Elemental Sub-Lattice Occupation and Microstructural Evolution in γ/γ' Co-12Ti-4Mo-Cr Alloys.

We report on comparative atom probe tomography investigations of γ/γ'-forming Co­12Ti­4Mo­Cr alloys. Moderate additions of Cr (2 and 4 at%) reduced the γ/γ' lattice misfit and increased the γ' volume fraction of a Co­12Ti­4Mo alloy significantly. These microstructural changes were accompanied by changes in the elemental partitioning between γ and γ' and site-occupancy in γ'. Spatial distribution maps revealed that Mo occupied both Co and Ti sub-lattice sites in γ'. In agreement with the experimental data, thermodynamic calculations predicted a stronger tendency for Mo to occupy the Co-sites than for Cr and an increase in Cr fraction on the Ti-sites with increasing Cr content.

The design and fabrication of a multilayered graded GNP/Ni/PMMA nanocomposite for enhanced EMI shielding behavior.

A multilayered graded structure can maximize the electromagnetic interference (EMI) shielding properties of a nanocomposite for a specific amount of a conductive filler in a polymer matrix. In this study, multilayered graded nanocomposites of graphene nanoplatelet (GNP)/Ni/polymethyl methacrylate (PMMA) were developed to achieve enhanced EMI shielding behavior. Both multilayered and monolayered nanocomposites were fabricated by controlling the compositions of GNP/Ni in the PMMA matrix. The contributions of the multilayered nanocomposite to EMI shielding were investigated and compared with the shielding effectiveness of the monolayered nanocomposite. The multilayered nanocomposite shows enhanced shielding effectiveness of around 61 dB in the X-band, which is more than three orders of magnitude higher than that of the monolayered nanocomposite. It has been confirmed that the measurements of reflection, absorption and total shielding effectiveness are in good accordance with the theoretically calculated results. The primary shielding mechanism was absorption due to conductive dissipation. The enhanced absorption of electromagnetic waves is attributed to an abrupt increase in the conductivity between layers in the direction of wave propagation in a multilayered nanocomposite due to impedance matching with the air and internal reflection between layers.