R-T-B Rare Earth Magnet Alloy Grain Growth Control
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Solution Overview
Problem
Current R-T-B based rare earth sintered magnets face limitations in improving magnetic properties and squareness ratio due to inadequate control of abnormal grain growth, particularly because the coercive force is not sufficiently enhanced by the R-rich phase in existing alloys.
Innovation Solution
An alloy composition with a main phase (A) of R2T14B, having a specific length range and area ratio, and potentially including voids, is developed to control grain growth and enhance magnetic properties, where the main phase includes R2T14B and an R-rich phase, with specific angle orientations and void distributions to optimize magnetic performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If R oxide is added to control abnormal grain growth, then grain growth is suppressed, but coercive force is insufficient due to inadequate R-rich phase generation
Solution Approach 1:
The invention extracts R oxide from the alloy composition entirely, replacing it with R metal. This removal of the problematic R oxide component eliminates the trade-off between grain growth control and coercive force generation, as R metal provides both functions simultaneously without the harmful effects of oxide inclusions.
Solution Approach 2:
The invention changes the chemical state of rare earth element from oxidized form (R oxide) to metallic form (R metal). This parameter change in the oxidation state transforms the material's properties, enabling the R metal to generate sufficient R-rich phase for high coercive force while still controlling grain growth effectively.
2Stability of the object's composition
If pulverizing conditions are precisely controlled to manage grain diameter, then abnormal grain growth is suppressed, but manufacturing complexity increases
Solution Approach 1:
The invention performs preliminary action by adding R metal to the alloy composition before pulverization. This pre-treatment establishes the foundation for abnormal grain growth suppression at the material composition level, reducing the need for extremely precise pulverizing condition control and simplifying the overall manufacturing process.
Solution Approach 2:
The invention changes the approach from controlling physical parameters (pulverizing conditions) to controlling chemical composition (R metal content). This parameter shift from physical to chemical control simplifies the manufacturing process by leveraging material composition rather than requiring precise mechanical processing parameters.
3Strength
If main phase area ratio is increased to improve magnetic properties, then Br and Hcj improve, but abnormal grain growth occurs
Solution Approach 1:
The invention creates a composite microstructure consisting of main phase (R2Fe14B), R-rich phase, and grain boundary phase. This composite structure allows the main phase to achieve high area ratio for improved magnetic properties while the R-rich phase and grain boundary phase work together to suppress abnormal grain growth, resolving the contradiction between magnetic performance and grain growth control.
Solution Approach 2:
The invention applies local quality by distributing R metal specifically at grain boundaries and forming R-rich phase in those regions. This localized concentration of R metal provides grain growth suppression at critical interfaces while allowing the main phase interior to achieve high density and magnetic properties without being constrained by excessive grain growth control measures.
Data Source
AI summary
Provided is an alloy for R-T-B based rare earth magnet. “R” is one or more of a rare earth element, ‘T’ is one or more of a transition metal element essentially including Fe or Fe and Co, and “B” is boron. The alloy includes a single or a plural number of main phase (A), having a minimum length of 10 μm or more and a maximum length of 30 μm or more and 300 μm or less, in a cross section cut along a thickness direction of the alloy. The main phase (A) includes an R2T14B phase, and an area ratio of the main phase (A) to an entire cross section is 2% or more and 60% or less.