The main strengthening mechanism for Inconel 718 (IN718), a Ni-based superalloy, is precipitation hardening by γ' and γ″ particles. It is thus essential, for good alloy performance, that precipitates ...with the desired chemical composition have adequate size and dispersion. The distribution of the γ' and γ″ phases and their chemical composition were investigated in the nickel-based Inconel 718 superalloy by taking advantage of the new capabilities of scanning transmission electron microscopy and energy-dispersive X-ray spectrometry using a windowless multiple detector, a high-brightness Schottky electron gun, and a spherical aberration corrector in the illumination probe optics. A small routine was developed to deconvolute the respective compositions of γ' and γ″ nanoprecipitates embedded in the γ matrix. Keeping the electron probe current low enough-a few hundred pA-prevented excessive irradiation damage during the acquisition of element maps and brought their spatial resolution down to the atomic column level to track their element compositions. The present results agree with and complement atomic probe tomography observations and Thermo-Calc predictions from the literature. The presence of an Al enrichment at the γ'/γ″ interface-which may control the γ″ phase coarsening-is observed in the last row of Al-Nb-Ti columns along this interface. In addition, a few columns with similar composition changes are found randomly distributed in the γ' phase.
The atomic redistribution processes occurring in multiparticle nanostructures are hardly understood. To obtain a more detailed insight, we applied high‐resolution microscopic, diffraction and ...spectroscopic characterization techniques to investigate the fine structure and elemental distribution of various bimetallic aerogels with 1:1 compositions, prepared by self‐assembly of single monometallic nanoparticles. The system Au–Ag exhibited a complete alloy formation, whereas Pt–Pd aerogels formed a Pd‐based network with embedded Pt particles. The assembly of Au and Pd nanoparticles resulted in a Pd‐shell formation around the Au particles. This work confirms that bimetallic aerogels are subject to reorganization processes during their gel formation.
Mix and match: The alloying behavior of Au–Ag, Pt–Pd, and Au–Pd 1:1 bimetallic aerogels was investigated by high‐resolution microscopic, diffraction, and spectroscopic techniques. Unexpected elemental distributions were observed that demonstrate the strong dependence on the kinetic energy introduced into the system by nanoparticle collision during the gel formation.
The ATI 718Plus® is a creep-resistant nickel-based superalloy exhibiting high strength and excellent oxidation resistance in high temperatures. The present study is focused on multiscale 2D and 3D ...characterization (morphological and chemical) of the scale and the layer beneath formed on the ATI 718Plus superalloy during oxidation at 850 °C up to 4000 h in dry and wet air. The oxidized samples were characterized using various microscopic methods (SEM, TEM and STEM), energy-dispersive X-ray spectroscopy and electron diffraction. The 3D visualization of the microstructural features was achieved by means of FIB-SEM tomography. When oxidized in dry air, the ATI 718Plus develops a protective, dense Cr2O3 scale with a dual-layered structure. The outer Cr2O3 layer is composed of coarser grains with a columnar shape, while the inner one features fine, equiaxed grains. The Cr2O3 scale formed in wet air is single-layered and features very fine grains. The article discusses the difference between the structure, chemistry and three-dimensional phase distribution of the oxide scales and near-surface areas developed in the two environments. Electron microscopy/spectroscopy findings combined with the three-dimensional reconstruction of the microstructure provide original insight into the role of the oxidation environment on the structure of the ATI 718Plus at the nanoscale.
Microstructure as well as micro-mechanical and tribological properties of hard surface layers formed on Timetal 834 alloy during its nitridation or oxynitridation under glow discharge were ...investigated. The tests show that both layers exhibited higher microhardness and Young’s modulus as well as much better wear resistance than the untreated alloy.
The microstructure investigations, performed by light microscopy and analytical transmission electron microscopy methods, show that improved micro-mechanical and tribological properties of surface-treated alloy are related to the presence of a multiphase micro/nanostructure containing several sublayers with different morphologies and composition.
Noble Metal Alloys The combination of STEM EDX, XRD, and EXAFS data analysis drew a coherent picture of the characteristic alloying behavior of various bimetallic nanostructured aerogels with an ...atomic ratio of 1 : 1, which were synthesized by a two‐step gelation process at low temperature. Elemental mapping revealed that only the Au–Ag system exhibits a complete alloy formation in the as‐synthesized state. Unlike Au–Ag, Pt–Pd aerogels formed an unexpected Pd‐based network with embedded Pt particles. The assembly of Au and Pd nanoparticles even resulted in an unforeseen Pd‐shell formation around the Au particles. For more information see the Communication by A. Eychmüller et al. on page 13446 ff.
Nano-hydroxyapatite/chitosan (nc-HA/chitosan) composite coatings were produced on two phase (α+β) Ti6Al7Nb titanium alloy substrates by electrophoretic deposition (EPD). The microstructure of the ...coatings was examined by scanning- and transmission electron microscopy methods as well as by X-ray diffractometry. The coatings, 770 nm–800 nm thick, were uniform, without any cracks or presence of large voids and they exhibited good adhesion to the titanium alloy substrate. The microstructure of the coatings consisted of nc-HA needle-like particles homogeneously embedded in a chitosan matrix. The deposited coatings exhibited good adhesion to the substrate. The best adhesion to the titanium alloy was determined for the coating deposited from suspensions containing 4 g/L of HA at 10 V during 240 s. The results confirm EPD as a convenient method to develop uniform and crack-free nanoscale organic-inorganic composite coatings on two phase titanium alloy substrates with potential application in orthopedic and dental implants.
•Cr2O3 scale having tens nanometer sized grains was formed on Sanicro 25 at 650°C.•M23C6 carbides was thermodynamically unstable in Cr-depleted zone. Beneath the Cr2O3 a layer with short-range ...ordering typical for glass was formed.•Nanometer sized Cu-rich particles were precipitated from the austenitic matrix.
The Sanicro 25 austenitic steel is foreseen as a potential material for steam superheaters and reheaters in ultra-supercritical power plants. The aim of investigation was to characterize in detail an oxide scale grown on the Sanicro 25 tube after fireside oxidation at 650°C. The morphology of the oxide scale and the microstructure of the bulk material were investigated using advanced electron microscopy methods. A multilayered and multicomponent oxide scale containing mainly Cr2O3 was found on the surface exposed to combustion gases. Directly under the oxide scale, a chromium-depleted zone with no M23C6 carbides was observed.
A Ni based single crystal superalloy from the 2
nd
generation, PWA 1484, and one from the 4
th
generation, PWA 1497, were comparatively studied by scanning electron microscopy, energy dispersive ...X-ray spectroscopy and nanoindentation technique in an atomic force microscope (NI-AFM) after high temperature creep deformation. During primary creep of both generations of superalloys, γ′ precipitates start to coalesce and grow directionally. Further creep deformation leads to the topological inversion and coarsening of the rafted microstructure. The NI-AFM technique was used for measurements of the hardness of the γ and γ′ phases in as-received and creep deformed samples in various conditions. The g matrix of the PWA 1497 superalloy is on average 0.8 GPa harder than that of PWA 1484 that can be explained by higher content of Re and Ru, since they partition predominantly to the matrix phase.
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