Understanding the Role of Element Grain Boundary Diffusion Mechanism in Nd–Fe–B Magnets

2021 ◽  
pp. 2109529
Author(s):  
Lizhong Zhao ◽  
Jiayi He ◽  
Wei Li ◽  
Xiaolian Liu ◽  
Jian Zhang ◽  
...  
Keyword(s):  
Grain Boundary ◽  
Boundary Diffusion ◽  
Diffusion Mechanism ◽  
Grain Boundary Diffusion

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

Materials ◽  
2019 ◽  
Vol 12 (23) ◽  
pp. 3881 ◽  
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.

Diffusion and solubility of holmium ions in barium titanate ceramics

2004 ◽  
Vol 19 (12) ◽  
pp. 3512-3520 ◽  
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.

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

2005 ◽  
Vol 237-240 ◽  
pp. 266-270 ◽  
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.

The role of solute segregation in grain boundary diffusion

1982 ◽  
Vol 379 (1776) ◽  
pp. 159-178 ◽  
Keyword(s):  
Grain Boundary ◽  
Boundary Diffusion ◽  
Boundary Energy ◽  
Grain Boundary Diffusion ◽  
Enrichment Ratio ◽  
Tin Alloys ◽  
Bulk Diffusivity ◽  
Tin Content ◽  
Grain Boundary Transport

In measurements of grain boundary transport it is the product of the grain boundary enrichment ratio and the grain boundary diffusivity that is usually obtained. This work presents the first study in which these two terms are separated and in which the role of the grain boundary composi­tion in grain boundary diffusion is analysed in detail. This leads to the general prediction that the grain boundary diffusion of solute and solvent will be reduced by strongly segregating solutes if they do not simultaneously enhance the bulk diffusivities. The converse occurs if the solute weakly segregates but strongly enhances the bulk diffusivities. The diffusion measurements are made in iron–tin alloys in the tempera­ture range 563–750 °C by using radiotracers, and the segregation measure­ments, similarly, by Auger electron spectroscopy. The measured bulk diffusivities are similar to those found previously. The grain boundary diffusivities, determined via Suzuoka’s (1964) analysis, for iron and tin in pure iron have pre-exponential coefficients of 225 x 10 -4 and 9.2 x 10 -4 m 2 s -1 and activation energies of 165770 and 166600 J mol -1 respectively. Contrary to the increase in the bulk diffusivity produced by the ‘fast’ diffuser, tin, both grain boundary diffusivities are sharply reduced as the tin content rises. These and earlier results are interpreted through the effect of tin segregation on the grain boundary energy described by the theory of Borisov et al . (1964).

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