Grain boundary engineering of sintered magnetic alloys and the compositions derived therefrom
The present disclosure is directed at methods of preparing rare earth-based permanent magnets having improved coercivity and remanence, the method comprising one or more steps comprising: (a) homogenizing a first population of particles of a first GBM alloy with a second population of particles of a second core alloy to form a composite alloy preform, the first GBM alloy being substantially represented by the formula: AC b R x Co y Cu d M z , the second core alloy being substantially represented by the formula G 2 Fe 14 B, where AC, R, M, G, b, x, y, and z are defined; (b) heating the composite alloy preform particles to form a population of mixed alloy particles; (c) compressing the mixed alloy particles, under a magnetic field of a suitable strength to align the magnetic particles with a common direction of magnetization and inert atmosphere, to form a green body; (d) sintering the green body; and (e) annealing the sintered body. Particular embodiments include magnets comprising neodymium-iron-boron core alloys, including Nd 2 Fe 14 B.
1. A composition comprising a GBM alloy represented by the formula (Nd 0.01-0.18 Pr 0.01-0.18 Dy 0.3-0.5 Tb 0.3-0.5 )aa (Co 0.85-0.95 Cu 0.04-0.15 Fe 0.01-0.08 )bb (Zr 0.00-1.00 )cc; wherein:
(i) aa is a value in a range of from 42 atom % to 75 atom %;
(ii) bb is a value in a range of from 6 atom % to 60 atom %; and
(iii) cc is a value in a range of from 0.01 atom % to 18 atom %;
wherein the combined amount of Nd+Pr is greater than 12 atom %;
wherein, within aa, the combined amounts of Nd+Pr+Dy+Tb is from about 95 atom % to about 100 atom %;
wherein, within bb, the combined amounts of Co+Cu+Fe is from about 95 atom % to about 100 atom %; and
wherein aa+bb+cc is from about 0.995 to about 1.
2. The composition of claim 1 , wherein:
the atomic ratio of Nd to Pr is 100:0, 25:75, 50:50, 75:25, or 0:100.
3. The composition of claim 1 , wherein the alloy is described by a stoichiometric formula of (Nd 0.16 Pr 0.05 Dy 0.392 Tb 0.40 ) aa (Co 0.86 Cu 0.12 Fe 0.02 ) bb (Zr 1.00 ) cc , the individual variances of any of the parenthetical values independently being ±0.01, ±0.02, ±0.04, 0.06±0.0.8, or ±0.1.
4. The composition of claim 1 , wherein:
(i) a mean particle of the GBM alloy is in a range of from about 1 micron to about 4 microns; and/or
(ii) the composition is in a form containing columnar and globulite crystals; and/or
(iii) the composition is in an amorphous form.