Enhancement of Corrosion Fatigue Strength by Spraying Pressure and Coating Composition of WC-Co Cermet Sprayed Catings
Mitsuo KIDO, Tetsuya HIRANO, Tarou TOKUDA, Yoshiko SHINHARA, Shozo NAKAMURA and Yoshio HARADA
Abstract:The authors previously reported that the corrosion fatigue strength of thermally sprayed coatings was enhanced by changing the powder composition. This effect was recognized at low stress area near endurance limit on S-N curve but not the high stress amplitude level. This study focused on the spraying pressure as well as the powder composition. The mechanical, corrosion, and corrosion fatigue fracture properties were investigated for three thermal spray materials fabricated by a spray gun with variable pressure. The corrosion fatigue strength of a specimen coated by WC/NiCrMo-A was the highest in the three type of coated specimen. It is thought that the mechanochemical response was controlled by a combination of : (1) The residual compressive stress generated by high spraying pressure for decreasing the effective stress, and (2) Enhanced corrosion resistance resulting from easy passivation of the coating components and the densification of the coating without any penetration of the solution into the base metal/coating- interface. Key Words:WC cermet sprayed coatings, HVOF method, Spraying pressure, Corrosion fatigue, Residual stress, Mechanochemical reaction, Corrosion pit, Passivation film