Brake Disc Coating Stack for Corrosion and Wear Resistance
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Solution Overview
Problem
Current methods for improving wear and corrosion resistance of brake discs, such as thermal spraying and gas nitrocarburizing, do not meet the stricter requirements for longer life and corrosion resistance.
Innovation Solution
A corrosion-resistant coating system is created on a cast iron brake disc using pulsed water jet activation to increase surface roughness, followed by nitrocarburization and oxidation to form a diffusion layer, which enhances wear resistance and provides a strong base for a thermally sprayed top layer, and then applying a thermal spray coating with a cermet material to improve adhesion and corrosion resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If thermal spraying is applied directly to the cast iron surface, then the coating can be applied, but the adhesion of the coating is insufficient and wear resistance is poor
Solution Approach 1:
The cast iron surface undergoes water jet activation and nitrocarburization before thermal spraying to create a diffusion layer with improved surface properties. This preliminary treatment enhances coating adhesion and wear resistance by preparing the substrate surface in advance.
Solution Approach 2:
The solution creates a composite structure consisting of the cast iron substrate, a nitrocarburized diffusion layer, and a thermally sprayed top coat. This multi-layer composite system combines the benefits of each layer to achieve superior adhesion and wear resistance.
2Strength
If the surface is activated by water jet to increase roughness, then coating bonding is improved, but the surface roughness may deteriorate braking properties
Solution Approach 1:
The water jet activation is performed as a preliminary step before nitrocarburization and thermal spraying. The subsequent nitrocarburization and oxidation processes modify the roughened surface to create a diffusion layer that maintains coating bonding benefits while restoring surface properties for optimal braking performance.
Solution Approach 2:
The surface roughness parameters are controlled within specific ranges during water jet activation. The roughness is increased enough to improve coating bonding but kept within limits that do not adversely affect braking performance. The nitrocarburization process further modifies surface parameters to achieve the optimal balance.
3Reliability
If a thick top layer is applied to cover cut cavities and graphite lamellae, then coverage is improved, but the layer thickness increases material consumption
Solution Approach 1:
The water jet activation and nitrocarburization are performed as preliminary steps to prepare the surface and create a diffusion layer. This preparation reduces the number and size of defects that need to be covered, allowing for a thinner top coat that still provides adequate coverage and reduces material consumption.
4Reliability
If gas nitrocarburizing is used to improve wear and corrosion resistance, then the diffusion layer is formed, but the corrosion resistance does not meet stricter requirements
Solution Approach 1:
The solution merges gas nitrocarburizing with oxidation treatment and thermal spraying. The nitrocarburization forms a diffusion layer for wear resistance, while the subsequent oxidation and thermal spraying provide enhanced corrosion protection, combining the benefits of multiple processes to meet stricter requirements.
Solution Approach 2:
The corrosion protection is achieved through a composite system where the nitrocarburized diffusion layer provides wear resistance and the oxidized surface with thermal spray coating provides enhanced corrosion resistance. This multi-layer composite approach exceeds the corrosion protection of nitrocarburizing alone.
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 significantly increases the adhesion and corrosion resistance of the brake disc coating, making it insensitive to local damage and maintaining braking performance by forming a dense oxide layer and improving wear resistance.
Implementation Method 1
The pulsed water jet is furthermore loaded or superimposed by ultrasound in such a way that cavitation beads are formed in the water jet, whereas the ultrasound 'load' is tuned such that the beads are thrown against the surface to be treated, implode there and increase that way the surface roughness.
Implementation Method 2
The pulsed water jet is furthermore loaded or superimposed by ultrasound
Implementation Method 3
Hereinafter the surface is nitrocarburized so that a corresponding diffusion layer is formed on it.
Implementation Method 4
Hereinafter the surface is nitrocarburized so that a corresponding diffusion layer is formed on it
Implementation Method 5
Thereupon the surface is subjected to an oxidation process in a next step, which means that the surface or a part of the diffusion layer is oxidised (including the more than insignificant formation of Fe 3 O 4 ).
Implementation Method 6
Finally, the top layer is applied by thermal spraying.
Data Source
Figure 1a~1b
Figure 2a~2b
Figure 3
AI summary
The invention relates to a method of producing a corrosion resistant coating system on a cast iron substrate preferably in the shape of a brake disc, the coating system being completed by a thermally sprayed top layer, characterised in that the cast iron substrate is first subjected to activation by means of a pulsed water jet after completion of machining which increases the surface roughness of the surface thus treated, whereupon the surface is nitrocarburized so that a corresponding diffusion layer is formed on it, whereupon the surface is subjected to an oxidation process in a next step and only then the top layer is applied by thermal spraying.