Study on micro-mechanism of carbon atom diffusion in surface nanocrystallization low carbon alloy steel using molecular dynamics simulation

Abstract

Molecular dynamics (MD) simulation was successfully used to explore the mechanism of carbon atom diffusion in supersonic fine particle bombardment (SFPB) pretreated low carbon alloy steel during vacuum carburization. Results of experiment and simulation demonstrated that the plastic deformation was occurred and high surface energy achieved on the surface of low carbon alloy steel during the process of SFPB. The defects were formed inside the crystal including vacancies, 1/2 <111>, <100> and <110> types of dislocations, and the number of defects gradually increased with the increase of bombardment time and speed. Compared with defect-free materials, the large number of defects increase the diffusion coefficient by several orders of magnitudes. The internal defects of the material, including vacancies, dislocations and grain boundaries induce the rise of carbon atom diffusion coefficient, accordingly. While the effect of dislocation types was not obvious to diffusion coefficient. The carburizing temperature has a significant effect on the carbon atom diffusion rate of SFPB pretreated samples, when comparing with that of non-pretreated ones.