Porous Iron-Nitride Magnet Processing for Bulk Fe16N2 Formation
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Solution Overview
Problem
Existing methods for producing bulk iron-nitride materials with high magnetic properties face challenges in achieving a polycrystalline microstructure and efficient thermomechanical processing, limiting the production of rare-earth-free permanent magnets with high energy products.
Innovation Solution
A method involving melting an iron source, fast belt casting, annealing at austenite transformation temperatures, reducing in hydrogen, and nitriding to produce bulk iron-nitride materials with a polycrystalline microstructure, including a Fe16N2 phase, controlled grain sizes, and non-magnetic elements at grain boundaries, enhancing magnetic properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If high temperature nitriding (above 590°C) is used to form γ-FeN and subsequent quenching to form α′-Fe8N, then the Fe16N2 phase can be obtained through annealing, but the Fe16N2 phase ratio remains less than 50% and the process is complex
Solution Approach 1:
The invention changes the nitriding temperature parameter from conventional high temperature (above 590°C) to low temperature (below 200°C), which directly forms the Fe16N2 phase without requiring subsequent annealing steps. This parameter change simplifies the process while achieving over 50% Fe16N2 phase ratio.
Solution Approach 2:
The invention uses nanoparticle precursors that are pre-engineered with specific properties (20 nm size, high surface area) before nitriding. This preliminary preparation enables direct formation of Fe16N2 at low temperature, avoiding the need for complex multi-step high temperature processing.
2Manufacturing precision
If low temperature nitriding (below 200°C) is used with 20 nm α-Fe nanoparticles, then single phase Fe16N2 can be obtained, but only nanoparticles can be used as raw material
Solution Approach 1:
The invention introduces non-magnetic elements (B, Cu, Al, Si, Ti, Zr, Nb, Ta, W, C, N, O) at grain boundaries to create local differences in magnetic properties. This allows bulk materials to exhibit enhanced magnetic performance by concentrating non-magnetic phases at specific locations (grain boundaries) rather than uniformly distributing them.
Solution Approach 2:
The invention creates composite structures with magnetic Fe16N2 grains and non-magnetic element-rich grain boundaries. This composite approach combines the high saturation magnetization of Fe16N2 with the grain boundary strengthening and magnetic isolation effects of non-magnetic elements, achieving superior overall magnetic properties.
3Ease of manufacture
If conventional thermomechanical processing (forging, rolling, extrusion) is applied to bulk metallic materials, then intermediate or final products can be obtained, but the necessary thermomechanical processing for bulk iron-nitride materials has not been established
Solution Approach 1:
The invention segments the bulk material into fine grains (average size 10 μm or less) through controlled solidification and thermomechanical processing. This segmentation creates a polycrystalline microstructure that is easier to process while maintaining reliable magnetic properties through the high density of grain boundaries.
Solution Approach 2:
The invention introduces porosity (5-50% volume fraction) as an additional microstructural feature alongside grain structure. This porosity is created through controlled gas entrapment during solidification and serves multiple functions: strengthening the material, providing sites for non-magnetic element segregation, and influencing magnetic domain structure.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method produces bulk iron-nitride materials with high saturation magnetization and coercivity, achieving energy products comparable to those of Nd2Fe14B magnets, and eliminates the need for rare earth elements, suitable for applications in motors and generators.
Implementation Method 1
melting an iron source to obtain a molten iron source
Implementation Method 2
fast belt casting the molten iron source to obtain a cast iron source
Implementation Method 3
annealing the bulk iron-containing material at an austenite transformation temperature and subsequently cooling the bulk iron-containing material
Implementation Method 4
reducing the bulk iron-containing material in hydrogen
Implementation Method 5
nitriding the bulk iron-containing material to obtain the bulk iron-nitride material
Data Source
AI summary
In general, the disclosure is directed to bulk iron-nitride materials having a polycrystalline microstructure having pores including a plurality of crystallographic grains surrounded by grain boundaries, where at least one crystallographic grain includes an iron-nitride phase including any of a body centered cubic (bcc) structure, a body centered tetragonal (bct), and a martensite structure. The disclosure further describes techniques producing a bulk iron-nitride material having a polycrystalline microstructure, including: melting an iron source to obtain a molten iron source; fast belt casting the molten iron source to obtain a cast iron source; cooling and shaping the cast iron source to obtain a bulk iron-containing material having a body-centered cubic (bcc) structure; annealing the bulk iron-containing material at an austenite transformation temperature and subsequently cooling the bulk iron-containing material; and nitriding the bulk iron-containing material to obtain the bulk iron-nitride material.