Theory and Methods for Martensite Design: Session 3
Program Organizers: Greg Olson, Northwestern University; Ricardo Komai, QuesTek Innovations LLC

Wednesday 8:00 AM
July 12, 2017
Room: Gold Coast
Location: Hyatt Regency Chicago

Session Chair: Greg Olson, Northwestern University

8:00 AM  Invited
An Information-driven Approach to the Design of Low Hysteresis Shape Memory Alloys: Turab Lookman1; 1Los Alamos National Laboratory
    There has been considerable interest over the last few years in accelerating the process of materials design and discovery. Finding new materials with targeted properties has largely been guided by intuition and trial and error, and with increasing complexity (e.g. chemical), the number of possibilities becomes exceedingly large for an Edisonian approach to be practical. The Materials Genome Initiative (MGI) has spurred considerable activity and brought new researchers into the nascent field of materials informatics. The activity has also highlighted some of the open questions in this emerging area, including identifying key features, guiding the next experiment to aid the learning process, and incorporating domain knowledge to make better predictions. I will show how an adaptive design strategy, tightly coupled to experiments, can guide the discovery of new compositions of NiTi-based alloys with very small dissipation.

8:40 AM  
On the Microstructural Origin of Mechanical and Thermal Hysteresis in Shape Memory Alloys: Gunther Eggeler1; Stefanie Jaeger1; Burkhard Maass1; Oliver Kastner1; Jan Frenzel1; 1Ruhr University Bochum
    All shape memory effects rely on the martensitic transformation, where a high temperature phase (austenite) transforms to a low temperature phase (martensite) on cooling. The reverse transformation occurs on heating. The transformation is characterized by Ms and Mf (martensite start and finish temperatures) and by As and Af (austenite start and finish temperatures). The associated transformation peaks have maxima Mp and Ap. The hysteresis associated with the thermal transformation is ΔTH=Ap-Mp. Martensite can also be stress induced. On loading of austenite, the formation of stress induced martensite starts at a critical stress σM, the reverse transformation on unloading occurs at σA<σM, one can define a mechanical hysteresis ΔσH= σM-σA. We explain the physical, crystallographic, chemical and microstructural nature of these two hysteretic phenomena and show that they are closely related.

9:20 AM  
Martensitic Transformation Terminated in "Gas-liquid"-type Critical Point: Volodymyr Chernenko1; Saurabh Kabra2; Elena Villa3; Victor Lvov4; Jose Manuel Barandiaran5; Hideki Hosoda6; 1University of Basque Country (UPV/EHU)&Ikerbasque; 2Rutherford Appleton Laboratory, ISIS; 3IENI-CNR; 4Institute of Magnetism, Kyiv; 5BCMaterials & University of the Basque Country (UPV/EHU); 6Tokyo Institute of Technology
    We found that the line of martensitic transformations (MTs) of Ni-Fe(Co)Ga is terminated in a "gas-liquid"-type critical point, CP(318K, 109MPa) of the stress–temperature phase diagram. Below CP a tensile superelastic deformation of 14% and pronounced hysteresis were obtained whereas above it an anhysteretic nonlinear deformation of similar value was observed. In-situ neutron diffraction of aforementioned single crystals during compression tests at different temperatures indicates a stress-induced MT with two-phase coexistence below CP, and continuous change of the lattice parameter from austenite to a post-critical state above CP. The Landau-type theory describes the existence of an end-point on the stress-temperature phase diagram of the first-order MT. It also predicts that CP can be experimentally observed for the alloys with low shear modulus ( a few GPa). The Fe-Pd alloy was found recently to be another example of this behavior, showing a CP at 280K and 40 MPa.

9:40 AM  
A Computational Approach to Design Martensitic Microstructure in Carbon Steels: Shengyen Li1; Steve Mates1; Mark Stoudt1; Carelyn Campbell1; Greta Lindwall1; Sindhura Gangireddy1; 1National Institute of Standards and Technology
    Martensite is a critical microstructural component in many materials, including many steels. Being able to tailor the desired volume fraction and stability of martensite for specific applications has been a long time goal. A materials design infrastructure integrating phase-based, mechanistic, and constitutive models and experimental data has been developed using a python-based framework. This generic materials design toolkit (GMDT) has been implemented to provide new insights into high speed machining applications where the workpiece experiences rapid heating and deformation, which produces unexpected microstructures and material behavior. This work uses the GMDT framework to combine dilatometry, scanning electron microscopy, microhardness, X-ray diffraction, and high-strain rate Kolsky bar compression test data with existing models (e.g. Olson-Cohen, constitutive plastic deformantion) and neural networks to predict the phase transformation behavior and properties. An example relating predicited phase transformations and stress-strain relationships to the experimental observations in rapidly heated and deformed 1045 steel is presented.

10:00 AM Break