Fracture toughness, impact strength, bending strength - mechanical properties of sintered neodymium iron boron

http://www.magnet-forever.comWhat are the mechanical properties of materials? The mechanical properties of materials generally include strength, hardness, plasticity, and toughness, which have different physical meanings. Strength refers to the maximum ability of a material to resist external destructive forces. Strength can be divided into tensile strength (tensile strength) according to the different forms of external force application. It refers to the ultimate compressive strength under tension, the ultimate bending strength under pressure, and the strength when the external force is perpendicular to the material axis and causes the material to bend after being applied. Ultimate hardness refers to the ability of the material to resist local hard objects pressing into its surface, and is an indicator for comparing the hardness of various materials. The higher the hardness, the stronger the metal's ability to resist plastic deformation. Plasticity refers to the ability of a solid substance to resist deformation under certain external forces. It is the ability of a material to permanently deform without being destroyed under external forces. Resilience represents the ability of a material to absorb energy during plastic deformation and fracture processes. The better the toughness, the less likely brittle fracture will occur. In materials science and metallurgy, toughness refers to the resistance of a material to fracture when subjected to forces that cause it to deform. It is the ratio of the energy absorbed by the material before fracture to its volume. Mechanical properties of sintered neodymium iron boron

Sintered neodymium iron boron belongs to brittle materials, and its mechanical properties are hard and brittle, with high strength and low toughness. There is almost no plastic deformation before fracture, which means it fractures during the elastic deformation stage. The following figure compares the magnetic energy product (BH) m and fracture toughness of various permanent magnet materials. We can observe that sintered neodymium iron boron has the highest magnetic energy product (BH) m, while its fracture toughness is still comparable to Sm2Tm17, SmCo5, and ferrite permanent magnets, as they are all permanent magnet materials based on intermetallic compounds and belong to brittle materials. The fracture toughness of bonded rare earth permanent magnet materials, Fe Cr Co, and magnetic steel is the best, but their magnetic energy product (BH) m is much lower than that of sintered neodymium iron boron.

Three indicators are commonly used to describe the mechanical properties of brittle materials:

Fracture toughness typically reflects the strength of a material when cracks propagate, measured in MPa · m1/2. The testing of fracture toughness of materials requires the use of tensile testing machines, stress sensors, extensometers, signal amplification dynamic strain gauges, etc. Additionally, the specimens should be made into thin sheets. Impact strength (impact fracture toughness) reflects the energy absorbed by a material during the fracture process under impact stress, measured in J/m2. The measurement value of impact strength is too sensitive to the size, shape, processing accuracy, and testing environment of the sample, and the measurement value dispersion will be relatively large. Bending strength is measured by the three-point bending method to determine the bending and fracture strength of materials. Due to the ease of sample processing and simple measurement, it is most commonly used to describe the mechanical properties of sintered neodymium iron boron magnets. Dongchedi has found the approximate fluctuation range of the mechanical performance indicators of sintered neodymium iron boron given by some scholars based on different experiments. Due to its brittle nature, the experimental data has a high degree of dispersion.

The high strength and low toughness exhibited by sintered neodymium iron boron permanent magnet materials are determined by their own crystal structure. In addition, the following two factors can affect the bending strength of sintered neodymium iron boron and are also ways to improve its strength. The Nd content has a certain influence on the strength of sintered neodymium iron boron. Experimental results show that under certain conditions, the higher the Nd content, the higher the material strength. Adding other metal elements has a certain impact on the strength of sintered neodymium iron boron. When a certain amount of Ti titanium, Nb niobium, or Cu copper is added, the impact fracture toughness of the permanent magnet is improved; When a small amount of Co cobalt is added, the bending strength of the permanent magnet is improved. The insufficient comprehensive mechanical properties of sintered neodymium iron boron are one of the important reasons limiting 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, it will enable sintered neodymium iron boron to play a greater role in military, aerospace and other fields, entering a new period of development.