Anomalous strength anisotropy of γ'-Fe_4N identified by first-principles calculations

摘要

γ' -phase Fe_4N holds great promise for applications in magnetic recording devices and its (001) plane shows the highest stiffness according to elastic constant calculations. Here we demonstrate by first-principles stress-strain calculations that, contrary to the prevailing view, γ'-Fe_4N exhibits the greatest strength and strongest wear resistance in its (011) plane. This unusual behavior stems from the nonlinear stress response at large strains which cannot be derived from elastic parameters. We analyze the underlying deformation mechanism and discuss implications of the present results on the design of hard coating materials in general.