Extreme elastic anisotropy of cementite, Fe3C: First-principles calculations and experimental evidence

First-principles results for the full set of elastic constants (stiffnesses) cij of cementite, Fe3C, revealed an extreme elastic anisotropy with a very small c44 amounting to only about 1/10 of c55 and c66. Synchrotron X-ray diffraction stress measurements were performed on Fe3C layers grown on α-Fe exhibiting a planar state of compressive residual stress. These data exhibit a characteristic hkl-dependence of the stress-induced reflection shifts, and provide experimental proof for the extreme elastic anisotropy of Fe3C.