Effect of Oxidation and Hot Corrosion on Stress Corrosion Cracking Susceptibility of Inconel 738 Alloy

Increasing the operating temperature of industrial machinery requires compatible materials to the higher temperature, which will maintain their strength with desired properties. The marine, petrochemical, and aerospace industries involve contact of base alloys of industrial machinery and appliances with the environment consisting of oxygen and salts such as NaCl, Na2SO4, and V2O5. Thus, the substrate, i.e., superalloy, is coated with thermal barrier coatings (TBC) to protect the material from oxidation and hot corrosion. But due to wear-tear, intricate shapes, and designs, some parts of the substrate may be exposed to the environment. When the oxygen and salts react with the base alloy at high temperatures, it forms oxide products and corrosive salts. This may adversely affect the working of the industrial component. Thus, in the present study, Inconel 738 alloy specimens were coated with the salts NaCl, Na2SO4, and V2O5 in different combinations of proportions. The coated and not coated specimens were kept in the furnace for 500 h with a constant temperature maintained at 900°C. After this process, the specimens were tested on a slow strain rate testing machine (SSRT) for a low strain rate of 10–6 s–1. Scanning electron microscopy (SEM) was used to observe the fractured specimens to study the morphology of the fractured area. The elemental analysis was done by using electron dispersive spectroscopy (EDS). The X-ray diffraction (XRD) technique was used for analyzing the scale formed on the surface.