Sintered NdFeB Magnets

Sintered neodymium iron boron (NdFeB) magnets are renowned for their exceptional magnetic properties, but their mechanical performance—particularly fracture toughness, impact strength, and flexural strength—is equally critical for demanding industrial applications. As a leading sintered NdFeB magnet manufacturer, we engineer materials that balance magnetic power with structural reliability. This blog dives into the mechanical metrics defining NdFeB durability and how they impact real-world performance.   Fracture toughness usually reflects the strength of a material when cracks expand, and its unit is MPa·m1/2. The fracture toughness test of a material requires the use of a tensile testing machine, stress sensor, extensometer, signal amplification dynamic strain gauge, etc. In addition, the sample must be made into a thin sheet.   Impact strength (impact fracture toughness) reflects the energy absorbed by the material during the fracture process under the 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 measured value dispersion will be relatively large.   Bending strength is the bending fracture strength of materials measured by the three-point bending method. It is most commonly used to describe the mechanical properties of sintered NdFeB magnets because of the ease of sample processing and simple measurement.     The high strength and low toughness of sintered NdFeB permanent magnet materials are determined by their own crystal structure. In addition, the following two factors will affect the bending strength of sintered NdFeB and are also ways to improve its 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 bending strength of the permanent magnet is improved.   The low comprehensive mechanical properties of sintered NdFeB is one of the important reasons that limit its application in a wider range of fields. If the toughness of the product can be improved while ensuring that the magnetic properties are improved or unchanged, sintered NdFeB will play a greater role in the military, aerospace and other fields and enter a new period of development.

Sintered NdFeB magnets are core functional components and are widely used in instruments and equipment such as motors, electroacoustics, magnetic attraction, and sensors. The magnets are subject to environmental factors such as mechanical force, hot and cold changes, and alternating electromagnetic fields. If the working environment is over the standard, it will seriously affect the function of the equipment and cause huge losses. Therefore, in addition to magnetic performance, we also need to pay attention to the mechanical, thermal, and electrical properties of magnets, which will help us better design and use magnet, and is also of great significance for improving their service stability and reliability.   Mechanical Properties   The mechanical properties of magnets include hardness, compressive strength, bending strength, tensile strength, impact toughness, etc. NdFeB is a typical brittle material. The hardness and compressive strength of magnets are high, but the bending strength, tensile strength, and impact toughness are poor. This makes it easy for magnets to lose corners or even crack during processing, magnetization, and assembly. Magnets are usually fixed in components and equipment by means of slots or adhesives, and shock absorption and buffering protection are also provided.   The fracture surface of sintered NdFeB is a typical intergranular fracture. Its mechanical properties are mainly determined by its complex multiphase structure and are also related to the formula composition, process parameters, and structural defects (voids, large grains, dislocations, etc.). Generally speaking, the lower the total amount of rare earth, the worse the mechanical properties of the material. By adding low-melting-point metals such as Cu and Ga in appropriate amounts, the toughness of neodymium magnet can be enhanced by improving the distribution of grain boundary phases. Adding high-melting-point metals such as Zr, Nb, and Ti can form precipitation phases at the grain boundaries, which can refine the grains and inhibit crack extension, helping to improve strength and toughness; but excessive addition of high-melting-point metals will cause the hardness of the magnetic material to be too high, seriously affecting processing efficiency.   In the actual production process, it is difficult to take both the magnetic properties and mechanical properties of magnetic materials into account. Due to cost and performance requirements, it is often necessary to sacrifice their ease of processing and assembly.   Thermal Properties   The main thermal performance indicators of NdFeB magnets include thermal conductivity, specific heat capacity and thermal expansion coefficient.   The performance of neodymium magnet gradually decreases with the increase of temperature, so the temperature rise of permanent magnet motor becomes a key factor affecting whether the motor can run under load for a long time. Good heat conduction and heat dissipation can avoid overheating and maintain the normal operation of the equipment. Therefore, we hope that the magnetic steel has a higher thermal conductivity and specific heat capacity, so that the heat can be quickly conducted and dissipated, and at the same time, the temperature rise will be lower under the same heat.   Electrical Properties   In the alternating electromagnetic field environment of the permanent magnet motor, the magnetic steel will produce eddy current loss and cause temperature rise. Since the eddy current loss is inversely proportional to the resistivity, increasing the resistivity of the NdFeB permanent magnet will effectively reduce the eddy current loss and temperature rise of the magnet. The ideal high-resistivity magnetic steel structure is to form an isolation layer that can prevent electron transmission by increasing the electrode potential of the rare earth-rich phase, so as to achieve the wrapping and separation of the high-resistance grain boundary relative to the main phase grains, thereby improving the resistivity of the sintered NdFeB magnet. However, neither the doping of inorganic materials nor the layering technology can solve the problem of magnetic performance deterioration. At present, there is still no effective preparation of magnets with both high resistivity and high performance.