The application of sintered NdFeB permanent magnets is mainly to use its magnetic properties, but due to the different use environments and conditions, in addition to the requirements for magnetic properties, there are also requirements for mechanical properties and chemical properties. For example, some permanent magnets are used in high-speed rotating machinery to withstand a large centrifugal force, or used in a vibration environment, or subjected to extremely high acceleration (3g~5g), or when the magnet is installed, it is subject to stress. It may peel off, drop edges, drop corners or crack, etc., so it is a matter of course to have requirements on the mechanical properties of the magnet. What are the mechanical properties of materials?
The mechanical properties of materials generally include strength, hardness, plasticity and toughness, and these mechanical properties parameters have different physical meanings.
Strength refers to the maximum ability of a material to resist damage from external forces. According to the different forms of external force, the strength is divided into:
Tensile strength (tensile strength), refers to the limit of strength when the external force is pulling force.
Compressive strength refers to the strength limit when the external force is pressure.
Bending strength refers to the strength limit when the external force is perpendicular to the axis of the material and makes the material bend after the action.
Hardness refers to the ability of a material to locally resist hard objects being pressed onto its surface. It is an index for comparing the softness and 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 a certain external force. It is the ability of a material to permanently deform without being destroyed under the action of an external force.
Toughness indicates the ability of a material to absorb energy during plastic deformation and fracture. 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 it is subjected to a force that causes it to deform. It is the ratio of the energy that a material can absorb before fracture to its volume. Mechanical properties of sintered NdFeB.
Sintered NdFeB is a brittle material, and its 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.
For brittle materials, three indicators are commonly used to describe the mechanical properties of materials:
Fracture toughness usually reflects the strength when there is crack expansion in the material, and the unit is MPa m1/2. To test the fracture toughness of materials, tensile testing machines, stress sensors, extensometers, signal amplification dynamic strain gauges, etc. should be used, and the samples should be made into flakes.
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 measurement value of impact strength is too sensitive to the size, shape, processing accuracy and test environment of the sample, and the dispersion of the measurement value will be relatively large.
The flexural strength is measured by the three-point bending method to measure the flexural fracture strength of the material. 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.
Knowing Magnetic Emperor has found the general fluctuation range of sintered NdFeB mechanical performance indicators given by some scholars based on different tests. Because it is a brittle material, the test data is highly dispersed.
The characteristics of high strength and low toughness of sintered NdFeB permanent magnet materials are determined by its own crystal structure. In addition, the following two factors will affect the bending strength of sintered NdFeB permanent magnets, which 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 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 NdFeB is one of the important reasons that limit its application in wider fields. If the toughness of the product can be improved while ensuring that the magnetic properties are improved or unchanged, it will make sintered NdFeB Military, aerospace and other fields play a greater role and enter a new period of development.