High-Temperature Oxidation Behavior of Sputtered IN 738 Nanocrystalline Coating

A sputtered nanocrystalline coating of IN 738 alloy was obtained by means of magnetron sputtering. The isothermal oxidation behavior at 800, 900, and 1000°C and the cyclic oxidation behavior at 950°C of the coating were studied in comparison with IN 738 cast alloy. The results indicated that a double external oxide scale was formed on the nanocrystalline coating at 900, 950, and 1000°C without internal oxide and nitride. The scale consisted in an outer mixture of Cr2O3, TiO2, and NiCr2O4 and an inner, continuous Al2O3 layer, which offered good adhesive and protectiveness. However, at 800°C a continuous Al2O3 scale could not be formed during oxidation of nanocrystalline coating and aluminum was still oxidized internally.