Atomistic simulations of solid solution strengthening of α-iron

This paper addresses the problem of solid solution strengthening of α-iron. The strengthening effect by alloying of substitutionally or interstitially dissolved atoms is obtained by simulating the interaction of a dislocation in an α-iron crystal with random as well as special arrangements of dissolved atoms. For the detection of the position of a dislocation during the simulation an algorithm is implemented which allows to analyze dislocation movements in detail. Solid solution strengthening is determined for different concentrations of Cu and Ni atoms. It is found that the movement of edge dislocations in the case of Ni atoms is nearly unhindered in contrast to when Cu atoms are present. The critical shear stress for dislocation movement is found to be significantly higher for Cu-alloyed α-iron as compared to Ni-alloyed α-iron. Interstitial C atoms in α-iron are significantly stronger obstacles for the dislocation movement than substitutional Cu atoms. The strengthening level thereby attains values similar to those found in experiments. In order to analyze the mechanisms of solid solution strengthening, a model system is used by the construction of a special interaction potential in which by the choice of the interaction parameters the lattice constants and the shear modulus of the alloyed element can be modified independently. Especially, dissolved elements can be simulated which are different from α-iron only by their lattice constants or only by their shear modulus, respectively. In this way it is found that dissolved elements with a smaller shear modulus than α-iron lead to a larger strengthening value than elements with a larger shear modulus than α-iron. Moreover, elements with a larger lattice constant than α-iron are found to be stronger obstacles than elements with a smaller lattice constant than α-iron.