Corrosion Behavior in a 3.5 wt% NaCl Solution of Amorphous Coatings Prepared through Plasma-Spray and Cold-Spray Coating Processes

摘要

Amorphous coatings prepared through plasma-spray and cold-spray coating processes were studied to understand the effects of macroscopic defects (e.g. micro-pores) on corrosion behavior. Gas-atomized powders with a nominal composition of Fe68.6C7.1Si3.3B5.5P8.7Cr2.3Al2.0Mo2.5 (at.%) were used for the coatings. Pores of various sizes and inter-particle boundaries were found in the two types of coatings, both of which exhibited relatively low corrosion currents (<10(-5) A/cm(2)) and high pitting potentials (>1.0 V). Even coatings of identical alloy composition exhibited significantly different corrosion behavior depending on the spray process used. In immersion tests in the 3.5 wt% NaCl solution, the cold spray coating exhibits much higher resistance to the formation of corrosion products than the thermal spray coating. Corrosion products start to form around micro-pores and inter-particle boundaries in which oxidation occurred during coating processes. Due to the oxidation, partial crystallization occurred in inter-particle boundaries and micr-pore surfaces in which corrosion products tend to preferentially form.