TY - JOUR
T1 - A study on the Nd-rich phase evolution in the Nd-Fe-B sintered magnet and its mechanism during post-sintering annealing
AU - Kim, Tae Hoon
AU - Lee, Seong Rae
AU - Namkumg, Seok
AU - Jang, Tae Suk
N1 - Funding Information:
This research was supported by a Grant from the Fundamental R&D Program for Core Technology of Materials funded by the Ministry of Commerce, Industry and Energy and the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (2011-007200), Republic of Korea.
PY - 2012/10/5
Y1 - 2012/10/5
N2 - We investigated the microstructural evolution and the phase transformation of the RE-rich (Nd-Dy-O) phase, the Cu-rich (Nd-Cu-Co-O) triple junction phase (TJP), the mixed TJP, and their grain boundary phase (GBP) in the sintered Nd-Fe-B base magnet as a function of the post-sintering annealing (PSA) steps. The round-shaped RE-rich phase and triangular-shaped Cu-rich TJP have an fcc-NdO (a = 0.499 nm) type structure in the as-sintered state. These phases are gradually transformed into the hexagonal Nd 2O 3 (h-Nd 2O 3, a = 0.383 and c = 0.600 nm) type structure during the 1st and 2nd PSA steps. The Cu-enriched TJP, which contains a large amount of Cu (about 40 at.%), was transformed into the cubic Nd 2O 3 (C-Nd 2O 3, a = 1.108 nm) type structure after the 2nd PSA, suggesting that Cu-enrichment could be a trigger for the formation of the meta-stable C-Nd 2O 3 phase. The h-Nd 2O 3 GBP, formed from the Cu-rich phase and the mixed TJP in the as-sintered magnet, was also transformed into Cu-enriched C-Nd 2O 3, which is embedded in the amorphous matrix, during the 2nd PSA. The formation of the C-Nd 2O 3 TJP and the GBP after the 2nd PSA is the major factor involved in enhancing the coercivity (from 21.7 to 29.7 kOe). The mechanism of the phase evolution and the coercivity enhancement is discussed based on these results.
AB - We investigated the microstructural evolution and the phase transformation of the RE-rich (Nd-Dy-O) phase, the Cu-rich (Nd-Cu-Co-O) triple junction phase (TJP), the mixed TJP, and their grain boundary phase (GBP) in the sintered Nd-Fe-B base magnet as a function of the post-sintering annealing (PSA) steps. The round-shaped RE-rich phase and triangular-shaped Cu-rich TJP have an fcc-NdO (a = 0.499 nm) type structure in the as-sintered state. These phases are gradually transformed into the hexagonal Nd 2O 3 (h-Nd 2O 3, a = 0.383 and c = 0.600 nm) type structure during the 1st and 2nd PSA steps. The Cu-enriched TJP, which contains a large amount of Cu (about 40 at.%), was transformed into the cubic Nd 2O 3 (C-Nd 2O 3, a = 1.108 nm) type structure after the 2nd PSA, suggesting that Cu-enrichment could be a trigger for the formation of the meta-stable C-Nd 2O 3 phase. The h-Nd 2O 3 GBP, formed from the Cu-rich phase and the mixed TJP in the as-sintered magnet, was also transformed into Cu-enriched C-Nd 2O 3, which is embedded in the amorphous matrix, during the 2nd PSA. The formation of the C-Nd 2O 3 TJP and the GBP after the 2nd PSA is the major factor involved in enhancing the coercivity (from 21.7 to 29.7 kOe). The mechanism of the phase evolution and the coercivity enhancement is discussed based on these results.
KW - Magnetization
KW - Microstructure
KW - Powder metallurgy
KW - Rare-earth alloys and compounds
KW - Transmission electron microscopy (TEM)
UR - http://www.scopus.com/inward/record.url?scp=84862760210&partnerID=8YFLogxK
U2 - 10.1016/j.jallcom.2012.05.075
DO - 10.1016/j.jallcom.2012.05.075
M3 - Article
AN - SCOPUS:84862760210
SN - 0925-8388
VL - 537
SP - 261
EP - 268
JO - Journal of Alloys and Compounds
JF - Journal of Alloys and Compounds
ER -