Advanced Thermo-mechanical Characterization of Materials with Special Emphasis on In Situ Techniques: In Situ Techniques IV
Sponsored by: TMS Structural Materials Division, TMS: Advanced Characterization, Testing, and Simulation Committee, TMS: Nanomechanical Materials Behavior Committee, TMS: Thin Films and Interfaces Committee
Program Organizers: Amit Pandey, LG Fuel Cell Systems Inc.; Sanjit Bhowmick, Hysitron; Jeff Wheeler, ETH Zurich; María Teresa Pérez Prado, IMDEA Materials Institute; Robert Wheeler, MicroTesting Solutions LLC; Josh Kacher, Georgia Tech

Tuesday 2:00 PM
February 28, 2017
Room: 32A
Location: San Diego Convention Ctr

Session Chair: Bob Wheeler, Microtesting Solutions; Jeff Wheeler, ETH Zürich

2:00 PM  Invited
Optimum Layer Thickness for High Temperature Mechanical Properties of ARB Cu/Nb Nanoscale Multilayers: Jon Molina-Aldareguia1; Jeromy Snel1; Miguel Monclus1; Nathan Mara2; Irene Beyerlein2; Javier Llorca1; 1IMDEA Materials Institute; 2Los Alamos National Laboratory
    Cu/Nb metallic multilayers with individual layer thicknesses in the range 7 nm to 63 nm were manufactured by accumulated roll bonding. Micropillars of square cross section of 5 x 5 µm2 and an aspect ratio 2-3 were milled with a focused ion beam. The mechanical properties of the Cu/Nb multilayers were determined by means of in situ micropillar compression tests within a scanning electron microscope. Test were carried out at different strain rates (10 -2 to 10-4 s-1) and temperatures (25ºC to 400ºC) and the yield strength, strain rate sensitivity and activation volume were determined from these tests for each multilayer as a function of temperature. In addition, the deformation and fracture mechanisms were ascertained from in situ observations during deformation and from transmission electron microscopy analysis of foils extracted from the deformed micropillars.

2:30 PM  
Influence of Dislocation Density and Grain Boundaries on the Scaling Behaviour of Ultrafine-grained BCC Micropillars: Reinhard Fritz1; Alexander Leitner1; Verena Maier-Kiener1; Daniel Kiener1; 1Montanuniversität Leoben
    While size effects in micron-sized single crystalline (sxx) specimens are well investigated, controversial results have been reported for miniaturized ultrafine-grained (ufg) specimens in literature. In this work, two different bcc metals, Cr and W, with different critical temperatures and thus varying scaling exponents were investigated. Sxx as well as ufg pillars with sample sizes ranging from 0.2 to 4 µm were tested performing in-situ SEM microcompression tests at room and elevated temperatures, whereby for ufg pillars a novel, interesting strength scaling exponent was observed. Furthermore, the dislocation density was also varied within these ufg samples by using an in-situ heating technique to recover the highly distorted microstructures. Within this presentation, we will shed more light into the governing deformation mechanisms and finally we will demonstrate whether grain boundaries or dislocation density are responsible for the occurring scaling behaviour in the ufg micropillars.

2:50 PM  
Micro-Mechanical Characterization of Micro-Architectured Tungsten Coating at Elevated Temperatures: Quan Jiao1; Gidong Sim1; Jaafar El-Awady1; 1Johns Hopkins University
    Recent advance in surface engineering has led to a new set of thermal barrier coating based on refractory metal. Dendritic tungsten coating developed by ULTRAMET has a few applications in extreme environments, but the thermo-mechanical behaviors are not well studied. Our previous work has shown the coating is porous with a columnar microstructure and reported a buckling failure mode with a strength of ~1.5GPa from microcompression test. In this work, to further understand the thermo-mechanical behavior, in situ mechanical tests are performed on different sample sizes at room and elevated temperatures. In situ micro tension tests on micron-sized dog bone sample fabricated along the thickness direction show a low tensile strength, and fractography analysis shows it is due to the early development of fracture at grain boundary. In addition, in situ microcompression tests at elevated temperature (100~400ºC) are performed to study the temperature effect on the deformation mode, failure behavior, and mechanical response of the material.

3:10 PM  
Multiscale 3D Imaging of Damage in an Angle-Interlocked Ceramic Matrix Composite under In-Situ Mechanical Loading Using Lab X-Ray Microscopy: Hrishikesh Bale1; Robert Ritchie2; David Marshall3; 1Carl Zeiss X-ray Microscopy; 2Department of Materials Science and Engineering, University of California, Berkeley; 3Teledyne Scientific Co.
    Ceramic woven textile composites represent a new class of integrally woven composites for high-temperature applications, where both strength and thermal conductivity are important. For high performance and reliability, a key issue is geometrical defects in the textile reinforcement, which trigger failure mechanisms and compromise strength. Due to the intricate 3D architecture of woven composites, damage initiation, propagation and failure is extremely challenging to investigate. 3D x-ray microscopy allows non-destructive imaging of the sample under simultaneous in-situ mechanical loading in the laboratory. Particularly for woven composites, it provides rich data that resolves cracks initiated at several different sites under load. We present results obtained on a 3 layer angle-interlocked woven composite subjected to in-situ mechanical loading. Through successive tomographic scans collected at different loads, the crack extension was tracked. These results provide 3D experimental data further useful to validate the fidelity of predictive modeling codes that simulate failure in composites.

3:30 PM Break

3:50 PM  Invited
In Situ Thermo-mechanical Characterization of Materials: Xiaodong Li1; 1University of Virginia
    Functional devices are often constructed with building blocks of dissimilar materials. The devices experience thermal and mechanical deformations in packaging and operation. It is of critical importance to obtain full-field deformation data of these heterogeneous materials in the controlled thermal and mechanical conditions. Digital image correlation (DIC) based thermal and mechanical strain mapping techniques were used to probe micro/nanoscale thermal and mechanical deformations of nanostructures and coatings. Through in situ high-temperature DIC, we unveiled new, critical delamination and fracture mechanisms of thermal barrier coatings (TBCs). Full-field DIC strain maps of cross-sectioned TBCs during thermal cycling up to 1200°C revealed the coupled formation mechanisms of vertical and horizontal cracks, which showed that horizontal cracks were formed by vertical crack deflection/branching. These techniques provide new guidelines for the design and reliability control of nanostructures and TBCs.

4:20 PM  
Probing the Dynamic Response of Ordered Lattice Materials: J. Lind1; J. Hawreliak2; B. Maddox1; M. Barham1; M. Messner1; B. Jensen3; N. Barton1; M. Kumar1; 1Lawrence Livermore National Laboratory; 2Washington State University; 3Los Alamos National Laboratory
    Additive manufacturing has opened up the possibility of designing and creating lattice structures that were previously not possible. Their remarkable strength-to-weight scaling has garnered much interest, but one must ask if their strength, which depends uniquely on their geometric and topological character, still holds when deformed dynamically? Taking advantage of the Dynamic Compression Sector at the Advanced Photon Source, we performed gas gun experiments combined with x-ray phase contrast imaging on additively manufactured polymer lattice and foam structures. With micron spatial and 100ns temporal resolution, the local deformation characteristics can be extracted by tracking nodal displacements within the material. Properties such as local ligament strain, maximum supported strain, compaction behavior, and elastic wave evolution can be extracted. We will discuss on-going comparison of results with direct numerical simulations. This work was performed under the auspices of the US Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

4:40 PM  
Pushing the Envelope in Variable Temperature Nanoindentation: High and Cryogenic Temperature Measurements: Nicholas Randall1; Marcello Conte1; Gaurav Mohanty2; Jakob Schwiedrzik2; Jeffrey Wheeler3; Bertrand Bellaton1; 1Anton Paar TriTec; 2EMPA; 3ETH Zurich
    This talk presents the design and development of a novel nanoindentation system that can perform reliable load-displacement measurements over a wide temperature range (from -150 to 800 °C) emphasizing the procedures required for performing accurate nanomechanical measurements. This system utilizes an active surface referencing technique comprising of two independent axes, one for surface referencing and another for indentation. The differential depth measurement technology results in negligible compliance of the system and very low thermal drift rates at high temperatures. The sample, indenter and reference tip are heated/cooled separately and the surface temperatures matched to obtain drift rates as low as 5nm/min at 800 °C. Instrumentation development, system characterization, experimental protocol, operational refinements and thermal drift characteristics over the temperature range will be presented. Extensive test results on a variety of materials will be shown. Finally, the current status and future roadmap for variable temperature nanoindentation testing will be summarized.

5:00 PM  
Effect of Ausforming on Isothermal Transformation Below Ms in NiCrMoV Steel Studied by In-situ Neutron Diffraction: Wu Gong1; Stefanus Harjo2; Akinobu Shibata1; Takuro Kawasaki2; Yo Tomota3; Tomoya Shinozaki4; Nobuhiro Tsuji1; 1Kyoto University; 2Japan Atomic Energy Agency; 3National Institute for Materials Science; 4Kobe Steel, Ltd.
    Recently, the physical simulator for thermo-mechanically controlled processing (TMCP) has been installed at the engineering neutron diffractometer ‘TAKUMI’ in J-PARC, which makes it possible for in-situ neutron diffraction experiments during TMCP at elevated temperatures. Low-temperature bainite structure in steels exhibits excellent mechanical properties due to its refined microstructure. It has been recently confirmed that the bainitic transformation can occur even below the martensite start temperature (Ms). In the present study, we performed in-situ neutron diffraction experiments by the aforementioned simulator to elucidate the effect of ausforming on isothermal transformation below Ms in a NiCrMoV steel. The formation of bainite below Ms was confirmed. Ausforming suppressed the kinetics of martensitic transformation but showed a weak effect on the subsequent bainitic transformation. The amount of retained austenite at room temperature became larger as a result of ausforming.