Steam Oxidation Resistance of Ni-Cr Thermal Spray Coatings on 9Cr-1Mo Steel. Part 1: 80Ni-20Cr

The steam oxidation resistance of 80%Ni-20%Cr metallic coatings has been evaluated at four different steam temperatures in the range of 600-750°C. Substrate used for the study was 9Cr-1 Mo type steel. The thermal spray coatings were carried out using two different processes, viz., atmospheric plasma spray (APS) and high velocity oxy fuel (HVOF) spray. Thickness of the coatings was about 40 and 60μm respectively. The results show that the thick and dense HVOF coating showed a better steam oxidation resistance than the thin porous APS coatings. At prolonged aging (1 000 h) the HVOF coating showed the best protection till the temperature range of 650°C. Beyond this temperature the presence of Fe 2 O 3 was noticed at the coating surface. The reason for the protectiveness and failure at higher temperatures (above 650°C) are discussed in detail.