Study On The Effect Of Dy/Tb Grain Boundary Diffusion On The Mechanical Properties Of Sintered NdFeB

With the rapid development of new energy vehicles and digital products,the demand for the third generation of rare earth permanent magnet materials(sintered Nd Fe B magnets)has increased dramatically due to their excellent magnetic properties:high magnetic energy product,high coercivity,high anisotropic field,etc.The development of new energy vehicles and digital products not only demands higher magnetic properties of sintered Nd Fe B magnets but also demands higher mechanical properties of magnets.The grain boundary diffusion of heavy rare earth is one of the main means to improve the coercivity of sintered Nd Fe B.In this paper,the effect of grain boundary diffusion on the mechanical properties of sintered Nd Fe B is investigated,the bending strength of sintered Nd Fe B after grain boundary diffusion with different thicknesses of heavy rare earth films is systematically studied,and the relationship between the distribution of Dy and Tb elements inside the magnet and the mechanical properties,fracture morphology and fracture mechanism of the magnet after diffusion is discussed.The change of mechanical properties after diffusion in the grain boundary of magnets with different orientations was investigated.It was found that the high-temperature heat treatment process in the grain boundary diffusion process leads to a significant decrease in the bending strength of magnets.The addition of Dy,Tb in the grain boundary diffusion process can alleviate the bending strength reduction of magnets caused by heat treatment.The diffusion of Dy,Tb will change the fracture mechanism of the magnet.The excess of Dy,Tb will lead to a large increase in the fracture through the crystal.The bending strength of the magnet decreases with the increase of the film thickness after diffusion.When the thickness of Dy,Tb films are 6 μm and 4 μm,respectively,the bending strength of the magnet after grain boundary diffusion is 479.45 MPa and 468.83 MPa;at this time,the magnet obtains the optimal bending strength while the coercivity is greatly increased.It was found that the bending strength of the magnets after grain boundary diffusion of Tb with different orientations was increased compared to that of the heat treated magnets only.The bending strength decreases after the diffusion of Tb grain boundary in the main phase grains,which increases the penetration fracture and decreases the bending strength.In this paper,the influence mechanism of heavy rare earth Dy,Tb grain boundary diffusion on the flexural strength of magnets is systematically described,which fills the gap in the research field of the influence of heavy rare earth grain boundary diffusion on the mechanical properties of magnets and is important for the subsequent optimization of grain boundary diffusion process and the production and preparation of sintered Nd Fe B.