TY - JOUR
T1 - Suppression mechanism of abnormal grain growth by Zr addition in pressless processed Nd-Fe-B sintered magnets
AU - Itakura, Masaru
AU - Sugiyama, Koichi
AU - Akamine, Hiroshi
AU - Nishida, Minoru
AU - Nakamura, Michihide
AU - Mizoguchi, Tetsuhiko
AU - Iriyama, Takahiko
N1 - Funding Information:
This work was partly supported by JSPS KAKENHI Grant Number JP20H02425 .
Publisher Copyright:
© 2021 Elsevier B.V.
PY - 2021/12/20
Y1 - 2021/12/20
N2 - Microstructures of pressless processed (PLP) Nd-Fe-B sintered magnets with and without Zr addition were investigated by scanning electron microscopy and scanning/transmission electron microscopy. In the Zr-free magnet, huge polygonal abnormal grains (AGs) about 100 times larger than the normal grain size were generated by PLP sintering at 975 °C. Electron backscattered diffraction analysis revealed that the PLP sintered magnet had a biaxial oriented texture of fine Nd2Fe14B grains with the orientation of the AGs significantly deviated from the biaxial oriented grains. By adding a small amount of Zr, fine plate-like Zr-B precipitates with a long period stacking ordered structure derived from the ZrB2 phase formed on the growth surfaces of Nd2Fe14B grains with a crystallographic orientation relationship. There were two Nd-rich grain boundary (GB) phases, namely, orthorhombic Nd3(Co, Cu) and metastable CaF2-NdO2, which became liquid during sintering. The boron consumption associated with the formation of Zr-B precipitates increased the Nd-rich GB phases, resulting in a homogeneous distribution of the liquid phase around the Nd2Fe14B grains. Therefore, the addition of Zr effectively suppressed the abnormal grain growth during PLP sintering owing to the pinning effect of the Zr-B precipitates and the formation of a homogeneous liquid phase distribution.
AB - Microstructures of pressless processed (PLP) Nd-Fe-B sintered magnets with and without Zr addition were investigated by scanning electron microscopy and scanning/transmission electron microscopy. In the Zr-free magnet, huge polygonal abnormal grains (AGs) about 100 times larger than the normal grain size were generated by PLP sintering at 975 °C. Electron backscattered diffraction analysis revealed that the PLP sintered magnet had a biaxial oriented texture of fine Nd2Fe14B grains with the orientation of the AGs significantly deviated from the biaxial oriented grains. By adding a small amount of Zr, fine plate-like Zr-B precipitates with a long period stacking ordered structure derived from the ZrB2 phase formed on the growth surfaces of Nd2Fe14B grains with a crystallographic orientation relationship. There were two Nd-rich grain boundary (GB) phases, namely, orthorhombic Nd3(Co, Cu) and metastable CaF2-NdO2, which became liquid during sintering. The boron consumption associated with the formation of Zr-B precipitates increased the Nd-rich GB phases, resulting in a homogeneous distribution of the liquid phase around the Nd2Fe14B grains. Therefore, the addition of Zr effectively suppressed the abnormal grain growth during PLP sintering owing to the pinning effect of the Zr-B precipitates and the formation of a homogeneous liquid phase distribution.
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U2 - 10.1016/j.jallcom.2021.161244
DO - 10.1016/j.jallcom.2021.161244
M3 - Article
AN - SCOPUS:85112398643
VL - 887
JO - Journal of Alloys and Compounds
JF - Journal of Alloys and Compounds
SN - 0925-8388
M1 - 161244
ER -