Relaxation time effects in the stacking fault energy of noble metal alloys

Abstract

The stacking fault energy, γ, in noble metal alloys can be expressed as a sum of two terms: δu_fe, the contribution due to the conduction electrons; and δu_c, the contribution due to thed electrons. For noble metals and alloys δu_c 〉 δu_fe while for multivalent normal metals δu_fe 〉 δu_c. The theory is first discussed in terms of recent calculations of the pseudopotential form factors of the noble metals (Moriarty) and some of the typical solutes (Shaw). The theory is then extended in a phenomenological fashion to include the effects of a finite relaxation time, τ, of the conduction electrons. It is shown that, for concentrated noble metal alloys with the electron-to-atom ratio,Z 〉 1.14 and multivalent normal metals, δuf_e and hence γ will be dependent on both temperature and deformation through their effects on τ. An increase in τ results in a decrease in the magnitude of δu_fe. In the case of concentrated noble metal alloys this results in an increase in γ with increasing t while for multivalent normal metals γ decreases with increasing τ.