Research On The Die-upset Mircostructure Of The Nanocryatalline Two-phase Nd-Fe-B Alloy

In this paper, the high energy ball milling nanocomposite （Nd, Pr）₂Fe₁₄B/α-（Fe, Co） isprepared by hot pressed/hot deformation process. By the XRD, VSM and SEM, we analysis themilling time effect on the hot pressed magnets, as well as the FeCo content effect on the die-upsetmagnet.The main technical parameters weight ratio of ball to powder is20:5. The hot pressed magnetis prepared by ball milling powers of （Nd, Pr）₂Fe₁₄B/α-（Fe, Co） nanocomposite alloys, hot pressedin temperature973K for2minutes.The results show that: The results show that: With the milling time extended from30minutes to190minutes, the soft magnetic phase α-（Fe, Co） of hot pressed magnets of double alloys （Nd, Pr）of2Fe₁₄B/α-（Fe, Co） grain size is gradually refined from47nm down to26nm,and the hardmagnetic phase （Nd, Pr）₂Fe₁₄B grain size is not changed obviously, with fluctuating between11¹8nm. With milling time of dual alloy magnetic powders extended and grain refinement, thecoercivity Hcjof hot pressed magnets is increased from655kA/m of30minutes ball milling time to796kA/m of60minutes ball milling time firstly.The coercivity reduces to656kA/m when the ballmilling time is90minutes, and finally to829kA/m when the ball milling time is190minutes.The main technical parameters weight ratio of ball to powder is20:6. The （Nd, Pr）₂Fe₁₄B/α-（Fe,Co） magnet is prapared by die-upset using the ball milling powders. The die-upset temperature is1123K, the pressure is about60MPa and time is8minutes, deformation ratio is70%.The results show that: high energy ball milling of die-upset （Nd, Pr）₂Fe₁₄B/α-（Fe, Co）composition magnets have （Nd, Pr）₂Fe₁₄B phase and α-（Fe, Co） phase. With FeCo contentsincreased from5wt.%to12wt.%, the ratio of I（410）/I（110）is reduced, which indicates that the texturedegree of hot deformation magnets is impromented. The aspect ratio of α-（Fe, Co） phase of thepressed magnets are prepared by double alloys powers is1.5-10.The aspect ratio of α-（Fe, Co）phase of hot deformation magnets is15-40, which is bigger than the pressed magnets. The resultsindicat that the α-（Fe, Co） phase forms the flake structure,which is perpendicular to the directionof the pressure of the hot deformation. The magnetic measurements indicate that the flakestructure of α-（Fe, Co） phase and hard magnetic phase （Nd, Pr）₂Fe₁₄B have a strong exchangecoupling,which made the coercivity have430kA/m.when the mass fraction FeCo is5wt%of the hot deformation magnets.If we put a big stress, increase the temperature and extend the pressingtime appropriately in the hot pressed/hot deformation,we can increase the density of magnets andimprove the residual magnetization of the magnets effectively.