R-T-B Alloy Powder Microstructure Control for High Coercivity
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Solution Overview
Problem
Rare earth-based anisotropic bonded magnets with high coercivity are challenging to develop due to inadequate control over the microstructure of R-T-B alloy powders, particularly the grain boundary phases, which affects their magnetic properties and usability in high-temperature environments.
Innovation Solution
The development of R-T-B based alloy powders with specific microstructural characteristics, including main phase grains of R2T14B and R-rich grain boundary phases, where the grain boundary phases cover 10-40% of the main phase grains' circumference with a roundness of 0.1-0.6, achieved through the HDDR method, ensuring high coercivity and magnetic properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the atmosphere during the desorption and recombination process is controlled to adjust the reaction rate, then the magnetic properties of the alloy powders are improved, but the microstructure of the grain boundary phases cannot be well controlled
Solution Approach 1:
The invention changes the chemical composition parameters of the alloy by adding specific elements (Al, Si, Ti, V, Cr, Mn, Ni, Cu, Zn, Ga, Zr, Nb, Mo, In, Sn, Hf, Ta, or W) at controlled concentrations (0.01-5.0 at%). This compositional modification enables precise control over grain boundary phase formation and microstructure development during the HDDR process, resolving the contradiction between improving magnetic properties and controlling microstructure.
Solution Approach 2:
The added elements act as intermediaries that preferentially segregate to grain boundaries during the desorption and recombination processes. These intermediary elements modify the grain boundary phase composition and structure, thereby controlling the overall microstructure while maintaining the magnetic properties of the main phase grains.
2Temperature
If the coercivity of the alloy powders is increased for high-temperature applications, then the magnet can be used in hot environments, but the microstructure control becomes more difficult
Solution Approach 1:
The invention applies local quality by creating distinct compositional regions: the main phase grains maintain their R2Fe14B structure for high coercivity, while the grain boundary phases are enriched with specific elements (Al, Si, Ti, V, Cr, Mn, Ni, Cu, Zn, Ga, Zr, Nb, Mo, In, Sn, Hf, Ta, or W) to control microstructure. This local compositional differentiation enables the magnet to operate at high temperatures while maintaining manufacturable microstructure.
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 resulting R-T-B based alloy powders exhibit excellent magnetic properties and high coercivity, enabling their use in high-temperature applications such as the engine compartment of vehicles, enhancing energy efficiency and magnetic performance.
Implementation Method 1
the hydrogenation process, decomposition process, desorption process and recombination process are performed in order
Implementation Method 2
the hydrogenation process, decomposition process, desorption process and recombination process are performed in order
Implementation Method 3
the hydrogenation process, decomposition process, desorption process and recombination process are performed in order
Data Source
AI summary
The present invention provides R-T-B based alloy powders, wherein R represents at least one rare earth element, and T represents at least one element selected from the group consisting of ferrum and cobalt. The R-T-B based alloy powders have main phase grains, grain boundary phases and additive phases. The main phase grains are composed of R2T14B and have an average grain size of 200 nm or more and 500 nm or less. The grain boundary phases are richer in R than the main phase grains. With respect to any cross section of the R-T-B based alloy powders, the coverage of the main phase grains defined by equation 1 with the grain boundary phases with a roundness defined by equation 2 being 0.1 or more and 0.6 or less, is 10% or more and 40% or less.coverage≡∑ili∑jLjli:CircumferenceofeachgrainboundaryphaseLj:Circumferenceofeachmainphasegrain〈equation1〉Roundness=4πA/L2〈equation2〉A represents the area of the cross section of the grain boundary phase, and L represents the circumference of the cross section of the grain boundary phase.