Microstructural and Magnetic Studies of Hddr Magnets from High Boron NdFeB(Zr) Alloys

1999 ◽  
Vol 577 ◽  
Author(s):  
DN Brown ◽  
AJ Williams ◽  
O Gutfleisch ◽  
M Strangwood ◽  
IR Harris
Keyword(s):  
Grain Size ◽  
Magnetic Properties ◽  
Magnetic Property ◽  
Grain Boundaries ◽  
Hot Pressing ◽  
Magnetic Studies ◽  
Rich Phase ◽  
Marked Influence ◽  
High Boron ◽  
Zr Alloys

ABSTRACTSome boron-rich (with respect to the Nd 2Fe,4B composition) NdFeB alloys (with and without small additions of zirconium) have been investigated in an attempt to understand the influence of zirconium in the subsequent magnetic properties of HDDR hot pressed magnets. It was found that zirconium additions had a marked influence on the as-cast microstructures with a general refinement of the grain size and evidence of a zirconium-rich phase (probably ZrB2) at the grain boundaries. The magnetic property measurements of fully dense, isotropic HDDR hot pressed magnets indicated that those containing zirconium maintained their coercivity to significantly higher hot pressing temperatures and this was attributed to the pinning of grain boundaries by the zirconium rich phase.

scholarly journals Structure and Properties of Nd-Fe-B Alloy Subjected to HDDR Process

2016 ◽  
Vol 61 (1) ◽  
pp. 217-220 ◽  
Author(s):  
M. Szymański ◽  
B. Michalski ◽  
M. Leonowicz ◽  
Z. Miazga
Keyword(s):  
Grain Size ◽  
Magnetic Properties ◽  
Phase Transformation ◽  
Grain Boundaries ◽  
Master Alloy ◽  
Structure And Properties ◽  
Rich Phase ◽  
Average Grain Size ◽  
Reversal Phase ◽  
Neodymium Magnets

In this paper the Hydrogenation, Disproportionation, Desorption and Recombination (HDDR) route was tested, for the Nd-Fe-B master alloy, as a prospective procedure for recycling of sintered scrap neodymium magnets. The HDDR method is based on the hydrogen induced reversal phase transformation of Nd-Fe-B alloy: Nd2Fe14B + (2±x) H2 = 2NdH2±x + Fe2B + 12Fe. Microstructural observations (SEM), phase constitution studies (XRD) and measurement of magnetic properties (VSM) were done to investigate the HDDR transformation progress. It was observed that disproportionation reaction starts at the grain boundaries, where the Nd-rich phase is located. Average grain size was reduced and coercive material was produced as a result of the HDDR process. Obtained results are similar to literature data.

Effect of Boron on Magnetic Properties and Corrosion Resistance of High Energy Magnets

2009 ◽  
Vol 79-82 ◽  
pp. 1043-1046 ◽  
Author(s):  
L.Q. Yu ◽  
Y.P. Zhang ◽  
Q.T. Fu
Keyword(s):  
Grain Size ◽  
Magnetic Properties ◽  
Corrosion Resistance ◽  
Stoichiometric Composition ◽  
High Energy ◽  
Easy Plane ◽  
Main Phase ◽  
High Energy Density ◽  
Content Increase ◽  
Rich Phase

Element boron played an important role on magnetic properties and corrosion resistance of high energy density NdFeB products. The magnets were prepared by traditional powder metallurgy technique. It was found that with addition of 5.53 % B there was easy-plane phase formed. It owned not only lower remanence Br and coercivity iHc, but also poor corrosion resistance of magnet. As B content increase, the magnetic properties improved greatly, and obtained better properties at a content 5.7-5.87 % B. As increased B content further, superabundance B element formed too much B rich phase and led to Br decrease. Volume percent of phases calculated by theory formula, with the consumption of 0.1 % Nd oxided, it can be found that as B content increased from 5.53 %, the volume of main phase increased and easy-plane type Nd2Fe17 phase decreased in magnet, which resulted in Br, iHc increase. As B content increased higher than 5.82 %, more B rich phases formed which well isolated main phase grains and resulted in iHc increase. But too much B rich phase would decrease main phase proportion and lead to Br decrease. Examination of microstructure of magnets showed as B content increased from 5.53 % to 6.16 %, average matrix grain size was enlarged from 6.5µm to 8.2µm, and the proportion of sharp shape grains relatively increased as well. Abnormal grain growth was easily happened at higher B content. In addition, the decreased squareness Hk/iHc of magnets at higher B content also suggested inconsistent distribution of grain size and shape. Corrosion current density measured by polarization test for magnet with addition of 5.76 % B, near stoichiometric composition of Nd2Fe14B, owned lowest value and best corrosion resistance. Formation of Nd2Fe17 phase (lower B content) or B rich phase (higher B content) was not benefit for corrosion resistance improvement.

High-resolution TEM and analytical study of second-phase particles in Al2O3

1983 ◽  
Vol 41 ◽  
pp. 46-47
Author(s):  
K. J. Morrissey ◽  
Y. Kouh ◽  
C. B. Carter
Keyword(s):  
Grain Size ◽  
High Resolution ◽  
Grain Boundaries ◽  
Hot Pressing ◽  
Analytical Study ◽  
Second Phase ◽  
Initial Powder ◽  
Compact Density ◽  
Second Phase Particles ◽  
High Resolution Tem

The influence of additives such as MgO, NiO, and ZrO2 and impurities such as Na, K, and Ca on the sintering of alumina compacts has been the focus of a considerable amount of research. Since these additives affect compact density and grain size it is of interest to determine the behavior of the elements during processing. That is, it is important to know whether Ca and Mg segregate to grain boundaries or are located in the second-phase particles. Current results suggest that Ca is found uniformly at the grain boundaries and that Mg is accommodated in the second-phase particles.The present investigation is concerned with identifying second-phase particles in different commercially-produced Al2O3 compacts and studying both their structure and composition. Preliminary results have been discussed previously. The investigation has dealt mainly with two different alumina compacts. One compact was prepared from an initial powder containing 0.25% MgO, a small amount of intentionally added Ni, and was prepared by hot pressing.

scholarly journals Study of Structure and Magnetic Properties of SmCo10 Alloy Prepared by Different Methods

2018 ◽  
Vol 2018 ◽  
pp. 1-10
Author(s):  
Xiang Chi ◽  
Ying Li ◽  
De-quan Er ◽  
Xu-hao Han ◽  
Xiu-li Duan ◽  
...  
Keyword(s):  
Grain Size ◽  
Magnetic Properties ◽  
Grain Boundaries ◽  
Melt Spinning ◽  
Phase Distribution ◽  
Cast Alloy ◽  
Structural Parameters ◽  
Homogeneous Distribution ◽  
Annealed Alloy ◽  
Average Grain Size

In this paper, the phase compositions, microstructures, atomic structures, and magnetic properties of Co-rich SmCo10 alloys prepared by arc-melting, annealing, and melt-spinning were studied. It was found that as-cast alloy is composed of Th2Zn17-type Sm2Co17 matrix with an average grain size of ∼45 μm accompanied by lamellar eutecticum (consisting of α-Co and Th2Zn17-type Sm2Co17) distributed at grain boundaries. The annealed alloy has the same phase composition and phase distribution as the as-cast alloy except that the average grain size decreases to ∼35 μm, and the eutecticum has more homogeneous distribution on the matrix. Simultaneously, the atomic structure of Sm2Co17 is unchanged with only a decrease in structural disorder after annealing. The as-spun ribbons are composed of ∼95.5 vol.% TbCu7-type Sm2Co17 and the rest α-Co. The short rod-shaped α-Co grains are intermittently distributed at the grain boundaries of equiaxed Sm2Co17 grains. The as-spun ribbons show a higher coercivity, and the annealed alloy shows maximum magnetization. The structural parameters were calculated by Extended X-ray Absorption Fine Structure (EXAFS), and the relationship between structure and magnetic properties was discussed in detail.

High Strain Rate Deformation and Damage in Ceramic Materials

1993 ◽  
Vol 115 (3) ◽  
pp. 292-299 ◽  
Author(s):  
G. Raiser ◽  
R. J. Clifton
Keyword(s):  
Grain Size ◽  
Grain Boundaries ◽  
High Purity ◽  
Hot Pressing ◽  
Glassy Phase ◽  
Plane Waves ◽  
Weight Percent ◽  
Ultrafine Grain ◽  
Triple Junctions ◽  
Dynamic Tensile Strength

The objective of this investigation is to use a plate impact recovery experiment to identify the dominant failure mechanisms in conventional α-Al2O3 ceramics and thereby gain insight into the most promising, failure-resistant microstructures. A “soft-recovery” configuration is used wherein a star-shaped flyer impacts a square specimen. The impedances, shapes, thicknesses and orientation of all plates are designed to ensure a known history of longitudinal, planar stress waves throughout a central octagonal region of the specimen. The plane waves generated from this experiment are monitored by a laser interferometer system that allows data to be collected at four separate locations. The validity of the approach is demonstrated by a shot in which all plates were stressed within their elastic range. Subsequently, several experiments were conducted at nearly the same stress level with commercially sintered aluminas having different grain size and different glass content. These experiments, taken as a whole, demonstrate that improvement in alumina’s dynamic compressive properties is obtained by reducing the grain size. In compression, a reduction in grain size lowers average residual stresses at triple junctions and grain boundaries and makes the material less susceptible to inelastic deformation and sliding at triple junctions and grain boundaries. A reduction in the weight percent of pre-processing impurities (and therefore the amount of intergranular glassy phase) yields strong improvements in the dynamic tensile strength of the ceramic. A decrease in the amount of glassy phase tends to make tensile damage less likely by improving grain boundary strength. These trends were tested by conducting recovery experiments on a high-purity, small-grain alumina, processed in-house through hot pressing. Both the compressive resistance and, especially, the tensile resistance were superior to those found for all other tested specimens. The overall results suggest that the best failure resistance will be obtained for new, high-purity, ultrafine-grain ceramics that are prepared by hot pressing of nanometer scale powders.

scholarly journals Effect Of The Desorption-Recombination Temperature On The Microstructure And Magnetic Properties Of HDDR Processed Nd-Fe-B Powders

2015 ◽  
Vol 60 (2) ◽  
pp. 1499-1501
Author(s):  
J.-G. Lee ◽  
H.-R. Cha ◽  
S. Liu ◽  
J.-H. Yu ◽  
Y.-K. Baek ◽  
...  
Keyword(s):  
Magnetic Properties ◽  
Grain Boundaries ◽  
Grain Growth ◽  
Rich Phase ◽  
Homogenizing Annealing ◽  
Casting Alloys ◽  
Microstructure And Magnetic Properties

Abstract The effect of the desorption-recombination temperature on the microstructure and magnetic properties of hydrogenation-disproportionation-desorption-recombination (HDDR) processed Nd-Fe-B powders was studied. The NdxB6.4Ga0.3Nb0.2Febal (x=12.5-13.5, at.%) casting alloys were pulverized after homogenizing annealing, and then subjected to HDDR treatment. During the HDDR process, desorption-recombination (DR) reaction was induced at two different temperature, 810°C and 820°C. The higher Nd content resulted in enhanced coercivity of the HDDR powder, and which was attributed to the thicker and more uniform Nd-rich phase along grain boundaries. But this uniform Nd-rich phase induced faster grain growth. The remanence of the powder DR-treated at 820°C is higher than that DR-treated at 810°C. In addition, it was also confirmed that higher DR temperature is much more effective to improve squareness.

scholarly journals Aluminum Substitutions in Nd-Fe-B Sintered Magnets

1987 ◽  
Vol 96 ◽  
Author(s):  
J. K. Chen ◽  
G. Thomas
Keyword(s):  
Magnetic Properties ◽  
Grain Boundaries ◽  
Permanent Magnets ◽  
Rich Phase ◽  
Sintered Magnets ◽  
Sintered Permanent Magnets

ABSTRACTA microstructural and microanalytical study of aluminum substituted Nd-Fe-B sintered permanent magnets were carried out to determine the effect, if any, of aluminum on structure, composition, and magnetic properties, particularly on the observed increase in coercivity. It was found that Al enrichment occurred in the Nd-rich phase at the grain boundaries. The possible role(s) of this enrichment on the observed coercivity increase are discussed.

Study on the Magnetic Properties and Microstructure of Single-Stage Hot-Deformed Nd-Fe-B Magnets

2015 ◽  
Vol 815 ◽  
pp. 281-286
Author(s):  
Yi Long Ma ◽  
Qian Shen ◽  
An Ruo Zhou ◽  
Jian Chun Sun ◽  
Chun Hong Li ◽  
...  
Keyword(s):  
Grain Size ◽  
Magnetic Properties ◽  
Hot Deformation ◽  
Hot Pressing ◽  
Deformation Rate ◽  
Deformation Temperature ◽  
Poor Performance ◽  
Orientation Degree ◽  
Cold Pressing ◽  
Coarse Grains

The Nd-Fe-B powder was prepared to bulk by cold pressing, and then was hot-deformed by the vacuum hot-pressing machine. Effects of hot-deformation temperature and rate on the density, anisotropy, performance and microstructure were studied. The results showed that the grain size was small, but the density and orientation degree was low, thus leading to poor performance when the deformation temperature was too low or deformation rate was too large. When the temperature was higher than 750 °C or the rate was lower than 0.1mm/s, the anisotropic magnets with good density and texture could be obtained. However, the magnetic properties of hot-deformed magnets deteriorated due to the present of coarse grains. From the microstructure of hot-deformed magnets it could be seen that there were plenty of coarse and irregular grains, which have a higher Nd content than the plate-like grains. The optimum magnetic properties could be obtained at deformation temperature of 700 °C and rate of 0.1 mm/s.

Modeling the Magnetic Properties of Non-Oriented Electrical Steels Based on Microstructural Parameters

2011 ◽  
Vol 702-703 ◽  
pp. 734-737 ◽  
Author(s):  
Hadi Pirgazi ◽  
Roumen H. Petrov ◽  
Leo Kestens
Keyword(s):  
Grain Size ◽  
Magnetic Properties ◽  
Chemical Composition ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Quantitative Model ◽  
Experimental Results ◽  
Pole Density ◽  
Electrical Steels ◽  
Magnetization Behavior

Magnetic properties of electrical steels such as magnetization behavior and electrical losses are mainly related to chemical composition, crystallographic orientation and microstructure. By now, several models have been proposed to empirically correlate magnetic properties and affecting parameters. A quantitative model based on physical understanding of the interaction between the magnetic field variables (e.g. domain structure) and local microstructural variables (e.g. grain orientation and misorientation, grain boundary plane inclination) is still missing. To obtain a better understanding of the interaction between grain boundaries and domain walls, the magnitude of free pole density at grain boundaries was taken into account. Experimental results from 3-dimentional EBSD experiments were employed to measure the grain boundary orientation for several samples with different chemical composition and grain size. The free pole density was calculated using the relative misorientation between adjacent grains, and was included in a model together with grain size, magnetocrystalline anisotropy energy and silicon equivalent. By comparison with the experimental results of the magnetic induction measured at low, medium and high magnetic fields, is shown that the magnetization behavior can be more accurately predicted when the above mentioned phenomena are taken into account.

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