EXPLORING THE IMPACT OF COMPOSITION ON THE MICROSTRUCTURE, HARDNESS, AND STACKING FAULT ENERGY OF FENIALCRCO HIGH-ENTROPY ALLOYS

• Main Author: Teja Sukma, Fauzi
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/87977
• Institution: Institut Teknologi Bandung

Traditional alloy design is limited to mixing a few main elements, but technological advancements demand the development of alloys with high strength and ductility, particularly for high-temperature applications like aircraft engines. High-entropy alloys (HEAs) have emerged as a solution, combining multiple elements in equal proportions to produce superior properties such as high strength, high-temperature resistance, and corrosion resistance. HEAs outperform traditional alloys due to effects like slow diffusion and lattice distortion. This study aims to develop FeNiAlCrCo and Fe35NiAlCrCo alloys with low Stacking Fault Energy (SFE) and evaluate their microstructure, phases, and hardness through experimental characterization and molecular dynamic simulations. The study was carried out in three stages: alloy synthesis, characterization, and hardness testing. Pure metals Fe, Ni, Al, Cr, and Co were weighed according to the specified composition, melted in an electric arc furnace using copper molds to form the alloy in the shape of buttons, and then homogenized to ensure compositional uniformity. In the second stage, the buttons were cut into coupons and characterized using XRD, OM, and SEM-EDS to examine the microstructure. The final stage involved hardness testing to analyze the mechanical properties of the resulting alloys. The FeNiAlCr alloy exhibited a BCC phase with an A2 crystal structure rich in Fe- Cr and a B2 structure rich in Al-Ni, with a lattice parameter of 2.8814 ?. The addition of Co reduced the Al composition and promoted the transformation to the FCC phase, with 31.78% FCC phase and 68.22% BCC phase. The addition of Fe to the Fe35NiAlCrCo alloy resulted in the formation of a more stable FCC phase due to an increase in the valence electron concentration (VEC), with an FCC area fraction of 48.75% and BCC area fraction of 51.25%. The morphology of the FeNiAlCr alloy showed a lamellar structure near the grain boundaries and rodshaped structures clustered in the center, while the addition of Co changed the microstructure to equiaxed with FCC layers at the grain boundaries and plate- or rod-shaped structures within the grains. The hardness values for the FeNiAlCr, FeNiAlCrCo, and Fe35NiAlCrCo alloys were 495 HV, 501 HV, and 392 HV, respectively, with FeNiAlCrCo exhibiting the highest hardness due to its high BCC concentration. The Stacking Fault Energy (SFE) value for FeNiAlCrCo was approximately 2 mJ/m2 lower than that of Fe35NiAlCr, with the primary deformation mechanism being twinning, which enhances the strength, toughness, and formability of the alloy.