Cermet Coating via Liquid-Entrained Thermal Spray
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Solution Overview
Problem
Conventional combustion-based thermal spray processes for cermet coatings face issues with particle clogging, oxidation, and decarburization due to small particle sizes and high combustion temperatures, leading to suboptimal coating quality and properties.
Innovation Solution
Injecting a liquid and cermet particles with a median size of less than 5 microns into the combustion stream of a thermal spray gun, where they form an entrained feedstock stream at temperatures below the melting point, to prevent substantial melting and re-solidification, resulting in fine-grained, dense coatings with reduced oxidation and decarburization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional HVOF or HVAF processes are used with small particle sizes (less than 15-20 microns), then coating quality may be improved, but particle clogging and agglomeration occur in the equipment
Solution Approach 1:
A liquid carrier (water, alcohol, or other liquid) is introduced as an intermediary medium to transport the fine cermet particles (less than 5 microns) into the combustion stream. The liquid prevents particle agglomeration and clogging during feeding, while being vaporized in the combustion zone to leave the fine particles available for coating deposition.
2Speed
If high combustion temperatures are used in HVOF or HVAF processes, then particle acceleration is improved, but oxidation and decarburization of ceramic particles occur
Solution Approach 1:
The fine cermet particles are rapidly accelerated through the high-temperature combustion stream and deposited onto the substrate before significant oxidation or decarburization can occur. The short residence time in the high-temperature zone minimizes harmful chemical reactions while maintaining high particle velocities for good coating adhesion.
Solution Approach 2:
The process uses high combustion temperatures to achieve particle acceleration, but the key parameter change is the particle size reduction to less than 5 microns. This size reduction allows the particles to be heated and accelerated rapidly through the combustion zone and deposited before extensive oxidation or decarburization occurs, effectively using the high temperature benefit while minimizing its harmful effects.
3Stability of the object's composition
If conventional thermal spray processes are used with fine particles, then coating homogeneity may be improved, but particle clogging in equipment occurs
Solution Approach 1:
The process uses a liquid carrier (hydraulic approach) to transport fine cermet particles through the feed system and into the combustion stream. The liquid medium prevents particle aggregation and equipment clogging by keeping particles suspended and separated during feeding, while the high-velocity combustion stream provides the pneumatic acceleration needed for coating deposition.
4Speed
If high velocity combustion stream is used, then particle acceleration is improved, but particle temperature increases leading to melting and re-solidification
Solution Approach 1:
The fine cermet particles are rapidly accelerated through the high-temperature combustion stream and deposited onto the substrate before significant heating and melting can occur. The short residence time in the high-temperature zone allows high particle velocities to be achieved while minimizing temperature increase and avoiding melting and re-solidification cycles.
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
This method produces coatings with improved homogeneity, higher acceleration of particles, and reduced oxidation or decarburization, maintaining the characteristics of the feedstock particles, resulting in enhanced wear resistance and coating density.
Implementation Method 1
combusting a fuel and an oxidant in a combustion chamber of a thermal spray gun to form a combustion stream
Implementation Method 2
injecting a liquid and a feedstock material into the combustion stream in the combustion chamber to form an entrained feedstock stream
Implementation Method 3
a temperature of the plurality of cermet particles in the entrained feedstock stream is less than a melting temperature of the plurality of cermet particles
Implementation Method 4
directing the entrained feedstock stream on a surface of a substrate to form a coating
Data Source
AI summary
One aspect of the present invention includes an article. The article includes a substrate and a coating disposed on the substrate, wherein the coating includes a plurality of cermet particles bonded along their prior particle boundaries. The plurality of cermet particles have a median particle size less than about 5 microns and less than 25 percent of the plurality of cermet particles include melted and re-solidified particles. Gate valves are also presented.