The magnetic performance and mechanical properties including hardness, brittleness, fracture toughness and strength characteristics of the as-sintered and the optimal aged Nd-Fe-B magnets were examined in this work. A...The magnetic performance and mechanical properties including hardness, brittleness, fracture toughness and strength characteristics of the as-sintered and the optimal aged Nd-Fe-B magnets were examined in this work. A new method of Vickers hardness indentation combined with acoustic emission was used to test the brittleness of the magnets.The results show that the magnetic properties of the magnets could be improved through aging treatment, especially the intrinsic coercive force. But it is accompanied by a decrease of strength and fracture toughness. Theoretical calculation confirms that acoustic emission energy accumulated count value could be used to characterize the material brittleness. The bending fracture morphologies of the as-sintered and the optimal aged Nd Fe B magnets were investigated with the emphasis on the relationship between mechanical properties and microstructure using a field emission scanning electron microscopy(FE-SEM). The research results indicate that the intergranular fracture is the primary fracture mechanism for both as-sintered and optimal aged Nd Fe B magnets. Aging treatment changes the morphology and distribution of the Nd-rich phases, reducing the sliding resistance between Nd_2Fe_(14)B main crystal grains and lowers the grain boundary strength, which is the main reason for the strength and fracture toughness decrease of the aged Nd-Fe-B magnets.展开更多
In this work, a low temperature ageing process for the high coercivity Dy-doped Nd-Fe-B magnets was developed by the optimizing ageing process. The experimental results show that there is no difference in microstructu...In this work, a low temperature ageing process for the high coercivity Dy-doped Nd-Fe-B magnets was developed by the optimizing ageing process. The experimental results show that there is no difference in microstructures, crystal orientation, magnetic and mechanical properties between the low-temperature aged and the two-stage aged sintered Dy-doped Nd-Fe-B magnets. Because of the uneven stress distribution in the sintered Dy-doped Nd-Fe-B magnet and the high activation of Dy element, Dy atoms could diffuse into the main crystal phase and the grain boundary phases of the magnets during low-temperature ageing process, which results in the reasonable distribution of Dy element and formation of the thin and uniform grain boundary phases, which are the main reasons to improve intrinsic coercivity of the Dy-doped Nd-Fe-B magnets by the low-temperature ageing.展开更多
The Nd Fe B/Co multilayer films were prepared by magnetron sputtering. After that, the samples were annealed at 600 ℃ for 20 min. The surface morphology, phase structures and magnetic properties of Mo（50 nm）/[Nd F...The Nd Fe B/Co multilayer films were prepared by magnetron sputtering. After that, the samples were annealed at 600 ℃ for 20 min. The surface morphology, phase structures and magnetic properties of Mo（50 nm）/[Nd Fe B（100 nm）/Co（y）]×10/Mo（50 nm） thin films were researched by AFM, XRD and VSM, respectively. The results show that the films show stronger perpendicular magnetic anisotropy. When the thickness of Co layers is 10 nm, the coercivity Hc⊥ is the maximum, 295 k A/m. However, for y=10-20, the reduced remanence M/Ms of films has increased. When the thickness of Co layers is 20-30 nm, the Nd Fe B/Co multilayer films obtained more superior magnetic properties with M/Ms =0.95.展开更多
基金Project((2012)1743)supported by the China National Major Special Program for the Rare Earth and Rare Metallic Materials
文摘The magnetic performance and mechanical properties including hardness, brittleness, fracture toughness and strength characteristics of the as-sintered and the optimal aged Nd-Fe-B magnets were examined in this work. A new method of Vickers hardness indentation combined with acoustic emission was used to test the brittleness of the magnets.The results show that the magnetic properties of the magnets could be improved through aging treatment, especially the intrinsic coercive force. But it is accompanied by a decrease of strength and fracture toughness. Theoretical calculation confirms that acoustic emission energy accumulated count value could be used to characterize the material brittleness. The bending fracture morphologies of the as-sintered and the optimal aged Nd Fe B magnets were investigated with the emphasis on the relationship between mechanical properties and microstructure using a field emission scanning electron microscopy(FE-SEM). The research results indicate that the intergranular fracture is the primary fracture mechanism for both as-sintered and optimal aged Nd Fe B magnets. Aging treatment changes the morphology and distribution of the Nd-rich phases, reducing the sliding resistance between Nd_2Fe_(14)B main crystal grains and lowers the grain boundary strength, which is the main reason for the strength and fracture toughness decrease of the aged Nd-Fe-B magnets.
基金Project((2012)1743)supported by the Chinese National Major Special Project for the Rare Earth and Rare Metallic Materials
文摘In this work, a low temperature ageing process for the high coercivity Dy-doped Nd-Fe-B magnets was developed by the optimizing ageing process. The experimental results show that there is no difference in microstructures, crystal orientation, magnetic and mechanical properties between the low-temperature aged and the two-stage aged sintered Dy-doped Nd-Fe-B magnets. Because of the uneven stress distribution in the sintered Dy-doped Nd-Fe-B magnet and the high activation of Dy element, Dy atoms could diffuse into the main crystal phase and the grain boundary phases of the magnets during low-temperature ageing process, which results in the reasonable distribution of Dy element and formation of the thin and uniform grain boundary phases, which are the main reasons to improve intrinsic coercivity of the Dy-doped Nd-Fe-B magnets by the low-temperature ageing.
文摘The Nd Fe B/Co multilayer films were prepared by magnetron sputtering. After that, the samples were annealed at 600 ℃ for 20 min. The surface morphology, phase structures and magnetic properties of Mo（50 nm）/[Nd Fe B（100 nm）/Co（y）]×10/Mo（50 nm） thin films were researched by AFM, XRD and VSM, respectively. The results show that the films show stronger perpendicular magnetic anisotropy. When the thickness of Co layers is 10 nm, the coercivity Hc⊥ is the maximum, 295 k A/m. However, for y=10-20, the reduced remanence M/Ms of films has increased. When the thickness of Co layers is 20-30 nm, the Nd Fe B/Co multilayer films obtained more superior magnetic properties with M/Ms =0.95.
