VCM Magnet Coating Structure for Low-Pressure Hydrogen Resistance
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Solution Overview
Problem
Voice coil motors (VCMs) used in storage devices like HDDs face damage and magnetic property deterioration when exposed to low-pressure hydrogen atmospheres due to hydrogen embrittlement, despite the use of rare earth sintered magnets with metal plating layers.
Innovation Solution
A magnetic circuit configuration component for VCMs featuring rare earth sintered magnets with a multi-layer coating structure comprising a copper plating layer and a nickel plating layer, followed by a metal oxide or nitride layer, which prevents chipping, cracking, and magnetic property degradation in hydrogen environments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a metal plating layer is applied to the rare earth sintered magnet, then the magnet's resistance to hydrogen embrittlement is improved, but the magnet still suffers from chipping and cracking damage in low-pressure hydrogen environments
Solution Approach 1:
The patent applies a composite coating structure consisting of multiple layers: a base metal plating layer (such as nickel or copper) combined with a ceramic layer (such as aluminum oxide or aluminum nitride). This composite structure combines the benefits of metal plating (good adhesion and baseline corrosion resistance) with the superior hardness and chemical inertness of ceramic materials, providing comprehensive protection against both hydrogen embrittlement and mechanical damage like chipping and cracking.
Solution Approach 2:
The patent specifies precise parameter ranges for the coating layers, including thickness (ceramic layer: 1-10 μm, metal plating layer: 5-20 μm), composition ratios, and sintering temperatures (1000-1200°C). By optimizing these parameters, the coating achieves the right balance between hardness (for crack resistance), adhesion (to prevent delamination), and chemical stability (for hydrogen resistance), thereby resolving the contradiction between improved reliability and maintained strength.
2Duration of action of moving object
If the rare earth sintered magnet is exposed to low-pressure hydrogen atmosphere for prolonged periods, then the operational duration is extended, but the magnetic properties deteriorate due to hydrogen embrittlement
Solution Approach 1:
The ceramic coating layer acts as an intermediary barrier between the hydrogen environment and the rare earth sintered magnet. Materials like aluminum oxide and aluminum nitride have extremely low hydrogen permeability and high chemical stability, effectively blocking hydrogen atoms from reaching and embrittlting the magnet. This intermediary layer allows the magnet to operate indefinitely in low-pressure hydrogen environments without magnetic property deterioration.
Solution Approach 2:
The ceramic coating creates an inert protective environment around the magnet, isolating it from the reactive hydrogen atmosphere. The coating's chemical inertness prevents hydrogen diffusion and chemical reactions with the magnet material, thereby maintaining magnetic properties stable over extended operational periods in hydrogen-filled storage devices.
3Ease of manufacture
If a simple metal plating layer is used on the magnet, then the manufacturing process is simplified, but the protection against chipping and cracking is insufficient
Solution Approach 1:
The manufacturing process applies the ceramic coating layer first through slip casting or slurry deposition, then performs sintering to form a hard protective layer. After sintering, a metal plating layer is applied over the ceramic surface using conventional electroplating or chemical deposition techniques. This sequence of preliminary actions ensures that the hard ceramic layer is established before adding the metal layer, maximizing crack resistance while maintaining manufacturing feasibility through standardized coating and sintering processes.
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 proposed solution effectively prevents damage and maintains magnetic properties of the magnets even after prolonged exposure to low-pressure hydrogen, ensuring precise actuator control and reliable data storage operations.
Implementation Method 1
hydrogen embrittlement is caused, and the material is broken, cracked, or pulverized
Implementation Method 2
a metal plating layer and a metal oxide layer and/or a metal nitride layer are provided on a surface of the rare earth sintered magnet body directly or via an n-layer (n is an integer and n≥1) metal plating layer
Data Source
AI summary
A magnetic circuit configuration component for a VCM includes a pair of yokes, a pair of magnets provided on inner surfaces of the yokes, and a support member or a support column that maintains a gap between the magnets to fix the yokes to each other, the magnet is a rare earth sintered magnet having a surface on which coating is performed, a composition of the magnet consists of, by weight, R (R is one or more types of rare earth elements selected from Nd, Pr, Dy, Tb, Ce, La, and Gd) of 28% to 34%, Co of 2% or less, B of 0.5% to 2%, one or more types selected from Ni, Nb, Al, Ti, Zr, Cr, V, Mn, Mo, Si, Sn, Ga, Cu, and Zn as an additive of 2% or less, and the balance of Fe, and the coating includes a metal plating layer of a predetermined thickness and a metal oxide layer and/or a metal nitride layer of 0.01 μm to 2 μm.