Effect of Lanthanum Oxide as Thermal Barrier on the Aluminization Process of Nickel Base Superalloy (BV-18)

        This research studied, the effect of lanthanum oxide as a thermal barrier on the highly effective aluminization process of a nickel-base  superalloy was studied. The aluminization  process was carried out using the solid cementation  method at a temperature of (1000oC) in a vacuum atmosphere and for Periods of (2, 4, 6) hours after stabilizing the thermal barrier material(lanthanum oxide) on the samples. It was observed that the rate of mass gained and the rate of thickness of the resulting coating increase with time until it reaches the saturation point and takes the form of a parabolic curve. Examination with a scanning electron microscope (SEM-EDS) of the surface of a sample painted for six hours showed the presence of a high percentage of aluminum of the element lanthanum  in addition to other elements of the base alloy material, Optical microscope examination showed that the coating layers are composed of three multi-phase regions (the outer layer, the inner layer, and the Interdiffusion  zone), while X-ray analyses  showed presence of some phases with a high melting point, such as (LaNi5, Al2La, and NiAl), which reflected positively on the alloy's resistance to hot corrosion, evident through the stability in the mass of the coated samples after testing them at a temperature of (900oC) in the presence of salt vapor from a mixture of sodium sulphate and sodium chloride.