Investigation of Changes in Microstructure of Remelted Air Plasma Sprayed NiCrAlY Coating after Short Thermal Exposure in Air with the Assistance of Microhardness Measurements

摘要

In present work, the NiCrAlY coatings were sprayed onto the surface of nickel-based superalloy INCONEL 713LC substrates by means of conventional air plasma spray technique. Subsequently an aluminium sheet was cladded onto the coating surface by means of uniaxial cold pressing. The samples prepared by this way were annealed at the temperatures of 650, 850 and 1000°C for two hours in argon-flow atmosphere. NiCrAlY coatings were enriched by aluminium and the coating imperfections presented in a coating were eliminated. The remelted NiCrAlY coating specimens were annealed at a temperature of 800°C for fifty hours in ambient atmosphere. The microstructural changes and phase transformations after short thermal exposure in air of the remelted NiCrAlY plasma sprayed coatings were observed. Generally, a change was observed in the phase composition of remelted coatings from phases rich in aluminium to phases less rich in aluminium owing to thermal exposure in air. The increase in the microhardness of the whole remelted coating after thermal exposure was caused by the increase in the amount of Al_3Ni_2 intermetallic phase in the remelted coating.