to the tilt axis. Crystal dislocations are absorbed in the tilt boundary with concomitant reconstruction of their cores. In the twin boundary, a broader range of interactions is observed, including defect transmission from matrix to twin and decomposition in the interface into discrete defects. The role of crystallographic features and interfacial structure is elucidated by comparing interaction processes in the two interfaces. The core structure of interfacial defects can be complex and contributes significantly to total defect energy.
Twinning Deformation in Martensite Microstructure
Authors: Ackland G.J. , Pinsook U. 
Published: April 2011

AbstractMolecular dynamics is used to study twinning deformation in a martensite microstructure obtained from rapid cooling β zirconium through the bcc-hcp transition. The microstructure is composed of (1011) twin boundaries and boundary dislocations which sometimes spread across the twins to form stacking faults. A series of such equilibrium microstructures subjected to discrete, increasing < 1012 > (1011) shear strain. The stress-strain curve has stick-slip behaviour with yield stress of ≈ 5.OKbar and yield strain of ≈ 3.8%. Deformation occurs through movement of twin boundaries in segments between boundary dislocations. Straight perfect twin boundaries do not move.
Influence of Grain Size on Recrystallisation During hot Working of Austenitic Stainless Steels
Authors: Whiteman J. A. , Choi Y. , Sellars C.M. 
Published: April 2011

AbstractDuring the hot rolling of austenitic stainless steels, complete static recrystallisation is expected between passes unless finishing temperatures are low. Typically progressive refinement takes place to grain sizes in the range 20–50μm. However, most experimental studies of the effect of strain, strain rate, temperature and initial grain size on recrystallisation kinetics and recrystallised grain size under hot working conditions have been carried out on initial grain sizes greater than 50μm. Empirical relationships from these data and from more limited results of CMn steels have been extrapolated to smaller grain sizes for use in models of microstructural evolution during rolling.Recent development of a physically based model for the effects of initial grain size, assuming that site saturated nucleation occurs at grain corners, grain edges, grain faces and at intragranular sites leads to interdependence of the effects of strain and grain sizeon nucleation density and hence on recrystallised grain size and recrystallisation rate. Experimental evidence available in the literature and some new results on finer grained Type 316 stainless steel are reviewed and compared with the expectations from the model.
The Determination of Evolving Microstructure Using Constitutive Relationships
Authors: Diak B.J. , Saimoto S. 
Published: April 2011

AbstractThe evolution of the constitutive parameter, the mean slip distance, λ, is monitored during tensile deformation of 3.2 μm grain size aluminum at 200 K. Transmission electron microscopy (TEM) confirms that the grain size, D, sets an upper limit to λ.
Thixotropy of Semisolid Metals
Authors: Alexandrou Andreas N. , Burgos Gilmer R. , Entov Vladimir M. 
Published: April 2011

AbstractUnderstanding the time-dependent flow behavior of metal alloys in semisolid state is essential for the further development of the process. In the present investigation, the thixotropic behavior of semisolid slurries is modeled using conservation equations and the Herschel-Bulkley fluid model. The rheological parameters are assumed to be functions of the solid volume fraction, and of a structural parameter that changes with processing history. The evolution of the structural parameter is described by a first order kinetic differential equation that relates the rate of build-up and break-down of the solid skeleton. The model is implemented into a computer code to predict die filling.