Interactions of Phase Transformations and Plasticity: Session 1
Program Organizers: Valery Levitas, Iowa State University

Monday 10:40 AM
July 10, 2017
Room: Water Tower
Location: Hyatt Regency Chicago

Session Chair: Valery Levitas, Iowa State University

10:40 AM  Invited
On Variants, Blocks and Packets of Martensite and Their Interaction with Crystal Plasticity: Thomas Antretter1; Manuel Petersmann1; Georges Cailletaud2; Ulrich Ehlenbröker3; Annika Vieweg4; 1Montanuniversitaet Leoben; 2Mines ParisTech; 3Paderborn University; 4Materials Center Leoben
    The mechanical behavior of martensitically transforming steels is a direct result of the evolution and arrangement of martensite variants inside a grain interacting with the mechanisms of crystal plasticity. This work elucidates the details of variant arrangements in blocks and packets based on crystallographic considerations. On that level, i.e. the grain level, slip systems can also be resolved. A micromechanical model is presented that includes variables such as the fractions of individual variants as well as the shear rate of individual slip systems. Open parameters of the model are identified by means of EBSD measurements carried out on specimens having experienced different preceding loading histories.

11:20 AM  
Simulation of Effect of Phase Transformation on Material Deformation Textures: Shivram Kashyap Sridhar1; Anthony Rollett1; 1Carnegie Mellon University
    Phase transformation between B2 austenite and B19' martensite characterize the Shape memory and Superelastic properties of Nickel Titanium (NiTi). The superelastic properties make NiTi a suitable candidate for minimally invasive biomedical devices. However, this transformation also plays an important role in determining cold working crystallographic textures. In this work we try to incorporate martensitic transformations as a deformation mode in the ViscoPlastic Self Consistent (VPSC) simulations. VPSC is a micromechanical model based algorithm that solves the anisotropic Eshelby inclusion in a Homogeneous Effective Medium (HEM) problem. We try to explore the effect of simultaneous slip activity in austenite and martensitic transformations on plastic response of the material. We shall try and compare our simulation results with the experimental results observed in literature and from our work.

11:35 AM  
The TRIP Effect of Austenitic Steels under Multiaxial Loading: Wei-Neng Hsu1; Efthymios Polatidis2; Tobias Panzner3; Miroslav Smid2; Helena Van Swygenhoven1; 1Swiss light source, Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland/Neutrons and X-rays for Mechanics of Materials, IMX, Ecole Polytechnique Federale de Lausanne, CH-1012 Lausanne, Switzerland; 2Swiss light source, Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland; 3Laboratory for Neutron Scattering, NUM, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
     The deformation-induced martensitic transformation in TRIP steels has been mainly studied upon uniaxial deformation. A few studies point towards a disagreement in whether transformation is facilitated or retarded under multiaxial stress-states or strain path changes. Using a biaxial deformation-rig installed at the neutron strain-scanning beamline POLDI of the Swiss neutron spallation source (SINQ), the influence of proportional and non-proportional loading on the transformation behavior of a metastable austenitic stainless steel (Type 304) was studied.The in-situ diffraction measurements carried out during uniaxial, equibiaxial deformation and strain path changes provide insights to the microstructural and phase evolution, the distribution of internal stresses in the phases and the residual stress after unloading. Post-mortem microstructural characterization of the morphological changes induced by the deformation, (e.g. shear-band formation, deformation-induced twinning etc.) are correlated to the results obtained from in-situ techniques and discussed with respect to the nature of the deformation.

11:50 AM  
TRIP Effect in a Constant Load Creep Test at Room Temperature: Noriyuki Tsuchida1; Stefanus Harjo2; 1University of Hyogo; 2Japan Atomic Energy Agency
    In order to investigate TRIP (transformation induced plasticity) effect in different deformation style, a room temperature creep test under the constant load was conducted by using a TRIP-aided multi-microstructure steel. As a result, the volume fraction of deformation-induced martensite in the constant load creep test was larger than that in the tensile test. In-situ neutron diffraction experiments during the constant load creep test were performed to discuss its reason. The lattice plane strains of austenite and ferrite phases obtained by the neutron diffraction experiments are independent of <hkl> grain families whereas those by the tensile test depend on <hkl> grains. The deformation-induced martensitic transformation behavior in the both test are discussed from the viewpoints of such the differences of lattice strains or intergranular stress.

12:10 PM Break