Gradient Coating Structure for Corrosion-Resistant Friction Material
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Solution Overview
Problem
Conventional friction materials bonded to a back plate via copper plating suffer from inferior corrosion resistance due to pinholes, leading to rust and reduced bonding strength, and thick copper plating results in dimensional variations and increased costs.
Innovation Solution
A friction material with a specific coating layer structure comprising a first coating layer of Cu, Ni, and Fe alloy and a second coating layer with varying Cu and Ni content gradients, preventing pinhole penetration and improving adhesion and corrosion resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If copper plating thickness is increased to not less than 30 μm to fill pinholes and improve corrosion resistance, then corrosion resistance is improved, but coating thickness variation increases, plating time becomes longer, and costs increase
Solution Approach 1:
The coating layer is divided into multiple layers with different compositions and functions: a first coating layer (Cu, Ni, Fe alloy) that fills pinholes and provides corrosion resistance, and a second coating layer with Cu and Ni content gradients that optimizes adhesion and reduces stress. This segmentation allows each layer to be optimized for its specific function rather than requiring a single thick uniform layer
Solution Approach 2:
The second coating layer has spatially varying composition with Cu and Ni content gradients that change from the interface toward the outer surface. This local quality variation optimizes adhesion at the interface while maintaining corrosion resistance at the surface, and reduces residual stress throughout the layer thickness
2Reliability
If copper plating thickness is increased to not less than 30 μm to improve corrosion resistance, then corrosion resistance is improved, but plating time becomes longer and costs increase
Solution Approach 1:
The total coating thickness is distributed across multiple layers with the first coating layer filling pinholes and the second coating layer providing gradient composition. This segmentation achieves the required corrosion protection with a thinner total coating than a conventional single layer, thereby reducing plating time and costs
Solution Approach 2:
The coating system uses composite material structure with Cu, Ni, and Fe alloys in specific combinations and gradients. This composite approach provides superior corrosion resistance per unit thickness compared to conventional copper plating, allowing thinner total coating and reduced plating time
3Strength
If copper plating is applied to bond friction part to back plate, then adhesion is achieved, but pinholes form in the plating leading to rust formation and reduced bonding strength
Solution Approach 1:
The coating is segmented into a first layer that specifically addresses pinhole filling and corrosion protection, and a second layer that provides adhesion and stress management. This segmentation allows the pinhole-filling function to be optimized without compromising adhesion strength
Solution Approach 2:
The first coating layer acts as an intermediary between the back plate and the second coating layer, filling pinholes and preventing corrosion at the critical interface region. This intermediary layer protects the bonding interface from corrosion while maintaining strong adhesion
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 friction material achieves superior corrosion resistance and adhesion by preventing pinhole penetration and reducing residual stress, with controlled layer thickness and composition for uniformity and cost-effectiveness.
Implementation Method 1
made by diffusion bonding of a metallic lining material to an iron back plate via copper coating through sintering
Implementation Method 2
forming plating of not less than 30 μm in coating thickness by electroplating
Data Source
Figure 1~2
AI summary
A friction material comprises an Fe part which contains Fe as a main component, a coating layer formed on a surface of the Fe part, and a friction part formed on a surface of at least a part of the coating layer, and the coating layer comprises a first coating layer and a second coating layer which have a specific average thickness and a specific component in order from Fe part side, and in the second coating layer, in order of positions at which the thickness is 20%, 40%, 60% and 80% of the second coating layer from the side of the first coating layer to the side opposite thereto, a Cu content increases and a Ni content decreases.