Mechanical properties of sintered NdFeB magnets
Sintered NdFeB magnets are brittle materials, and their mechanical properties are hard and brittle, that is, high strength and low toughness, and there is almost no plastic deformation before fracture, that is, it breaks in the elastic deformation stage.
We found that sintered NdFeB has the highest energy product (BH)m, and the fracture toughness is still comparable to that of Sm2Tm17, SmCo5, and ferrite permanent magnets, because they are all permanent magnet materials based on intermetallic compounds, which are brittle Material. Bonded rare earth permanent magnet materials, Fe-Cr-Co, and magnetic steel have the best fracture toughness, but their magnetic energy product (BH) m is much lower than that of sintered NdFeB.
Brittle materials are commonly used three indicators to describe the mechanical properties of materials:
Fracture toughness usually reflects the strength of the material when there is crack expansion, and the unit is MPa·m1/2. The fracture toughness test of the material should use a tensile testing machine, stress sensor, extensometer, signal amplification dynamic strain gauge, etc. In addition, the sample should be made into a thin sheet.
Impact strength (impact fracture toughness) reflects the energy absorbed by the material during the fracture process under the action of impact stress, and the unit is J/m2. The measured value of impact strength is too sensitive to the size, shape, processing accuracy and test environment of the sample, and the dispersion of the measured value will be relatively large.
The flexural strength is the flexural fracture strength of the material measured by the three-point bending method. Because the sample is easy to process and simple to measure, it is most commonly used to describe the mechanical properties of sintered NdFeB magnets.
We found the approximate fluctuation range of the mechanical properties of sintered NdFeB given by some scholars based on different experiments. Because it is a brittle material, the experimental data has a large dispersion.
The characteristics of high strength and low toughness exhibited by sintered NdFeB permanent magnet materials are determined by their own crystal structure. In addition, the following two factors will affect the flexural strength of sintered NdFeB permanent magnets, which are also ways to improve their strength. .
The Nd content has a certain influence on the strength of sintered NdFeB. The experimental results show that under certain conditions, the higher the Nd content, the higher the material strength.
Adding other metal elements has a certain influence on the strength of sintered NdFeB. When a certain amount of Ti, Nb or Cu is added, the impact fracture toughness of the permanent magnet is improved; when a small amount of Co is added, the flexural strength of the permanent magnet is improved.
The comprehensive mechanical properties of sintered NdFeB are not high enough, which is one of the important reasons to limit its application in wider fields. The military, aerospace and other fields will play a greater role and enter a new period of development.