Dissolution and diffusion properties of carbon in tungsten

Area of Science:

• Materials Science
• Computational Materials Science
• Physical Chemistry

Background:

• Tungsten (W) is a critical material in various high-temperature applications.
• Understanding the behavior of interstitial impurities like carbon (C) is crucial for optimizing W properties.
• Previous studies have explored C in W, but detailed atomic-level insights into solution and diffusion are needed.

Purpose of the Study:

• To investigate the structural and energetic preferences of carbon atoms in tungsten.
• To determine the diffusion mechanisms and kinetics of carbon and vacancies in tungsten.
• To elucidate the interaction between carbon atoms in tungsten.

Main Methods:

• First-principles calculations were employed to model the system.
• Calculations focused on determining solution energies, binding energies, and diffusion coefficients.
• The study analyzed the preferred interstitial sites for single and double carbon atoms.

Main Results:

• Single carbon atoms are energetically favorable at octahedral interstitial sites (OIS) in W with a solution energy of 0.78 eV.
• Double carbon atoms form pairs at neighboring OISs along the (210) direction with a binding energy of +0.50 eV, indicating an attractive interaction.
• Carbon diffusion coefficient is 1.32 × 10⁻¹⁹ m²/s and vacancy diffusion coefficient is 3.11 × 10⁻²³ m²/s at 600 K.

Conclusions:

• Carbon atoms exhibit a strong tendency to occupy OIS in tungsten.
• The attractive interaction between carbon atoms may lead to localized high concentrations and carbide formation.
• The determined diffusion coefficients provide essential kinetic data for understanding carbon transport in tungsten.