Mechanical Properties and Deformation Mechanisms of High-Entropy Alloys by Molecular Dynamic Simulation

• Main Authors: Mei-Yi Chen, 陳媺易
• Other Authors: 陳俊杉
• Format: Others
• Language: zh-TW
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/fu45ku

碩士 === 國立臺灣大學 === 土木工程學研究所 === 106 === High-entropy alloys were defined by Yeh in 1995. Due to their excellent mechanical properties, high-entropy alloys have gained much attention from academia and industry. However, deformation mechanisms of high-entropy alloys have not been thoroughly clarified. Therefore, the objective of this thesis is to investigate the effect of individual element composition and microstructure on mechanical properties and deformation mechanisms using molecular dynamics simulation. In this study, we established atomistic models using molecular dynamics simulation. The material of high-entropy alloys, composed of cobalt, chromium, iron, manganese, and nickel, is known as Cantor Alloy. We adjusted the proportion of cobalt, chromium, iron, manganese, and nickel in the Cantor Alloy system by 0% to 30% and randomized the atoms evenly with the Monte Carlo method. We used the modified embedded atom method (MEAM) potential energy function for molecular dynamics simulation and simulated high-entropy alloys under uniaxial tensile loading. We clarified the important factors, such as individual element composition and microstructure, and analyzed how these important factors affect the mechanical properties and deformation mechanisms of the Cantor Alloy system. We also found the optimum element composition of Cantor Alloy system for mechanical properties and deformation mechanisms. In this study, we found that change of the proportion of cobalt, nickel, and chromium from 0% to 30%, the strength and Young’s Modulus increase with the proportion and change of the proportion of manganese and iron from 0% to 30%, the strength and Young’s Modulus decrease with the proportion. We analyzed the stress distribution of individual elements and we considered that strength and Young’s Modulus of the Cantor Alloy system are related to the strength and Young’s Modulus of the metal elements. In this study, we mainly analyzed three deformation mechanisms, such as slip-induced plasticity (SLIP), twinning-induced plasticity (TWIP), and transformation-induced plasticity (TRIP). We investigated the relationship between three deformation mechanisms and elongation. The simulation results show that most of dislocations, stacking faults (SF), and twin boundaries (TB) occur on the (111) surface of the face centered cubic crystal structure. Simulation results show that more dislocations and SFs enhance the ductility. In addition, we changed the proportion of manganese by 30% and the deformation mechanism is TRIP. We changed the proportion of nickel from 0% to 20%. As the proportion of nickel decreases, the stability of the hexagonal closest packing of the microstructure increases, and the hexagonal closest packing occurs more. The trend of simulations is consistent with the trend of experimental measurements. We also found that equimolar composition is not the optimum composition of Cantor Alloy system for mechanical properties and deformation mechanisms. In this study, we found that change of the proportion of manganese and iron from 0% to 30%, the ductility increases with the proportion. Ductility is related to the deformation mechanisms. Elongation produced by SLIP + TWIP + TRIP deformation mechanism is greater than 50%, which is the best elongation. We analyzed and classified the elongations of SLIP + TWIP + TRIP, SLIP + TRIP, and SLIP + TWIP deformation mechanisms. We found that elongations produced by SLIP + TWIP + TRIP deformation mechanism are greater than those produced by SLIP + TRIP deformation mechanism. Elongations produced by SLIP + TRIP deformation mechanism are greater than those produced by SLIP + TWIP deformation mechanism.