Effect of Isothermal Treatment on Ni3Al Coatings Deposited by Air Plasma Spraying System

Ni₃Al coatings were obtained on AISI 321 steel samples by air plasma spraying system. The behavior of heat treatment on intermetallic coatings were evaluated after exposure at various temperatures i.e. 500ºC to 800ºC. The stay time in this regard was varied from 10 to 100 hours. The coatings were then characterized by X-Ray diffraction analysis, optical and scanning electron microscopy, eddy current measurements and stress analysis. It was observed that the formation of NiO increases drastically with time and temperature. The hardness of the coating increases with the formation of NiO. It was noted that the residual stresses can be correlated with the formation of NiO. Further, the development of residual stresses can be monitored by a non-destructive technique i.e. eddy current method.