Applications of Solidification Fundamentals: Characterization of Solidification Structures II
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Solidification Committee
Program Organizers: Andre Phillion, McMaster University; Amber Genau, University of Alabama at Birmingham; Lifeng Zhang, University of Science and Technology Beijing

Monday 2:00 PM
February 27, 2017
Room: 19
Location: San Diego Convention Ctr

Session Chair: Sabine Bottin-Rousseau, Institut des Nanosciences de Paris; Amy Clarke, Colorado School of Mines

2:00 PM  Invited
Real-time Study on Microstructure Evolution of a Three-phased Eutectic System in Quasi-2D Samples: Samira Mohagheghi1; Melis Serefoglu1; 1Koc University
    For three-phased eutectic systems with isotropic interfacial energies, the stable periodic microstructure obtained upon controlled solidification conditions is found to be ABAC-type, where each letter stands for one phase constituting the eutectic system. In this work, we performed directional solidification (DS) and rotating directional solidification (RDS) experiments using In-Bi-Sn eutectic system. These setups are mounted on special optical microscopy system, which enables observation of solidification front from top and bottom simultaneously and hence facilitates characterization of complex 3D mechanisms of spacing adjustment. We map the morphological stability diagram for the ABAC pattern in quasi-2D samples, characterize the instabilities and explain how system can rearrange itself to recover the ABAC pattern after these instabilities. Additionally, we demonstrate how the existence of anisotropy in crystal/crystal interfacial energies affects the overall microstructure.

2:20 PM  Invited
Effect of Crystal Orientation Relationships on Lamellar Eutectic Solidification Microstructures: Sabine Bottin-Rousseau1; Oriane Senninger1; Gabriel Faivre1; Silvčre Akamatsu1; 1UPMC-CNRS
    We studied crystal-orientation effects on lamellar-eutectic microstructures during thin-sample directional solidification of the nonfaceted eutectic In-In2Bi alloy. Two types of eutectic grains were observed: (i) floating grains, with regular microstructures typical of an isotropic system, and (ii) locked grains, within which the lamellae generally grow tilted, and align with a few particular directions. In each grain, we measured the orientation of the two eutectic (In-rich tetragonal ε, and hexagonal In2Bi) phases by x-ray diffraction (pole figures). In all the locked grains, we could identify a coincidence orientation relationship between ε and In2Bi. In a majority of them, a {111} (fct) plane of ε was parallel to a {11-20} plane of In2Bi. The three different lamellar-locking directions observed during solidification in those grains were close to the three planes of the {11-20} family in In2Bi. By contrast, no coincidence orientation relationships were found in the floating grains.

2:40 PM  
Influence of Crystal Orientation on the Dynamical Selection of Propagative Cellular Solidification Patterns: Younggil Song1; Sabine Bottin-Rousseau2; Silvere Akamatsu2; Alain Karma1; 1Northeastern University; 2CNRS - UPMC
    We investigate the dynamics of tilted-cell patterns in dilute alloys during directional solidification of single crystals with a finite misorientation. In situ experiments and phase-field simulations in thin samples bring evidence of a selection of the cell spacing by a propagative source-sink mechanism. It operates on larger space and time scales than the competitive growth mechanism at play during the initial transient. Tertiary branching at the diverging edge of the sample (source) selects a spacing close to the upper pattern-stability limit. This spacing invades the sample to yield a uniform microstructure, except in a small region near the converging edge of the sample (sink). We propose an evolution equation for that dynamics in terms of the local dependence of the cellular drift velocity on the spacing and a generic phase-diffusion uniformization process. This fundamental knowledge is key to improving elaboration processes of single crystals or textured polycrystals for advanced materials.

3:00 PM  
4D Synchrotron X-ray Quantification of the Cellular to Dendritic Transition: Biao Cai1; Peter Lee1; Andrew Kao2; Andre Phillion3; Koulis Pericleous4; 1University of Manchester; 2University of Greenwich; 3McMaster University; 4University of Greenwich
    Solidification morphology directly impacts the properties of materials; hence investigating the morphological evolution of dendritic structures is important to fields ranging from alloy manufacturing to battery failure prediction. We have used 4D (3D plus time) synchrotron X-ray tomographic imaging to capture the transition from a cellular to columnar dendritic morphology, together with the subsequent development of the columnar dendrites in a temperature gradient stage. The cellular morphology was found to be highly complex, with frequent lateral bridging. The onset Mullins-Sekerka morphological instability of the cellular front, resulting in protrusions forming and becoming dendrites was observed and quantified. Other mechanisms affecting the solidification microstructure, including dendrite coarsening and fragmentation were also captured and the quantitative results compared to analytic models. The results demonstrate that 4D imaging can both inform and validate solidification models.

3:20 PM  
Thermal Analysis of Cu-Cu2O Eutectic: Cécile FOSSE1; Manuel Castro-Román2; Jacques Lacaze1; Luc Robbiola1; 1Université de Toulouse; 2CINVESTAV Saltillo
    Archeological artifacts and remains (up to several thousands of years) obtained from cast copper have been discovered in various sites all around the world. The microstructure of these artifacts mainly consists in a fibrous Cu-Cu2O eutectic surrounding dendrites of a primary phase that can be either copper or Cu2O. This eutectic has been rarely studied, and one has to go back to Eastwood (1934) for a detailed description of the eutectic morphology. This author showed that the eutectic grains consist in densely packed fibers in the center, which bend and coarsen at the periphery. In an attempt to reproduce this microstructure in laboratory, investigation of the eutectic structure was performed and it was found for hypereutectic composition that Cu2O dendrites are surrounded by a thick halo of copper. This appears to correspond to a significant undercooling for the formation of the copper-rich phase which is here investigated by thermal analysis.

3:40 PM Break

4:00 PM  
Microstructural Development During Thin Film Solidification: Comparison of Experiments and Simulations: Theron Rodgers1; Amy Clarke2; John Gibbs3; James Mertens3; Daniel Coughlin3; Harrison Whitt3; Joseph McKeown4; John Roehling4; J. Baldwin3; Seth Imhoff3; Damien Tourret3; Jonathan Madison1; 1Sandia National Laboratories; 2Colorado School of Mines; 3Los Alamos National Laboratories; 4Lawrence Livermore National Laboratory
    In this work, Dynamic Transmission Electron Microscopy (DTEM) was used for in-situ observations of solidification dynamics in metallic alloys. A pulsed laser was used to melt as deposited, 100 nm-thick metallic alloy films and time-resolved imaging captured solid-liquid interfacial dynamics and microstructural evolution at the microsecond time-scale. With a recently developed simulation method based upon a modified Kinetic Monte Carlo approach, predictions of grain microstructure in polycrystalline systems with well-defined solidification fronts are used to simulate solidification phenomena observed in the DTEM experiments. Both spatial and time-resolved comparisons between experiments and simulations of aluminum-silicon alloy films with various compositions will be presented and discussed. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.

4:20 PM  
Investigation of the Metatectic Reaction in Boron Containing Steels: Kara Luitjohan1; Matthew Krane1; Volkan Ortalan1; David Johnson1; 1Purdue University
    The U.S. government has issued a challenge to various automakers to increase the fuel economy of passenger vehicles to 54.5 mpg by 2025. One method to achieve this goal is through the use of advanced high strength steel, including boron containing steels. Boron containing steels are difficult to commercially produce due to a predicted metatectic reaction where solid delta-ferrite transforms to liquid and austenite upon cooling. However, this reaction and how various alloying elements affect the reaction are not well characterized. To control boron segregation along the length of the ingot, various alloys are levitation zone melted, and the resulting microstructures are characterized with scanning and transmission electron microscopy along with confocal scanning laser microscopy. These experimental results are compared to predicted phase diagrams and calculated solidification profiles.

4:40 PM  
Solidification Characteristics of CNTs/Mg Composite with Ultrasonic: Yuansheng Yang1; Fuze Zhao1; Xiaohui Feng1; 1Institute of Metal Research, Chinese Academy of Sciences
    Carbon nano-tubes (CNTs)/Mg composite has low density and good mechanical properties. One of fabrication methods for CNTs/Mg composite is casting which key step is dispersing CNTs in alloy melting uniformly. This paper researches the dispersion behavior of CNTs and solidification CNTs/Mg composite by ultrasonic processing. Experimental results show that CNT clusters can be separated in alloy melt well with high power ultrasonic processing. One of ultrasonic effects is acoustic streaming which causes dispersion of CNT clusters at the macro level, and another one is acoustic cavitation by which the CNT clusters are separated in melt at the micro level. The CNT cluster separation under ultrasonic is caused by bubble collapse. Higher sound pressure amplitude is good for the separation of CNT clusters. When sound pressure amplitude is high, the bubble threshold initial radius is small and more bubbles would collapse. With high power ultrasonic processing, the as-cast microstructure is refined.

5:00 PM  
Microstructure Characteristics of A356 Nanocomposites Manufactured via Ultrasonic Cavitation Processing under Controlled Solidification Conditions: Yang Xuan1; Laurentiu Nastac1; 1The University of Alabama
    Adding nanoparticles into aluminum alloy can fabricate nanocomposites with good mechanical properties. Recent studies performed at the Solidification Laboratory, The University of Alabama, showed that the use of ultrasonic cavitation during solidification can significantly refine the microstructure of A356 anocomposites. This is because during the fabrication of nanocomposite castings, ultrasonic cavitation processing can produce strong convection and shock waves, which promote both the dendrite fragmentation and the increase of the nuclei in the melt. In the present work, the relationship between the nanocomposite microstructure and the cooling rate during solidification has been studied in detail. A356 alloy and Al2O3 /SiC nanoparticles were used as the matrix alloy and the reinforcements, respectively. Ultrasonic cavitation was applied during the solidification process. Two-zone induction furnace was applied to control the temperature gradients during solidification at a desired value. The microstructure of the cast nanocomposites has been investigated in detail by OM and SEM-EDS.