On corrosion behaviour of HVOF sprayed Ni 3 Si intermetallic powders

Abstract

Ni₃Si intermetallic powders were deposited onto 420 stainless steel substrate using high velocity oxy-fuel (HVOF) process. In this regard, microstructure properties relationships were evaluated in fabricated coatings. X-ray diffractometery, scanning electron microscopy, microhardness testing, potentiodynamic polarisation and electrochemical impedance spectroscopy (EIS) measurements were performed to study the phase composition, microstructure and properties of the coatings. The microstructure of coatings was composed of supersaturated Ni(Si) solid solution islands embedded in an Ni₅Si₂ matrix. The results showed that this microstructure strongly affected properties of coatings. In this regard, the hardness of coatings was found to be 620 HV(50 g) due to presence of Ni₅Si₂. It was also found that the corrosion rate of HVOF Ni–Si coatings in 70H₂SO₄ medium was lower than that of stainless steel substrate. Further investigations showed that the microgalvanic corrosion between Ni(Si) and Ni₅Si₂ phases was a determinant factor in corrosion performance of HVOF Ni–Si coatings.