machine repair, coating service, production    

HVOF coatings

Titan Sisak hvof The high velocity oxy-fuel spray (HVOF) process is a new addition to the family of thermal spray processes. As it uses a supersonic jet, setting it apart from conventional powder flame spray, the speed of particle impact on the substrate is much higher, resulting in improved coating characteristics.
The HVOF process efficiently combusts oxygen and a gas to produce high kinetic energy with controlled heat input. The coating material, in powder form, is introduced into and uniformly heated by the hot gas stream to semi-molten condition. The flame and powder are accelerated by a converging / diverging nozzle to produce supersonic gas (~ 2200m/s or 5 Mach).
The high-speed gas stream takes a specific form of diamond rings (diamond shock) that resulted from the flow of gases at very high pressures and flow rates.

Characteristics of HVOF coatings

Very high bond and cohesive strength,

Smooth surface finish ,

Excellent wear resistance,

Coatings are very clean, hard, and dense with fine, homogeneous structures,

Very low porosity,

Very low oxide content,

Excellent powder phase conservation (no transformations and evaporation)

HVOF process is standardized in the aerospace and military industries for coatings that tend Titan Sisak HVOFto decompose at elevated process temperatures, such as tungsten carbides and chrome carbides. Palette of powder material is diverse and includes the previously mentioned carbides in metal matrix, as well as Nickel – Cobalt based alloys (Stellite, Hastelloy, Triballoy, Inconel, Rene, MCrAlY).

Uniqueness of process is the possibility of applying repair materials such as combinations of martensitic-ferritic structure with a high proportion of corrosion resisting elements (Mo, Nb, Ta).

Coatings obtained by HVOF process can be applied in areas of different forms of wear and presently the world's most applications are replacement for hard chrome. So for this reason, some materials are certified by the aviation industry (hydraulic landing gear pistons, segments of the combustion chamber engine, turbine blades, etc.), military industry (rotor hub and blades), and the electric power industry (parts of high-pressure pumps, the stuffing, the motion of the rotor, etc.)

Typical mechanical properties of HARD CHROME REPLACEMENT ALLOY - Tungsten carbide cobalt chrome (WC-Co-Cr)
Corrosion and wear resistance
1200-1350 HV0.3
< 0,3 %
Wear Rate (ASTM G65 B)
<4 mm3
Bond strength
>83 Mpa *
Service temperature
< 540 °C
Corrosion Resistance
Very good in NaCl (1M), good in HCl (1M) and NaOH (1M)
Typical applications
Landing gears, Compressor shafts, Pump seals, Piston rods, Ball, gate and dump valves


*value for adhesion-bond strength depends on the tensile strength of the glue that is used for testing, where HVOF coating exceed its maximum value in order to satisfy all the standards for individual applications. However, by using non standardized methods, adhesion strength of ~125 MPa was measured.).