All-Conference Events: Tuesday morning session, Part 1 of 2
Program Organizers: Aaron Stebner, Colorado School of Mines
Tuesday 8:00 AM
July 11, 2017
Room: Crystal Ballroom B
Location: Hyatt Regency Chicago
Session Chair: Richard James, University of Minnesota
8:00 AM Invited
Algorithmic Discovery of Mechanisms for the Martensitic Phase Transformation: Xian Chen1; Yintao Song2; Richard James2; Aaron Stebner3; 1The Hong Kong University of Science and Technology; 2University of Minnesota; 3Colorado School of MInes
E. C. Bain’s method of identifying the lattice correspondence and transformation strain in ferrous FCC-to-BCC martensitic transformations underlies the modern crystallographic theories of martensite. The Bain correspondence was derived based on the intuition of “a mode of atomic shift requiring minimum motion...” This mechanism has been widely accepted for numerous ferrous and nonferrous martensitic materials having cubic-like austenite phase. For transformations between complex crystal structures, seeking the lattice correspondence giving minimum average atomic movement becomes tedious due to the nonuniqueness of the choice of sublattice and lattice invariant shear. We have written a rigorous algorithm, StrucTrans, for determining the lattice correspondence of a martensitic transformation between arbitrary lattices giving least transformation strain. This algorithm gives unexpected new correspondences and transformation strains for some classic and emerging cases, and calls into question some long accepted mechanisms of transformation. These results are given, and recent experimental investigation for new mechanisms is presented.
8:40 AM Invited
Guided by Martensite: Kaushik Bhattacharya1; 1California Institute of Technology
Martensitic phase transformations are solid to solid phase transitions involving a change of crystal structure and mechanical change in shape. This results in a competition between local `chemical energy’ that dictates the crystal structure, the non-local elastic interactions that results from coherence and defects that lead to incoherence. This competition leads to the characteristic martensitic microstructure and interesting properties including the shape-memory effect as well as the defect mediated hardening of steels. The theoretical study of martensitic microstructure going back to the seminal crystallographic theory of martensite has led to a sophisticated methodology for understanding this completion. This talk will describe how this methodology has and continue to provide new insights into the study of other phenomena including ferroelectricity, liquid crystal elastomers and deformation twinning.
9:20 AM Invited
Phase Transformations under High Pressure and
Large Plastic Deformations: Multiscale Theory and Interpretation of Experiments
: Valery Levitas1; 1Iowa State University
Superposition of large plastic shear at high pressure in rotational diamond anvil cell (RDAC) leads to significant (by a factor of 3-10) reduction of phase transformation (PT) pressure and new phases that were not obtained under hydrostatic conditions. Multiscale theory and computation approaches were developed to study these phenomena. Phase field approach to interaction between dislocations and PT was developed and applied to study nanoscale mechanisms. This model was calibrated utilizing molecular dynamic simulations under multiaxial loading. Microscale strain-controlled kinetic equation was derived as a coarse graining of the nanoscale model. It was implemented within a macroscale theory for strain-induced PT for the finite element studies of the behavior of a sample in RDAC under various conditions. Obtained at all four scale results have been summarized as the methods for controlling PTs by controlling stress, plastic strain, and defect structures.
10:00 AM Break