Application Of HD Powders In Sintered NdFeB

The equipment to produce NdFeB powders by Hydrogen Desorption has been designed. The main matters encountered during its trial opration have been simply explained and the methods to solve them are put forward. The primary theory of absorption and desorption was also explained. The effects of primary process parameters, such as hydrogen pressure, time and temperature on the magnetic properties of NdFeB have been researched. The structure and magnetic properties have been analyzed by means of Optical Metallographic Microscopy, Scanning Electronic Microscopy, X-ray Diffraction Analysis, Infrared Oxygen Detector and Magnetic Properties Measurement. The results are as following:The rate of Hydrogen Desorption and the quantity of hydrogen absorption have relations with the activity of the surface of alloy ingots. The fresh and more active alloy ingots are more efficiency. The precondition to normally proceed the hydrogen desorption in room temperature is the existing of enough Nd-rich phase in the ingots. The optimum condition in hydrogen desorption process is P=0.15Mpa, t=30min.The key step to prepare high performance sintered NdFeB magnets is to select reasonable hydrogen desorption balance pressure, neither extremely low nor superiorly high. The former will destroy the protection of hydrogen and result in oxidation of the magnetic powder, eventually decreasing the magnetic energy product. But the latter will decrease the alignment of sintered magnets. The optimum condition in hydrogen desorption pressure is P=800-100000Pa.Comparing the magnets prepared by traditional ball milling process, the magnets prepared by hydrogen desorption have lower residual magnetization and maximum magnetic energy product. The main reason are as following: on one hand, the Nd-rich phases in the hydrogen desorpted powders is so brittle that they are easily milled too fine and some are run off seriously, and then inducing low density. On the other hand, the alignment of the magnets prepared by hydrogen desorption are much low. So the hydrogen desorption process should be modified, and the solution methods can be the substitution of traditional ingots with strip cast, the enhancement of the alignment magnetic field and the addition of Nd-rich phase or(and) lubricantbefore the press.Another key factor prepare high performance sintered NdFeB magnets is the suitable sintering process. The magnetic performance of the magnet after two-step tempering has obvious enhancement than one-step tempering, and the tempering under 600 C can improve the coercivity of NdFeB magnet extremely. Tempering can cause the boundary of main phase more straight and regular, and the quantity of micro-particles in the grain boundary will increase and these particles nail the neighbor boundaries. The co-effect of these factors improved the cocercivity of magnets.