INFLUENCE OF ALLOYING ELEMENT ON THE STACKING FAULT ENERGY OF COCRMO ALLOY BY COMPUTATIONAL THERMODYNAMIC AND FIRST PRINCIPLES CALCULATION

• Main Author: Surya Nanda, Fahrizal
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/56620
• Institution: Institut Teknologi Bandung

Industrial development and research on medical devices is one of the national priority programs to overcome dependence on imported medical devices. One of the metal alloys that has the potential to be developed as a medical device is CoCrMo alloy. To produce microtubes for high-quality stent applications, the cobalt-based alloy must have good formability. For this reason, it is necessary to select the alloying elements to produce a good combination of mechanical properties, corrosion resistance, and biocompatibility of CoCrMo alloys. Conventional alloy designs by trial and error have limitations in terms of time and cost. By performing computational methods, various alloying elements can be modeled easily so that the desired mechanical properties are obtained with much lower time and cost. In this study, the design of the CoCrMo alloy was modeled by calculating the value of Stacking Fault Energy (SFE) with the addition of alloying elements in the form of Cu, Fe, and Ni with computational methods of thermodynamic calculations and first principle. A series of simulations for calculating SFE of CoCrMo alloys have been carried out to study the effect of alloying element concentration and temperature on the SFE value of CoCrMo alloys. Each simulation process was carried out at an alloying element concentration of 4.5; 9; and 13.5 at.%. In the thermodynamic calculation, the SFE value of CoCrMo alloy is calculated in the temperature range of 0-1500 °C. In the first principle method, calculations are also carried out to determine the equilibrium lattice parameters of the CoCrMo alloy. The effect of alloying element concentration and supercell structure on the electronic structure of the CoCrMo alloy was studied at a temperature of 0 K using the first principle method. The SFE value of the CoCrMo alloy increases with the increase in temperature and concentration of Cu, Fe, and Ni alloying elements. The simulated CoCrMo alloy equilibrium lattice parameters are close to the reference CoCrMo alloy lattice parameters (3.548 Å). The alloying element Cu provides the highest increase in the SFE value of CoCrMo alloys both from thermodynamic and first principle calculations, with the highest values of -3.1 mJ/m2 (first principle) and -37.8 mJ/m2 (thermodynamic calculations) at a concentration of 13,5 at.%. The addition of alloying elements and the supercell structure of the CoCrMo alloy affect the SFE value and the electronic structure of the CoCrMo alloy. The supercell structure that has the lowest minimum total energy has a lower SFE value as well. Increasing the concentration of Fe and Ni alloying elements will increase the charge depletion area, while the addition of Cu alloying elements will increase the charge accumulation area. The combination of Cu and Fe alloying elements will increase the SFE value of the CoCrMo alloy higher than if only adding Fe and Cu elements with the same respective compositions.