Weekly Seminar: Phase field method to martensitic phase transformations, dislocations and their interaction at the nanoscale



Phase field method to martensitic phase transformations, dislocations and their interaction at the nanoscale

  • Dr. Mahdi Javanbakht
  • 5 May 2018
  • Lecture Hall

 

Abstract:

Martensitic phase transformations (PTs), dislocations and their interaction play a key role for the formation of unique nanostructures, mechanical properties, and complex phenomena in different materials such as steels, shape memory alloys and ceramics. A martensitic nanostructure consists of a fine mixture of different phases separated by interfaces with the widths of few nanometers. Phase field method (PFM) is one the most important methods to model such nanostructures which is able to study the problems both at the nanoscale and at times and sizes much larger than those of molecular dynamics. For modeling the phase-dislocation interaction, a novel PFM for PTs is developed which represents correct expressions for surface tension, interface energies and surface energy. Also, a novel PFM is developed for dislocations which introduces a correct model for equilibrium and stability of dislocations as well as their nucleation and growth. Using the above two PFMs, and considering the essential requirements of the interaction event, a comprehensive model for the phase-dislocation interaction is represented. Finite element method is applied to solve the coupled system of phase field-elasticity equations (based on COMSOL and self-developed codes) and is implemented for several important nanoscale problems such as stress-, thermal-, and surface-induced PTs, phasedislocation nanostructures under high pressure and large plastic shear, growth and arrest of martensitic plates, hysteresis due to defects, promotive and suppressive effects of dislocations on PTs. The current models can be developed for various problems such as different PTs and chemical reactions.