Limitations in the Grain Boundary Processing of the Recycled HDDR Nd-Fe-B System

Fully dense spark plasma sintered recycled and fresh HDDR Nd-Fe-B nanocrystalline bulk magnets were processed by surface grain boundary diffusion (GBD) treatment to further augment the coercivity and investigate the underlying diffusion mechanism. The fully dense SPS processed HDDR based magnets were placed in a crucible with varying the eutectic alloys Pr68Cu32 and Dy70Cu30 at 2–20 wt. % as direct diffusion source above the ternary transition temperature for GBD processing followed by secondary annealing. The changes in mass gain was analyzed and weighted against the magnetic properties. For the recycled magnet, the coercivity (HCi) values obtained after optimal GBDP yielded ~60% higher than the starting recycled HDDR powder and 17.5% higher than the SPS-ed processed magnets. The fresh MF-15P HDDR Nd-Fe-B based magnets gained 25–36% higher coercivities with Pr-Cu GBDP. The FEG-SEM investigation provided insight on the diffusion depth and EDXS analysis indicated the changes in matrix and intergranular phase composition within the diffusion zone. The mechanism of surface to grain boundary diffusion and the limitations to thorough grain boundary diffusion in the HDDR Nd-Fe-B based bulk magnets were detailed in this study.

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Nd-Fe-B Magnets: The Gradient Change of Microstructures and the Diffusion Principle after Grain Boundary Diffusion Process

Materials ◽

10.3390/ma12233881 ◽

2019 ◽

Vol 12 (23) ◽

pp. 3881 ◽

Cited By ~ 1

Author(s):

Yaojun Lu ◽

Shuwei Zhong ◽

Munan Yang ◽

Chunming Wang ◽

Liuyimei Yang ◽

...

Keyword(s):

Surface Layer ◽

Grain Boundary ◽

Diffusion Process ◽

Shell Structure ◽

Boundary Diffusion ◽

Diffusion Mechanism ◽

Temperature Stability ◽

Grain Boundary Diffusion ◽

Core Shell ◽

Core Shell Structure

The diffusion of Tb in sintered Nd-Fe-B magnets by the grain boundary diffusion process can significantly enhance coercivity. However, due to the influence of microstructures at different depths, the coercivity increment and temperature stability gradually decreases with the increase of diffusion depth, and exhibit good corrosion resistance at a sub-surface layer (300–1000 μm). According to the Electron Probe Micro-analyzer (EPMA) test results and the diffusion mechanism, the grain boundary and intragranular diffusion behavior under different Tb concentration gradients were analyzed, and the diffusion was divided into three stages. The first stage is located on the surface of the magnet, which formed a thick core-shell structure and a large number of RE-rich phases. The second stage is located in the sub-surface layer, forming a uniform and continuous RE-rich phase and thin core-shell structure. The third stage is located deeper in the magnet, and the Tb enrichment only existed at the triangular grain boundary.

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Diffusion and solubility of holmium ions in barium titanate ceramics

Journal of Materials Research ◽

10.1557/jmr.2004.0466 ◽

2004 ◽

Vol 19 (12) ◽

pp. 3512-3520 ◽

Cited By ~ 14

Author(s):

Junichi Itoh ◽

Hajime Haneda ◽

Shunichi Hishita ◽

Isao Sakaguchi ◽

Naoki Ohashi ◽

...

Keyword(s):

Barium Titanate ◽

Grain Boundary ◽

Diffusion Coefficients ◽

Boundary Diffusion ◽

Diffusion Mechanism ◽

Annealed Sample ◽

Lattice Diffusion ◽

Grain Boundary Diffusion ◽

A Site ◽

Titanate Ceramics

Ho ion solubility and diffusivity were evaluated in barium titanate ceramics in which Ho ions were implanted with an accelerating voltage of 500 keV. The depth profile of the ions was composed of three regions in the post-annealed sample: the first was the precipitation region, the second was a region created by lattice diffusion of Ho ions, and the third was a region created by grain-boundary diffusion. The Ho lattice diffusion characteristics were similar to those of Ni ion diffusion in barium titanate ceramics, and we concluded that the diffusion mechanism was the same as that responsible for Ni ions. The Ho ions diffused through the B-site (Ti-site) and were then exchanged with A-site ions. This mechanism suggests that a small number of Ho ions dissolved in the B-site. Preferential grain-boundary diffusion was also observed. The grain-boundary diffusion coefficients were four to five orders of magnitude larger than the volume diffusion coefficients. The solubility of Ho ions was estimated to be a few thousand parts per million in barium titanate ceramics.

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Molecular-dynamics studies of grain-boundary diffusion. II. Vacancy migration, diffusion mechanism, and kinetics

Physical Review B ◽

10.1103/physrevb.29.5363 ◽

1984 ◽

Vol 29 (10) ◽

pp. 5363-5371 ◽

Cited By ~ 29

Author(s):

Thomas Kwok ◽

Paul S. Ho ◽

Sidney Yip

Keyword(s):

Molecular Dynamics ◽

Grain Boundary ◽

Boundary Diffusion ◽

Diffusion Mechanism ◽

Grain Boundary Diffusion ◽

Vacancy Migration ◽

Mechanism And Kinetics

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Measurement of the Impurity Diffusivity of Cu in Fe by Laser Induced Breakdown Spectrometry

Defect and Diffusion Forum ◽

10.4028/www.scientific.net/ddf.237-240.266 ◽

2005 ◽

Vol 237-240 ◽

pp. 266-270 ◽

Cited By ~ 8

Author(s):

Chan Gyu Lee ◽

Jung Han Lee ◽

Byeong Seon Lee ◽

Yong Ill Lee ◽

Toshitada Shimozaki ◽

...

Keyword(s):

Grain Boundary ◽

Diffusion Coefficients ◽

Boundary Diffusion ◽

Volume Diffusion ◽

Diffusion Mechanism ◽

Grain Boundary Diffusion ◽

Impurity Diffusion ◽

Boundary Diffusion Coefficient ◽

Laser Induced Breakdown ◽

Good Agreement

The impurity diffusion coefficients of Cu in Fe have been determined in the temperature range of 1073 - 1163 K by means of Laser Induced Breakdown Spectrometry (LIBS). The volume diffusion coefficients for Cu impurity diffusion in a-iron found in this work are in good agreement with the previously published result. The grain boundary diffusion coefficient gb D s d was also calculated using the volume diffusivity and processing the tails of the measured profiles. The values of the activation energy for volume and grain boundary diffusion were approximately 280 and 161 kJmol-1, respectively. This indicates the possibility of a monovacancy diffusion mechanism in case of volume diffusion. The results for the diffusion coefficients are Dv= 2.2 ×10-2exp(-280 kJmol-1/RT) m2s-1 and gb D s d = 2.6 ×10-11exp(-161 kJmol-1/RT) m3s-1.

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A quantitative demonstration of the grain boundary diffusion mechanism for the oxidation of metals

Philosophical Magazine A ◽

10.1080/01418618208239905 ◽

1982 ◽

Vol 45 (5) ◽

pp. 823-833 ◽

Cited By ~ 151

Author(s):

A. Atkinson ◽

R. I. Taylor ◽

A. E. Hughes

Keyword(s):

Grain Boundary ◽

Boundary Diffusion ◽

Diffusion Mechanism ◽

Grain Boundary Diffusion

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Electromigration Characterization for Multilevel Metallizations using Textured AlCu

MRS Proceedings ◽

10.1557/proc-428-75 ◽

1996 ◽

Vol 428 ◽

Cited By ~ 3

Author(s):

Larry M. Ting ◽

Qi-Zhong Hong

Keyword(s):

Grain Boundary ◽

Beneficial Effect ◽

Crystallographic Texture ◽

Boundary Diffusion ◽

Diffusion Mechanism ◽

Grain Boundary Diffusion ◽

Improvement Effect ◽

Electromigration Lifetime ◽

Edge Dislocations

AbstractElectromigration lifetime dependence on crystallographic texture for AlCu interconnects is determined. It is found that enhancement of AlCu texture at <111> orientation improves EM endurance. But this beneficial effect is limited after a certain level of texture enhancement is reached. The effect of lifetime improvement is proved to result from a decrease in atomic diffusivity. Saturation of the lifetime improvement effect for highly textured AlCu indicates a change in the main diffusion mechanism for electromigration, possibly from the regular grain boundary diffusion to diffusion through edge dislocations.

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