In this study, the erosion-corrosion experiment of Ni based alloys in high-temperature and high-pressure supercritical water environment was performed. SiO 2 and Al 2 O 3 particles with the average diameter of 30 µm and 50 µm were used as erodent. The special designed specimens were fixed on a blade impeller , and the erosion tests were performed in a high pressure autoclave with a magnetic stirrer system. Results show that the basic corrosion mechanism is not changed by the erosion process. A Cr-rich inner oxide layer and a Fe/Ni rich outer oxide layer were formed on the alloy surface. However, the oxidation rates of the alloys were affected by the erosion process. Parts of the outer Fe and Ni oxides were removed by the erodent particles during the tests. The inner Cr oxide layer still exists owing to the self-healing ability of the Cr 2 O 3 layer, acting as a barrier to resist further corrosion of the alloys. The factors that affect the degree of erosion and the erosion-corrosion mechanism in SCW environment is analyzed.
In this study, a Cr coating was fabricated on Ni-based alloys to prevent under-deposit corrosion. The effect of salt deposition on the structural integrity of the Cr coating in SCW environment with/without oxygen was investigated. Results show that the Cr coating kept its integrity after exposure in SCW environment, successfully avoided the metallic ions leaching from Ni-based alloys. The structure of the oxide layer after exposure is a thin Fe 2 O 3 or FeCr 2 O 4 layer and a Cr 2 O 3 layer. The oxidation rate of the Cr coating decreased to one third of the sample after exposure in the same environment without salt deposit layer, indicating that the inward mass-transfer of oxygen to the alloy surface was inhibited by the salt deposit layer. The volume expansion of the sample due to the growth of Cr oxide layer was restrained by the salt deposit layer, forming a growth stress in the coating.
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