Laboratory exposures that simulated the oxidation-related attack in natural gas-fired reciprocating
engines were conducted on Ni-Cr alloys with and without aluminide coatings. Exposure of uncoated Ni-
Cr alloy specimens to humid air at 800°C resulted in a mass loss due to CrO2(OH)2 evaporation and
internal oxidation. Both model and commercial aluminide coatings reduced the amount of attack. The
reaction products and Al interdiffusion were evaluated.