Theory and Methods for Martensite Design: Session 2
Program Organizers: Greg Olson, Northwestern University; Ricardo Komai, QuesTek Innovations LLC

Tuesday 10:20 AM
July 11, 2017
Room: Gold Coast
Location: Hyatt Regency Chicago

Session Chair: Annika Borgenstam, KTH, Royal Institute of Technology

10:20 AM  Invited
A TEM and Simulation Study of Interface Migration in an FCC/BCC System: Juan Du1; Frederic Mompiou2; Zhi-Peng Sun1; Ben Xu1; Wenzheng Zhang1; 1Tsinghua University; 2CEMES-CNRS
    A correct description of the long range strain field associated with a phase transformation is crucial to quantitative understanding, modelling and possible designing a transformation microstructure. The description is a challenging task for systems consisting of a martensitic or Widmanstätten structure, since the strain field largely depends on incomplete information of the structures and the migration of the transformation interfaces. In this work, migration of interfaces between Widmanstätten austenite and ferrite were investigated using an in-situ TEM. A prominent long range strain field near the moving interface was analyzed. Migration of typical habit planes between fcc and bcc, consisting of a single set of dislocations, was simulated with a molecular dynamic method. The migration behaviors were found to vary with the Burgers vectors of the dislocations. The motion of some interfaces is associated with a migration-shear coupling effect, which is roughly consistent with the phenomenological theory of martensite crystallography.

11:00 AM  
Revisiting Ferrous Martensite with First-principles Calculation: Hideyuki Ohtsuka1; Zhufeng Hou1; Kaneaki Tsuzaki2; 1National Institute for Materials Science; 2Kyushu University
    We have focused on the tetragonality of ferrous martensite, and applied the ab initio calculation to Fe-C and Fe-N systems to solve the long-standing problems, such as, why carbon and nitrogen atoms prefer the octahedral sites in bcc-Fe, why tetragonality data of Fe-C and Fe-N martensites are on one straight line as a function of atomic concentration of the interstitial atoms, how the tetragonality changes according to the configuration of interstitial atoms, and so on. Tetragonality of Fe-C and Fe-N systems obtained by first-principles calculation increases linearly with increasing interstitial atoms and agrees well with experimental results. When the Fe-C-Fe pairs are parallel with each other in the supercell of Fe54C2, the tetragonality is 1.036 and agrees with experimental value, strain energy is low, formation enthalpy is low and the existence probability under the assumption of Boltzmann distribution is high. In other cases, the existence probability is nearly zero.

11:20 AM  Invited
Elastic Domains: From Twinned Martensite to Self-Assembled Micro-/Nano-Structures: Alexander Roytburd1; 1University of Maryland at College Park
    Elastic domains, which minimize elastic energy at constrained phase transformations in solids, is a general phenomenon since all solid phase transformations are accompanied by spontaneous strains. This concept was invented to interprete[1] the formation and evolution of polytwin microstructures in martensite.[2] Then this concept was successfully applied to analyze solid-solid phase transformations in bulk[3] and epitaxial films. [4] These investigations have led to the formulation of principles of engineering of elastic homophase (“twins”) and heterophase polydomain structures with optimal functional properties.[5] The concept of heterophase polydomains has been applied to engineering of epitaxial nanocomposites consisting of different crystalline materials, in particular, multiferroic nanocomposites. Promising new results are obtained for engineering of domain structures in highly stressed films.

12:00 PM Break