R-T-Cu-Mn-B Sintered Magnet Coercivity via Cu and Mn
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Solution Overview
Problem
The challenge lies in increasing the coercivity of rare-earth-transition metal-boron (R-T-B) based sintered magnets while minimizing the use of expensive and rare rare-earth elements like Dy and Tb, and overcoming limitations in adding Cu, which affects remanence and coercivity due to surface energy and grain boundary phase issues.
Innovation Solution
An R-T-Cu-Mn-B based sintered magnet composition is developed, with specific ranges for R, Cu, and Mn, including a higher percentage of Cu and Mn to enhance coercivity, where Cu forms interfacial films and Mn stabilizes the main phase, allowing for increased Cu addition without decomposing the R2T14B compound, even with reduced crystal grain size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If Dy or Tb is added to increase coercivity, then coercivity is improved, but cost increases and main phase formation is interfered with
Solution Approach 1:
The patent replaces expensive rare-earth elements (Dy, Tb) with cheaper transition metal elements (Cu, Mn, Co) to achieve the same coercivity enhancement. Cu and Mn act as substitutes that provide similar magnetic strengthening effects without the high cost and formation interference issues associated with Dy and Tb.
Solution Approach 2:
The patent changes the compositional parameters by introducing specific ratios of Cu (0.01-0.5 at%) and Mn (0.01-0.5 at%) along with Co (0.1-5 at%) to modify the magnetic properties. This parameter adjustment allows achieving high coercivity through transition metal addition rather than relying on expensive rare-earth elements.
2Strength
If Cu is added to increase coercivity, then coercivity is improved, but remanence decreases
Solution Approach 1:
The patent combines Cu and Mn in specific ratios (Cu: 0.01-0.5 at%, Mn: 0.01-0.5 at%) to achieve synergistic effects. The combination allows Cu to enhance coercivity while Mn helps maintain remanence by stabilizing the main phase and preventing excessive Cu-induced degradation.
Solution Approach 2:
The patent creates a composite alloy system R-T-Cu-Mn-B that integrates multiple elements with complementary functions. The composite structure leverages Cu for coercivity enhancement, Mn for remanence maintenance, and Co for overall magnetic property optimization, achieving balanced performance.
3Strength
If crystal grain size is reduced to increase coercivity, then coercivity is improved, but interface between main and grain boundary phases increases
Solution Approach 1:
The patent introduces transition metal elements (Cu, Mn, Co) as intermediary substances that preferentially locate at the grain boundary interfaces. These intermediaries improve the quality and magnetic properties of the grain boundary phase, allowing fine grain structures to maintain good interfacial characteristics and achieve high coercivity without excessive interface degradation.
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
This approach significantly increases coercivity and maintains remanence, providing improved thermal resistance and magnetization stability, enabling the use of these magnets in applications like motors.
Implementation Method 1
Cu would be distributed in the form of a film over the interface between the main phase and the grain boundary phase and eliminate microscopic defect surrounding the main phase
Implementation Method 2
Mn stabilizes the main phase, allowing for increased Cu addition without decomposing the R2T14B compound
Implementation Method 3
a sintered magnet obtained from a compacted powder
Data Source
Figure 1
Figure 2
AI summary
An R-T-Cu-Mn-B based sintered magnet includes: 12.0 at% to 15.0 at% of R, which is at least one of the rare-earth elements that include Y and of which at least 50 at% is Pr and/or Nd; 5.5 at% to 6.5 at% of B; 0.08 at% to 0.35 at% of Cu; 0.04 at% to less than 0.2 at% of Mn; at most 2 at% (including 0 at%) of M, which is one, two, or more elements that are selected from the group consisting of Al, Ti, V, Cr, Ni, Zn, Ga, Zr, Nb, Mo, Ag, In, Sn, Hf, Ta, W, Au, Pb and Bi; and T as the balance, which is either Fe alone or Fe and Co and of which at most 20 at% is Co if T includes both Fe and Co.