STUDY ON HOT CORROSION RESISTANCE OF HIGH ENTROPY ALLOY AL0,75COCRCUFENI IN NA2SO4-V2O5 MOLTEN SALT UNDER ISOTHERMAL CONDITION AT 1000 OC

• Main Author: Abdillah Parawangsa, Danu
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/85488
• Institution: Institut Teknologi Bandung

High entropy alloys contain at least five principal elements, each with an atomic percentage between 5-35%. The combination of elements in these high entropy alloys has many beneficial properties, making them potential alternative materials for high-temperature operation components, such as rocket nozzles. Rocket nozzles, designed to optimize the expansion of combustion exhaust gases to achieve supersonic speeds, require materials that can withstand extreme temperatures and pressures. Combustion exhaust gases containing sulfate and vanadium salts can also induce hot corrosion in component materials. This research aims to test the hot corrosion resistance of the Al0.75CoCrCuFeNi alloy, which can potentially be an alternative material for high-temperature operation components. A series of experiments were conducted to study the microstructure evolution and hot corrosion behaviour of the Al0.75CoCrCuFeNi alloy. The experiments began with the melting of alloying elements in a single DC arc furnace, followed by homogenization of the as-cast alloy in a horizontal tube furnace at 1100°C for 10 hours. The homogenized alloy was then cut and subjected to hot corrosion testing by coating the sample surface with a Na2SO4-V2O5 salt mixture at 1000°C for 9, 16, 25, and 50 hours using a horizontal tube furnace. The alloy samples that underwent hot corrosion testing were characterized using optical microscopy, Xray diffraction (XRD), dan scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS). The as-cast, as-homogenized, and as-corroded Al0.75CoCrCuFeNi alloy exhibits a microstructure consisting of FCC dendrites rich in Fe-Co-Cr, FCC interdendrites rich in Cu, and interdendrites rich in Ni-Al. During hot corrosion testing, the BCC phase becomes the most dominant area for pitting corrosion penetration. The hot corrosion kinetics of this alloy follow a parabolic oxidation law with an oxidation rate constant of 0.02025 mg².cm??.s?¹. The weight change of the samples increases rapidly up to 16 hours of testing and tends to slow down after 16 hours. The hot corrosion of the Al0.75CoCrCuFeNi alloy begins with the formation of Fe-Cr-Co-Ni spinel oxides and Al?O?. In the initial stage of corrosion, acidic salt melts dissolve the spinel oxides and Al?O? into metal cations and form Al?S?, Cu?S, and CrS sulfides at the oxide-substrate interface. The formation of vanadates in the early stage also accelerates the corrosion process. Subsequently, basic salt melts dissolve the spinel oxides and Al?O? into metal anions. In the final stage, complexes of Al?O?, Al?S?, and CrS form in the pitting areas.