First-principles study of solid solution softening in Mo alloys
Abstract
Impurity additions usually decrease the dislocation mobility and result in the solid solution hardening (SSH). The opposite effect, the so called solid solution softening (SSS), exists in bcc alloys for low temperature and low impurity concentrations and its nature is still open to discussion. Based on FLMTO electronic structure calculations, we investigated the intrinsic mechanism of hardening and softening in bcc Mo alloys due to transition metal additions. The effect of impurities on the dislocation structure and mobility was analyzed within the framework of the generalized Peierls-Nabarro model for non-planar cores with first-principles stacking fault energetics. All impurities with extra electron concentrations (Pt, Ir, Os and Re) lead to the reduction of the stacking fault energies compared with unalloyed Mo that result in the lowering of the energy barrier for double kink nucleation. This finding explains the experimental tendencies in softening rates at low temperatures and impurity content. Our calculations reveal the electronic reasons for the SSS in Mo alloys; in agreement with experiment, the effect of impurities depends on atomic number (electron concentration) and no correlation exists with the size and modulus mismatch.
- Publication:
-
APS March Meeting Abstracts
- Pub Date:
- March 2004
- Bibcode:
- 2004APS..MARS27004M