8,611 research outputs found
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Direct imaging of short-range order and its impact on deformation in Ti-6Al.
Chemical short-range order (SRO) within a nominally single-phase solid solution is known to affect the mechanical properties of alloys. While SRO has been indirectly related to deformation, direct observation of the SRO domain structure, and its effects on deformation mechanisms at the nanoscale, has remained elusive. Here, we report the direct observation of SRO in relation to deformation using energy-filtered imaging in a transmission electron microscope (TEM). The diffraction contrast is enhanced by reducing the inelastically scattered electrons, revealing subnanometer SRO-enhanced domains. The destruction of these domains by dislocation planar slip is observed after ex situ and in situ TEM mechanical testing. These results confirm the impact of SRO in Ti-Al alloys on the scale of angstroms. The direct confirmation of SRO in relationship to dislocation plasticity in metals can provide insight into how the mechanical behavior of concentrated solid solutions by the material's thermal history
In situ scanning electron microscopy indentation studies on multilayer nitride films: Methodology and deformation mechanisms
Systematic studies of the deformation mechanisms of multilayer transition metal nitride coatings TiN/CrN, TiN/NbN, and NbN/CrN, and corresponding reference coatings of TiN, NbN, and CrN deposited by a direct current (dc) magnetron sputtering process onto silicon ă100ă have been performed. Mechanical characterization was conducted using a combination of microindentation and nanoindentation in the load range 30 to 150 mN and 0.5 to 3.5 mN, respectively. For both load ranges, scanning electron microscopy (SEM) in situ indentation was used to observe the indentation process including any pileup, sink-in, and fracture mechanisms specific to each coating. The coatings' microstructure, both before and after indentation, was analyzed using transmission electron microscopy (TEM). It was possible to both correlate the indentation load-displacement response to surface roughness effects and fracture modes (substrate and film cracking) and observe deformation mechanisms within the coating
UHMWPE/SBA-15 nanocomposites synthesized by in situ polymerization
Different nanocomposites have been attained by in situ polymerization based on ultra-high molecular
weight polyethylene (UHMWPE) and mesoporous SBA-15, this silica being used for immobilization of the
FI catalyst bis [N-(3-tert-butylsalicylidene)-2,3,4,5,6-pentafluoroanilinato] titanium (IV) dichloride and as
filler as well. Two distinct approaches have been selected for supporting the FI catalyst on the SBA-15
prior polymerization. A study on polymerization activity of this catalyst has been performed under
homogenous conditions and upon heterogenization. A study of the effect of presence of mesoporous
particles and of the immobilization method is also carried out. Moreover, the thermal characterization,
phase transitions and mechanical response of some pristine UHMWPEs and UHMWPE/SBA-15 materials
have been carried out. Relationships with variations on molar mass, impregnation method of catalyst and
final SBA-15 content have been established
Catastrophic vs Gradual Collapse of Thin-Walled Nanocrystalline Ni Hollow Cylinders As Building Blocks of Microlattice Structures
Lightweight yet stiff and strong lattice structures are attractive for various engineering applications, such as cores of sandwich shells and components designed for impact mitigation. Recent breakthroughs in manufacturing enable efficient fabrication of hierarchically architected microlattices, with dimensional control spanning seven orders of magnitude in length scale. These materials have the potential to exploit desirable nanoscale-size effects in a macroscopic structure, as long as their mechanical behavior at each appropriate scale â nano, micro, and macro levels â is properly understood. In this letter, we report the nanomechanical response of individual microlattice members. We show that hollow nanocrystalline Ni cylinders differing only in wall thicknesses, 500 and 150 nm, exhibit strikingly different collapse modes: the 500 nm sample collapses in a brittle manner, via a single strain burst, while the 150 nm sample shows a gradual collapse, via a series of small and discrete strain bursts. Further, compressive strength in 150 nm sample is 99.2% lower than predicted by shell buckling theory, likely due to localized buckling and fracture events observed during in situ compression experiments. We attribute this difference to the size-induced transition in deformation behavior, unique to nanoscale, and discuss it in the framework of âsize effectsâ in crystalline strength
Review of the Synergies Between Computational Modeling and Experimental Characterization of Materials Across Length Scales
With the increasing interplay between experimental and computational
approaches at multiple length scales, new research directions are emerging in
materials science and computational mechanics. Such cooperative interactions
find many applications in the development, characterization and design of
complex material systems. This manuscript provides a broad and comprehensive
overview of recent trends where predictive modeling capabilities are developed
in conjunction with experiments and advanced characterization to gain a greater
insight into structure-properties relationships and study various physical
phenomena and mechanisms. The focus of this review is on the intersections of
multiscale materials experiments and modeling relevant to the materials
mechanics community. After a general discussion on the perspective from various
communities, the article focuses on the latest experimental and theoretical
opportunities. Emphasis is given to the role of experiments in multiscale
models, including insights into how computations can be used as discovery tools
for materials engineering, rather than to "simply" support experimental work.
This is illustrated by examples from several application areas on structural
materials. This manuscript ends with a discussion on some problems and open
scientific questions that are being explored in order to advance this
relatively new field of research.Comment: 25 pages, 11 figures, review article accepted for publication in J.
Mater. Sc
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Advances in test and measurement of the interface adhesion and bond strengths in coating-substrate systems, emphasising blister and bulk techniques
In this paper, recent advances in the minimum-destructive testing of the adhesion of coating-substrate systems are reviewed, focusing on key techniques such as micro- and nano-scale levels of indentation, scratching, laser-induced wave shock, as well as the blister and buckle approach. Along with adhesion failure tests, the latest and most extensive applications of the adhesion test methods in nano-, micro- and bulk-coating technology and the associated techniques to determine the minimum damage defects left on the coatings are discussed and their use reviewed
Phase transformations induced by spherical indentation in ion-implanted amorphous silicon
The deformation behavior of ion-implanted (unrelaxed) and annealed ion-implanted (relaxed) amorphous silicon(a-Si) under spherical indentation at room temperature has been investigated. It has been found that the mode of deformation depends critically on both the preparation of the amorphous film and the scale of the mechanical deformation.Ex situmeasurements, such as Raman microspectroscopy and cross-sectional transmission electron microscopy, as well as in situ electrical measurements reveal the occurrence of phase transformations in all relaxed a-Si films. The preferred deformation mode of unrelaxed a-Si is plastic flow, only under certain high load conditions can this state of a-Si be forced to transform. In situ electrical measurements have revealed more detail of the transformation process during both loading and unloading. We have used ELASTICA simulations to obtain estimates of the depth of the metallic phase as a function of load, and good agreement is found with the experiment. On unloading, a clear change in electrical conductivity is observed to correlate with a âpop-outâ event on load versus penetration curves
Hybrid materials based on polyethylene and MCM-41 microparticles functionalized with silanes: catalytic aspects of in situ polymerization, crystalline features and mechanical properties
New nanocomposites based on polyethylene have been prepared by in situ polymerization of ethylene in
presence of mesoporous MCM-41. The polymerization reactions were performed using a zirconocene
catalyst either under homogenous conditions or supported onto mesoporous MCM-41 particles, which
are synthesized and decorated post-synthesis with two silanes before polymerization in order to promote
an enhanced interfacial adhesion. The existence of polyethylene chains able to crystallize within
the mesoporous channels in the resulting nanocomposites is figured out from the small endothermic
process, located at around 80 C, on heating calorimetric experiments, in addition to the main melting
endotherm. These results indicate that polyethylene macrochains can grow up during polymerization
either outside or inside the MCM-41 channels, these keeping their regular hexagonal arrangements.
Mechanical response is observed to be dependent on the content in mesoporous MCM-41 and on the
crystalline features of polyethylene. Accordingly, stiffness increases and deformability decreases in the
nanocomposites as much as MCM-41 content is enlarged and polyethylene amount within channels is
raised. Ultimate mechanical performance improves with MCM-41 incorporation without varying the
final processing temperature
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