Evaluation of the synergistic erosion-corrosion behaviour of HVOF thermal spray coatings

• WC-CoCr, Cr3C2-NiCr or Al2O3 coatings were deposited on S355 steel via HVOF.
• Coated specimens were exposed to high velocity slurry erosion-corrosion testing.
• The contributing factors of erosion, corrosion and synergy were calculated.
• Cr3C2-NiCr and Al2O3 specimens experienced enhanced mass loss over uncoated S355.
• WC-Co samples yielded a 61% reduction in mass loss with a 56% drop in scar depth.

The present study examines three High Velocity Oxy Fuel deposited coatings, Tungsten Carbide, Chromium Carbide and Aluminium Oxide, under slurry erosion-corrosion conditions. Coatings produced in this manner typically exhibit superior density and hardness over alternative thermal spray technologies, therefore are suitable for use in corrosive and highly erosive environments. The scope of the study concentrates on isolation of the contributing factors of erosion, corrosion and synergy through applied electrochemistry, as well as metallographic analysis to evaluate the mechanisms causing coating degradation. The aim of which is to provide comprehensive data on the performance of the mentioned coatings under erosion-corrosion in conditions representing a flowing environment. Results demonstrate the breakdown of Chromium Carbide and Aluminium Oxide coatings result in enhanced mass loss over the uncoated S355 steel. Despite this, results have shown Tungsten Carbide with a Cobalt binder to be an effective protective coating, resulting in a significant reduction in total material loss over uncoated S355 steel.