Presentation Information
[P2-59]Enhanced Coercivity in Sm(Fe0.8Co0.2)11-xTiCux Strips through Grain Boundary Phase Optimization
*Hai Bo FENG1, Feng Yang LIU1, Hang ZHAO1 (1. CISRI (China))
Keywords:
Permanent Magents,REFe12,Coercivity,Grain Boudary Phase
SmFe12-based alloys exhibit promising potential for new generation permanent magnets, due to their high saturation magnetization (1.64 T) and anisotropy field (12 T). Nevertheless, the SmFe12 binary alloy is thermodynamically unstable and requires stabilizing elements (M) for bulk magnets sintering. The addition of non-magnetic stable elements, such as Ti, V, Si, Mo, Cr, and Al, would deteriorate the Ms and Curie temperature (Tc) in the Sm(Fe,M)12 phase. In order to improve Ms and Tc, Co can be used instead of 20 at.% Fe. In the SmFe11Ti-based sintered ingot, a ferromagnetic grain boundary with an iron content of about 75 at. % formed, resulting in low coercivity. In this work, introduction of the low melting point element Cu can promote the formation of non-magnetic grain boundaries. The effect of Cu enrichment in the grain boundary phase on magnetic properties of the Sm(Fe0.8Co0.2)11-xTiCux (x=0-0.5) strips was investigated.
Figures 1(a) and 1(b) show the magnetization curve and magnetic properties dependence on Cu content of Sm(Fe0.8Co0.2)11-xTiCux (x=0, 0.1, 0.2, 0.3, 0.4, 0.5) strips at room temperature. The maximum Ms value of the strips is 10.7 kGs when x=0.2. When Cu content increases from 0 to 0.5, the remanence monotonically increases from 1.9 kGs to 5.4 kGs. The coercivity increases from 0.3 kOe(x=0) to 0.7 kOe (x=0.1), then decreases to 0.5 kOe when x=0.2. With Cu consistent addition, the coercivity increases to 2.1 kOe when x=0.5.
The Sm(Fe0.8Co0.2)11Ti strip consists of SmFe12 phase, SmFe9 phase and SmFe2 phase. With Cu addition, Sm-Cu phase increases from 0 to 9.1 wt.% in the strips. When the fraction of non-magnetic Sm-Cu phase increases, Ms decreases to 9.3 kGs. The content of ferromagnetic phases (1:12 phase and 1:9 phase) decreases constantly, resulting in Ms reduction. The precipitation of α-(Fe,Co,Ti) phase in the Sm(Fe0.8Co0.2)10.5TiCu0.5 strip may lead to Ms and Br increase.
Table 1 shows phase compositions of the Sm(Fe0.8Co0.2)11-xTiCux strips. When Cu content increased from 0 to 0.5, Fe content of the grain boundary phase decreased from 43.8 at.% to 12.6 at.%. Due to the immiscibility of Cu-Fe system, Cu effectively suppressed Fe content of the grain boundary, forming non-ferromagnetic grain boundary phases. When x=0.5, the proportion of (Sm,Cu)-rich grain boundary phase increases to 9.1 wt.% and the coercivity increases to 2.1 kOe in strips. Fig.1 (c-e) shows the TEM images of Sm(Fe0.8Co0.2)10.5TiCu0.5 strip, where multiple grains and continuous grain boundary phases was observed. The grains 1-3 correspond to 1:12 phase, and grain boundary phases 4-6 correspond to (Sm,Cu)-rich phases. In Fig.1 (d), the HAADF image shows a (Sm,Cu)-rich grain boundary phase about 10 nm thick between the two grains. 1:12 main phase grains can be well isolated with continuous non-ferromagnetic grain boundary, leading to the weakened exchange-coupling of 1:12 grains. Moreover, the average grain size reduces to ~2 μm with the content of (Sm,Cu)-rich grain boundary phase increases. Therefore, the grain size decrease and formation of Fe-lean grain boundary leads to the improvement of coercivity.
Figures 1(a) and 1(b) show the magnetization curve and magnetic properties dependence on Cu content of Sm(Fe0.8Co0.2)11-xTiCux (x=0, 0.1, 0.2, 0.3, 0.4, 0.5) strips at room temperature. The maximum Ms value of the strips is 10.7 kGs when x=0.2. When Cu content increases from 0 to 0.5, the remanence monotonically increases from 1.9 kGs to 5.4 kGs. The coercivity increases from 0.3 kOe(x=0) to 0.7 kOe (x=0.1), then decreases to 0.5 kOe when x=0.2. With Cu consistent addition, the coercivity increases to 2.1 kOe when x=0.5.
The Sm(Fe0.8Co0.2)11Ti strip consists of SmFe12 phase, SmFe9 phase and SmFe2 phase. With Cu addition, Sm-Cu phase increases from 0 to 9.1 wt.% in the strips. When the fraction of non-magnetic Sm-Cu phase increases, Ms decreases to 9.3 kGs. The content of ferromagnetic phases (1:12 phase and 1:9 phase) decreases constantly, resulting in Ms reduction. The precipitation of α-(Fe,Co,Ti) phase in the Sm(Fe0.8Co0.2)10.5TiCu0.5 strip may lead to Ms and Br increase.
Table 1 shows phase compositions of the Sm(Fe0.8Co0.2)11-xTiCux strips. When Cu content increased from 0 to 0.5, Fe content of the grain boundary phase decreased from 43.8 at.% to 12.6 at.%. Due to the immiscibility of Cu-Fe system, Cu effectively suppressed Fe content of the grain boundary, forming non-ferromagnetic grain boundary phases. When x=0.5, the proportion of (Sm,Cu)-rich grain boundary phase increases to 9.1 wt.% and the coercivity increases to 2.1 kOe in strips. Fig.1 (c-e) shows the TEM images of Sm(Fe0.8Co0.2)10.5TiCu0.5 strip, where multiple grains and continuous grain boundary phases was observed. The grains 1-3 correspond to 1:12 phase, and grain boundary phases 4-6 correspond to (Sm,Cu)-rich phases. In Fig.1 (d), the HAADF image shows a (Sm,Cu)-rich grain boundary phase about 10 nm thick between the two grains. 1:12 main phase grains can be well isolated with continuous non-ferromagnetic grain boundary, leading to the weakened exchange-coupling of 1:12 grains. Moreover, the average grain size reduces to ~2 μm with the content of (Sm,Cu)-rich grain boundary phase increases. Therefore, the grain size decrease and formation of Fe-lean grain boundary leads to the improvement of coercivity.
