1992 Volume 41 Issue 2 Pages 101-106
The high-temperature protectiveness of Si3N4 films formed on Ni coupons by IBED process has been evaluated by oxidation tests between 1000 and 1400K in purified oxygen for up to 720ks. The oxidation kinetics follows a linear rate law during the initial periods and it then approaches a parabolic rate law. The main oxide identified was NiO. The nitride film crystallizes during the heating or initial periods of oxidation resulting in introduction of mechanical defects in the film. As a result of this, the protectiveness decreases with an increase in the temperature. The annealing of the Ni substrate has no significant influence on the protectiveness. A very thin film rich in Si remains on the outer surface of the NiO scale after 100ks oxidation at 1200 and 1300K.