Effect of heat treatment on the corrosion resistance of Ni-based and Cu-based amorphous alloy coatings

Ni57Ti18Zr20Si2Sn3 and Cu54Ni6Zr22Ti18 amorphous feedstock fabricated by gas atomization were deposited on mild steel substrate by the kinetic spray technique. These as-sprayed coating samples were annealed at each suitable temperature to form three different matrix structures: amorphous, partially crystallized on amorphous and fully crystallized. Each structure was confirmed by XRD, TEM and DSC analyses. In the results of electrochemical tests conducted in a simulated acid rain solution, the amorphous structured coatings exhibit a superior corrosion resistance to the crystallized coatings with high polarization resistance, and the corrosion resistance decreased with increasing fraction of crystallization. As a function of time, the amorphous structure coatings maintained high protective efficiency and low porosity for 9 days immersion. The Ni-based alloy coatings showed better corrosion resistance than the Cu-based ones for each type of structure.