STUDY OF MICROSTRUCTURE STABILITY IN AL0.75COCRCUFENI HIGH ENTROPY ALLOY WITH ISOTHERMAL OXIDATION AT TEMPERATURES OF 900?, 1000?, AND 1100?

• Main Author: Ade Syabihis, Ahmad
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/78382
• Institution: Institut Teknologi Bandung

The AlxCoCrCuFeNi alloy is a type of high-entropy alloy (HEA) that is designed for high- temperature applications due to its excellent mechanical properties, high melting point, and remarkable high-temperature resistance. The elements used in this alloy are more cost-effective compared to refractory elements, making it costeffective. The development of this alloy continues by varying the compositions of its elements. In this experiment, the variation was made by partially replacing some aluminum in the equiatomic AlCoCrCuFeNi alloy with other elements, resulting in Al0.75CoCrCuFeNi. The alloy underwent homogenization first and then underwent isothermal oxidation at three different temperature levels: 900°C, 1000°C, and 1100°C. A series of isothermal oxidation experiments were conducted to investigate the stability of the microstructure and oxidation behavior in the Al0.75CoCrCuFeNi alloy. The experiments began by melting the alloy elements using a single DC electric arc furnace and then homogenizing them at 1100°C for 10 hours in an argon environment. After this stage, the metal material was cut into coupon samples, which were then subjected to isothermal oxidation testing at temperatures of 900°C, 1000°C, and 1100°C, with variations in holding times of 2 hours, 16 hours, 40 hours, and 168 hours. The oxidized alloy was characterized using XRD, SEM-EDS, optical microscopy, and a micro vickers hardness tester. Based on the conducted experiments, the as-homogenized Al0.75CoCrCuFeNi alloy had two constituent phases: an FCC phase in the dendritic region and a Cu-rich FCC phase in the interdendritic region, along with a solid solution rich in AlNi. The hardness values of the Al0.75CoCrCuFeNi alloy decreased from 900°C to 1100°C. During the oxidation process, various oxides formed, including Al2O3, Cr2O3, Fe3O4, CoO, CuO, NiO, and spinel oxide ((Al,Cr,Ni)(Al,Fe,Ni)2O4), each with different formation mechanisms at each temperature. The oxidation kinetics of the Al0.75CoCrCuFeNi alloy at 900°C, 1000°C and 1100 followed a parabolic rule, indicating that oxide growth was controlled by diffusion mechanisms. The activation energy result for the oxidation of this alloy was determined to be 57.119 kJ/mol.