R-T-B Sintered Magnet Boride Phase for Abnormal Grain Growth Control
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Solution Overview
Problem
R-T-B-based sintered magnets face challenges in suppressing abnormal grain growth, which decreases coercivity and squareness, especially when impurities like O, C, and N are reduced, making it difficult to utilize the pinning effect of rare earth-impurity compounds effectively.
Innovation Solution
Forming a boride phase on preferential growth planes of crystal grains, specifically using elements like Ti, Zr, Hf, Nb, or Cr to create a boride phase that inhibits abnormal grain growth epitaxially, thereby maintaining high coercivity and squareness without relying on impurity compounds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If impurity content (O, C, N) is reduced to maintain high coercivity, then the pinning effect of rare earth-impurity compounds is insufficient, but abnormal grain growth suppression is compromised
Solution Approach 1:
The patent introduces a boride-forming element (Ti, Zr, Hf, Nb, or Cr) as an intermediary substance that forms a boride phase at grain boundaries. This boride phase acts as a mediator to suppress abnormal grain growth, replacing the pinning effect previously provided by rare earth-impurity compounds. The boride-forming element serves as a bridge between boron addition and grain boundary stabilization, enabling effective grain growth control even with low impurity content.
Solution Approach 2:
The patent changes the chemical composition parameters by specifying precise ranges for boride-forming elements (0.01-0.5 mass%) and boron (0.9-1.2 mass%). By adjusting these compositional parameters, the system transitions from relying on impurity-based pinning to utilizing controlled boride phase formation for grain boundary stabilization, maintaining coercivity while preventing abnormal grain growth.
2Reliability
If boride phase is formed at grain boundary triple points, then some abnormal grain growth suppression is achieved, but the suppression effect is insufficient compared to forming on preferential growth planes
Solution Approach 1:
The patent applies local quality by directing the boride phase formation to specific locations with different effectiveness. Instead of uniform distribution or only at triple points, the boride phase is preferentially formed on grain boundary planes that coincide with preferential growth planes of the main phase crystal grains. This localized placement maximizes the suppression effect on abnormal grain growth while minimizing negative impacts on coercivity.
Solution Approach 2:
The patent employs preliminary action by adding the boride-forming element before sintering, allowing it to pre-position at grain boundaries during the sintering process. This preliminary placement ensures that when sintering occurs, the boride phase is already formed at critical grain boundary locations, preventing abnormal grain growth from initiating in the first place rather than attempting to stop it after growth begins.
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 boride phase effectively suppresses abnormal grain growth, maintaining high coercivity and squareness by aligning with the crystal planes of the main phase, even with reduced impurity content, and improving the magnetic properties of the sintered magnet.
Implementation Method 1
a boride phase which includes a compound phase based on the boride of the boride forming element M, and is generated on a preferential growth plane of the crystal grain of the main phase
Implementation Method 2
impurity elements O, C and N are liable to form a stable rare earth-impurity compound, that is, an oxide, carbide, or nitride containing a rare earth in a grain boundary phase
Data Source
AI summary
The present invention relates to an R-T-B-based sintered magnet including: a rare earth element R; a metal element T which is Fe, or includes Fe and Co with which a part of Fe is substituted; boron; and a boride forming element M which is a metal element other than rare earth elements and the metal element T and forms a boride, in which the R-T-B-based sintered magnet includes: a main phase which includes a crystal grain of an R-T-B-based alloy; and a boride phase which includes a compound phase based on the boride of the boride forming element M, and is generated on a preferential growth plane of the crystal grain of the main phase.