Brake Disc Coating with Tungsten Carbide for Wear and Corrosion
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Solution Overview
Problem
Brake elements, such as brake discs, made from gray cast iron face issues with high weight, corrosion, and wear, leading to premature replacement and increased particulate emissions, with existing coatings facing challenges in adhesion and process complexity.
Innovation Solution
A brake element with a base body coated by two build-up layers, where the first layer is an austenitic chromium-nickel-molybdenum steel and the second layer is a composite of an iron alloy matrix with intercalated tungsten carbide particles, applied using energy beam processes to ensure strong adhesion and corrosion protection, while maintaining low manufacturing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If gray cast iron is used for brake elements, then high volumetric heat capacity and thermal shock resistance are achieved, but high weight, corrosion tendency, and wear increase
Solution Approach 1:
The patent applies a composite coating structure consisting of a metallic base layer (austenitic steel with Cr, Ni, Mo) and a ceramic-containing wear protection layer (with tungsten carbide particles). This composite structure provides both the thermal resistance benefits and reduced weight compared to solid gray cast iron, while adding corrosion and wear protection.
2Reliability
If thermal spraying processes are used to apply corrosion and wear protection coatings, then corrosion resistance and wear resistance are improved, but adhesion under thermomechanical loads becomes problematic
Solution Approach 1:
The patent introduces a metallic intermediate layer (austenitic steel containing Cr, Ni, Mo) between the gray cast iron substrate and the ceramic-containing wear protection layer. This intermediate layer acts as a mediator that improves adhesion by providing a transition zone with compatible mechanical properties and enhanced bonding capability, preventing direct thermal spraying adhesion problems.
Solution Approach 2:
The patent modifies the substrate surface parameters by creating a metallurgically bonded intermediate layer with specific compositional gradients (Cr, Ni, Mo content) and microstructural characteristics. This parameter change in the intermediate layer enables better adhesion of the subsequently applied ceramic-containing coating under thermomechanical loads.
3Strength
If the surface is roughened by abrasive blasting or other treatments to increase coating adhesion, then adhesion is improved, but process complexity increases
Solution Approach 1:
Instead of complex surface roughening treatments, the patent changes the material parameters of the intermediate layer through controlled metallurgical bonding during the thermal spraying process itself. The intermediate layer's composition and microstructure are optimized to provide inherent adhesion without requiring additional surface preparation steps.
4Strength
If adhesion promoter layers are used as intermediate layers to increase coating adhesion, then adhesion is improved, but manufacturing costs increase
Solution Approach 1:
The metallic intermediate layer serves multiple functions simultaneously: it provides adhesion promotion, corrosion protection, thermal stress management, and a compatible substrate for the ceramic-containing wear protection layer. This multi-functionality eliminates the need for separate adhesion promoter layers, reducing manufacturing complexity and 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 achieves high wear resistance, corrosion protection, and reduced particulate emissions, with optimized layer thicknesses and adhesion strengths, ensuring a longer lifespan and improved appearance of the brake element.
Implementation Method 1
Significantly stronger bonding is possible using a metallurgical bond, for which it is necessary to use thermal energy to enable the atomic diffusion process at the boundary surface between the substrate and the coating
Implementation Method 2
On the other hand, the second option is a melting process in which the heating takes place after the spraying operation, as described in DE 10 2005 008 569 A1
Data Source
AI summary
A brake element for a motor vehicle, having a base body that is planar at least in areas, to the planar sides (of which at least two build-up layers are applied in each case, at least in areas. The build-up layers form a surface which, in the mounted state of the brake element on the motor vehicle, is used as a friction surface for a brake pad. There is a bonding zone in which both a material of the base body and a material of a build-up layer adjacent thereto are present. The second build-up layer is made of a composite of an iron alloy matrix with intercalated tungsten carbide particles. A proportion of the volume of the intercalated tungsten carbide particles to the volume of the iron alloy matrix is in a range of 1% to 19%.