Method for preparing Nd—Fe—B-diffused permanent magnets based on pressure gradients
The present invention discloses a method for preparing Nd—Fe—B-diffused permanent magnets based on pressure gradients, involving the steps preparing a Nd—Fe—B permanent magnet precursor through a mechanical grinding process, a press molding process, and a sintering process; cutting the Nd—Fe—B permanent magnet precursor into a Nd—Fe—B permanent magnet sample with a lateral size of 80-150 μm and a thickness of 5-20 μm; and forming a film of rare earth elements or other metal elements on one side of the Nd—Fe—B permanent magnet sample by magnetron sputtering as a diffusion source, so as to obtain a lateral heterojunction structure. For this method, it is possible to enable the rare earth elements to efficiently and uniformly penetrate the Nd 2 Fe 14 B grains and the grain boundaries, so as to noticeably enhance coercivity and thermal stability of materials without damaging crystalline orientation, reducing magnetic energy product loss and improving overall performance of permanent magnets.
1 . A method for preparing Nd—Fe—B-diffused permanent magnets based on pressure gradients, comprising the steps of
(1) preparing a Nd—Fe—B permanent magnet precursor through a mechanical grinding process, a press molding process, and a sintering process;
(2) cutting the Nd—Fe—B permanent magnet precursor into a Nd—Fe—B permanent magnet sample with a lateral size of 80-150 μm and a thickness of 5-20 μm;
(3) forming a film of rare earth elements or other metal elements on one side of the Nd—Fe—B permanent magnet sample by magnetron sputtering as a diffusion source, so as to obtain a lateral heterojunction structure;
(4) putting the lateral heterojunction structure into a diamond anvil cell (DAC), and setting an asymmetrically filled medium zone inside a pad of the diamond anvil cell, which has one end as the diffusion source filled with NaCl, and another end filled with c-BN or KBr, so as to form a lateral pressure difference; and
(5) performing local laser heating or overall electric heating while maintaining a pressure gradient, so that the rare earth elements or the metal elements in the diffusion source to diffuse into a Nd—Fe—B matrix, so as obtain a high-performance Nd—Fe—B permanent magnet;
wherein within the pressure gradient formed in the diamond anvil cell through a Type-IV metal pad structure, a low-pressure conduction zone corresponds to the zone filled with NaCl, a high-pressure retention zone corresponds to the zone filled with c-BN or KBr, and the lateral pressure difference is 2-15 GPa.
2 . The method for preparing Nd—Fe—B-diffused permanent magnets based on pressure gradients according to claim 1 , wherein the Nd—Fe—B permanent magnet precursor contains an Nd 2 Fe 14 B main phase and a Nd-rich phase.
3 . The method for preparing Nd—Fe—B-diffused permanent magnets based on pressure gradients according to claim 1 , wherein the rare earth elements include one or both of Dy and Tb, and the metal elements include one or more of Al, Ti, Co, Cr, Ni, Fe, Cu, Nd, and In.
4 . The method for preparing Nd—Fe—B-diffused permanent magnets based on pressure gradients according to claim 1 , wherein the diffusion source formed by the magnetron sputtering is a mono-elemental film with a thickness of 50-200 nm, a argon pressure for the magnetron sputtering is 2-5 mTorr, a power of the magnetron sputtering is 50-150 W, a rate of the magnetron sputtering is 0.03-0.15 nm/s, and a temperature of a substrate for the magnetron sputtering does not exceed 60° C.
5 . The method for preparing Nd—Fe—B-diffused permanent magnets based on pressure gradients according to claim 1 , wherein in the process of performing the magnetron sputtering the power of the magnetron sputtering is initially set as a lower value and adjusted in real time by monitoring temperatures.
6 . The method for preparing Nd—Fe—B-diffused permanent magnets based on pressure gradients according to claim 1 , wherein the step of performing local laser heating is executed by way of focusing a 1064 nm or 532 nm wavelength picosecond laser beam on the diffusion source for local irradiation at 500-900° C. for 10-120 minutes.
7 . The method for preparing Nd—Fe—B-diffused permanent magnets based on pressure gradients according to claim 1 , wherein the step of performing overall electric heating is executed by way of energizing an external electrode of the diamond anvil cell to raise temperatures and monitoring the temperatures in real time to maintain diffusion in constant temperature.
8 . The method for preparing Nd—Fe—B-diffused permanent magnets based on pressure gradients according to claim 1 , wherein the lateral heterojunction formed by the diffusion source causes the elements to directionally diffuse from a diffusion end toward a center of the Nd—Fe—B permanent magnet sample under the action of the pressure gradient, so as to form a diffusion path perpendicular to a main surface of the Nd—Fe—B permanent magnet sample.
9 . The method for preparing Nd—Fe—B-diffused permanent magnets based on pressure gradients according to claim 1 , wherein the rare earth elements are controlled to be uniformly distributed at Nd 2 Fe 14 B grain boundaries with the aid of the pressure gradient, so as to enhance coercivity and thermal stability while maintaining magnetic anisotropy and reduce magnetic energy product loss.