Soft Magnetic Powder Microstructure for Self-Heating-Limited Annealing
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Solution Overview
Problem
The existing methods for manufacturing soft magnetic powders face challenges in forming small-sized nanocrystals at high density due to self-heating issues during heat treatment, leading to deteriorated magnetic properties.
Innovation Solution
A method involving two heat treatments of alloy powder, with specific temperature controls to achieve an Avrami constant of 1.7 or more in the first treatment and lower in the second, along with careful crystallinity management, to form soft magnetic powders with crystallites of 30 nm or less and an amorphous phase, enhancing magnetic properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If heat treatment is conducted to form nanocrystals, then magnetic properties are improved, but self-heating occurs causing temperature control difficulty and crystal grain enlargement
Solution Approach 1:
The heat treatment process is divided into multiple stages with different temperature profiles. The patent applies segmented heating where the temperature is controlled in distinct phases to prevent self-heating effects while still achieving nanocrystal formation. This segmentation allows the system to avoid the harmful self-heating phenomenon that occurs in conventional single-stage heat treatment.
Solution Approach 2:
The patent employs periodic heating and cooling cycles during heat treatment. By applying periodic thermal action rather than continuous heating, the process allows heat dissipation between heating pulses, preventing cumulative self-heating effects. This periodic approach maintains temperature control while still providing sufficient thermal energy for nanocrystal formation.
2Reliability
If heat treatment temperature is increased to form nanocrystals, then crystallization is promoted, but crystal grain size increases and magnetic property deteriorates
Solution Approach 1:
The patent changes multiple parameters simultaneously including heating rate, holding time, and peak temperature to achieve the desired crystal grain size. By adjusting these parameters in combination rather than relying solely on temperature increase, the process promotes nanocrystal formation while maintaining grain size control. The specific parameter regime includes rapid heating followed by controlled holding at optimized temperatures.
Solution Approach 2:
The patent creates a composite microstructure consisting of nanocrystalline phases embedded in an amorphous matrix. This composite structure combines the benefits of crystalline order for magnetic properties with the disorder of amorphous phases that suppress grain growth. The resulting material has a dual-phase structure that achieves both high crystallinity for magnetic performance and fine grain size control.
3Temperature
If heat treatment temperature is decreased to prevent self-heating, then temperature control is improved, but nanocrystal formation is insufficient
Solution Approach 1:
The patent applies preliminary heating at moderate temperatures before the main nanocrystal formation stage. This preliminary action prepares the material by initiating partial crystallization and relieving internal stresses, which reduces the tendency for self-heating during subsequent high-temperature treatment. By performing this preparatory step, the process prevents the harmful self-heating effect while still achieving adequate nanocrystal formation.
Solution Approach 2:
The patent performs preliminary heat treatment steps that create favorable conditions for subsequent nanocrystal formation. These preliminary actions include initial heating to dissolve precipitates, create a homogeneous microstructure, and prepare the material for controlled nanocrystal precipitation. This preliminary preparation ensures that the main heat treatment can proceed at lower temperatures while still achieving sufficient nanocrystal formation.
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 method effectively produces soft magnetic powders with high density nanocrystals, reducing core loss and improving magnetic permeability and saturation magnetic flux density, resulting in superior magnetic properties for coil components.
Implementation Method 1
subjecting the alloy powder to a first heat treatment; and subjecting the alloy powder subjected to the first heat treatment to a second heat treatment
Implementation Method 2
crystalizing the rapidly-cooled body by subjecting a heat treatment thereto to form crystal grains
Implementation Method 3
a method for manufacturing a Fe-based soft magnetic alloy is known, the method comprising: rapidly cooling a molten metal of an alloy to form a rapidly-cooled body in a shape of thin strip or powder comprising an amorphous phase as a main phase; and crystalizing the rapidly-cooled body
Data Source
AI summary
A soft magnetic powder according to the present disclosure comprises a particle which comprises a plurality of nanosized crystallites and an amorphous phase existing around the crystallites, wherein the crystallites have an average grain diameter of 30 nm or less, and the amorphous phase has an average thickness of 30 nm or less; and wherein when a minor axis of a cross section of the particle is determined as r, an average Fe concentration in the amorphous phase is lower than an average Fe concentration in the crystallites in a region where a depth from a surface of the particle is 0.2 r or more and 0.4 r or less.