R-T-B Sintered Magnet Two-Stage Sintering for Stable Coercivity
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The development of sintered R-T-B based magnets faces challenges in maintaining high coercivity (HcJ) and squareness ratio (Hk/HcJ) due to dispersion in composition and production conditions, particularly when the boron content is low, leading to decreased magnetic characteristics.
Innovation Solution
A method involving a two-stage sintering process with specific temperature and time controls, including a first-stage heating to a high temperature, cooling, and a second-stage reheating, to achieve a dense and uniform crystal texture, thereby stabilizing HcJ and Hk/HcJ.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a single-stage sintering process is used, then the sintering time is short, but the coercivity HcJ and squareness ratio Hk/HcJ are unexpectedly decreased due to dispersion in composition and production conditions
Solution Approach 1:
The sintering process is divided into two distinct stages: a first-stage sintering at a higher temperature (1000-1100°C) for a shorter time (0.5-2 hours) to form a dense structure, followed by a second-stage sintering at a lower temperature (900-1000°C) for a longer time (2-10 hours) to refine the grain structure and stabilize magnetic properties. This segmentation allows each stage to serve a specific function, resolving the contradiction between short sintering time and high reliability of magnetic properties.
Solution Approach 2:
The invention changes the temperature and time parameters between the two sintering stages. The first stage uses higher temperature (1000-1100°C) and shorter time (0.5-2 hours), while the second stage uses lower temperature (900-1000°C) and longer time (2-10 hours). This parameter variation optimizes the sintering process to achieve both high productivity and reliable magnetic properties, particularly coercivity HcJ and squareness ratio Hk/HcJ.
2Quantity of substance
If the boron content is reduced to improve magnetic performance, then the remanence Br increases, but the coercivity HcJ and squareness ratio Hk/HcJ become highly sensitive to composition dispersion
Solution Approach 1:
The invention maintains boron content within a specific range (0.8-1.2 mass%) and uses two-stage sintering with optimized temperature and time parameters to compensate for the reduced boron content. This approach allows achieving high remanence Br while maintaining stable coercivity HcJ and squareness ratio Hk/HcJ through precise process control rather than relying solely on high boron content.
Solution Approach 2:
The two-stage sintering process provides process feedback control: the first stage establishes a dense structure that reduces sensitivity to composition variations, and the second stage refines the grain structure to stabilize magnetic properties. This feedback mechanism ensures that even with low boron content (0.8-1.2 mass%), the coercivity HcJ and squareness ratio Hk/HcJ remain high and stable.
3Manufacturing precision
If the sintering temperature is increased to improve density and magnetic properties, then the remanence Br increases, but the grain growth becomes abnormal and coercivity HcJ decreases
Solution Approach 1:
The sintering process is segmented into two stages with different temperature profiles. The first stage uses higher temperature (1000-1100°C) for a short time (0.5-2 hours) to achieve rapid densification without excessive grain growth. The second stage uses lower temperature (900-1000°C) for a longer time (2-10 hours) to refine grain structure uniformly. This segmentation resolves the contradiction between achieving high density and maintaining uniform grain structure.
Solution Approach 2:
The two-stage sintering process applies periodic thermal action: a high-temperature pulse followed by a lower-temperature prolonged treatment. This periodic thermal profile allows the material to first densify rapidly, then gradually refine its grain structure, achieving both high density and uniform grain morphology without abnormal grain growth.
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 ensures high coercivity and squareness ratio without extending sintering time, improving magnetic characteristics and productivity while avoiding abnormal grain growth.
Implementation Method 1
a sintering step of sintering a compact of an R-T-B based alloy powder. The sintering step includes a first-stage step of heating the compact to a first sintering temperature T1 to form a first-stage sintered body
Implementation Method 2
a cooling step of decreasing the temperature of the first-stage sintered body to a cooling temperature T0
Data Source
AI summary
A method for producing an R-T-B-based sintered magnet comprises a sintering step for sintering a shaped product of R-T-B-based alloy powder. This sintering step includes: a first step for heating the shaped product at a first sintering temperature T1 to prepare a first sintered body; a cooling step for lowering the temperature of the first sintered body to a cooling temperature T0; and a second step for heating the first sintered body at a second sintering temperature T2 to prepare a second sintered body. The first sintering temperature T1 and the second sintering temperature T2 are higher than 900° C., and the cooling temperature T0 is 900° C. or lower. A first sintering time t1 for which the first sintering temperature T1 is maintained in the first step is shorter than a second sintering time t2 for which the second sintering temperature T2 is maintained in the second step.