More Like this

1. Enhancing Thermal Interface Conductance to Graphene Using Ni− Pd Alloy Contacts

   https://doi.org/https://dx.doi.org/10.1021/acsami.0c06953?ref=pdf  

   Saha, Dipanjan ; Yu, Xiaoxiao ; Du, Yanhao ; Guo, Zhitao ; Xiong, Feng ; Gellman, Andrew J. ; Malen, Jonathan A. ( July 2020 , ACS applied materials interfaces)

   To identify superior thermal contacts to graphene, we implement a high-throughput methodology that systematically explores the Ni−Pd alloy composition spectrum and the effect of Cr adhesion layer thickness on thermal interface conductance with monolayer graphene. Frequency domain thermoreflectance measurements of two independently prepared Ni−Pd/Cr/graphene/ SiO2 samples identify a maximum metal/graphene/SiO2 junction thermal interface conductance of 114 ± (39, 25) MW/m2 K and 113 ± (33, 22) MW/m2 K at ∼10 at. % Pd in Ninearly double the highest reported value for pure metals and 3 times that of pure Ni or Pd. The presence of Cr, at any thickness, suppresses this maximum. Although the origin of the peak is unresolved, we find that it correlates with a region of the Ni−Pd phase diagram that exhibits a miscibility gap. Cross-sectional imaging by high-resolution transmission electron microscopy identifies striations in the alloy at this particular composition, consistent with separation into multiple phases. Through this work, we draw attention to alloys in the search for better contacts to two-dimensional materials for next-generation devices. 

   more » « less
2. Elemental partitioning and corrosion resistance of Ni–Cr alloys revealed by accurate ab-initio thermodynamic and electrochemical calculations

   https://doi.org/10.1038/s41529-023-00414-w  

   Huang, Liang-Feng ; Xie, Yusi ; Sieradzki, Karl ; Rondinelli, James M. ( December 2023 , npj Materials Degradation)

   Elemental partitioning during thermal processing can significantly affect the corrosion resistance of bulk alloys operating in aggressive electrochemical environments, for which, despite decades of experimental and theoretical studies, the thermodynamic and electrochemical mechanisms still lack accurate quantitative descriptions. Here, we formulate an ab initio thermodynamic model to obtain the composition- and temperature-dependent free energies of formation (Δ_fG) for Ni–Cr alloys, a prototypical group of corrosion-resistant metals, and discover two equilibrium states that produce the driving forces for the elemental partitioning in Ni–Cr. The results are in quantitative agreement with the experimental studies on the thermodynamic stability of Ni–Cr. We further construct electrochemical (potential–pH) diagrams by obtaining the required Δ_fGvalues of native oxides and (oxy)hydroxides using high-fidelity ab-initio calculations that include exact electronic exchange and phononic contributions. We then analyze the passivation and electrochemical trends of Ni–Cr alloys, which closely explain various oxide-film growth and corrosion behaviors observed on alloy surfaces. We finally determine the optimal Cr content range of 14–34 at%, which provides the Ni–Cr alloys with both the preferred heat-treatment stability and superior corrosion resistance. We conclude by discussing the consequences of these findings on other Ni–Cr alloys with more complex additives, which can guide the further optimization of industrial Ni–Cr-based alloys.

    

   more » « less
3. High-throughput Alloy and Process Design for Metal Additive Manufacturing

   Sheikh, S. ; Vela, B. ; Honarmandi, P. ; Morcos, P. ; Shoukr, D. ; Abdelrahman, M. K. ; Karaman, I. ; Elwany, A. ; Arroyave, R. ( April 2023 , arXivorg)

   Designing alloys for additive manufacturing (AM) presents significant opportunities. Still, the chemical composition and processing conditions required for printability (ie., their suitability for fabrication via AM) are challenging to explore using solely experimental means. In this work, we develop a high-throughput (HTP) computational framework to guide the search for highly printable alloys and appropriate processing parameters. The framework uses material properties from stateof- the-art databases, processing parameters, and simulated melt pool profiles to predict processinduced defects, such as lack-of-fusion, keyholing, and balling. We accelerate the printability assessment using a deep learning surrogate for a thermal model, enabling a 1,000-fold acceleration in assessing the printability of a given alloy at no loss in accuracy when compared with conventional physics-based thermal models. We verify and validate the framework by constructing printability maps for the CoCrFeMnNi Cantor alloy system and comparing our predictions to an exhaustive ’in-house’ database. The framework enables the systematic investigation of the printability of a wide range of alloys in the broader Co-Cr-Fe-Mn-Ni HEA system. We identified the most promising alloys that were suitable for high-temperature applications and had the narrowest solidification ranges, and that was the least susceptible to balling, hot-cracking, and the formation of macroscopic printing defects. A new metric for the global printability of an alloy is constructed and is further used for the ranking of candidate alloys. The proposed framework is expected to be integrated into ICME approaches to accelerate the discovery and optimization of novel high-performance, printable alloys. 

   more » « less
4. High-temperature Stability of an Iron-rich Smectite: Implications for Smectite Formation on Mars

   Jenkins, D.M. ; DePasquale, B.M. ( December 2020 , American Geophysical Union meeting, Fall 2020 Meeting)

   null (Ed.)

   Iron-rich phyllosilicates on Mars comprise nearly 90% of the H2O- and OH-bearing phases observed directly by rovers and remotely by orbiters (Chemtob et al., 2017, JGR). Theories concerning the possible origin of Fe-rich smectite during Mars’ earliest history (phyllosian) are hard to test because of limited knowledge of the upper-thermal stability of Fe-rich phyllosilicates. In this study we present data on the upper-thermal stability of a pure-iron smectite to put some minimum constraints on its possible high-temperature origin early in Mars history either from a primordial atmosphere or by hydrothermal activity. Smectite coexisting with quartz and magnetite was synthesized from the oxides in the system Na2O-FeO-Fe2O3-Al2O3-SiO2-H2O at 500°C and 2 kbar and fO2 near FMQ. Reversal experiments involved mixtures with equal portions of the smectite-synthesis and breakdown products (quartz, fayalite, albite, magnetite (mt) treated in the presence of about 10 wt% H2O over the range of 1-3 kbar and 530-640°C. The average composition (electron microprobe) of smectite formed both in synthesis and in reversal experiments was Na0.35(Fe2+2.28Fe3+0.31Al0.41)(Al1.07Si2.93)O10(OH)2·nH2O, where ferric iron was calculated by summing the octahedral cations to 3.0. Reversals for the reaction smec+mt1 = fayalite+albite+mt2+quartz+H2O were obtained at 538±8, 590±10, and 610±10°C at 1, 2, and 3 kbar, respectively, where mt1 and mt2 have the approximate compositions Fe2.8Si0.2O4 and Fe2.8Al0.1O4, respectively, with all other phases being pure. This smectite has up to 2 interlayer H2O at 25°C (and high humidity), losing 1 H2O at <50°C, and the second at 125 ± 25°C. Thermodynamic modeling of this reaction was used to extrapolate the upper-thermal stability of this Fe-smectite down to 10 bars and approximately 239°C. Applications of these results indicate the maximum temperature for forming Fe-smectite from a dense primordial atmosphere of 100 bars is 390 ± 25°C. Crustal storage of water in Fe-smectite ranges up to a maximum of 10.7 wt% at ~2 km and 40°C, 7.4 wt% at 6 km and 120°C, and 3.8 wt% H2O at 32 km and 625°C for a Noachian geotherm of 20°C/km. Plain language summary: This study presents experimental limits on the temperatures at which the clay mineral smectite might form on Mars, either from a dense primordial atmosphere (390°C at 100 bars) or by high-temperature hydrothermal activity (625°C at 32 km). Because this study deals with iron end-member clay, these are minimum temperatures; any solid solution with magnesium will increase these temperatures. 

   more » « less
5. Electrodeposited thin-film Cu x Sb anodes for Li-ion batteries: enhancement of cycle life via tuning of film composition and engineering of the film-substrate interface

   https://doi.org/10.1039/c8ta01798k  

   Schulze, Maxwell C. ; Schulze, Roland K. ; Prieto, Amy L. ( January 2018 , Journal of Materials Chemistry A)

   Electrodeposited Cu–Sb thin films on Cu and Ni substrates are investigated as alloy anodes for Li-ion batteries to elucidate the effects of both the film composition and substrate interactions on anode cycling stability and lifetime. Thin films of composition Cu x Sb (0 < x < 2) exhibit the longest cycle lifetimes nearest x = 1. Additionally, the Cu–Sb films exhibit shorter cycle lifetimes when electrodeposited onto Cu substrates when compared to equivalent films on Ni substrates. Ex situ characterization and differential capacity analysis of the anodes reveal that significant interdiffusion occurs during cycling between pure Sb films and Cu substrates. The great extent of interdiffusion results in mechanical weakening of the film–substrate interface that exacerbates film delamination and decreases cycle lifetimes of Cu–Sb films on Cu substrates regardless of the film's composition. The results presented here demonstrate that the composition of the anode alone is not the most important predictor of long term cycle stability; the composition coupled with the identity of the substrate is key. These interactions are critical to understand in the design of high capacity, large volume change materials fabricated without the need for additional binders. 

   more » « less