Microstructure and properties of Ta-reinforced cobalt based composite coatings processed by direct laser deposition

Abstract

Circulating water pump is an important component in coastal nuclear power plant, and is prone to suffering erosion and corrosion from the sea water. In the present study, Ta-reinforced cobalt-based composite coatings were prepared on the surface of a martensitic stainless steel by direct laser deposition technology. The effect of Ta on the phase composition, microstructure, micro-hardness, residual stress, corrosion resistance and erosion performance of the cobalt-based composite coatings was systematically investigated. The results indicated that the addition of Ta can lead to the formation of dispersed TaC ceramic particles in the coatings. In the meantime, TaC particles with flaky shape greatly changed the morphology of reticular eutectic carbides and residual stress distribution in the coatings. The potentiodynamic polarization testing and electrochemical impedance spectroscopy (EIS) measurements showed that the addition of Ta had no prominent influence on the corrosion resistance of cobalt-based coatings. Generally speaking, the coating with 30 wt% Ta addition exhibited the best comprehensive performance considering micro-hardness measurement, residual stress value, potentiodynamic polarization testing, and slurry erosion testing under two erosion angles. In situ synthesized TaC phases could effectively alleviate the impact of solid particles in the erosion process, and improve the erosion resistance of the cobalt-based composite coating.