TRANSFORMATION TOUGHENING EXPLORED VIA MOLECULAR-DYNAMICS AND MONTE-CARLO SIMULATIONS

The microscopic mechanism of 'transformation toughening' is thought to be the stress reduction at a crack tip resulting from a displacive ph ase transformation induced by the stress field of a crack under extern al loading. Whether transformation toughening or 'transformation embri ttlement' is the result depends on many different characteristics of t he displacive transformation, as well as the geometry of the stress fi eld of the crack. Since both crack and displacive transformation dynam ics are sufficiently rapid to be suitably simulated in a molecular dyn amics scheme we have explored this approach with the ordered intermeta llic NiAl, employing embedded atom method (EAM) potentials. These pote ntials, in tum, have allowed the construction of a Ginzburg-Landau str ain free energy functional (with all the material dependent parameters determined from molecular dynamics simulations), which may then be us ed to carry out Monte Carlo simulations of the crack-transformation zo ne interaction on a substantially larger spatial scale. These various types of simulation will be described and the results analysed.