Method for producing sintered ndfeb magnet

Abstract

A method for producing a sintered NdFeB magnet having high coercivity and capable of being brought into applications without lowering its residual magnetic flux density or maximum energy product and without reprocessing. The method includes applying a substance containing dysprosium (Dy) and/or terbium (Tb) to the surface of the sintered NdFeB magnet forming a base body and then heating the magnet to diffuse Dy and/or Tb through the grain boundary and thereby increase the coercivity of the magnet. This method is characterized in that: (1) the substance containing Dy or Tb to be applied to the surface of the sintered NdFeB magnet is substantially a metal powder; (2) the metal powder is composed of a rare-earth element R and an iron-group transition element T, or composed of R, T and another element X, the element X capable of forming an alloy or intermetallic compound with R and/or T; and (3) the oxygen content of the sintered NdFeB magnet forming the base body is 5000 ppm or lower. The element T may contain nickel (Ni) or cobalt (Co) to produce an anticorrosion effect.

1 . A method for producing a sintered NdFeB magnet by a process including applying a substance containing dysprosium and/or terbium to a surface of the sintered NdFeB magnet forming a base body and then heating the magnet to diffuse dysprosium and/or terbium through grain boundaries thereof and thereby increase a coercivity of the magnet, wherein:
 (1) the applied substance is substantially a metal powder;   (2) the metal powder is composed of a rare-earth element R and an iron-group transition element T, or composed of the elements R, T and another element X, the element X capable of forming an alloy or intermetallic compound with the element R and/or T; and   (3) an oxygen content of the sintered NdFeB magnet forming the base body is 5000 ppm or lower.   
     
     
         2 . The method for producing a sintered NdFeB magnet according to  claim 1 , wherein the oxygen content is 4000 ppm or lower. 
     
     
         3 . The method for producing a sintered NdFeB magnet according to  claim 1 , wherein the iron group transition element T in the metal powder contains nickel and/or cobalt by a total of 10% (by weight) or more of an entirety thereof. 
     
     
         4 . The method for producing a sintered NdFeB magnet according to  claim 1 , wherein following three processes are performed in this order:
 (1) applying an adhesive layer on the surface of the sintered NdFeB magnet forming the base body;   (2) putting the sintered NdFeB magnet with the adhesive layer applied thereon, the metal powder and impact media into a container, and vibrating or stirring a content thereof to form a powdered layer made of the metal powder with a uniform thickness on the surface of the sintered NdFeB magnet forming the base body; and   (3) heating the sintered NdFeB magnet with the powdered layer formed thereon to cause grain boundary diffusion.   
     
     
         5 . The method for producing a sintered NdFeB magnet according to  claim 2 , wherein the iron group transition element T in the metal powder contains nickel and/or cobalt by a total of 10% (by weight) or more of an entirety thereof. 
     
     
         6 . The method for producing a sintered NdFeB magnet according to  claim 2 , wherein the following three processes are performed in this order:
 (1) applying an adhesive layer on the surface of the sintered NdFeB magnet forming the base body;   (2) putting the sintered NdFeB magnet with the adhesive layer applied thereon, the metal powder and impact media into a container, and vibrating or stirring a content thereof to form a powdered layer made of the metal powder with a uniform thickness on the surface of the sintered NdFeB magnet forming the base body; and   (3) heating the sintered NdFeB magnet with the powdered layer formed thereon to cause grain boundary diffusion.   
     
     
         7 . The method for producing a sintered NdFeB magnet according to  claim 3 , wherein the following three processes are performed in this order:
 (1) applying an adhesive layer on the surface of the sintered NdFeB magnet forming the base body;   (2) putting the sintered NdFeB magnet with the adhesive layer applied thereon, the metal powder and impact media into a container, and vibrating or stirring a content thereof to form a powdered layer made of the metal powder with a uniform thickness on the surface of the sintered NdFeB magnet forming the base body; and   (3) heating the sintered NdFeB magnet with the powdered layer formed thereon to cause grain boundary diffusion.   
     
     
         8 . The method for producing a sintered NdFeB magnet according to  claim 5 , wherein the following three processes are performed in this order:
 (1) applying an adhesive layer on the surface of the sintered NdFeB magnet forming the base body;   (2) putting the sintered NdFeB magnet with the adhesive layer applied thereon, the metal powder and impact media into a container, and vibrating or stirring a content thereof to form a powdered layer made of the metal powder with a uniform thickness on the surface of the sintered NdFeB magnet forming the base body; and   (3) heating the sintered NdFeB magnet with the powdered layer formed thereon to cause grain boundary diffusion.   
     
     
         9 . The method for producing a sintered NdFeB magnet according to  claim 1 , wherein a content of the element R in the metal powder is 10% or higher and 60% or lower by weight. 
     
     
         10 . The method for producing a sintered NdFeB magnet according to  claim 9 , wherein the content of the element R is 25% or higher and 45% or lower by weight. 
     
     
         11 . The method for producing a sintered NdFeB magnet according to  claim 1 , wherein the content of the element T in the metal powder is 20% or higher and 80% or lower by weight. 
     
     
         12 . The method for producing a sintered NdFeB magnet according to  claim 11 , wherein the content of the element T is 30% or higher and 75% or lower by weight. 
     
     
         13 . The method for producing a sintered NdFeB magnet according to  claim 3 , wherein the element T contains nickel and/or cobalt by a total of 20% (by weight) or more of the entirety thereof. 
     
     
         14 . The method for producing a sintered NdFeB magnet according to  claim 1 , wherein an average grain size of the metal powder is 5 μm or smaller. 
     
     
         15 . The method for producing a sintered NdFeB magnet according to  claim 14 , wherein the average grain size is 0.3 to 3 μm.