The microstructures of cast ingot, annealed ingots and sintered bodies of Nd15(Fe0.585Co0.3Ni0.1Ti0.015)77B8 alloy were investigated with analytical electron microscopes to clarify the changes of the phases with successive processing. Five phases were identified in the specimens, namely Nd2(Fe0.6Co0.3Ni0.1)14B, Nd(Fe1-x-yCoxNiy)4B, Nd(Ni1-xCox), Nd(Fe1-x-yCoxNiy)2 and TiB2. In addition, (Nd1-yTMy)2O3 (TM Fe, Ni, Co) phase was also identified in the sintered specimen. An Nd-rich phase was not observed in the present specimens. The phases, except the main magnetic phase (Nd2TM14B), were different in crystal structure from those in ternary Nd-Fe-B magnets. The majority of NdTM4B dissolved to supply B atoms to TiB2 during the sintering. Some of the Nd(Ni1-xCox) phase reacted with O atoms absorbed during the milling and/or sintering process, and formed Nd1-yTMy)2O3 precipitate during the sintering. The remaining Nd(Ni1-xCox) phase precipitated as thin precipitates at grain boundaries. It is suggested that the phases enriched with Ni and the absence of the Nd-rich phase give rise to the high corrosion resistance of Nd-(Fe, Co, Ni, Ti)-B magnets.
All Science Journal Classification (ASJC) codes
- Mechanics of Materials
- Mechanical Engineering
- Metals and Alloys
- Materials Chemistry