An Investigation on High-Temperature Oxidation and Hot Corrosion Resistance Behavior of Coated TLP (Transient Liquid Phase)-Bonded IN738-LC

Abstract

Despite all achievements to improve nickel-based superalloy, these classes of alloys are still prone to degradation via high-temperature oxidation and hot corrosion. Repairing damaged parts could decrease the life cycle, cost of equipment, and a transient liquid phase (TLP) bonding is a favorable method that has successfully been used for this purpose. One way to increase the lifetime of the repaired parts and the main body is to utilize protective coating. In the current study, aluminized coating was applied on IN738-LC which was first bonded by TLP process. Coating performance on the joint centerline compared to the other parts of the sample was investigated using a scanning electron microscope (SEM and FESEM) and X-ray diffraction method (XRD). The oxidation test result showed that coating provided less protection on the joint centerline due to coating’s chemical composition difference in this area: particularly Fe and Cr. XRD results showed that at the initial time of oxidation, all (α, γ, δ and θ)-Al2O3 were formed and by prolonged exposure were transformed to α-Al2O3. The hot corrosion test also proved that the joint centerline and the diffusion-affected zone were less resistant to the corrosion attack of 3Na2SO4 + NaCl salts and severity of damage in these zones were clearly distinguished from microscopic images.