scholarly journals Ultrahigh Strength and Shear-Assisted Decohesion of Sliding Silver Nanocontacts Studied in situ

2021 ◽  
Author(s):  
Takaaki Sato ◽  
Zachary Milne ◽  
Masahiro Nomura ◽  
Naruo Sasaki ◽  
Robert Carpick ◽  
...  
Keyword(s):  
High Strength ◽  
Contact Forces ◽  
Ideal Strength ◽  
Transmission Electron ◽  
Contact Width ◽  
Theoretical Predictions ◽  
Von Mises ◽  
Von Mises Stresses ◽  
Applied Stresses

Abstract The behavior of materials in sliding contact is challenging to determine since the interface is normally hidden from view. Using a custom microfabricated device, we conducted in situ, ultrahigh vacuum transmission electron microscope measurements of crystalline silver nanocontacts under combined tension and shear, permitting simultaneous observation of contact forces and contact width. While classically, silver exhibits substantial sliding-induced plastic junction growth, the nanocontacts exhibit only limited plastic deformation despite high applied stresses. This difference arises from the nanocontacts’ high strength, as we find the von Mises stresses at yield points approach the ideal strength of silver. We attributed this to the nanocontacts’ nearly defect-free nature and small size. The contacts also separate unstably, with pull-off forces well below classical predictions for rupture under pure tension. This provides in situ confirmation that shearing reduces nanoscale pull-off forces, consistent with recent theoretical predictions but never before directly observed.

In situ observation of the martensitic transformation in (Mg,Y)-PSZ

1986 ◽  
Vol 44 ◽  
pp. 500-501
Author(s):  
R-R. Lee
Keyword(s):  
Martensitic Transformation ◽  
High Strength ◽  
Nucleation And Growth ◽  
In Situ Observation ◽  
Considerable Potential ◽  
Transmission Electron ◽  
Structural Applications ◽  
Applied Stresses ◽  
Kinetics Of

Partially-stabilized ZrO2 (PSZ) ceramics have considerable potential for advanced structural applications because of their high strength and toughness. These properties derive from small tetragonal ZrO2 (t-ZrO2) precipitates in a cubic (c) ZrO2 matrix, which transform martensitically to monoclinic (m) symmetry under applied stresses. The kinetics of the martensitic transformation is believed to be nucleation controlled and the nucleation is always stress induced. In situ observation of the martensitic transformation using transmission electron microscopy provides considerable information about the nucleation and growth aspects of the transformation.

Large plasticity in magnesium mediated by pyramidal dislocations

Science ◽  
2019 ◽  
Vol 365 (6448) ◽  
pp. 73-75 ◽  
Author(s):  
Bo-Yu Liu ◽  
Fei Liu ◽  
Nan Yang ◽  
Xiao-Bo Zhai ◽  
Lei Zhang ◽  
...  
Keyword(s):  
Energy Efficiency ◽  
Electron Microscope ◽  
Plastic Strain ◽  
Crystal Size ◽  
High Stress ◽  
High Strength ◽  
High Plasticity ◽  
Transmission Electron ◽  
Small Crystal Size

Lightweight magnesium alloys are attractive as structural materials for improving energy efficiency in applications such as weight reduction of transportation vehicles. One major obstacle for widespread applications is the limited ductility of magnesium, which has been attributed to 〈c+a〉 dislocations failing to accommodate plastic strain. We demonstrate, using in situ transmission electron microscope mechanical testing, that 〈c+a〉 dislocations of various characters can accommodate considerable plasticity through gliding on pyramidal planes. We found that submicrometer-size magnesium samples exhibit high plasticity that is far greater than for their bulk counterparts. Small crystal size usually brings high stress, which in turn activates more 〈c+a〉 dislocations in magnesium to accommodate plasticity, leading to both high strength and good plasticity.

Effective Stresses and Plastic Strain Rates in a Superalloy: a High Temperature In Situ Study by Synchrotron X-Ray TCD

2006 ◽  
Vol 524-525 ◽  
pp. 775-780 ◽  
Author(s):  
Alain Jacques ◽  
Olivier Ferry ◽  
Frédéric Diologent ◽  
Pierre Caron ◽  
Pierre Bastie
Keyword(s):  
High Temperature ◽  
Plastic Strain ◽  
Tensile Axis ◽  
Young Modulus ◽  
High Energy ◽  
Strain Rates ◽  
Data Scatter ◽  
Von Mises ◽  
Von Mises Stresses

Variations in the lattice parameters of γ and γ' phases perpendicular to the [001] tensile axis were recorded in situ at ~10 minutes intervals using the Triple Axis Diffractometer of the High Energy (ID15) beamline at ESRF. Testing was carried out on an AM1 superalloy specimen with a raft microstructure at high temperature (1072°C) under load steps between 0 MPa and 300 MPa. These data were used to evaluate the Young modulus and the effective (Von Mises) stresses within the γ' rafts and γ corridors, as well the average plastic strain rates of each phase. The recorded stress data scatter was within the MPa range, and should be good enough to probe the elementary mechanisms of plasticity.

In Situ Synthesis of A MoSi2/SiC Composite Using Solid State Displacement Reactions

1992 ◽  
Vol 273 ◽  
Author(s):  
C. H. Henager ◽  
J. L. Brimhall ◽  
J. S. Vetrano ◽  
J. P. Hirth
Keyword(s):  
Solid State ◽  
Phase Distribution ◽  
High Strength ◽  
Dark Field ◽  
Fine Grained ◽  
Dark Field Imaging ◽  
Sic Particles ◽  
Transmission Electron ◽  
Displacement Reactions

ABSTRACTA high-strengthin situcomposite of MoSi2/SiC was synthesized using a solid state displacement reaction between Mo2C and Si by blending Mo2C and Si powders and vacuum hotpressing the powders at 1350°C for 2 h followed by 1 h at 1700°C. The resulting microstructure consisted of 1-μm diameter β-SiC particles (30 vol%) uniformly dispersed in a fine grained MoSi2matrix. Transmission electron microscopy was used to study the fine-scale morphology and phase distribution of the composite. Evidence for a small amount of grain boundary glass phase was observed using diffuse dark field imaging. The β-SiC particles were distributed mainly on grain boundaries and triple points within the MoSi2matrix. These findings were used to rationalize the observed mechanical property behavior.

Interaction of Oxide Surfaces with Water: Environmental Transmission Electron Microscopy of MgO Hydroxylation

2005 ◽  
Vol 11 (6) ◽  
pp. 524-533 ◽  
Author(s):  
Marija Gajdardziska-Josifovska ◽  
Renu Sharma
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Water Pressure ◽  
Dissociative Adsorption ◽  
Environmental Transmission ◽  
Transmission Electron ◽  
Theoretical Predictions ◽  
Adsorption Of Water ◽  
Environmental Transmission Electron Microscopy

Environmental transmission electron microscopy (ETEM) is opening an important window for in situ studies of interaction of water with oxides. Studies of MgO smoke nanocrystals under partial pressures of water ranging from 10 mTorr to 10 Torr found their {100} neutral surfaces to be extremely resistant to dissociative adsorption of water and hydroxylation, in agreement with recent theoretical predictions. ETEM observations of electron irradiation driven MgO smoke nanocrystal hydroxylation displayed the anticipated volume expansion, but revealed complex shape changes with elongations toward oxide corners. The reaction rate was found to increase with electron flux at constant water pressure. In situ selected area diffraction studies of MgO single crystals showed that the hydroxide grows with its basal (0001) plane parallel to the polar MgO (111) planes. This is the same crystallographic relationship as in dehydroxylation experiments, but with four variants. Electron energy loss spectroscopy found oxygen K-edge changes consistent with bulk hydroxylation.

scholarly journals Strength can be controlled by edge dislocations in refractory high-entropy alloys

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Chanho Lee ◽  
Francesco Maresca ◽  
Rui Feng ◽  
Yi Chou ◽  
T. Ungar ◽  
...  
Keyword(s):  
High Strength ◽  
Recent Theory ◽  
High Entropy Alloys ◽  
High Entropy ◽  
Refractory Elements ◽  
Transmission Electron ◽  
In Situ Neutron Diffraction ◽  
Edge Dislocations ◽  
Strength Retention

AbstractEnergy efficiency is motivating the search for new high-temperature (high-T) metals. Some new body-centered-cubic (BCC) random multicomponent “high-entropy alloys (HEAs)” based on refractory elements (Cr-Mo-Nb-Ta-V-W-Hf-Ti-Zr) possess exceptional strengths at high temperatures but the physical origins of this outstanding behavior are not known. Here we show, using integrated in-situ neutron-diffraction (ND), high-resolution transmission electron microscopy (HRTEM), and recent theory, that the high strength and strength retention of a NbTaTiV alloy and a high-strength/low-density CrMoNbV alloy are attributable to edge dislocations. This finding is surprising because plastic flows in BCC elemental metals and dilute alloys are generally controlled by screw dislocations. We use the insight and theory to perform a computationally-guided search over 107 BCC HEAs and identify over 106 possible ultra-strong high-T alloy compositions for future exploration.

“In Situ” observation by Transmission Electron Microscope of the deformation and fracture micromechanisms in 7050 aluminum alloy

1990 ◽  
Vol 48 (4) ◽  
pp. 522-523
Author(s):  
W.A. Monteiro ◽  
O.E. Alarcon ◽  
A.M.M. Nazar
Keyword(s):  
Aluminum Alloy ◽  
High Strength ◽  
Propagation Mode ◽  
In Situ Observation ◽  
Brittle Behavior ◽  
Transmission Electron ◽  
Deformation And Fracture ◽  
7050 Aluminum Alloy ◽  
In Situ Deformation

During the last ten years the "in situ" deformation experiments by transmission electron microscopy have been used in metals to study the micromechanism of plastic deformation and fracture propagation mode occuring from the crack tip.These studies were performed in mono and policrystals metals with the aim to investigate the dislocation emission from crack tip phenomena relating it with the ductil versus brittle behavior of materials.The material used in this experiment was a high strength aluminum alloy 7050 contained recrystal1ized and unrecrystal1ized microstructures, as the obtained by thermomechanical treatment in previous work .Due to the small dimensions of the miniature tensile specimens (2.7 × 6.8 × 0.02 mm ) and the requisite to obtain a lot of samples without introduction of strain during manufacture, the specimens was performed using a lithographic process.

TEM Investigations of Titanium Processed by ECAP Followed by Cold Rolling

2006 ◽  
Vol 503-504 ◽  
pp. 805-810 ◽  
Author(s):  
Bernhard Mingler ◽  
V.V. Stolyarov ◽  
Michael Zehetbauer ◽  
Wolfgang Lacom ◽  
Hans Peter Karnthaler
Keyword(s):  
Cold Rolling ◽  
Room Temperature ◽  
High Strength ◽  
Tensile Tests ◽  
Coarse Grained ◽  
Angular Pressing ◽  
Transmission Electron ◽  
Cp Ti ◽  
Annealing Experiments

Conventional coarse grained (CG) commercial pure (CP) Ti Grade 2 was studied after cold rolling (CR) at room temperature, and after equal channel angular pressing (ECAP) at 450° C followed by CR, by transmission electron microscopy (TEM) methods. CR of the CG material leads to a microstructure showing initially twins with (0112) type and later subgrains separated by lowangle grain boundaries. CR carried out after ECAP yields the fragmentation of fine grains (300 – 800 nm) mostly bounded by high-angle boundaries into elongated subgrains (~ 100 nm). It was shown with in-situ annealing experiments in the TEM that this microstructure is thermally stable up to a temperature of 450° C. Tensile tests showed that the combination of ECAP with CR has the potential to produce at the same time high strength (941 MPa) and high ductility (16.7%).

Techniques for Studying Nanoparticle Sintering by Plan-View In Situ Transmission Electron Microscopy

1998 ◽  
Vol 4 (3) ◽  
pp. 248-253 ◽  
Author(s):  
M. Yeadon ◽  
J.C. Yang ◽  
R.S. Averback ◽  
J.M. Gibson
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Single Crystal Substrate ◽  
Plan View ◽  
Supported Nanoparticles ◽  
Transmission Electron ◽  
Theoretical Predictions ◽  
Crystal Substrate

We discuss various techniques for the characterization of supported nanoparticles by in situ plan-view transmission electron microscopy. In particular, we discuss here mechanisms of image contrast formation by particles undergoing reorientation on the surface of a single crystal substrate. We consider reorientation by a variety of mechanisms including rotation, sintering and grain growth, and surface diffusion. Experimental observations are presented and the data compared with theoretical predictions.

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