Atom Probe Tomography for Advanced Characterization of Metals, Minerals and Materials III: Applications in Alloys and Ceramics
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS Structural Materials Division, TMS: Nuclear Materials Committee, TMS: Phase Transformations Committee
Program Organizers: Haiming Wen, Missouri University of Science and Technology; David Seidman, Northwestern University; Keith Knipling, Naval Research Laboratory; Gregory Thompson, University of Alabama; Simon Ringer, University of Sydney; Arun Devaraj, Pacific Northwest National Laboratory; Gang Sha, Nanjing University of Science and Technology

Wednesday 2:00 PM
February 26, 2020
Room: Theater A-1
Location: San Diego Convention Ctr

Session Chair: Keith Knipling, U.S. Naval Research Laboratory; Arun Devaraj, Pacific Northwest National Laboratory


2:00 PM  Invited
Material Alterations in Intense Mechanical and Chemical Contacts: Shanoob Balachandran Nair1; David Mayweg1; Yu Qin1; Ebrahim Norouzi1; Lutz Morsdorf1; Alfons Fischer1; Dierk Raabe1; Michael Herbig1; 1Max-Planck-Institut fuer Eisenforschung
    Intense mechano-chemical contacts occur in a broad range of crucial technological applications such as bearings, rails or hip implants. The reaction of materials to these conditions thus does not only concern a part’s lifetime but often also a patient’s well-being. The complex underlying processes can only be understood by joint chemical and structural characterization at the nanometer scale. This makes atom probe tomography in conjunction with transmission electron microscopy the ideal tools for this investigation. We conduct these methods to unravel the mechanism behind the emission of cobalt-ions from hip implants, the processes of carbide-decomposition in bearings and during high pressure torsion and the origin of ductility in metallic glasses.

2:30 PM  
Elucidating Solute Clustering and Precipitation of Al-Cu-Mg-Ag-Si Model Alloys: Jiehua Li1; Zhiehng An2; Fredrik Hage3; Quentin Ramasse3; Gang Sha2; 1Univ of Leoben; 2Nanjing University of Science and Technology; 3SuperSTEM Laboratory
    Solute clustering and precipitation in an Al–Cu–Mg–Ag–Si model alloy has been investigated by atom probe tomography (APT) as well as high-angle annular dark-field (HAADF) imaging and electron energy loss spectroscopy (EELS) in the scanning transmission electron microscope (STEM). Nine types of solute clusters were observed by APT in the as-quenched alloy and after ageing the alloy at 180°C for 1h. Three types of precipitates were observed by APT and HAADF-STEM after ageing at 180°C for 24h and 100h. The plate-like Ω (AlCuMgAg) precipitates evolve continuously from the MgAgCu and MgAgCuSi clusters, rather than via heterogeneous nucleation on their precursors (i.e. MgAgCu and MgAgCuSi clusters). Our results thus reveal links between a variety of solute clusters and the different types of precipitates in the Al–Cu–Mg–Ag–Si model alloy. Such information can in the future be used to control the precipitation by tailoring solute clustering.

2:50 PM  
Atom Probe Tomography of Refractory High Entropy Alloys: Patrick Callahan1; David Beaudry1; Noah Philips2; Keith Knipling1; 1Naval Research Laboratory; 2ATI Specialty Alloys and Components
    High entropy alloys (HEAs) typically contain five or more principal elements in nearly equiatomic proportions, significantly expanding the composition space and attainable properties of novel metallic materials. Despite the potential advantages of HEAs, fundamental questions remain, particularly regarding the mechanisms of dislocation motion and diffusion in these alloys. Atom-probe tomography (APT) is a precise atom-by-atom investigation of a sample and produces 3D reconstructions with sub-nanometer resolution, chemical sensitivities near 10 ppm, and volumes approaching 250×250×1000 nm^3. This provides uniquely powerful insights into phenomena such as atomic clustering, short range order, and anti-clustering, which are not yet well understood in HEAs. However, these analyses require optimum spatial and spectral data and in this talk we present the effects of APT laser pulse energy, laser pulse frequency, and specimen tip base temperature on the analysis yield, data quality, and the propensity for generating complex ions in equiatomic MoTaTiZrW and HfNbTaTiZr refractory HEAs.

3:10 PM  Invited
Coupled APT and TEM Investigation of Cu Assisted Nucleation of L12 Precipitates in FCC-based High Entropy Alloys: Bharat Gwalani1; Sriswaroop Dasari1; Vishal Soni1; Rajarshi Banerjee1; 1University of North Texas
    Second phase precipitation in high entropy alloys (HEAs) or complex concentrated alloys (CCAs) can be rather complex due to the multi-component system coupled with the competition between multiple possible phases. This study will focus on Cu clustering and its impact on L12 precipitation in FCC-based high entropy alloys (HEAs), Al0.3CuCrFeNi2 and Al0.3Cu0.3Ti0.2CrFeNi. Detailed characterization via coupling of APT, SEM, and TEM reveal novel insights into Cu clustering within the FCC matrix of these HEAs, leading to heterogeneous nucleation sites for the gamma prime precipitates. The subsequent partitioning of Cu into the gamma prime precipitates indicates their stabilization due to Cu addition. The role of Cu revealed by this study can be employed in the design of precipitation strengthened HEAs, as well as in a more general sense applied to other types of superalloys, with the objective of potentially enhancing their mechanical properties at room and elevated temperatures.

3:40 PM Break

4:00 PM  
Understanding Early Stages of Nanoscale Hydriding and Oxidation Mechanisms in Metallic Systems via Atom Probe Tomography and Multimodal Chemical Imaging: Elizabeth Kautz1; Sten Lambeets1; Bharat Gwalani1; Daniel Perea1; Daniel Schreiber1; Arun Devaraj1; 1Pacific Northwest National Laboratory
    Metal alloys undergo surface reactions when exposed to reactive gaseous environments (e.g. hydrogen, oxygen), which impact material performance and component lifetime. Such gas-surface reactions are extremely important to several applications, however mechanisms of hydride and oxide phase formation are still inadequately understood. Here, an environmental reactor chamber attached to an atom probe tomography system is used to study early stages of compositional changes at alloy surfaces. For select systems (Zirconium, Uranium), we study the oxide/metal interface chemistry at elevated temperature for varying times. Changes in composition after hydrogen gas loading are also investigated for Zirconium. APT results are correlated with analysis performed via STEM, XANES, and nano scratching to provide unique insight into structural and chemical state changes before/after oxidation, and adhesion of the oxide film. This multimodal approach can be used to elucidate atomic scale mechanisms of initial, adherent oxide layer formation and hydrogen absorption in industrially relevant alloys.

4:20 PM  
Atom Probe Tomography Study of Fission Products in Neutron Irradiated U-Mo Fuel: Maalavan Arivu1; Andrew Hoffman1; Haiming Wen1; 1Missouri University of Science and Technology
    U-Mo fuel has gained interest in replacing high enriched fuels for high performance research reactors. Previous studies using transmission electron microscopy (TEM) have shown interesting features in irradiated U-Mo fuels including the formation of fission gas bubble superlattices. TEM is, however, limited in its ability to accurately measure chemical data for nanoscale features. In this study, we have used atom probe tomography (APT) in order to gain a clearer picture of the 3-D chemical makeup of the features in irradiated U-Mo fuel. Through this APT investigation, Xe gas bubbles were found though not always forming a superlattice structure. Nd clusters were also observed and often formed their own superlattice structure. Grain boundaries were found to be enriched in fission products, and near large gas bubbles and grain boundaries, the enrichment of Xe caused surrounding regions to become depleted in Xe, forming denuded zones free of any gas bubbles.

4:40 PM  
Characterization of Mechanical Properties of the A356 Cast Aluminum Alloy in Accordance with the Cluster Formation Behaviors at Different Aging Temperatures: Won Sang Shin1; Kyo Jin Hwang1; Dong-Hyuk Jung1; Yoon-Jun Kim1; 1Inha University
     An A356 cast aluminum alloy (Al–7wt.%Si–0.3wt.%Mg), contains approximately 50% eutectic microstructure. Such a high content of Si plays a significant role in strengthening of the alloy by controlling eutectic morphology, precipitation of various intermetallic compounds, and formation of Al-Si-Mg based clusters in α-matrix.We present the formation behaviors of Al-Si-Mg-Mn nanoclusters in the alloy using an Atom Probe Tomography (APT). Samples were differently aged at the temperatures of 110℃, 130℃, and 150℃. As a result of the cluster analysis, the characteristics of clusters according to the temperature such as the mean radius, <R>, the number density of clusters per volume, NV, were obtained. The A356 alloy exhibited 4 types of clusters formed in α-matrix depending on their atomic concentration ratios among Al, Mg, and Mn. The results from tensile tests for those samples indicate tensile strength and elongation are strongly dependent of the cluster types, <R>, and NV.

5:00 PM  
APT-based Stoichiometry Measurements of Single Crystal ThO2: Amrita Sen1; Mukesh Bachhav2; Janelle Wharry1; 1Purdue University; 2Idaho National Laboratory
    The objective of this study is to obtain accurate stoichiometric measurements of single crystal ThO2 using Laser-Atom Probe Tomography (APT). Compositional accuracy of insulators and metal-oxides materials by APT is known to be influenced by operating parameters such as laser energy, field condition, and base temperature. Systematic variation of these parameters reveals improved ThO2 stoichiometry with increasing laser energy and decreasing base temperature. However, interpretation of these results is not straightforward. As with other oxides, poor laser absorption due to low thermal conductivity of ThO2 results in non-uniform field evaporation behavior, introducing thermal effects into the obtained mass spectra. Generally, such thermal effects negatively impact compositional accuracy. However, ThO2 is distinct from other oxides in that improved stoichiometry is achieved from the thermally-affected mass spectra, compared to results from spectra with better mass resolution. The cause for this behavior, and its influence on interpretation of data will be discussed.