Cohesive Strength of Metal/Ceramic Interfaces Fe/$\it M$[C,N] and the Role of Misfit Dislocations and Interface Roughness

The dispersed inclusions of carbides and nitrides were shown to provide superior fracture toughness and increased strength for steels. To obtain a fundamental understanding of their effect, we investigated the theoretical cohesive strength of Fe/$\it M$[C,N] ($\it M$=Ti,V,Nb,Mo) interfaces using the first principles calculations with the full-potential linearized augmented plane wave (FLAPW) method. For the coherent $\langle 100 \rangle$\{001\}Fe//$\langle 110 \rangle$\{001\}$\it M$C interfaces, the highest theoretical strength of 3.78 J/m$^2$ was obtained for the Fe/VC interface, and it decreases from V-Ti-Nb-Mo. The strength of nitride interfaces is 10-15\% lower than for carbides. Within the Peierls-Nabarro model with {\it ab initio} generalized stacking fault energetics, we estimated that the misfit dislocations which may form due to lattice misfit decrease the interface strength by 20\%. The strength of $\langle 110 \rangle$\{110\}Fe//$\langle 010 \rangle$\{100\}TiC semicoherent interfaces that contain primary misfit dislocations was found to be 30\% lower. The effect of interface steps and roughness on strength is also investigated. We further identify the origins of strong interfacial bonding based on electronic structure and charge densities analyzes.