Elastic properties of eta carbide (η-Fe_2C) from ab initio calculations: application to cryogenically treated gear steel

摘要

The elastic properties of η-Fe_2C (eta carbide) have been determined from ab initio density functional theory calculations using the generalized gradient approximation. The isotropic polycrystalline elastic modulus of η-Fe_2C has been calculated as the average of anisotropic single-crystal elastic constants determined from the ab initio simulations. The calculated polycrystalline elastic modulus was used to compute the elastic modulus of a case carburised gear steel subjected to shallow cryogenic treatment (SCT) and deep cryogenic treatment (DCT). This value was then compared with experimental values obtained from nanoindentation. The results confirmed that the changes in elastic modulus observed in the DCT steel can be attributed to the precipitation of η-Fe_2C. No changes in hardness have been observed between the SCT steel and the DCT steel. These data were then used to assess the surface contact fatigue behaviour of the SCT and DCT steels tested under elastohydrodynamic lubrication conditions.