Unstable stacking fault energy and peierls stress for evaluating slip system competition in body-centered cubic metals

Abstract

Determining the competition between the {110}⟨111⟩, {112}⟨111⟩ and {123}⟨111⟩ slip systems in body-centered cubic (BCC) metals is important to understand their mechanical properties. In this paper, the unstable stacking fault energy (γus) and Peierls stress (σp) of the three slip systems of a series of BCC metals are calculated in order to evaluate the competition among them. We find that γus of BCC metals is proportional to (B+G)/a2/3, where B, G and a are the bulk modulus, shear modulus and lattice constant, respectively. The calculations of γuss predict that the {110}⟨111⟩ dislocation slip is prior to the {112}⟨111⟩ and {123}⟨111⟩ slips, however, γus may not be used to identify the priorities of the latter two slips because γuss of these two slip systems are too close to each other. According to σps, the mobility of dislocations decreases in the sequence of {110}⟨111⟩, {112}⟨111⟩, {123}⟨111⟩ for all the metals considered except for K. Noticeably, it is shown that γus and σp are not monotonically related to each other.

Keywords

• First-principles method
• Generalized stacking fault energy
• Semi-discrete variational peierls-nabarro model
• Critical resolved shear stress