Interactions of Phase Transformations and Plasticity: Session 5
Program Organizers: Valery Levitas, Iowa State University

Thursday 8:00 AM
July 13, 2017
Room: Water Tower
Location: Hyatt Regency Chicago

Session Chair: Stefan Martin, TU Bergakademie Freiberg

8:00 AM  Invited
Predictive Characterization of the Inelastic Deformation in NiTi Shape Memory Alloys at the Microstructural Length-scales: Harshad Paranjape1; Ashley Bucsek1; Branden Kappes1; Hemant Sharma2; Joel Bernier3; Darren Dale4; J. Y. Peter Ko4; Peter Anderson5; Aaron Stebner1; 1Colorado School of Mines; 2Argonne National Laboratory; 3Lawrence Livermore National Laboratory; 4Cornell University; 5The Ohio State University
     Shape Memory Alloys (SMAs) show a rich thermo-mechanical response stemming from an austenite-martensite phase transformation and thus are candidates for several commercial applications. However, phase transformation is coupled with slip and the mechanical response of SMAs often degrades on cyclic loading. A micromechanical understanding of phase transformation and its interaction with slip is beneficial in mitigating the performance degradation.We present a toolbox comprising of high-energy X-ray diffraction and micromechanical modeling that can furnish details of the local strain fields, martensite microstructure evolution and slip system activation during superelastic loading of NiTi SMA. The characterization component in this toolbox is "predictive"' since it couples with the modeling counterpart to reveal features of microstructure and deformation that are not directly furnished through the experimental data. We provide two examples: Prediction of slip systems activated during compression of NiTi microcrystals and martensite microstructure selection during tension of NiTi bulk crystals.

8:40 AM  Invited
Deformation Microstructures in Compositionally Graded Beta-titanium Alloys: Xin Ji1; Koichi Tsuchiya2; Ivan Gutierrez-Urrutia2; Satoshi Emura2; Xiaohua Min3; 1University of Tsukuba; 2NIMS; 3Dalian University of Technology
    In a meta-stable beta titanium alloys, three different deformation modes (i. e., {332}<113> twinning, martensitic transformation and dislocation slip ) becomes active depending on the beta phase stability. We have investigated the deformation modes in Ti-12Mo alloy during tensile deformation at room temperature. The sample we used had heterogenous distribution of Mo. It was revealed that the different deformation mode appeared depending on the Mo concentration of the area. Particularly of interest is a continuous change from {332}<113> twin to alpha” martensite in a single deformation plate product, which led to distinct kink of the plate. Detailed mechanism of such microstructure formation and its effect on work hardening behavior will be discussed on the basis of EBSD and ECCI (Electron Channeling Contrast Imaging ) observations.

9:20 AM  
TEM Study of 304 Stainless Steel after Multiaxial Loading/load Path Change: Miroslav Smid1; Wei-Neng Hsu1; Tobias Panzner1; Efthymios Polatidis1; Helena Van Swygenhoven1; 1Paul Scherrer Institut
     304 stainless steel is an important structural material known for its deformation-induced twinning and martensitic transformation during mechanical loading. Post-mortem transmission electron microscopy (TEM) studies following uniaxial loading have revealed complex microstructure consisting of dislocations, stacking faults, deformation twins and strain-induced martensite. Thus far, the influence of multiaxial loading on mechanical properties and the microstructural evolution have not been studied.Recently, in-situ neutron diffraction measurements during biaxial loading of 304 steel cruciform samples were performed. In this presentation, the analysis of experimental results is presented. In addition, post-mortem TEM studies are performed to gain insight on how different biaxial stress states and strain paths influence the deformation mechanisms of 304 steel.

9:40 AM  
Compatible Strain Evolution in Two Phases Due to Epsilon Martensite Transformation in Duplex TRIP-assisted Stainless Steels with High Hydrogen Embrittlement Resistance: Yu Li1; Wei Li1; Xuejun Jin1; 1Shanghai Jiao Tong University
    Two duplex TRIP-assisted stainless steels have been investigated showing distinct γ-->ε-->α’ transformation sequences and a single γ-->α’ martensite transformation. The microscopic strain evolution was revealed by in-situ synchrotron XRD combined with EBSD. The direct γ-->α’ transformation route experiences a shift of strain localization from austenite to ferrite with massive dislocation accumulation in ferrite. The multistage γ-->ε-->α’transformation contributes to a good combination of strength and ductility. It is demonstrated that the compatible strain evolution in austenite and ferrite is achieved due to γ-->ε transformation. The following α’-martensite transformation supplies an extra work hardening capacity related to the dislocation pile-ups. The obtained compatible strain evolution due to ε-martensite can not only prevent the nucleation of hydrogen-induced micro-cracks but also alleviate the localized plastic deformation in ferrite, ensuring a higher elongation and resistance to hydrogen embrittlement.

10:00 AM Break