Current state of Fe-Mn-Al-C low density steels

Thermomechanical processing of advanced high strength steels

Large volume serial section tomography by Xe Plasma FIB dual beam microscopy.

Heterogeneous supported metal catalysts are critical for a wide range of chemical conversion technologies. While the fundamental properties of extended metal surfaces are well understood and active sites on such systems can be designed for targeted applications, much less is known about the properties of active sites formed at the interface of nanometer-scale metal structures and their underlying oxide support. The goal of this Perspective is to highlight recent progress in understanding and controlling metal–oxide support interfacial sites on high-surface-area catalysts. Focus is given to how metal particle size, support migration onto metal particles, and intentional deposition of oxides on metal particles can be used to create high concentrations of interfacial sites. The impact of interface formation on properties of nearby metal and oxide sites is discussed in the context of understanding if the uniqueness of interfacial sites stems from bifunctionality, or if the distinct electronic properties of at...

Approaches for Understanding and Controlling Interfacial Effects in Oxide-Supported Metal Catalysts

Strengthening and strain hardening mechanisms in a precipitation-hardened high-Mn lightweight steel

The influence of silicon on κ-carbide precipitation in lightweight austenitic Fe-30Mn-9Al-(0.59-1.56)Si-0.9C-0.5Mo cast steels was investigated utilizing transmission electron microscopy, 3D atom-probe tomography, X-ray diffraction, ab initio calculations, and thermodynamic modeling. Increasing the amount of silicon from 0.59 to 1.56 pct Si accelerated formation of the κ-carbide precipitates but did not increase the volume fraction. Silicon was shown to increase the activity of carbon in austenite and stabilize the κ-carbide at higher temperatures. Increasing the silicon from 0.59 to 1.56 pct increased the partitioning coefficient of carbon from 2.1 to 2.9 for steels aged 60 hours at 803 K (530 °C). The increase in strength during aging of Fe-Mn-Al-C steels was found to be a direct function of the increase in the concentration amplitude of carbon during spinodal decomposition. The predicted increase in the yield strength, as determined using a spinodal hardening mechanism, was calculated to be 120 MPa/wt pct Si for specimens aged at 803 K (530 °C) for 60 hours and this is in agreement with experimental results. Silicon was shown to partition to the austenite during aging and to slightly reduce the austenite lattice parameter. First-principles calculations show that the Si-C interaction is repulsive and this is the reason for enhanced carbon activity in austenite. The lattice parameter and thermodynamic stability of κ-carbide depend on the carbon stoichiometry and on which sublattice the silicon substitutes. Silicon was shown to favor vacancy ordering in κ-carbide due to a strong attractive Si-vacancy interaction. It was predicted that Si occupies the Fe sites in nonstoichiometric κ-carbide and the formation of Si-vacancy complexes increases the stability as well as the lattice parameter of κ-carbide. A comparison of how Si affects the enthalpy of formation for austenite and κ-carbide shows that the most energetically favorable position for silicon is in austenite, in agreement with the experimentally measured partitioning ratios.

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An Atom Probe Study of Kappa Carbide Precipitation and the Effect of Silicon Addition

An experimental study has been performed on the grain growth in a model Ni-based superalloy, with particular emphasis on the pinning effect of the second-phase particles. Extensive annealing experiments were performed, and the microstructural development was evaluated in detail using scanning and transmission electron microscopy. It was found that grain growth was strongly inhibited by the pinning effect of both the coarse γ′ phase and the inert precipitates. For samples heat-treated at temperatures below the γ′ solvus (1143 °C), the limiting grain size was determined by the size and volume fraction of the γ′ phase. For samples heat-treated at super-solvus temperatures, the stability of the MC-type carbides and yttrium oxides led to a nearly constant Zener limiting grain size over the temperature range 1143–1244 °C. Samples heat-treated at 1270 °C had larger grain sizes due to the coarsening and/or dissolution of the MC-type carbides and yttrium oxides.

Grain growth and particle pinning in a model Ni-based superalloy

Extended abstract of a paper presented at Microscopy and Microanalysis 2013 in Indianapolis, Indiana, USA, August 4 – August 8, 2013.

/pdf/xe-fib-milling-and-measurement-of-amorphous-silicon-damage-4kk0tdwc18.pdf

Xe+ FIB Milling and Measurement of Amorphous Silicon Damage

Electron beam induced crystallization of sputter deposited amorphous alumina thin films

The recent discovery of superconductivity in iron selenide has attracted considerable attention due to the simplicity of composition, unconventional nature of superconductivity, and ease of synthesis. We have synthesized superconducting FeSe nanowires with a simple catalyst-aided vapor transport reaction at 800 °C in an inert atmosphere. The precursors were chosen to be elemental Se and iron acetylacetonate [FeIII(C5H8O2)3]. These vaporized very easily, thereby facilitating transport, and also contributed to the formation of a carbonaceous shell encapsulating the FeSe nanowires. The superconductivity of these nanocables was confirmed through magnetic measurements and a Tc of ≈8 K was obtained for an ensemble of nanocables. The length of FeSe filling inside the carbon nanofibers could be varied by controlling the reaction conditions while the diameter of nanowires was dependent on the thickness of Au–Pd coating used as a catalyst. Extensive analysis through high-resolution microscopy revealed that there wa...

Kai Song

Papers

An Atom Probe Study of Kappa Carbide Precipitation and the Effect of Silicon Addition

Grain growth and particle pinning in a model Ni-based superalloy

Xe+ FIB Milling and Measurement of Amorphous Silicon Damage

Electron beam induced crystallization of sputter deposited amorphous alumina thin films

Synthesis of superconducting nanocables of FeSe encapsulated in carbonaceous shell.