Atomic Mechanism of Carbon Diffusion in Cementite

Abstract

Molecular dynamics is employed to investigate carbon diffusion in cementite. An approximation that carbon atoms can interact with each other only indirectly (via neighbouring iron atoms) is used. The interstitial mechanism of carbon diffusion in cementite is elucidated. The formation energy of defects (a carbon atom on an interstitial position and a vacant site on a regular carbon position) as well as the migration energy of carbon atoms are estimated in the temperature range 1273-1373 K.

Theoretical Studies of Diffusion Kinetics in Austenite

“…The final results of the corrected exchange frequencies are similar to those calculated in[1]:corr 11…”

“…w 31 = w 41 and w 13 = w 14 (1) proved for the usual interstitial model) we were able to make the necessary adjustments for these three exchange frequencies. For T = 1273K the set of the calculated exchange frequencies are (expressed in term of w 0 ) [1]:…”

“…The experimental data at 1273 K are exp D ε ≈ 8.44 [1] and for the exp α ε we accept the upper bound as exp (1) α ε ≈ 7.69 given in [6], and the lower bound exp (2) α ε ≈ 5.68 [7]. In [1], in order to adjust w 11 , w 21 and w 31 (and to be able to use experimental tracer diffusion data) we used tracer correlation factors that were calculated by Monte Carlo simulation. But for the split energy level at the second nn configuration conventional Monte Carlo simulation is not appropriate.…”

“…In [1] results of an extensive molecular dynamics studies were presented using Fe-Fe and Fe-C potentials. At the nn position the very weak C-C potential is represented only by self-blocking between C atoms, this affects only w 21 , w 11 and w 31 .…”

Stability and Shrinkage by Diffusion in Hollow Nanotubes

“…The driving force for this flux is the difference between the vacancy concentrations V c on the inner and external surfaces. In [7] using Gibbs-Thomson boundary conditions an exact solution was obtained of the kinetic equation of shrinking via the vacancy mechanism of a hollow mono-atomic nanosphere in quasi steady-state at the linear approximation. The collapse time as a function of the geometrical sizes of hollow nanospheres was determined.…”