Lead-Free Sliding Element With Nickel Diffusion Barrier
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Sliding elements with bismuth-based powder metal alloys face diffusion issues at low temperatures, leading to weakening of the tin-based overplate and reduced wear and seizure resistance in engine applications.
Innovation Solution
A sliding element composition featuring a copper-tin-bismuth base with added hard particles, sintered and bonded to a steel backing, and a tin overplate with nickel, which minimizes bismuth diffusion into the overplate, ensuring enhanced strength and wear resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If bismuth is added to the powder metal copper alloy to provide wear and seizure resistance, then wear resistance and seizure resistance are improved, but bismuth diffuses into the tin-based overplate at low temperatures and forms eutectic alloy that weakens the sliding element
Solution Approach 1:
A nickel barrier layer is introduced as an intermediary between the bismuth-containing copper alloy base and the tin-based overplate. This nickel layer acts as a diffusion barrier that prevents bismuth from migrating into the tin overplate at low temperatures, thereby eliminating the formation of weakening eutectic alloys while preserving the wear and seizure resistance provided by bismuth in the base material.
Solution Approach 2:
The sliding element is segmented into distinct layers with specific functions: the copper alloy base containing bismuth for wear resistance, a nickel barrier layer to prevent diffusion, and a tin-based overplate for surface protection. This segmentation isolates the bismuth in the base material from the tin overplate, allowing each layer to perform its intended function without adverse interactions.
2Reliability
If lead is added to the copper matrix to provide wear resistance by acting as a lubricant, then wear resistance is improved, but environmental considerations require lead-free alternatives
Solution Approach 1:
The composition of the copper alloy base is modified by substituting lead with bismuth and adjusting the concentrations of other alloying elements such as tin, phosphorus, and silicon. This parameter change eliminates the environmentally harmful lead while maintaining wear resistance through bismuth's lubricating properties and optimized alloy composition.
Solution Approach 2:
The patent uses readily available copper alloy powders with controlled compositions of common elements (Cu, Sn, Bi, P, Si) that can be economically produced, replacing expensive or environmentally restricted materials while achieving the desired performance through optimized formulation.
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 provides a lead-free sliding element with improved strength, wear resistance, and seizure resistance, maintaining performance across varying temperatures without the formation of eutectic alloys that weaken the component.
Implementation Method 1
The method further includes disposing the base on a backing; and sintering the base and backing
Implementation Method 2
At low temperatures, such as temperatures lower than typical engine temperatures, the bismuth of the powder metal base diffuses into the tin-based overplate and forms a eutectic alloy of tin and bismuth
Implementation Method 3
A tin overplate is disposed on the base. The tin overplate includes, in wt.％ of the tin overplate, tin in an amount of at least 50.0 wt.％, copper in an amount of 1.0 to 10.0 wt.％ and nickel in an amount up to 10.0 wt.％ The composition of the base is such that a tin overplate can be applied to the base, with minimal diffusion of the bismuth into the tin overplate
Implementation Method 4
Lead provides wear resistance by acting as a lubricant to the sliding element surface
Data Source
Figure 1~2
Figure 3~5
Figure 6~7
AI summary
A sliding element 20, such as a bushing or bearing, includes a sintered powder metal base 24 deposited on a steel backing 22. The base 24 includes a tin, bismuth, first hard particles 40, such as Fe3P and MoSi2, and a balance of copper. In one embodiment, a tin overplate 26 is applied to the base 24. A nickel barrier layer 42 can be disposed between the base 24 and the tin overplate 26, and a tin-nickel intermediate layer 44 between the nickel barrier layer 42 and the tin overplate 26. In another embodiment, the sliding element 20 includes either a sputter coating 30 of aluminum or a polymer coating 28 disposed directly on the base 24. The polymer coating 28 includes second hard particles 48, such as Fe203. The polymer coating 28 together with the base 24 provides exceptional wear resistance over time.