A. Tehranchi

T. Hickel, J. Neugebauer

Max-Planck-Institut für Eisenforschung GmbH, D-40237 Düsseldorf, Germany

Metastable defect phase diagrams theory and applications; planar defects in Mg based alloys

Thus far, the phase diagrams (PDs) were the roadmap for alloy design.  Here we augment this powerful tool by including the concept of metastability of phases due to the large barriers for formation of the new phases.  With this augmentation we establish the metastable defect phase diagrams (MDPDs) which can serve as a new route for tailoring the defect/microstructure state of alloys.  We demonstrate the power of this new approach by employing it design of Mg-based alloys. First, we use MDPDs to predict the conditions for inducing certain types of planar defects in Mg-based alloys. Then we focus on the intermetallic Laves phases that form in Mg-based alloys at higher alloying concentrations.  These phases have a significant impact on their mechanical properties. For example, they can enhance the creep resistance of the alloys and extend their application to higher temperature domains. However, the mechanisms of deformation of these phases are not fully understood. In this work, at first the formation energies of the different realizations of C14, C15, and C36 Laves phases in the composition domain, Mg_xAl_2-xCa with 0<x<2, using the ab initio simulations is calculated.  Using these formation energies, the phase diagram of the phases of interest is constructed.  In addition, we use MDPDs to understand the experimental results indicating different deformation mechanisms in C36 phase.