Ni-5wt% Al coatings deposited by twin wire arc spraying for molten aluminum attack protection.

Nickel Aluminum alloys are widely used materials as engineering components in harsh environments due to their resistance to corrosion, high melting temperature and excellent thermal conductivity. In this work, Ni-5wt%Al coatings were deposited by twin-wire arc spraying on tool grade steel. Moreover, process maps were constructed to study the thermal spraying method. A design of experiments was used to study the effect of N₂ pressure, stand-off distance (SOD), and current on the structure of the coating. The process map approach showed that higher SOD yields lower particle temperatures, higher currents reduce velocity, and increase temperature of in-flight particles and that a higher N₂ pressure increases particle velocity without further increase in temperature. Results also showed that an increase in current and SOD leads to maximum coating thickness and that an increase of N₂ pressure combined with a decrease of the SOD resulted in a low percentage of oxides. Optimal conditions for fabricating Ni-5wt%Al coatings were then determined. Optimized coatings underwent molten aluminum attack during several hours to define the rate of aluminum infiltration. Results showed no physical nor chemical interaction in between metallic coatings and molten aluminum, whereas uncoated tool grade substrates experienced oxidation, aluminum infiltration and formation of intermetallics.