Chromium Carbide Coatings – HVAF Thermal Spraying For Wear Resistance At Elevated Temperatures
Thermal sprayed chromium carbide coatings combat high-temperature wear due to the high wear resistance imparted by the hard carbide particles and the high temperature oxidation resistant nature of the Cr2O3 oxide formed over both phases of CR3C2-NiCr.
While tungsten carbide coatings provide better wear resistance when temperatures are under 510°C (950°F), high velocity sprayed chrome carbide coatings mitigate abrasive and erosive wear at temperatures up to 750°C (1380°F).
The corrosion resistance is provided by the NiCr matrix while the wear resistance is provided mainly by the carbide ceramic phase.
Cr3C2-NiCr Feedstock Properties
Chrome carbide coatings are sprayed with Cr3C2-NiCr agglomerated and sintered powder -30 +5 microns.
| Nominal composition | wt.% |
|---|---|
| Cr3C2 | base |
| Total carbon | 9.2-10.8 |
| Nickel | 18-22 |
| Chrome | 4.5-5.5 in the metal phase |
HVAF Chromium Carbide Coating Properties
Cr3C2-NiCr coating properties are influenced significantly by the spray process and spray parameters.
The abrasive wear rate for the chromium carbide coatings is controlled by several factors such as:
- the morphology of the starting powder
- the size and distribution of the chrome carbide particles
- the hardness of the chromium carbide particles relative to the abrasive particles
- the properties of the matrix and its volume fraction, and
- the coating process, which determines the coating characteristics such as:
- Phase composition
- Density
- Hardness
- Bond strength and
- The residual stresses
Typical Properties Of The Kermetico HVAF Chrome Carbide Coating
| Feature | S.I. Units | U.S. Units |
|---|---|---|
| Apparent metallographic porosity | <1.0% | |
| Bond strength to steel | 70 MPa @500µm | 10,000 PSI @0.020” |
| Coating hardness, HV300 | 950-1,100 | |
| Typical as-sprayed roughness Ra, micro-inch | 2-3.2 µm | 80-120 µinch |
| Maximum coating thickness | 1 mm | 0.040” |
| Maximum working temperature | 750°C | 1,380oF |
Kermetico HVAF applied chrome carbide coatings have excellent resistance to elevated temperature erosion and sliding wear.
- Impact resistance and fatigue resistance are good.
- Thermal shock resistance is excellent.
- General corrosion and elevated temperature corrosion resistance are very good.
Usually, this coating is used at elevated temperatures where tungsten carbide coatings do not work or when faster and a less costly finishing is necessary.
A specific characteristic of a Kermetico HVAF chromium carbide coating is that it remains ductile during the long-term service at high temperatures, in particular, above 600oC (1,100°F) .
The combustion temperature in the Kermetico HVAF process is well below the melting point of Cr3C2, which eliminates the possibility of the carbides dissolution into the nickel-chromium matrix during coating application.
As a result, there is no precipitation of carbides within the nickel-chromium matrix during the service of the HVAF coating and the metal matrix remains ductile.
Such precipitation of carbides is the main reason for the HVOF-sprayed coatings embrittlement and failure during high temperature service.
Typical Applications Of The High Velocity Air Fuel Chromium Carbide Coatings
Sliding wear, erosion, and fretting at elevated temperatures:
- Water-wall and superheater tubing in fluidized-bed and pulverized-coal power generation boilers
- Pump impellers
- Nozzles
- Gas turbine blades
- Ball valves and seats
- Piston rings
- Wear protection in hydraulic equipment as a hard chrome alternative.
Uniform high hardness and ductility, low stress and porosity lead to a substantial increase of service life of parts protected with Kermetico HVAF Cr3C2-NiCr coatings in comparison with HVOF. Our partner in India deposits chrome carbide coatings as well.