What is Thermal Spray Powder?
Thermal spray powder refers to micron-sized particles (typically 10-100μm) made of metals, alloys, ceramics, or composite materials. These powders are projected onto workpiece surfaces in a molten or semi-molten state through high-temperature spraying techniques to form functional coatings.
Common Types of Thermal Spray Powders
|
Material Category
|
Typical Composition
|
Applications
|
|
Metal Powders
|
Aluminum, Zinc, Nickel-based alloys
|
Corrosion protection (e.g., ships, bridges)
|
|
Ceramic Powders
|
Alumina, Zirconia, Tungsten Carbide
|
Wear resistance, thermal insulation (e.g., aircraft engine blades)
|
|
Composite Powders
|
Metal+Ceramic (e.g., WC-Co)
|
High-hardness tool coatings
|
|
Self-Fusing Alloy Powders
|
Nickel-Chromium-Boron-Silicon (NiCrBSi)
|
Repairing worn components
|
Comparison of Spraying Techniques
|
Technology
|
Temperature Range
|
Suitable Powders
|
Coating Characteristics
|
|
Flame Spraying
|
3,000°C
|
Metal, Plastic Powders
|
Porous, low cost
|
|
Plasma Spraying
|
15,000°C
|
Ceramics, High-melting-point alloys
|
Dense, high bond strength
|
|
High-Velocity Oxygen Fuel (HVOF) Spraying
|
3,000-4,000°C
|
Metal-ceramic composites
|
|
How to Assess the Quality of Spray Powders
When selecting high-quality spray powder materials, you can assess the following key indicators: sphericity, particle size distribution, flowability, loose packing density, and oxygen content.
1. Sphericity and Density
Generally, powders with high sphericity and dense structures can form excellent coatings. As sphericity increases, the flowability of the powder in the solid state also increases, which leads to more uniform and denser coatings.
2. Particle Size Distribution
Thermal spray powders need to be of specified particle sizes for different spraying processes. For example:
- Flame Spraying: Metal powders are generally smaller than 120 mesh, generally in the range of -180 to +320 mesh.
- Plasma Spraying: Ceramic powders are generally of -140 to +320 mesh or -500 to +300 mesh particle size.
- High-Velocity Oxygen Fuel Spraying (HVOF): Powder particle sizes are generally between 15 and 53 microns, but finer powders in the range of 5 to 25 microns.
- Some HVOF equipment can even spray ultra-fine powders with particle sizes below 10 microns.
3. Flowability
Good flowability ensures uniform powder feeding and prevents clogging of the powder feed channels. Generally, alloy powders flow well, while ceramic powders flow comparatively poorly. The higher the loose packing density of the agglomerated particles, the better the flowability.
4. Kinetic Energy and Coating Density
For the same spraying process conditions, the denser the coating, the higher the kinetic energy of the particles upon impact with the substrate. Therefore, the kinetic energy of the particles plays an important role in determining coating quality.
5. Oxygen Content
For alloy powders, oxygen content is one of the important physical parameters. During production, metal elements unavoidably undergo slight oxidation; the more severe the oxidation, the higher the oxygen content. Oxides in powder are harmful elements that will produce pores and inclusions in the coating. Therefore, oxygen content must be strictly controlled, and alloy powders should not normally contain more than 0.2% oxygen.
FAQs
1. Will Thermal Spray Powders Be Able to Restore Worn Industrial Parts?
Yes, thermal spray powders will be able to restore worn industrial parts. By using high-performance coatings through spraying, not only can the shape and size of the components be restored but also their wear resistance, corrosion resistance, and high-temperature resistance, thereby extending their service life.
2. What Powder Should One Use for Thermal Spraying in Marine Corrosion Protection?
When it comes to corrosion protection in seawater conditions, it is suitable to use zinc-based powders, aluminum-based powders, or stainless steel-based powders. These exhibit superior corrosion-resistant properties and can safeguard equipment from erosion by seawater and humid conditions.
3. What Powder Is Used in Thermal Barrier Coatings (TBC) on Aircraft Engine Blades?
Aircraft engine blade thermal barrier coatings (TBC) typically utilize stabilized yttria-partially stabilized zirconia (YSZ) powders. YSZ has superior thermal insulation and thermal expansion compatibility with the substrate and therefore effectively protects the blades from harsh, high-temperature gas flows.
