Nanostructured Mn-Al Permanent Magnets And Method of Producing Same

Patent metadata

Field	Value
Publication number	US-2016307677-A1
Application number	US-201214128163-A
Country	US
Kind code	A1
Filing date	Mar 20, 2012
Priority date	Jul 2, 2010
Publication date	Oct 20, 2016
Grant date	—

Abstract

A bulky consolidated nanostructured manganese aluminum alloy includes at least about 80% of a magnetic τ phase and having a macroscopic composition of Mn X Al Y Do Z , where Do is a dopant, X ranges from 52-58 atomic percent, Y ranges from 42-48 atomic percent, and Z ranges from 0 to 3 atomic percent. A method for producing a bulky nanocrystalline solid of formula MnxAlyDoz is provided. The method includes melting a mixture of metals to form a substantially homogenous solution, casting the solution to form ingots, measuring compositions of the ingots; crushing the ingots to form crushed powders, and milling the crushed powders to form nanocrystalline powders. The method further includes verifying the presence of τ phase and determining the amount of the τ phase, and simultaneously consolidating the nanocrystalline powders into a bulky nanocrystalline solid and undergoing phase transformation from ε phase to at least 80% τ phase.

First claim

1 . A bulky consolidated nanostructured manganese aluminum alloy comprising at least about 80% of a magnetic τ phase and having a macroscopic composition of Mn X Al Y Do Z , wherein
Mn is manganese,
Al is aluminum,
Do is a dopant,
X ranges from 52-58 atomic percent,
Y ranges from 42-48 atomic percent, and
Z ranges from 0 to 3 atomic percent.

2 . The bulky consolidated nanostructured manganese aluminum alloy of claim 1 , wherein the manganese aluminum alloy further comprising carbon, and having a macroscopic composition of 51 atomic percent manganese, 46 atomic percent aluminum and 3 atomic percent carbon.

3 . The bulky consolidated nanostructured manganese aluminum alloy of claim 2 , wherein the permanent magnetic properties comprise coercive forces of about 5.2 kOe.

4 . The bulky consolidated nanostructured manganese aluminum alloy of claim 1 , wherein the manganese aluminum alloy has a macroscopic composition of 54 atomic percent manganese, 46 atomic percent aluminum.

5 . The bulky consolidated nanostructured manganese aluminum alloy of claim 4 , wherein the permanent magnetic properties comprise coercive forces of about 4.8 kOe.

6 . A method for producing a bulky nanocrystalline solid comprising
melting a mixture of metals comprising between 52-58 atomic percent manganese and between 42-48 atomic percent aluminum to form a substantially homogenous solution; casting the solution to form ingots; measuring compositions of the ingots; crushing the ingots to form crushed powders; milling the crushed powders to form nanocrystalline powders; verifying the presence of τ phase and determining the amount of the τ phase; and simultaneously consolidating the nanocrystalline powders into a bulky nanocrystalline solid and undergoing phase transformation from ε phase to at least 80% τ phase.

7 . The method of claim 6 , further comprising characterizing microstructure of the bulky nanocrystalline solid and measuring magnetic properties of the bulky nanocrystalline solid.

8 . The method of claim 6 , further comprising annealing the nanocrystalline powders to determine conditions for consolidating the nanocrystalline powders.

9 . The method of claim 8 , further comprising annealing at temperatures between 200° C. and 600° C. to maximize the amount of the magnetic metastable τ phase transformed from a milled nanocrystalline unstable high-temperature ε phase, thereby minimizing presence of non-magnetic equilibrium β and γ 2 phases.

10 . The method of claim 8 , wherein the annealing time is shortened for higher annealing temperature to avoid decomposition of the τ-phase into γ 2 and β phases.

11 . The method of claim 6 , the step of consolidating the milled powders comprising backpressure assisted equal channel angular extrusion (ECAE).

12 . The method of claim 11 , further comprising increasing backpressure to consolidate the nanocrystalline powders.

13 . The method of claim 11 , further comprising controlling a temperature of the nanocrystalline powders within 200° C. to 600° C. during the ECAE to maximize presence of the τ phase.

14 . The method of claim 11 , further comprising decreasing rate of extrusion with increasing temperature to shorten annealing time at higher temperature to avoid decomposition of the τ-phase into γ 2 and β phases.

15 . The method of claim 11 , wherein the bulky nanocrystalline solid is in a form of rod shapes.

16 . The method of claim 15 , wherein the bulky nanocrystalline solid has a cross-section in one of square, rectangular, and circular shape.

17 . The method of claim 6 , further comprising repeating the step of consolidating the nanocrystalline powders until the bulky nanocrystalline solid having minimum defects.

18 . The method of claim 6 , wherein the bulky nanocrystalline solid is machinable.

19 . The method of claim 6 , wherein the mixture of metals further comprises a dopant comprising at least one of carbon and boron.

20 . The method of claim 6 , wherein the mixture of metals comprises 54 atomic percent manganese, and 46 atomic percent aluminum.

21 . The method of claim 6 , wherein the bulky nanocrystalline solid has a macroscopic composition of 54 atomic percent manganese and 46 atomic percent aluminum and coercive forces of about 5.2 kOe.

22 . The method of claim 6 , wherein the bulky nanocrystalline solid has a macroscopic composition of 54 atomic percent manganese and 46 atomic percent aluminum and coercive forces of about 4.8 kOe.

23 . A method for producing a bulky nanocrystalline solid comprising:
melting a mixture of metals comprising 51 atomic percent manganese, 46 atomic percent aluminum and 3 atomic percent carbon to form a substantially homogenous solution; casting the solution to form ingots; measuring compositions of the ingots; crushing the ingots to form crushed powders; milling the crushed powders to form nanocrystalline powders; verifying the presence of τ phase and determining the amount of the τ phase; and simultaneously consolidating the nanocrystalline powders into a bulky nanocrystalline solid and undergoing phase transformation from ε phase to at least 80% τ phase.

24 . The method of claim 21 , wherein the bulky nanocrystalline solid has a macroscopic composition of 51 atomic percent manganese, 46 atomic percent aluminum and 3 atomic percent carbon and coercive forces of about 5.2 kOe.

25 . The method of claim 21 , wherein the bulky nanocrystalline solid has a macroscopic composition of 54 atomic percent manganese and 46 atomic percent aluminum and coercive forces of about 4.8 kOe.

26 . The method of claim 21 , the step of consolidating the nanocrystalline powders comprising backpressure assisted equal channel angular extrusion (ECAE) and controlling a temperature of the nanocrystalline powders within 200° C. to 600° C. during the ECAE to maximum presence of the τ phase.

27 . A permanent magnet comprising bulky consolidated nano structured manganese aluminum alloy comprising at least about 80% of a magnetic phase and having a macroscopic composition of MnXAlYDoZ, wherein
Mn is manganese, Al is aluminum, Do is a dopant, X ranges from 5251-58 atomic %, percent, Y ranges from 42-48 atomic %, percent, and Z ranges from 0 to 3 atomic percent %.

28 . The magnet of claim 27 further comprising 3 atomic percent carbon.

Assignees

• Baker Ian
• Zeng Qi
• Dartmouth College

Inventors

• Baker Ian
• Zeng Qi

Classifications

• B22F1/00

  Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties · CPC title

• B22F2304/05

  Submicron size particles · CPC title

• B22F9/04

  starting from solid material, e.g. by crushing, grinding or milling ({C22C1/1084 takes precedence}; crushing, grinding or milling, in general, see the relevant subclasses, e.g. B02C) · CPC title

• B22F1/0003

  Operations & Transport · mapped topic

• B22F2003/248

  Thermal after-treatment · CPC title