Advanced Characterization of Martensite - 3D & High Resolution: Poster Session
Program Organizers: David Rowenhorst, U.S. Naval Research Laboratory; Michael Mills, The Ohio State University

Tuesday 5:30 PM
July 11, 2017
Room: Crystal Ballroom A
Location: Hyatt Regency Chicago

P2-1: Estimation of Solute Carbon Concentration by Electrical Resistivity Method in Low-carbon Martensitic Steel: Toshihiro Tsuchiyama1; Taiga Taniguchi1; Daichi Akama1; Setsuo Takaki1; Kenji Kaneko1; Masahide Yoshimura1; Masaaki Fujioka1; Ryuji Uemori1; 1Kyushu University
    Solute carbon in martensitic steel enhances the hardness of martensite, and also, influences the size of microstructure, axial ratio, dislocation density, age-hardenability, and so on. Therefore, it is important to know the concentration of solute carbon for understanding the martensitic structure and transformation. In this study, the electrical resistivity measurement was attempted as a method to estimate the solute carbon concentration indirectly. Firstly, the effect of grain boundary segregation of carbon and carbide precipitation were clarified by using a low-carbon ferritic steel. This method was then applied to 0.3%C martensitic steel and the electrical resistivity of as-quenched martensite and its change during low temperature tempering was investigated. Finally, the solute carbon concentration of as-quenched and tempered martensitic steels were quantitatively analyzed with consideration of the effects of dislocation density and the other solute elements.

P2-2: In-depth EBSD Investigation of Spatially Coupled Crystallographic Properties in Binary Fe-Ni Alloys: Pascal Thome1; Mahmut Ersanli1; Mike Schneider1; Eric Payton2; Victoria Yardley1; 1Ruhr-Universitšt-Bochum; 2Kazuo School of Engineering
     Binary Fe-Ni alloys with around 28 at. % Ni are well known to show a martensitic phase transformation whose morphological appearance is highly determined by crystallographic properties of the parent and product phase. Depending on the Ni concentration there is a large variety in terms of the evolving microstructures and the orientation relationships between austenite and martensite.To investigate this change of martensitic transformation in detail, custom algorithms were developed and applied to extract spatially coupled OR data from very extensive EBSD data sets and to perform detailed statistical analysis of the OR. A set of 10 specimens in the composition range 20-32.5 at.% Ni were cooled below their Ms temperatures via DSC to induce a martensitic transformation. After the cooling procedure, detailed EBSD scans were performed to investigate both the combinations of variants found and the spatial distribution of point orientations within these variants.

P2-3: In-Situ Study of Transformation in NiTiNOL using High Energy Diffraction Experiment.: Jinesh Dahal1; Aaron Stebner1; JUN-SANG PARK2; Hemant Sharma2; 1Colorado School Of Mines; 2APS
    Currently, various phenomenological and microstructural-based models have been implemented to understand the response of shape memory alloys under mechanical and thermal loadings. But, the micromechanics of the transformation coupled with plasticity has been difficult to characterize experimentally to inform numerical models for calibration and accuracy. A non-destructive, far field High Energy Diffraction (HED) experiments on biaxial samples has the capability to quantify transformation in individual grains during multiaxial loading in three dimensions. This has presented new opportunities to understand martensitic transformation and reorientation of martensite microstructures in grain scale level that can be linked to bulk material. In this poster, we intend to discuss the volume fraction and reorientation strain observed at various loading stages during our recent HED experiments subjected to various proportional and non-proportional loading paths.

P2-4: In-situ Synchrotron X-ray Diffraction Studies on Effects of Loading on bcc Phase Transformations of a 3rd Generation 1 GPa Advanced High Strength Steel: Parisa Eftekharimilani1; 1Delft University of Technology
    The paper describes the effect of loading on fcc- bcc phase transformations of an Advanced High Strength Steel (AHSS) during cooling using in-situ synchrotron diffraction patterns. Time-temperature-load synchrotron x-ray diffraction patterns were gathered. The volume fractions of the phases and the transformation kinetics during cooling and simultaneous loading were calculated. In addition, volume fractions of retained austenite at room temperature under different loading conditions were studied. The results show that applying a load during cooling of fcc phase significantly increases the volume fraction of bcc phase before start of martensitic transformation. The kinetics of phase transformations were affected by the applied loads. The volume fraction of retained austenite at room temperature varies in different samples and the highest retained austenite was obtained in the sample subjected to highest load.

P2-5: Quantitative Investigation of All-round Shape Memory Effect on a Ni 51at.%Ti Alloy using TEM Orientation Imaging: Xiayang Yao1; Yuanyuan Li2; Shanshan Cao2; Xiao Ma2; Xin-ping Zhang2; Dominique Schryvers1; 1EMAT, University of Antwerp; 2South China University of Technology
    Automated crystal orientation and phase mapping in TEM (ACOM-TEM) with a lateral resolution of around 2 nm is applied to quantitatively investigate the microstructure of Ni51Ti49 treated to show the all-round shape memory effect. The alloy was fabricated by arc melting from Ni and Ti powders with fast solidification, then subjected to constrained arc-shaped aging to introduce the all-round shape memory effect. The shape recovery property after constrained aging varies when changing the aging time and temperature. Using orientation and phase maps collected with ACOM-TEM, quantitative analysis was made on the distribution of Ni4Ti3 precipitates which significantly affect the performance of the all-round shape memory. Constrained arc-shaped is found to lead to different preferential orientation of Ni4Ti3 precipitates on different sides of the sample which further controls the shape transformation behaviour. Combining the ACOM-TEM data with DSC measures allows us to better understand the connection between sample treatment and behavior.