STUDY ON HOT CORROSION RESISTANCE OF AL0,75COCRCUFENI HIGH ENTROPY ALLOY IN NA2SO4 AND V2O5 MOLTEN SALT MIXTURE WITH CYCLIC HEATING AT 1000OC

• Main Author: Kusuma Wardhana, Ricco
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/86095
• Institution: Institut Teknologi Bandung

High entropy alloys have mechanical properties and microstructure superior to conventional alloys. The composition of high entropy alloys causes changes in the mechanical properties and microstructure of the alloys, giving them the potential to be used as high temperature materials in aircraft combustion chambers. Corrosive environments can reduce the mechanical properties of alloys, so it is necessary to develop alloys that are resistant to corrosion at high temperatures. In this study, hot corrosion resistance testing of Al0,75CoCrCuFeNi high entropy alloy was conducted to study the resistance of the alloy to corrosive environment at high temperature in a cyclic manner to simulate operation in an aircraft combustion chamber. A series of experiments were conducted to study the hot corrosion resistance of Al0,75CoCrCuFeNi high entropy alloy. The experiments were initiated by melting the alloys in a DC electric arc furnace and followed by homogenisation at 1100 oC for 10 hours. Cyclic hot corrosion tests were carried out at 1000oC in a salt mixture of 50%-weight Na2SO4 and 50%-weight V2O5 with a variety of cycle times, 4 cycles, 8 cycles, and 12 cycles, with each cycle consisting of heating for 1 hour in a horizontal tube furnace and cooling for 15 minutes outside the furnace with weighing the weight change at each cycle. The samples were then characterised using XRD, optical microscopy and SEM-EDS. Based on the experiments conducted, the Al0,75CoCrCuFeNi high entropy alloy has a microstructure consisting of Fe-Co-Cr FCC phase, Cu-rich FCC phase and A2 (disordered BCC) phase and BCC depletion areas were found on the surface due to the formation of Al2O3 and AlS oxides on the substrate surface. The hot corrosion event in this study can be viewed into 3 stages kinetically. In cycles 1-3 the hot corrosion rate has parabolic kinetics with a constant parabolic value of 1.559?10-5 mg.cm-2.s-1. In cycles 3-7 the hot corrosion rate has linear kinetics with a constant linear value of -0.012 mg.cm-2.s-1. In cycles 7-12 the hot corrosion rate has linear kinetics with a constant linear value of -0.0111 mg.cm-2.s-1. The hot corrosion mechanism starts with the formation of Al2O3, Cr2O3, Fe2O3 and NiO. Then the Na2SO4 salt will mix with the V2O5 salt to produce NaVO3 which reacts with Fe2O3 to form FeVO4. When the partial gas pressure of SO3 is higher, sulfidation will occur to form NiS and CrS. When the oxygen partial gas pressure is higher, oxygen enters the alloy and oxidises the sulphide CrS to Cr2O3. The more easily oxidised element Al will reduce Cr2O3 into Cr.