Sintered neodymium-iron-boron (NdFeB) permanent magnets are renowned for their superior magnetic properties. However, their mechanical and chemical properties are equally important in various applications. For example, magnets in high-speed rotating machinery must withstand significant centrifugal forces, vibrations, and extreme accelerations (3g to 5g). They may also experience stress during installation, leading to delamination, chipping, or cracking. Therefore, understanding the mechanical properties of these magnets is crucial.
Key Mechanical Properties
Mechanical properties include strength, hardness, plasticity, and toughness. Here’s a closer look at each:
Strength: The maximum resistance of a material to external forces.
Tensile Strength: Resistance to pulling forces.
Compressive Strength: Resistance to pressing forces.
Flexural Strength: Resistance to bending forces.
Hardness: The ability to resist indentation by a hard object, indicating resistance to plastic deformation.
Plasticity: The ability to undergo permanent deformation without breaking under external forces.
Toughness: The capacity to absorb energy during deformation and fracture, indicating resistance to brittle fracture.
Mechanical Performance of Sintered Neodymium-Iron-Boron
Sintered NdFeB is known for its brittleness, high hardness, and low toughness. This means it has high strength but fractures with little plastic deformation. In other words, it breaks during the elastic deformation stage.
Comparing the magnetic energy product (BH)m and fracture toughness of various permanent magnet materials shows that sintered NdFeB has the highest magnetic energy product but similar fracture toughness to Sm2Tm17, SmCo5, and ferrite magnets. Bonded rare-earth magnets, Fe-Cr-Co, and magnetic steel have better fracture toughness but lower magnetic energy products.
Key Indicators of Mechanical Properties for Brittle Materials
Fracture Toughness: Reflects strength when a crack expands, measured in MPa√m. Testing requires a tensile testing machine, stress sensors, and other equipment, with thin sheet samples.
Impact Strength: Reflects energy absorbed during fracture under impact stress, measured in J/m. This measurement is sensitive to sample size, shape, precision, and testing environment, resulting in varied values.
Flexural Strength: Measured using the three-point bending method to determine resistance to bending fracture. It’s popular for its ease of sample processing and measurement simplicity, making it commonly used to describe sintered NdFeB magnets.
Improving Flexural Strength
High Nd content and the addition of certain metallic elements can enhance the strength of sintered NdFeB:
Nd Content: Higher Nd content generally increases strength.
Metallic Additions: Adding elements like Ti (titanium), Nb (niobium), or Cu (copper) improves impact fracture toughness, while Co (cobalt) enhances flexural strength.
Conclusion
The mechanical properties of sintered neodymium-iron-boron magnets are crucial for their broader application. Improving toughness while maintaining or enhancing magnetic performance can expand their use in fields like aerospace and military. At MainRich Magnets, we optimize these properties to produce durable, high-performance magnets for various demanding applications.
