Plasma sprayed Cr₃C₂–Ni–Cr coating for oxidation protection of 2·25Cr–1Mo steel

Abstract

This paper investigated the influence of Cr₃C₂–Ni–Cr coating on high temperature oxidation behaviour of 2·25Cr–1Mo steel. The coating of Cr₃C₂–NiCr was made by plasma spray coating method. The isothermal corrosion test was carried in air oxidation environment at 973 K for 72 h and the weight change of the specimen during corrosion was measured at different interval. The corrosion rate and reaction kinetics were studied and the post corroded scales were characterised in SEM, EDS and XRD. The results clearly indicated that Cr₃C₂–NiCr coated specimen significantly improved the oxidation resistance. The improvement of oxidation resistance in presence of coating could be attributed to the formation of protective Cr₂O₃ layer and changed mechanism of scale growth from outer cation migration to inner anion migration. The detail mechanism of the oxidation behaviour of Cr₃C₂–NiCr coated and uncoated specimen was discussed in this paper.

Keywords:

• Boiler
• Oxidation
• Coatings
• Steel