EFFECT OF VACANCIES AND VOID DEFECTS ON THE STRUCTURAL AND MECHANICAL BEHAVIOR OF TUNGSTEN UNDER HARSH TEMPERATURE AND PRESSURE CONDITIONS

Abstract

The body-centered cubic transition metal tungsten is frequently used as a pressure calibration material at high temperatures and pressures due to its outstanding mechanical and thermal properties. In this study, molecular dynamics simulations were performed to investigate the behavior of tungsten under harsh temperature and pressure conditions and the impact of fundamental defects, particularly vacancies, and voids, on its physical, structural, and mechanical properties through their correlation with elastic constants. The study also covers mechanical stability, elastic properties, brittleness and ductility, and hardness. The simulations utilized two different embedded atom methods and one modified embedded atom method interatomic potentials. The results show that the fundamental structural characteristics and properties of pure tungsten crystal, including lattice constant, density, cohesive and vacancy formation energies, elastic constants, and moduli in the ground state for all three potentials, are in good agreement with previous experimental and theoretical calculations and results. The calculated results demonstrate that the elastic constants-related properties for defective structures also have the same trend as the perfect crystal. The presence of defects in the crystal causes a decrease in properties at all temperatures and pressures, directly correlated to the fraction of crystal defects. As the percentage of vacancies increases, a further reduction in the elastic constants is observed. Likewise, these findings reveal that the presence of scattered vacancies in the crystal structure causes a more significant decrease in the substance's properties than a void in the center of the crystal (with the same percentage). The presence of any vacancy weakens the interatomic bonds of the atoms around the vacancy, while the existence of a void in the center has less effect on the interatomic bonds of atoms further away from the center of the crystal.