Understanding the electrochemical properties at a localized
scale
is critically important to comprehend the origin of corrosion and
develop multifunctional materials with robust corrosion resistance,
particularly at conjoined metal interfaces typically encountered in
automobile manufacturing. Scanning electrochemical cell microscopy
(SECCM) is an emerging technique which enables to study the corrosion
of metal surfaces to be visualized at the microscopic level. In this
work, we developed scanning electrochemical cell impedance microscopy
(SECCIM) by combining SECCM with electrochemical impedance spectroscopy
(EIS) and explored the unique advantages of using SECCIM to measure
the corrosion kinetics on single-crystal Mg (0001) as the model surface
using direct current and alternating current polarization techniques.
Specifically, a theta capillary with a tip diameter of 10 μm
filled with a 0.01 M NaCl electrolyte was used as a probe to perform
spatially resolved potentiodynamic Tafel polarization and EIS. The
combination of traditional SECCM with EIS led to the development of
SECCIM and enabled us to study small interfacial events such as charge
transfer, adsorption, and emergence of resistive oxide films on the
surface using the distribution of relaxation time analysis. Furthermore,
by comparing localized SECCIM measurements with bulk electrochemical
measurements, we establish the reliability of SECCIM for the mapping
of corrosion potential and associated charge-transfer resistance on
the Mg (0001) surface. Our results indicate that SECCIM measurement
with Tafel and EIS analysis will provide an unparalleled ability to
characterize the pitting corrosion mechanism on the heterogeneous
surface of mixed-metal alloys and metal joints.
Ultra high molecular weight polyethylene (PE) is a structural polymer widely used in biomedical implants. The mechanical properties of PE can be improved either by controlled crystalline orientation (texture) or by the addition of reinforcing agents. However, the combinatorial effect has not received much attention. The objective of this study was to characterize the structure and mechanical properties of PE composites incorporating multiwall carbon nanotubes (MWCNT) and reduced graphene oxide (RGO) subjected to hot rolling. The wide angle X-ray diffraction studies revealed that mechanical deformation resulted in a mixture of orthorhombic and monoclinic crystals. Furthermore, the presence of nanoparticles resulted in lower crystallinity in PE with smaller crystallite size, more so in RGO than in MWCNT composites. Rolling strengthened the texture of both orthorhombic and the monoclinic phases in PE. Presence of RGO weakened the texture of both phases of PE after rolling whereas MWCNT only mildly weakened the texture. This resulted in a reduction in the elastic modulus of RGO composites whereas moduli of neat polymer and the MWCNT composite increased after rolling. This study provides new insight into the role of nanoparticles in texture evolution during polymer processing with implications for processing of structural polymer composites.
The present study aims to understand the evolution of textural and microstructural heterogeneity and its effect on evolution of mechanical properties of an equiatomic FCC CoCuFeMnNi high entropy alloy (HEA) disc subjected to high pressure torsion (HPT). HPT was performed on disc specimen with a hydrostatic pressure of 5 GPa for 0.1, 0.5, 1 and 5 turns at room temperature diffraction analysis shows decrease in crystalline size with simultaneous increase in dislocation density for five-turn HPT sample with increasing strain from centre to the periphery of the disc.Microstructural analysis using electron back scatter diffraction and transmission electron microscopy indicates extensive grain fragmentation (≈ 55 nm at the periphery of five-turn sample). The evolution of hardness from centre to the periphery of the disc cannot be explained only on the basis of evolution of grain size and dislocation density. The increase in contribution from solid solution strengthening due to partial dissolution of copper rich nano-clusters is expected to be the underlying cause for increase in the hardness. Thus, evolution of gradient microstructure, texture, and chemistry opens up new vistas for designing functionally graded materials for engineering materials.
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