Hot corrosion behaviour of Hastelloy X and Inconel 625 in an aggressive environment for superalloys for high-temperature energy applications

Hastelloy X and Inconel 625 are the nickel-based super alloys with outstanding resistance to high temperatures and oxidation. Hastelloy X is noted primarily for resistance to heat and oxidation, it also has good resistance to chloride stress–corrosion cracking and good resistance to carburization, excellent resistance to atmospheric reduction or carburization. Similarly, Inconel 625 is having the material properties as pitting and crevice corrosion resistance, high corrosion–fatigue strength, high tensile strength and resistance to chloride-ion stress–corrosion cracking. Sodium sulphate molten salt has high melting and boiling point as 800 °C and 1429 °C, respectively is studied with Hastelloy X. A eutectic mixture of 7:3, Sodium and potassium chloride having the melting and boiling point as 770 °C and 1420 °C is used with Inconel 625 in this study. Both the salts have been used in Concentrated Solar Power (CSP) technology as thermal energy storage applications. In this work, Hastelloy X stored with sodium sulphate and Inconel 625 stored with sodium and pottasium chloride molten salts are heated with an aggressive temperature environment approximately 900°. The experimental work was performed for 25 h of time period and the hot corrosion behaviour of Hastelloy X, Inconel 625 heated to very high temperature environment was studied. The mechanical tests, such as tensile and hardness tests were performed for both the super alloy specimens and the results were compared. Metallurgical characterization of the base substrates has been investigated with porosity images, X-ray diffraction results and scanning electron microscope images.