Working principle
HVOF (High Velocity Oxygen Fuel) is one of the highest-performance methods in the thermal spray family. Oxygen and fuel (usually propane, propylene or hydrogen) are mixed and burned in a combustion chamber; the resulting high-pressure gas stream accelerates the injected powder alloy to supersonic velocity (between Mach 1 and 2), so that the particles strike the surface in a semi-molten state. This high velocity and relatively controlled temperature produce a dense coating structure with low porosity and high bond strength.
Typical technical values
| Property | Typical value |
|---|---|
| Coating thickness | 150–400 µm |
| Bond strength | Above 68 MPa |
| Porosity | Below 1% |
| Particle velocity | Mach 1–2 (supersonic) |
Why is the coating so dense?
Particles striking the surface at very high velocity create an additional mechanical compaction (peening) effect on impact. This minimises porosity within the coating and voids between successive layers — the result is a very dense, homogeneous microstructure, different from that of a casting or a standard weld overlay.
Typical applications
HVOF coatings are widely used on hydropower turbine components, rolling mill rolls, pump and valve parts and oil & gas equipment. Alloys such as WC-Co-Cr, Cr₃C₂-NiCr and Inconel are preferred for applications that require resistance to wear and high-temperature corrosion.
Why choose this method?
Compared with conventional flame spray or plasma spray, HVOF delivers much lower porosity and higher bond strength. This directly improves the long-term performance and reliability of the coating — a decisive factor for operators who want to reduce the risk of failure, particularly in critical rotating equipment. Compared with hard chrome plating, it also offers both higher performance and lower environmental risk (no hexavalent chromium compounds are used).
Frequently Asked Questions
Up to what thickness can HVOF coatings be applied?
The typical practical range is 150-400 microns. If a thicker coating is required, a better approach is to build up the base with a weld-based method such as PTA and then apply a thin HVOF coating on top.
Can HVOF replace hard chrome plating?
In most industrial applications, yes — tungsten carbide based HVOF coatings offer equal or higher wear resistance than hard chrome plating, and the process is environmentally less problematic.
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