4 research outputs found
Study of the microstructure of a weld bead P91 steel by transmission electron microscopy
<p></p><p>ABSTRACT In the present work the microstructural characterization of a single-pass weld of 9Cr1MoVNb P91 steel performed by the flux-cored arc welding (FCAW) process in the âas weldingâ condition has been carried out by means of transmission electron microscopy. P91 steel offers a good weldability, but the mechanical properties of the welded joints are found to be inferior compared to the base metal. The heat affected zone (HAZ) of these types of steels is ~ 4 mm making it difficult to extract carbon replicas and thin foil to study the microstructure generated in each sub-zone of the ZAC: coarse grained ZAC (CGZAC), fine grained ZAC (FGZAC) and intercritical ZAC (ICZAC). Nev-ertheless, it was possible to extract replicas from each region to identify precipitates and using a focused ion beam (FIB-SEM), thin films could be extracted from a specific area to characterize the matrix microstructure. The precipitates present in each subzone of the ZAC were characterized as well as how the dissolution of M23C6 affects the matrix. At low peak temperatures and low heating / cooling rates such as those characterizing the fine grain zones (ICHAZ and FGHAZ) the M23C6 carbides were found to be partially dissolved and in contact with retained austenite. On the other hand, in the areas with the highest peak temperatures and high heating/cooling rates (CGHAZ and fusion zone) thin films of retained austenite were found on the austenitic grain boundaries and on the martensĂtica lath. On the other hand, in the areas with the highest peak temperatures and high heating / cooling rates (ZACGG and ZF) thin films of retained austenite on the austenitic grain edges and the martensite laths were found.</p><p></p
Local Structure-Driven Localized Surface Plasmon Absorption and Enhanced Photoluminescence in ZnO-Au Thin Films
Nanocomposite
films consisting of gold nanoparticles embedded in
zinc oxide (ZnO-Au) have been synthesized with different gold loadings
by reactive magnetron sputtering at near-room temperature followed
by ex situ annealing in air up to 300 °C. Using X-ray diffraction
and high resolution transmission microscopy it is shown that during
deposition gold substitutes zinc in ZnO as isolated atoms and in nanoparticles
still exhibiting the structure of ZnO. Both situations degrade the
crystalline quality of the ZnO matrix, but thermal annealing cures
it from isolated gold atoms and triggers the formation of gold nanoparticles
of size higher than 3 nm, sufficient to observe a strong activation
of localized surface plasmon resonance (LSPR). The amplitude of LSPR
absorption observed after annealing increases with the gold loading
and annealing temperature. Moreover, UV and visible photoluminescence
from the ZnO matrix is strongly enhanced upon activation of LSPR showing
strong coupling with the gold nanoparticles. Finally, modeling of
spectroscopic ellipsometry measurements unambiguously reveals how
curing the defects increases the optical bandgap of the ZnO matrix
and modifies the optical dielectric functions of the nanocomposite
and ZnO matrix
Efficient, Low Cost Synthesis of Sodium Platinum Bronze Na<sub><i>x</i></sub>Pt<sub>3</sub>O<sub>4</sub>
Efficient, Low Cost Synthesis
of Sodium Platinum Bronze
Na<sub><i>x</i></sub>Pt<sub>3</sub>O<sub>4</sub
Local Modification of the Microstructure and Electrical Properties of Multifunctional AuâYSZ Nanocomposite Thin Films by Laser Interference Patterning
Nanocomposite films consisting of
gold nanoparticles embedded in
an yttria-stabilized zirconia matrix (AuâYSZ) have been synthesized
with different gold loadings by reactive magnetron sputtering followed
by ex situ annealing in air or laser interference patterning (LIP)
treatment. It is shown that the electrical conductivity of the nanocomposite
films can be modified to a large extent by changing the gold loading,
by thermal annealing, or by LIP. The structural and microstructural
analyses evidenced the segregation of metallic gold in crystalline
form for all synthesis conditions and treatments applied. Thermal
annealing above 400 °C is observed to trigger the growth of pre-existing
nanoparticles in the volume of the films. Moreover, pronounced segregation
of gold to the film surface is observed for Au/(Au + Zr + Y) ratios
above 0.40, which may prevent the use of thermal annealing to functionalize
gold-rich AuâYSZ coatings. In contrast, significant modifications
of the microstructure were detected within the interference spot (spot
size close to 2 Ă 2 mm) of LIP treatments only for the regions
corresponding to constructive interference. As a consequence, besides
its already demonstrated ability to modify the friction behavior of
AuâYSZ films, the LIP treatment enables local tailoring of
their electrical resistivity. The combination of these characteristics
can be of great interest for sliding electrical contacts