First-principles calculations of elastic constants for epsilon-carbide and the consequences

Abstract

The elastic constants of ϵ-carbide at 0 K and zero pressure have been calculated using first-principle methods. The iron to carbon ratio for the carbide is not established and may, in fact, vary between 3 and 2. As a consequence, the calculations have been conducted as a function of the chemical composition using the special quasi-random structures method. In all cases, the elastic constants obtained are consistent with ϵ-carbide being mechanically stable. The analysis indicates that in comparison with cementite, ϵ-carbide should be more brittle; that when present as a precipitate in steel, it would be less effective in participating in the overall plastic deformation, and that its coherency strain field in the surrounding matrix should be less extensive than cementite.