Abstract: Molecular dynamics simulations of amorphous Si-C and Si-B-C systems were carried out in order to investigate the diffusion behavior, and analyze the influence of the addition of B on the thermal stability and creep resistance at high temperature of the amorphous systems. Universal force field was used to describe atomic interactions in the systems at 300K, 773K, 1273K, 1773K and
2073K. MSD curves and diffusion constants at different temperatures were calculated and compared. After the addition of B in the amorphous Si-B-C system, self-diffusion constants of constituent atoms decreased at the same temperature, and increased with temperatures in both the amorphous systems. The results show that self-diffusion of B tends to ascend apparently up to 2073K, which accounts for that phase separation of the amorphous state would take place
at about 2073K. Below this temperature, the Si-B-C system will remain the thermal stability and good creep resistance.

Key words: amorphous Si-B-C, molecular dynamics, diffusion constants