Sn-Based Overlay on Copper Alloy Plain Bearing
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Solution Overview
Problem
Copper diffusion from the copper-based alloy layer into the Sn-based overlay in plain bearings leads to performance deterioration, including reduced fatigue resistance and seizure risk, which existing countermeasures fail to adequately address.
Innovation Solution
An Sn-based overlay is deposited directly on a copper-based alloy layer with a total Sn and Ni content of 4 to 12 mass%, without an intermediate Ni barrier, to suppress Cu diffusion and enhance fatigue resistance, while maintaining a hardness of Hv 150 or less, thereby preventing performance deterioration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an Ni intermediate layer is interposed between the copper-based alloy layer and the Sn-based overlay to prevent diffusion, then Cu diffusion into the overlay is suppressed, but the device complexity and manufacturing cost increase
Solution Approach 1:
The patent removes the Ni intermediate layer from the bearing structure, extracting the problematic component that added complexity. Instead of using a separate diffusion barrier layer, the invention relies on the inherent diffusion resistance of the Sn-based overlay itself when properly formulated with specific alloying elements (Al, In, Ga, Ge, or Ti at 0.01-5 mass%), thereby simplifying the overall layer structure while maintaining effective prevention of Cu diffusion.
Solution Approach 2:
The patent introduces alloying elements (Al, In, Ga, Ge, or Ti) as intermediary substances within the Sn-based overlay that act as diffusion barriers. These elements mediate between the copper-based alloy layer and the Sn overlay by forming intermetallic compounds or segregation layers that prevent Cu diffusion, replacing the need for a separate Ni intermediate layer.
2Reliability
If an Ni intermediate layer is used to prevent diffusion, then Cu diffusion is suppressed, but manufacturing cost increases
Solution Approach 1:
The patent eliminates the Ni intermediate layer, removing the associated manufacturing costs for an additional plating step and material expenses. The simplified structure requires only the copper-based alloy layer and the Sn-based overlay with specific alloying content, reducing manufacturing complexity and cost while achieving the same diffusion prevention function.
Solution Approach 2:
The patent changes the compositional parameters of the Sn-based overlay by specifying minimum contents of alloying elements (Al, In, Ga, Ge, or Ti at 0.01-5 mass%). This parameter adjustment modifies the overlay's properties to provide inherent diffusion resistance, replacing the need for expensive intermediate layer materials and processing.
3Loss of substance
If the Sn-based overlay is made thinner to reduce material cost, then Cu diffusion occurs more readily, but if made thicker to prevent diffusion, then material cost increases
Solution Approach 1:
The patent optimizes the thickness parameter of the Sn-based overlay to 3-19 μm, which is thinner than conventional overlays but sufficient to prevent Cu diffusion when combined with the specified alloying element content (0.01-5 mass%). This parameter optimization reduces Sn material usage while maintaining effective diffusion prevention through the synergistic effect of controlled thickness and alloying composition.
Solution Approach 2:
The patent creates a composite Sn-based overlay by combining Sn with specific alloying elements (Al, In, Ga, Ge, or Ti). This composite material structure provides enhanced diffusion resistance per unit thickness compared to pure Sn, allowing for a thinner overlay design that maintains effective Cu diffusion prevention while reducing material cost.
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 solution effectively prevents Cu diffusion, maintaining the Sn-based overlay's thickness and improving compatibility, fatigue resistance, and seizure resistance, even under prolonged use and heat treatment, thus extending the bearing's operational life and reducing production costs.
Implementation Method 1
Cu of the copper alloy diffuses into the overlay and forms Cu-Sn based intermetallic compounds
Implementation Method 2
an Sn-based overlay which is applied on the plain-bearing alloy layer
Data Source
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AI summary
The copper alloy (lining) prevails in an overwhelmingly large amount in a plain-bearing layer structure. Cu of the plain bearing copper-alloy diffuses into the Sn-based overlay diffuses into the Sn-based overlay and detrimentally impairs the performance of the overlay. The present invention takes a measure against this problem. An Sn-based overlay having a thickness of 3 to 19 µm is deposited by electro-plating without an intermediate layer for diffusion prevention on a plain-bearing layer, which contains Sn and Ni in a total amount of more than 4 mass% to 20 mass% (the minimum amount of Sn is 4 mass%) and has a hardness of Hv 150 or less.