METHOD FOR PRODUCING NDFEB SYSTEM SINTERED MAGNET
A method for producing a NdFeB system sintered magnet in which a coating material containing a heavy rare-earth element R H applied to a base material of a NdFeB system sintered magnet is inexpensively prevented from adhering to a tray or similar device in a grain boundary diffusion treatment. The method includes the steps of applying a coating material containing a heavy rare-earth element R H to a base material and diffusing the element through grain boundaries in the base material by a grain boundary diffusion method. The coating material is applied to a sheet. The sheet is made to come in tight contact with the base material so that the coating material applied to the sheet contacts an application target surface of the base material. With the sheet held in tight contact with the base material, the grain boundary diffusion treatment (heat treatment) is performed on the base material.
1 . A method for producing a NdFeB system sintered magnet including a grain boundary diffusion treatment process in which, after a coating material containing a heavy rare-earth element is applied to a base material of a NdFeB system sintered magnet, the base material with the coating material applied is heated so as to diffuse the heavy rare-earth element in the coating material through grain boundaries into the base material, the method comprising steps of:
applying the coating material to a sheet;
making the sheet come in tight contact with the base material in such a manner that the coating material applied to the sheet comes in contact with an application target surface of the base material; and
performing the grain boundary diffusion treatment by heating the base material together with the sheet.
2 . The method for producing a NdFeB system sintered magnet according to claim 1 , wherein a number of hollow portions are provided on an application surface of the sheet.
3 . The method for producing a NdFeB system sintered magnet according to claim 2 , wherein the amount of coating material is regulated by adjusting a number and/or depth of the hollow portions.
4 . The method for producing a NdFeB system sintered magnet according to claim 1 , wherein a graphite sheet is used as the sheet.
5 . The method for producing a NdFeB system sintered magnet according to claim 1 , wherein the sheet is held in contact with the base material during the grain boundary diffusion treatment.
6 . The method for producing a NdFeB system sintered magnet according to claim 5 , wherein pressure is applied to the sheet during the grain boundary diffusion treatment so as to increase a degree of contact between the base material and the coating material.
7 . The method for producing a NdFeB system sintered magnet according to claim 1 , wherein the application target surfaces of a plurality of the base materials are entirely covered with a single sheet.
8 . The method for producing a NdFeB system sintered magnet according to claim 1 , wherein a plurality of base materials are vertically stacked, with each of the upper and lower surfaces of each base material being covered with the sheet.
9 . The method for producing a NdFeB system sintered magnet according to claim 1 , wherein an aging treatment is performed after the grain boundary diffusion treatment.
10 . The method for producing a NdFeB system sintered magnet according to claim 1 , wherein the sheet is made of a material in which the heavy rare-earth element is less diffusive than in the base material.
11 . The method for producing a NdFeB system sintered magnet according to claim 1 , wherein the sheet is made of a material which does not undergo a chemical or physical change during the grain boundary diffusion treatment.
12 . The method for producing a NdFeB system sintered magnet according to claim 1 , wherein the sheet is a flexible sheet.