HVOF Coating Layer Thickness and Corrosion Resistance
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Solution Overview
Problem
Existing processes for manufacturing parts, such as aeronautical components, rely heavily on chromium coatings, which are harmful to health and the environment, and struggle to achieve optimal layer thickness and resistance to mechanical stresses and corrosion.
Innovation Solution
A method involving HVOF spraying of a powder mixture with metal carbide grains of specific size and a substrate with controlled roughness, achieving a coating layer thickness between 30 and 50 μm, reduces the risk of layer detachment, maintains corrosion protection, and minimizes material mass and production time, eliminating the need for traditional rectification steps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thick coating layer is applied to protect the substrate, then corrosion protection is improved, but the risk of layer detachment under mechanical stress increases
Solution Approach 1:
The patent changes the grain size parameter of the coating material from conventional larger grains to nanometric grains (average size 450nm). This parameter change enables the coating to achieve both adequate thickness for corrosion protection and fine microstructure resistance to spalling under mechanical stress
Solution Approach 2:
The patent uses a composite material system consisting of nanometric metal carbide grains (WC, TiC, TaC, HfC, Mo2C, or NbC) dispersed in a metallic binder matrix (Co, Ni, Cu, Al, or their alloys). This composite structure provides both corrosion resistance from the carbide grains and ductility from the binder, preventing layer detachment
2Reliability
If a thick coating layer is applied to ensure adequate thickness, then corrosion protection is maintained, but the mass of the part increases
Solution Approach 1:
By changing the grain size parameter to nanometric dimensions (450nm average), the coating achieves higher density and better packing efficiency. This allows achieving the required corrosion protection at reduced thickness (30-50μm), thereby reducing the mass of the coating layer while maintaining protective function
3Reliability
If a thick coating layer is applied to ensure adequate thickness, then corrosion protection is maintained, but the production time increases due to traditional rectification steps
Solution Approach 1:
The nanometric grain size (450nm) enables the coating to be deposited in a thinner layer (30-50μm) that is sufficiently protective yet close to the final dimension. This eliminates the need for time-consuming grinding operations, requiring only a brief polishing step (5-10μm removal) to achieve the desired surface finish and geometry
Solution Approach 2:
The coating process is designed to deposit the layer at or very near the final required thickness from the outset. By controlling the deposition parameters and using nanometric grains that pack efficiently, the coating achieves the target dimension without requiring extensive post-processing rectification, thus performing the thickness adjustment action in advance during deposition
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 method enhances the resistance of the coating layer to mechanical stresses and corrosion, reduces the risk of spalling, maintains equivalent corrosion protection at reduced thickness, and lightens the part without compromising resistance, making it suitable for aircraft components.
Implementation Method 1
The HVOF spraying process refers to a method of spraying a powder mixture containing grains using combustion gases from the combustion of a fuel with an oxidizer. The speed and temperature of these gases are such that the grains of the powder mixture (in this case, metal carbide grains) are ejected onto a substrate with sufficient energy to adhere to it and thus form a coating layer.
Implementation Method 2
several unit measurements are taken by induction or eddy current, resulting in minimum and maximum thickness values (roughness troughs) of the layer
Implementation Method 3
several unit measurements are taken by induction or eddy current, resulting in minimum and maximum thickness values (roughness troughs) of the layer
Data Source
Figure 1~3
AI summary
Process for fabricating a part (1) comprising a metallic substrate (Sub) at least partially covered with a coating layer (Coat), the process comprising: - the preparation (A) of a surface of the substrate (Sub) to be covered, in order to obtain a prepared surface having a roughness Ra of between 0.6 and 1.6 μm and preferably of between 0.8 and 1.6 μm; - the formation (C) on the prepared surface of the substrate, of the coating layer (Coat), this coating layer (Coat) being formed by spraying, according to an HVOF spraying process, a pulverulent mixture containing metal carbide grains (G), these grains (G) having dimensions strictly less than 1 μm and the thickness (Thk min) of the coating layer (Coat) thus formed being less than 50 μm; next - the finishing by polishing (D) of at least one surface of said coating layer (Coat) so as to ensure that its roughness Ra is less than 1.6 μm.