Pr-Ga Alloy Diffusion for High Coercivity Sintered Magnets
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Solution Overview
Problem
Sintered R-T-B based magnets face a challenge in achieving high coercivity (HcJ) while maintaining high remanence (Br), especially in applications like electric vehicle motors, where Dy content is scarce and fluctuating, and existing solutions compromise on Br to reduce Dy usage.
Innovation Solution
A method involving a sintered R-T-B based magnet work with specific composition and heat treatment processes, using a Pr—Ga alloy to diffuse Pr and Ga into the grain boundaries, promoting high Br and HcJ without excessive Dy content, by performing first and second heat treatments within specific temperature ranges in a vacuum or inert gas ambient.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If RL in the R2T14B compound is partially replaced with RH (e.g., Dy or Tb) to improve HcJ, then coercivity is improved, but remanence Br decreases
Solution Approach 1:
The invention applies local quality by introducing a dual-phase grain boundary structure consisting of an R2T17 phase and an R6T13M phase with different compositions and functions. The R2T17 phase provides a matrix structure while the R6T13M phase (enriched in transition metal M) specifically enhances coercivity at grain boundaries. This localized compositional differentiation allows improved HcJ without requiring uniform substitution of light rare-earth elements throughout the entire magnet structure, thereby preserving remanence Br.
Solution Approach 2:
The invention employs composite materials by creating a grain boundary phase that is a composite of R2T17 and R6T13M phases. The R6T13M phase acts as a dispersed phase within the R2T17 matrix phase at grain boundaries. This composite structure combines the benefits of both phases: the R2T17 phase provides structural continuity while the R6T13M phase, with its higher transition metal content, provides enhanced magnetic anisotropy and coercivity. This composite approach achieves high HcJ without the need for extensive heavy rare-earth substitution that would compromise Br.
2Reliability
If RH content is increased to achieve higher HcJ, then coercivity is improved, but resource stability and supply reliability deteriorate
Solution Approach 1:
The invention applies the principle of using cheaper, more abundant elements to replace expensive, scarce elements. Specifically, the invention uses transition metal elements M (such as Co, Ni, Cu, Zn, Al, Si, or B) to form the R6T13M phase at grain boundaries, thereby reducing the dependency on scarce heavy rare-earth elements RH. The transition metals are more abundant and have stable supply chains, allowing the magnet to achieve high coercivity without being constrained by the supply instability and price fluctuations of Dy and Tb.
Solution Approach 2:
The invention applies parameter changes by modifying the compositional parameters of the grain boundary phase. Instead of relying solely on high RH content, the invention changes the phase composition to include R6T13M with elevated transition metal M content (where M contains 30-70 mass% of the phase). This compositional parameter change allows the system to achieve the desired coercivity through a different mechanism (transition metal-rich phase formation) rather than through heavy rare-earth substitution, thereby decoupling HcJ performance from RH supply stability.
3Reliability
If B amount is reduced to form R2T17 phase at grain boundaries, then HcJ is improved, but manufacturing precision and composition control become more difficult
Solution Approach 1:
The invention applies parameter changes by establishing specific compositional ranges and ratios that facilitate the spontaneous formation of the desired dual-phase grain boundary structure. The patent specifies that B content should be 0.80-0.99 mass% and that the magnet should satisfy the inequality [T]/55.85 > 14[B]/10.8. Additionally, the R6T13M phase is designed to contain 30-70 mass% transition metal M. These parameter specifications provide clear manufacturing targets and acceptance criteria, making composition control more straightforward despite the reduced B content. The defined parameter ranges ensure reproducible formation of the R2T17 + R6T13M grain boundary structure.
Solution Approach 2:
The invention applies local quality by concentrating the compositional complexity specifically at the grain boundaries while keeping the main phase composition relatively simple and well-defined (R2T14B). The R2T17 and R6T13M phases form locally at grain boundaries, allowing the bulk of the magnet to maintain a straightforward composition. This localization of complexity means that manufacturing precision requirements are focused on achieving the correct overall composition ratios, which then spontaneously segregate into the desired microstructure during sintering, rather than requiring precise control of every element throughout the entire material.
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 allows for the production of sintered R-T-B based magnets with enhanced Br and HcJ, reducing the reliance on scarce Dy and stabilizing magnetic properties, making them suitable for high-temperature applications like hybrid vehicle motors.
Implementation Method 1
a step of, while allowing at least a portion of the Pr—Ga alloy to be in contact with at least a portion of a surface of the sintered R-T-B based magnet work, performing a first heat treatment at a temperature which is greater than 600° C. but equal to or less than 950° C. in a vacuum or an inert gas ambient
Implementation Method 2
performing a first heat treatment at a temperature which is greater than 600° C. but equal to or less than 950° C.
Implementation Method 3
performing a second heat treatment in a vacuum or an inert gas ambient for the sintered R-T-B based magnet work having been subjected to the first heat treatment, at a temperature which is lower than the temperature effected in the step of performing the first heat treatment but which is not less than 450° C. and not greater than 750° C.
Data Source
AI summary
A sintered R-T-B based magnet work contains R: 27.5 to 35.0 mass % (R is at least one rare-earth element which always includes Nd), B: 0.80 to 0.99 mass %, Ga: 0 to 0.8 mass %, M: 0 to 2 mass % (M is at least one of Cu, Al, Nb and Zr), and a balance T (T is at least one transition metal element which always includes Fe, with 10% or less of Fe replaceable by Co). [T]/55.85>14[B]/10.8 is satisfied where [T] is the T content (mass %) and [B] is the B content (mass %). At least a portion of a Pr—Ga alloy is in contact with a portion of the sintered magnet work surface, and a first heat treatment is performed at a temperature between 600° C. and 950° C. A second heat treatment is performed at a temperature lower than the temperature of the first heat treatment and between 450° C. and 750° C.