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 have been deposited by twin-wire arc spraying (TWAS) on tool grade steel. Moreover; process maps were constructed to study the blueprint of the thermal spraying method. A design of experiments (DoE) was used to study the effect of N. pressure; stand-off distance (SOD); and current on the structure and microstructure of the coating. The process map approach showed that higher SOD yields lower particle temperatures; higher currents reduce velocity and increase temperature of inflight 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 (up to 305 μm) and that an increase of N. pressure combined with a decrease of the SOD resulted in a low percentage of oxides (down to 1.7%). An optimization of parameters was then conducted to find the optimal conditions for fabricating Ni-5wt%Al coatings. 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 at the interface.