Sandip P. Harimkar

Herein, a combinatorial approach is developed to conduct high‐throughput studies on the nanosecond pulsed laser‐induced dewetting phenomenon of bilayer Ag–Co metallic thin films. Laser irradiation results in the spontaneous rupture of these films in nanosecond timescale, forming bimetallic nanoparticles (NPs) through intermediate stages of hole formation and bicontinuous nanostructures. This approach utilizes bilayer thin films with thickness gradients in both Ag and Co layers (referred to as bigradient samples) while maintaining a constant overall thickness. The laser irradiation on such bigradient bilayer films facilitates control on Ag and Co ratio in the thin films, thus enabling material libraries of Ag–Co NPs covering a large compositional variation. The evolution of NPs with a correlation between NP diameter and interparticle spacings is further studied. The study reveals monotonic increase in NP size and interparticle spacing in Co/Ag bilayer arrangement, while an increase and subsequent decrease in the NP size is observed at 50% Ag in Ag/Co bigradient films. A transition from intermediate stage hole formation to bicontinuous nanostructures with changing composition is also observed. These changes in intermediate stage morphologies and dewetting mechanism are attributed to variation of the free energy of the bilayer system dominated by intermolecular interaction forces.

High entropy superalloys (HESA), an extension of high entropy alloys (HEAs), exhibit excellent high‐temperature properties with low density, making them a potential replacement for expensive and heavy superalloys. While multiple processing routes are available for HEAs, spark plasma sintering is becoming increasingly popular due to its ability to fabricate alloy powder in short period of time. Herein, the phase evolution and microstructural development of gas atomized Al_0.5CoCrFeNi₂ HESA powder fabricated using spark plasma sintering and the wear properties of the sintered specimen are reported. The alloy powder and all the specimen sintered in the range of 800–1050 °C show an extremely stable single‐phase face centered cubic structure. Relative density of 99% is achieved at 1000 °C and above with porosity pinning effect playing an important role in densification behavior and grain growth. In all the sintered specimen, a combination of adhesive, delamination, oxidation, and abrasive wear is observed, with the coefficient of friction lying in the range of 0.6–0.7.

Understanding the thermal stability of metallic glasses is critical to determining their safe temperatures of service. In this paper, the crystallization mechanism in spark plasma sintered Fe₄₈Cr₁₅Mo₁₄Y₂C₁₅B₆ metallic glass is established by analyzing the crystal size distribution using x-ray diffraction, transmission electron microscopy and in-situ small angle neutron scattering. Isothermal annealing at 700 °C and 725 °C for 100 min resulted in the formation of (Fe,Cr)₂₃C₆ crystals, measured from transmission electron micrographs, to be from 10 to 30 nm. The small angle neutron scattering intensity measured in-situ, over a Q-range of 0.02 to 0.3 Å⁻¹, during isothermal annealing of the sintered samples, confirmed the presence of (Fe,Cr)₂₃C₆ crystals. The measured scattering intensity, fitted by the maximum entropy model, over the Q-range of 0.02 to 0.06 Å⁻¹, revealed that the crystals had radii ranging from 3 to 18 nm. The total volume fraction of crystals were estimated to be 0.13 and 0.22 upon isothermal annealing at 700 °C and 725 °C for 100 min respectively. The mechanism of crystallization in this spark plasma sintered iron based metallic glass was established to be from pre-existing nuclei as confirmed by Avrami exponents of 0.25 ± 0.01 and 0.39 ± 0.01 at the aforesaid temperatures.

In this paper, the composition, structure, morphology and kinetics of evolution during isothermal oxidation of Fe₄₈Cr₁₅Mo₁₄Y₂C₁₅B₆ metallic glass powder in the supercooled region are investigated by an integrated ex-situ and in-situ characterization and modelling approach. Raman and X-ray diffraction spectra established that oxidation yielded a hierarchical structure across decreasing length scales. At larger scale, Fe₂O₃ grows as a uniform shell over the powder core. This shell, at smaller scale, consists of multiple grains. Ultra-small angle X-ray scattering intensity acquired during isothermal oxidation of the powder over a wide Q-range delineated direct quantification of oxidation behavior. The hierarchical structure was employed to construct a scattering model that was fitted to the measured intensity distributions to estimate the thickness of the oxide shell. The relative gain in mass during oxidation, computed theoretically from this model, relatively underestimated that measured in practice by a thermogravimetric analyzer due to the distribution in sizes of the particles. Overall, this paper presents the first direct quantification of oxidation in metallic glass powder by ultra-small angle X-ray scattering. It establishes novel experimental environments that can potentially unfold new paradigms of research into a wide spectrum of interfacial reactions in powder materials at elevated temperatures.

In this article, we report a photoprintable nanocomposite synthesized at room temperature in less than 10 s by aggressive mixing of two monomer solutions. Polycondensation occurs in the dispersed phase of the dynamic emulsion, microdroplets, in which the nanofillers are suspended. Hence, the synthesized composite microparticles have a high dispersion and high loading of nanofillers. Specifically, silver nanowire (AgNW)–nylon 66 blends with various Ag weight fractions are synthesized and studied. The poly(vinyl pyrrolidone) (PVP)‐functionalized AgNWs (by polyol synthesis) are singly dispersed and tethered to the nylon matrix by PVP with a slight depression of the glass‐transition temperature. The Ag–nylon powder melts under low‐intensity visible continuous wave laser radiation; this allows convenient photoprinting of the nanocomposite structures. Photoprinting is demonstrated at a radiation intensity of 0.3 kW/cm² (405 nm laser) and a scan rate of 5 mm/s for a 1.49 wt % Ag content. This enhanced photothermal characteristic of the nanocomposite, which allows printing at low radiation intensities, is attributed to the efficient coupling of light to the AgNW plasmon modes and the high dispersion of nanowires in the polymer. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47670.