Advanced Real Time Imaging: Alloys
Sponsored by: TMS Functional Materials Division, TMS: Advanced Characterization, Testing, and Simulation Committee, TMS: Alloy Phases Committee
Program Organizers: Jinichiro Nakano, MatterGreen; David Alman, National Energy Technology Laboratory; Il Sohn, Yonsei University; Hiroyuki Shibata, Tohoku University; Antoine Allanore, Massachusetts Institute of Technology; Candan Tamerler, University of Kansas; Noritaka Saito, Kyushu University; Neslihan Dogan, TU Delft; Zuotai Zhang, Southern University of Science and Technology; Bryan Webler, Carnegie Mellon University; Anna Nakano, US Department of Energy National Energy Technology Laboratory

Monday 2:30 PM
February 24, 2020
Room: Theater A-4
Location: San Diego Convention Ctr

Session Chair: Bryan Webler, Carnegie Mellon University


2:30 PM  Invited
Computational Real Time Imaging and Understanding of Microstructure Evolution: Bo Wang1; Xiaoxing Cheng1; Tiannan Yang1; Fei Li2; Long-Qing Chen1; 1Pennsylvania State University; 2Xi'an Jiaotong University
    Phase-field method is a powerful tool for computationally generating real-time images and understanding their evolution mechanisms. Here we present two examples to illustrate how the temporal microstructure images obtained from phase-field simulations can be used to understand experimental observations and guide experiments to achieve enhanced properties. The first example involves the phase-field simulations of real time ferroelectric domain evolution during the alternative current (AC) switching process of a ferroelectric crystal. The temporal image evolution revealed an unexpected positive correlation between an increase in ferroelectric domain size and enhancement in piezoelectric properties of relaxor-based ferroelectric single crystals. The second example is used to demonstrate how the ferroelectric polarization images generated using a dynamic phase-field model under GHz frequency AC field can be employed to understand the different electric conduction behaviors of domains and domain walls.

2:50 PM  Cancelled
In-situ Analysis of Incipient Melting in a Novel High Strength Al-Cu Cast Alloy using Laser Scanning Confocal Microscopy (LSCM): Bernoulli Andilab1; Comondore Ravindran1; Neslihan Dogan2; 1Ryerson Univ; 2McMaster University
    Incipient melting in a novel Al-Cu alloy was investigated. Overheating during heat treatment leads to incipient melting thereby compromising mechanical properties. Advanced microscopy and real time imaging techniques such as high temperature LSCM enable a direct in-situ observation of incipient melting and phase transformations. Hence, isothermal analysis was carried out using LSCM at elevated temperatures to analyze incipient melting with time. The predominant phase of this alloy was Al2Cu in both blocky and eutectic morphologies. The results showed that incipient melting was accompanied by a clustering of liquid droplets followed by a complete melting of Al2Cu at approximately 548 ℃. The in-situ analysis also revealed that eutectic Al-Al2Cu was found to melt prior to blocky Al2Cu. Further, localized melting was also observed to occur at a random sequence. As a result of incipient melting, the microstructure consisted of a proliferation of defects such as brittle ultra-fine eutectic clusters and porosity.

3:10 PM  
In-situ Heating S/TEM Observations of Weld Microstructure Evolution in Ni-30Cr Alloy with Tantalum and Molybdenum Additions: Cheng-Han Li1; Sriram Vijayan1; Carolin Fink1; Joerg Jinschek1; 1Ohio State University
    Microstructural evolution in Ni-30Cr weld metal with Ta and Mo additions upon in-situ heating was investigated using scanning/transmission electron microscopy (S/TEM). Ni-30Cr filler metals are commonly used for repair of structural components in nuclear power industry, but are somewhat prone to weld cracking, in particular in multi-pass repair applications. Intergranular cracking is effected by precipitation of secondary constituents along grain boundaries upon reheating of deposited weld metal. In-situ heating experiments in the TEM were performed to study the precipitation and transformation behavior under conditions that mimic thermal cycling during multi-pass welding. A MEMS-based heating holder was used to allow for controlled heating and cooling experiments with high spatial resolution. The significance of these in-situ observations for selection of filler metal composition and weld process parameters that yield desirable microstructures are discussed.

3:30 PM  
In-situ Observation of Hyperbranched Dendrite Growth: Tiberiu Stan1; Kate Elder1; Xianghui Xiao2; Peter Voorhees1; 1Northwestern University; 2Brookhaven National Laboratory
    Many properties of structural alloys are largely controlled by the microstructures left behind after solidification. In-situ observation of dendrite growth in aluminum alloys is possible through synchrotron-based 4D x-ray computed tomography (XCT). The datasets are reconstructed using TIMBIR to achieve high spatial (0.55 micron) and temporal (0.25 second) resolutions, and segmented using a variety of convolutional neural network machine learning architectures. The time-resolved XCT studies of Al-Zn and Al-Zn-Cr alloys give insights into solidification processes over a range of timescales. Unlike classical dendrite morphologies, we show that the free-growing hyperbranched dendrites in Al-Zn alloys are approximately self-similar during growth. At longer time scales, changes in relative solid and liquid densities are observed, which lead to dendrite arm fragmentation and motion both with and against gravity. The resulting 4D experiments give new insights regarding the evolution of dendrite morphologies, tip radii, symmetries, crystallographic growth directions, and interfacial curvatures.

3:50 PM  
In-situ Measurements of Dissolution of TiN in Liquid Cobalt: Ming Zhong1; Chris Pistorius1; Bryan Webler1; 1Carnegie Mellon University
    The dissolution of cubic carbonitrides in cobalt is a key step in the formation of the cobalt enriched zone (CEZ) during production of cemented carbide tool inserts. A model system of cobalt + TiN was used with confocal scanning laser microscope (CSLM) equipped with a hot stage to study dissolution at 1500°C and 1550°C in argon and nitrogen atmospheres. The dissolution rate of TiN was quantified and the rate-controlling step was hypothesized to be mass transfer of nitrogen in the liquid cobalt. This was tested by using the shrinking core model to calculate the diffusivity of nitrogen based on the measured dissolution rates. The measured diffusivities were found to be consistent with previously reported values. The findings of this work can be utilized in detailed models of CEZ formation during cemented carbide production.

4:10 PM Break

4:30 PM  Cancelled
In-situ Diagnosis and Modeling of Disorder Trapping in Rapid Solidification of Intermetallic Compound: Jianrong Gao1; 1Northeastern University
    Intermetallic compounds have a high chemical order in their crystal lattices. Because of this order, crystal growth of intermetallics often have sluggish kinetics compared to that of that of disordered solid solutions. However, the chemical order of intermetallics can be reduced or even suppressed by rapid solidification processing allowing for rapid growth of disordered crystals. This phenomenon is known as disorder trapping and may help improve deformability of as-cast material of intermetallics. To have insight into this kinetic phenomenon, rapid solidification of undercooled bulk melts of a few intermetallics was in situ observed using a high-speed camera. Dendritic tip velocities were determined by a quantitative analysis of camera images recorded in rapid solidification processes at varied bulk undercoolings. They were modeled analytically using a three-dimensional dendritic growth model in combination with a disorder trapping model.

4:50 PM  
Nanoscale 4D Microstructural Characterization of Corrosion in Aluminum Alloys using In-situ Transmission X-ray Microscopy (TXM): Sridhar Niverty1; Arun Singaravelu1; Xianghui Xiao2; Wah-Keat Lee2; Nikhilesh Chawla1; 1Arizona State University; 2Brookhaven National laboratory
    Precipitate location, size, and composition play a pivotal role in determining the initiation and propagation of corrosion damage in aluminum alloys. Visualizing the effect of precipitates on a local as well as a global length scale can be challenging due to the small length scales involved. 3D X-ray nanotomography using Transmission X-ray microscopy (TXM) has been employed to non-destructively study localized corrosion in aluminum alloys in 3.5 wt.% NaCl solution. Four-dimensional (4D) in situ experiments conducted on different aging conditions yielded extremely interesting insights into the complex interplay between precipitates, grain boundaries, and inclusions. Coupling this with EBSD and TEM has enabled us to study the role of grain boundary mismatch and track compositional changes of the precipitates before and after the experiment. The correlative microscopy approach used here has yielded a multi-faceted understanding of the corrosion initiation and progression in these alloys at the nanoscale, which will be discussed.

5:10 PM  
Time-Resolved X-ray Tomography Studies of Dendritic Evolution in Al-Cu Alloys: Kate Elder1; Tiberiu Stan1; Yue Sun1; Xianghui Xiao2; Peter Voorhees1; 1Northwestern University; 2Brookhaven National Laboratory
    Dendrites are ubiquitous structures that are central to setting material properties, but the mechanism behind how dendrites grow is not fully understood. Using X-ray synchrotron radiation experiments, dendritic growth of Al-Cu alloys, with varying compositions, is studied in four-dimensions (three dimensions and time) to track the evolution of the three-dimensional structures as a function of time using novel X-ray tomography algorithms. Starting from a temperature above the liquidus, samples were cooled at multiple cooling rates to observe dendritic growth. To extract useful information from these large datasets, we employ two-point spatial correlations and interfacial shape distributions to provide information on the differences in dendrite morphologies, branch spacing and interfacial curvatures due to different cooling rates and compositions. The data analysis methods as well as the results will be discussed.