Tribological Behavior And Corrosion Resistance Of HVOF-Sprayed Stellite Coatings

Despite being a well-known material, the tribological behavior and corrosion resistance of HVOF-sprayed Stellite coatings have not been investigated much in the literature.

Stellite-6 coatings were deposited onto AISI 304 substrates by a Diamond Jet 2600 HVOF torch. The densest coatings (porosity <1%) are obtained when operating with oxygen/fuel equivalence ratio λ≈0.85. As the equivalence ratio is raised, an increasingly large number of unmolten particles is embedded in the coatings.

These microstructural differences especially affect the corrosion resistance of coated systems. Only dense coatings offer good protection in an aerated 0.1 M HCl solution and display no sign of substrate corrosion after 5 test cycles (=100 h) according to ASTM B380-97.

At RT, the sliding and abrasive wear resistance of the HVOF-sprayed Stellite coatings is notably lower than that of bulk or clad equivalents, both because interlamellar delamination occurs as an additional wear mechanism in the HVOF-sprayed coating and the strain-induced “martensitic” transformation from an f.c.c. structure to an h.c.p. one is suppressed.

At higher temperatures, the sliding wear resistance of the HVOF-sprayed coatings becomes at least as good as that of bulk or clad Stellite, because interlamellar brittleness is lessened and a smooth, dense, protective, oxide-based tribo-layer is formed.