US-12624428-B2 - Iron nitride compositions

Abstract

All example composition may include a plurality of grains including an iron nitride phase. The plurality of grains may have an average wain size between about 10 nm and about 200 nm. An example technique may include treating a composition including a plurality of grains including au iron-based phase to adjust an average grain size of the plurality of grains to between about 20 nm and about 100 ma. The example technique may include nitriding the plurality of grains to form or grow an iron nitride phase.

Inventors

• Jian-Ping Wang
• Yanfeng Jiang
• Md MEHEDI
• Yiming Wu
• Bin Ma
• Jinming Liu
• Delin Zhang

Assignees

• REGENTS OF THE UNIVERSITY OF MINNESOTA

Dates

Publication Date

20260512

Application Date

20231110

Claims (5)

1. 1 . An alloy composition comprising: a plurality of grains comprising an iron nitride phase, wherein the alloy composition has a coercivity of at least about 2000 Oe, wherein the average grain size is less than about 50 nm, and wherein an average grain boundary size of the plurality of grains is between about 2 nm and about 5 nm, and comprising a nonmagnetic element or compound configured to form domain wall pinning sites at the grain boundaries, wherein the nonmagnetic element or compound is selected from Cu, Zr, Ta, Ni, Ru, SiO 2 , Al 2 O 3 , or combinations thereof.
2. 2 . The alloy composition of claim 1 , wherein the iron nitride phase comprises α″-Fe 16 N 2 .
3. 3 . The alloy composition of claim 2 , comprising greater than about 50% by volume of the α″-Fe 16 N 2 phase.
4. 4 . The alloy composition of claim 1 , wherein a majority of the plurality of grains have respective easy axes of magnetizing aligned in substantially the same direction.
5. 5 . A bulk permanent magnetic material comprising the alloy composition of claim 1 .

Description

CROSS-REFERENCE TO RELATED APPLICATION This application is a continuation of U.S. patent application Ser. No. 16/610,285, filed May 4, 2018, which claims priority to National Stage Application of International Patent App. No. PCT/US2018/031113, filed May 4, 2018, which claims the benefit of U.S. Provisional Patent Application No. 62/501,462, filed May 4, 2017, the entire disclosures of which are hereby incorporated by reference as if set forth in their entirety herein. GOVERNMENT RIGHTS This invention was made with government support under DE-AR0000199 awarded by the U.S. Department of Energy. The government has certain rights in the invention. TECHNICAL FIELD The disclosure relates to iron nitride compositions and iron nitride-based magnets, and techniques for forming iron nitride compositions and iron nitride-based magnets. BACKGROUND Permanent magnets play a role in many electromechanical systems, including, for example, alternative energy systems. For example, permanent magnets are used in sensors, actuators, electric motors or generators, which may be used in vehicles, wind turbines, and other alternative energy mechanisms. Many permanent magnets in current use include rare earth elements, such as neodymium, which result in high energy product. These rare earth elements are in relatively short supply, and may face increased prices and/or supply shortages in the future. Additionally, some permanent magnets that include rare earth elements are expensive to produce. For example, fabrication of NdFeB and ferrite magnets generally includes crushing material, compressing the material, and sintering at temperatures over 1000° C., all of which contribute to high manufacturing costs of the magnets. Additionally, the mining of rare earth can lead to severe environmental deterioration. Iron nitride magnets based on the Fe16N2/Fe8N phase are of interest as a magnetic material for applications ranging from data storage to electrical motors for vehicles, wind turbines, and other power generation equipment. The base elements (Fe, N) are inexpensive and widely available, in contrast to rare earth elements in rare earth element-based magnets, which are costly and subject to supply availability risks. The Fe16N2phase, which is the ordered version of Fe8N, has a large magnetic anisotropy constant and saturation magnetization but is difficult to manufacture. SUMMARY The disclosure describes example alloy compositions. In some examples, an example alloy composition may include a plurality of grains including an iron nitride phase. The plurality of grains has an average size between about 20 nm and about 100 nm. The disclosure describes example techniques for forming an alloy composition including a plurality of grains including an iron nitride phase. The plurality of grains has an average size between about 2 nm and about 100 nm. In some examples, an example technique may include treating an alloy composition including a plurality of grains including an iron-based phase to control an average grain size of the plurality of grains to between about 20 nm and about 100 nm. The example technique may include nitriding the plurality of grains to form or grow an iron nitride phase. The details of one or more examples are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims. BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a conceptual and schematic diagram illustrating an example alloy composition including a plurality of grains including an iron nitride phase. FIG. 2A is a conceptual and schematic diagram illustrating a crystallographic unit cell of α-Fe. FIG. 2B is a conceptual and schematic diagram illustrating a crystallographic unit cell of α″-Fe16N2. FIG. 3 is a flow diagram illustrating an example technique for forming an alloy composition including a plurality of grains including an iron nitride phase. FIG. 4 is a diagram illustrating the theoretical relationship between grain size, temperature, and nitrogen diffusion coefficient for example alloy compositions including iron nitride. FIG. 5 is a diagram illustrating the theoretical relationship between coercivity and average grain size for different volume ratios of Fe16N2. FIG. 6 is a diagram illustrating the theoretical relationship between coercivity and average grain size for a predetermined volume ratio of Fe16N2. FIG. 7 is a diagram illustrating an example observed relationship between coercivity and average grain size for a predetermined volume ratio of Fe16N2. FIG. 8 is a photograph illustrating the microstructure of an example alloy composition including an iron nitride foil, with an average grain size of 8±1.5 μm. FIG. 9 is a photograph illustrating the microstructure of an example alloy composition including an iron nitride foil, with an average grain size of 6±1.3 μm. FIG. 10 is a photograph illustrating the microstructure of an example alloy comp