Characterisation of Oxide Scales for Plasma Sprayed Ni-20Cr Coatings Oxidized at 900 deg C under Cyclic Conditions

摘要

Ni-20Cr powder was deposited on two superalloys; one being Ni-based Superni 718, whereas the other Fe-based Superfer 800H by a shrouded plasma spray process to enhance their high temperature oxidation resistance. Cyclic oxidation studies were conducted on the coated superalloys in air at 900 deg C for 50 cycles. Each cycle consisted of one hour heating in the Silicon Carbide tube furnace followed by 20 minutes of cooling in air. Thermogravimetric technique was used to approximate the kinetics of oxidation. All the coated superalloys nearly followed parabolic rate law. X-Ray Diffraction, SEM/EDAX and EPMA techniques were used to characterize the oxide scales formed on the exposed specimens. The coatings as well as the oxide scales formed on the exposed specimens were found to be intact with the substrate superalloys. The oxide scales were found to have phases like NiO, Cr_2O_3, and which may impart oxidation resistance at high temperatures.