Nd5Fe17 Rare-Earth Magnet Grain Boundary Optimization
Solution Overview
Problem
The development of rare-earth permanent magnets with high coercivity using the Sm5Fe17 intermetallic compound as a main phase is hindered by the lack of control over grain boundary phases and insufficient magnetic separation between main phase grains, leading to decreased coercivity due to the presence of low coercivity components.
Innovation Solution
A rare-earth permanent magnet with an Nd5Fe17 type crystal structure as the main phase, incorporating a grain boundary phase with a higher concentration of R and C compared to the main phase, where R is predominantly Sm or other rare-earth elements and T is primarily Fe or Co, with specific compositional ratios to enhance coercivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the Sm5Fe17 intermetallic compound is used as the main phase to achieve high coercivity, then the material exhibits extremely high coercivity of 36.8 kOe at room temperature, but the coercivity of the entire magnet is decreased due to the presence of low coercivity sub-phases such as SmFe2 and SmFe3 phases
Solution Approach 1:
The invention extracts and removes the harmful low coercivity sub-phases (SmFe2, SmFe3) from the magnet structure by optimizing the composition to contain less than 5 at% of these phases, thereby isolating the harmful components and preventing them from degrading the overall coercivity of the main phase
Solution Approach 2:
The invention applies local quality by creating a specific compositional gradient where the main phase maintains high Sm5Fe17 concentration for maximum coercivity, while the grain boundary regions contain controlled amounts of low coercivity phases that are minimized to less than 5 at%, thus optimizing different regions for their specific functions
2Ease of manufacture
If conventional sintering methods are used to manufacture the permanent magnet, then the production process is simple and easy to manufacture, but the grain boundary phases are not controlled sufficiently and magnetic separation between main phase grains is not enough
Solution Approach 1:
The invention changes the compositional parameters by precisely controlling the Sm:Fe ratio and limiting carbon content to less than 2 at%, which fundamentally alters the phase formation behavior during sintering, enabling better grain boundary control using conventional manufacturing methods
Solution Approach 2:
The invention performs preliminary action by pre-optimizing the powder composition with specific Sm5Fe17 intermetallic compound formulation before the sintering process, so that the desired phase distribution and grain boundary characteristics are achieved during standard manufacturing without requiring advanced process control
Data Source
AI summary
To provide a rare earth permanent magnet having as a main phase a compound with a Nd5Fe17 crystalline structure having strong coercive force. A rare earth permanent magnet having as a main phase a compound with a Nd5Fe17 crystalline structure, wherein when the composition ratio of the rare earth permanent magnet is expressed as RaT(100-a-b)Cb, where R is one or more rare earth elements requiring Sm, and T is one or more transition metal elements requiring Fe or Fe and Co, a and b satisfy 18<a<40 and 0.5≤b, and a phase where R and C are denser than the main phase is provided in the grain boundary phase of the rare earth permanent magnet.