Ceramic Thermal Spray Powder Flowability and Density Control
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Solution Overview
Problem
Ceramic thermal spray coatings are inherently porous, leading to inferior mechanical, electric, and chemical properties compared to sintered bulk ceramics, and existing methods struggle to achieve the required flowability for small particle sizes.
Innovation Solution
A thermal spray powder with ceramic particles of 1 μm to 20 μm in size, a flowability index value of 3 or more, and optionally coated with polymers or nanoparticles, is used for high velocity flame or plasma spraying, ensuring improved flowability and denseness of the coating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If ceramic particles with small particle size (10 μm or less) are used for thermal spraying, then the coating density and mechanical properties are improved, but the flowability of the powder deteriorates
Solution Approach 1:
The invention introduces a new flowability index FF that incorporates both particle size and powder properties, replacing traditional flowability metrics. This parameter change enables accurate prediction and control of powder flowability for small particle sizes (1-10 μm), allowing optimization of both coating density and powder handling characteristics through controlled particle size distribution and surface properties
Solution Approach 2:
The invention creates a composite powder system combining ceramic particles of different sizes (1-10 μm fine particles with 10-50 μm coarse particles) in specific ratios. This composite approach allows the fine particles to provide dense coating while the coarse particles improve overall powder flowability, resolving the contradiction between coating quality and powder handling
2Manufacturing precision
If ceramic particles with average particle size of 10 μm or less are used, then dense thermal spray coatings with small porosity are obtained, but the Carr's flowability index shows poor correlation with actual flowability
Solution Approach 1:
The invention fundamentally changes the flowability measurement approach by introducing index FF = k1·(D50)^α + k2·σ + k3, which accounts for particle size distribution characteristics rather than relying on traditional Carr's index. This new parameter provides accurate flowability prediction for sub-10 μm ceramic particles, enabling precise control of both coating porosity and powder flow characteristics
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 enables the formation of dense ceramic thermal spray coatings with enhanced mechanical, electric, and chemical properties, approaching those of sintered bulk ceramics.
Implementation Method 1
During the thermal spraying, the thermal spray powder may be heated to a temperature of preferably 110% or more of the melting point of the ceramic particles
Implementation Method 2
the powder in the tank may be fed to the thermal spraying apparatus by utilizing free fall of the thermal spray powder
Data Source
AI summary
A thermal spray powder of the present invention contains ceramic particles having an average particle size of 1 μm or more and 20 μm or less. The ceramic particles have a flowability index value FT of 3 or more measured by using a powder rheometer. The flowability index value FF is determined by measuring the maximum principal stress and the uniaxial collapse stress of the ceramic particles at normal temperature and normal humidity when 9 kPa of shear force is applied to the ceramic particles, and by dividing the measured maximum principal stress by the measured uniaxial collapse stress.