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topic 29745

Welded Stellite vs HVOF Tungsten Carbide CoCr powder



2004

What is the best HVOF powder (Stellite or Carbides) to coat Petrochemical Industry plug valves? Currently it is coated with a 2mm thickness TIG Welded Stellite coat.

Antonio B. Bravo Jr.
Coating Services - São Paulo, SP, Brazil


2004

I think the comparison is not simple. HVOF was developed for Tungsten and other metallic carbides, not for pure alloys. The objective, to avoid the very high temperature of plasma that alters the chemical stability of carbides and benefit from the impact obtained by supersonic velocity together with high hardness and density of carbides. They are composites with superior abrasion resistance but the adhesion is limited. They have around 1% porosity. On the other hand, Stellite (a homogeneous Co alloy) does not work at its best when HVOF sprayed so is most frequently applied by the spray and fuse process which produces a weld-like bond that HVOF equipments cannot match. This fusion also gives a pore free structure that is more resistant to corrosion. Its hardness is lower but continuous. G. Marrufo

Guillermo Marrufo
Monterrey, NL, Mexico

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