scholarly journals Dislocation-mediated shear amorphization in boron carbide

2021 ◽  
Vol 7 (8) ◽  
pp. eabc6714 ◽  
Author(s):  
Kolan Madhav Reddy ◽  
Dezhou Guo ◽  
Shuangxi Song ◽  
Chun Cheng ◽  
Jiuhui Han ◽  
...  
Keyword(s):  
Boron Carbide ◽  
Structural Transition ◽  
Activation Volume ◽  
Structural Evolution ◽  
Dislocation Nucleation ◽  
Superhard Materials ◽  
Rate Dependent ◽  
Transmission Electron ◽  
Lower Activation ◽  
Underlying Mechanisms

The failure of superhard materials is often associated with stress-induced amorphization. However, the underlying mechanisms of the structural evolution remain largely unknown. Here, we report the experimental measurements of the onset of shear amorphization in single-crystal boron carbide by nanoindentation and transmission electron microscopy. We verified that rate-dependent loading discontinuity, i.e., pop-in, in nanoindentation load-displacement curves results from the formation of nanosized amorphous bands via shear amorphization. Stochastic analysis of the pop-in events reveals an exceptionally small activation volume, slow nucleation rate, and lower activation energy of the shear amorphization, suggesting that the high-pressure structural transition is activated and initiated by dislocation nucleation. This dislocation-mediated amorphization has important implications in understanding the failure mechanisms of superhard materials at stresses far below their theoretical strengths.

Dislocation Character and Evolution Mechanism of Particles Reinforced Aluminum Matrix Composites Impacted by Pulsed Electromagnetic Field

2013 ◽  
Vol 575-576 ◽  
pp. 406-409 ◽  
Author(s):  
Xue Ting Yuan ◽  
Guirong Li ◽  
Hong Ming Wang ◽  
Yun Cai ◽  
Yu Tao Zhao ◽  
...  
Keyword(s):  
Dislocation Density ◽  
Aluminum Matrix ◽  
Structural Evolution ◽  
Elastic Interaction ◽  
Dislocation Nucleation ◽  
Aluminum Matrix Composites ◽  
Matrix Composites ◽  
Transmission Electron ◽  
Dislocation Movement ◽  
Pulsed Electromagnetic

Under the condition of different magnetic induced intensity as1.5T, 2.0T and2.5T, AlTiZr particles reinforced 7055 aluminum matrix composites were subject to the magnetic impact processing. The structural evolution was observed by transmission electron microscope. The result shows that, magnetic impact processing can induce dislocation with different morphologies and increase the dislocation density. The enhancement of dislocation density and elastic interaction between them can cause the resistance of dislocation movement and improve the strength of material. The magnetic pressure may exceed the yield strength of special orientation crystal. The increased temperature induced by heat effect will lower the yield point further. It is useful to dislocation nucleation and movement.

scholarly journals Directional amorphization of boron carbide subjected to laser shock compression

2016 ◽  
Vol 113 (43) ◽  
pp. 12088-12093 ◽  
Author(s):  
Shiteng Zhao ◽  
Bimal Kad ◽  
Bruce A. Remington ◽  
Jerry C. LaSalvia ◽  
Christopher E. Wehrenberg ◽  
...  
Keyword(s):  
Solid State ◽  
Boron Carbide ◽  
Shock Compression ◽  
Shear Stresses ◽  
Shear Direction ◽  
Ballistic Performance ◽  
Rate Dependent ◽  
Thermal Energy Conversion ◽  
State Process ◽  
Transmission Electron

Solid-state shock-wave propagation is strongly nonequilibrium in nature and hence rate dependent. Using high-power pulsed-laser-driven shock compression, unprecedented high strain rates can be achieved; here we report the directional amorphization in boron carbide polycrystals. At a shock pressure of 45∼50 GPa, multiple planar faults, slightly deviated from maximum shear direction, occur a few hundred nanometers below the shock surface. High-resolution transmission electron microscopy reveals that these planar faults are precursors of directional amorphization. It is proposed that the shear stresses cause the amorphization and that pressure assists the process by ensuring the integrity of the specimen. Thermal energy conversion calculations including heat transfer suggest that amorphization is a solid-state process. Such a phenomenon has significant effect on the ballistic performance of B4C.

scholarly journals Structural Evolution in Wet Mechanically Alloyed Co-Fe-(Ta,W)-B Alloys

Metals ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 800
Author(s):  
Vladimír Girman ◽  
Maksym Lisnichuk ◽  
Daria Yudina ◽  
Miloš Matvija ◽  
Pavol Sovák ◽  
...  
Keyword(s):  
Structural Changes ◽  
Magnetic Measurements ◽  
Structural Evolution ◽  
High Energy ◽  
Control Agent ◽  
X Ray Diffraction ◽  
Mechanically Alloyed ◽  
X Ray ◽  
Transmission Electron ◽  
X Ray Absorption

In the present study, the effect of wet mechanical alloying (MA) on the glass-forming ability (GFA) of Co43Fe20X5.5B31.5 (X = Ta, W) alloys was studied. The structural evolution during MA was investigated using high-energy X-ray diffraction, X-ray absorption spectroscopy, high-resolution transmission electron microscopy and magnetic measurements. Pair distribution function and extended X-ray absorption fine structure spectroscopy were used to characterize local atomic structure at various stages of MA. Besides structural changes, the magnetic properties of both compositions were investigated employing a vibrating sample magnetometer and thermomagnetic measurements. It was shown that using hexane as a process control agent during wet MA resulted in the formation of fully amorphous Co-Fe-Ta-B powder material at a shorter milling time (100 h) as compared to dry MA. It has also been shown that substituting Ta with W effectively suppresses GFA. After 100 h of MA of Co-Fe-W-B mixture, a nanocomposite material consisting of amorphous and nanocrystalline bcc-W phase was synthesized.

scholarly journals Imaging the Polymorphic Transformation in a Single Cu6Sn5 Grain in a Solder Joint

Materials ◽  
2018 ◽  
Vol 11 (11) ◽  
pp. 2229 ◽  
Author(s):  
Flora Somidin ◽  
Hiroshi Maeno ◽  
Xuan Tran ◽  
Stuart D. McDonald ◽  
Mohd Mohd Salleh ◽  
...  
Keyword(s):  
Solder Joint ◽  
Polymorphic Transformation ◽  
Structural Evolution ◽  
Real Space ◽  
Transformation Behavior ◽  
New Approach ◽  
Transmission Electron ◽  
Contrast Pattern ◽  
In Situ Observations

In-situ observations of the polymorphic transformation in a single targeted Cu6Sn5 grain constrained between Sn-0.7 wt % Cu solder and Cu-Cu3Sn phases and the associated structural evolution during a solid-state thermal cycle were achieved via a high-voltage transmission electron microscope (HV-TEM) technique. Here, we show that the monoclinic η′-Cu6Sn5 superlattice reflections appear in the hexagonal η-Cu6Sn5 diffraction pattern upon cooling to isothermal 140 °C from 210 °C. The in-situ real space imaging shows that the η′-Cu6Sn5 contrast pattern is initiated at the grain boundary. This method demonstrates a new approach for further understanding the polymorphic transformation behavior on a real solder joint.

Structural Evolution Upon Annealing of Multi-Layer Si/Fe Thin Films Prepared by Magnetron Sputtering

2007 ◽  
Vol 561-565 ◽  
pp. 1161-1164
Author(s):  
Xiao Na Li ◽  
Bing Hu ◽  
Chuang Dong ◽  
Xin Jiang
Keyword(s):  
Thin Films ◽  
Magnetron Sputtering ◽  
Room Temperature ◽  
Structural Evolution ◽  
Radio Frequency Magnetron Sputtering ◽  
Transmission Electron ◽  
Direct Band ◽  
The Stability ◽  
Sputtering System

Fe/Si multi-layer films were fabricated on Si (100) substrates utilizing radio frequency magnetron sputtering system. Si/β-FeSi2 structure was found in the films after the deposition. Structural characterization of Fe-silicide sample was performed by transmission electron microscopy, to explore the dependence of the microstructure of β-FeSi2 film on the preparation parameters. It was found that β-FeSi2 particles were formed after the deposition without annealing, whose size is less than 20nm ,with a direct band-gap of 0.94eV in room temperature. After annealing at 850°C, particles grow lager, however the stability of thin films was still good.

Temperature Dependent Structural Evolution of Graphene Layers on 4H-SiC(0001)

2011 ◽  
Vol 679-680 ◽  
pp. 797-800 ◽  
Author(s):  
Sushant Sonde ◽  
Carmelo Vecchio ◽  
Filippo Giannazzo ◽  
Corrado Bongiorno ◽  
Salvatore di Franco ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Structural Evolution ◽  
Morphological Transformation ◽  
Temperature Dependent ◽  
Microscopy Imaging ◽  
Graphene Layers ◽  
Force Microscopy ◽  
Atomic Force ◽  
Transmission Electron ◽  
Mode Atomic Force Microscopy

In this study we examined the structural evolution of graphene grown on 8° off-axis 4H-SiC(0001) substrates at temperatures from 1600°C to 1700°C in Ar ambient. Morphological transformation of SiC substrate after annealing was examined by Tapping Mode Atomic Force Microscopy. Moreover, by etching-out graphene layers from graphitized SiC substrates in selective trenches we determined the number of graphene layers. Numbers of graphene layers were then independently confirmed by Transmission Electron Microscopy imaging.

Structural evolution in lead substituted Bi–Sr–Ca–Cu–O superconductors

1991 ◽  
Vol 6 (2) ◽  
pp. 278-288 ◽  
Author(s):  
R. Ramesh ◽  
K. Remschnig ◽  
J.M. Tarascon ◽  
S.M. Green
Keyword(s):  
Structural Evolution ◽  
Homogeneous Sample ◽  
X Ray ◽  
Thermodynamics And Kinetics ◽  
Transmission Electron ◽  
Incommensurate Modulation ◽  
Kinetics Of ◽  
Pb Substitution ◽  
Microstructural Homogeneity

The structural evolution and cationic stoichiometry of Bi(Pb)–Sr–Ca–Cu–O superconductors have been studied using transmission electron microscopy and x-ray microanalysis. The nature of the incommensurate modulation changes systematically as increasing amounts of lead are added. X-ray microanalysis studies reveal that lead replaces Bi in the structure. Pb addition improves the microstructural homogeneity leading to the formation of a nearly homogeneous sample consisting of the “2223” phase. Based upon all the experimental results, it is inferred that the role of Pb substitution is related to the thermodynamics and kinetics of the formation of the n = 3 phase.

Rate dependent structural transition and cycling stability of a lithium-rich layered oxide material

2019 ◽  
Vol 21 (39) ◽  
pp. 21984-21990 ◽  
Author(s):  
Songyoot Kaewmala ◽  
Visittapong Yordsri ◽  
Wanwisa Limphirat ◽  
Jeffrey Nash ◽  
Sutham Srilomsak ◽  
...  
Keyword(s):  
Electric Vehicles ◽  
Cathode Materials ◽  
Structural Transition ◽  
Cycling Stability ◽  
Oxide Material ◽  
Oxide Materials ◽  
Promising Candidate ◽  
Layered Oxide ◽  
Rate Dependent

Lithium-rich layered oxide materials, xLi2MnO3·(1 − x)LiMO2 (M = Mn, Fe, Co, Ni, etc.), are a promising candidate for use as cathode materials in the batteries of electric vehicles (EVs).

scholarly journals Room-Temperature Creep Behavior and Activation Volume of Dislocation Nucleation in a LiTaO3 Single Crystal by Nanoindentation

Materials ◽  
2019 ◽  
Vol 12 (10) ◽  
pp. 1683 ◽  
Author(s):  
Yi Ma ◽  
Xianwei Huang ◽  
Yuxuan Song ◽  
Wei Hang ◽  
Taihua Zhang
Keyword(s):  
Creep Deformation ◽  
Room Temperature ◽  
Activation Volume ◽  
Rate Sensitivity ◽  
Dislocation Nucleation ◽  
Orientation Effect ◽  
Plastic Behavior ◽  
Mechanical Heterogeneity ◽  
Temperature Creep ◽  
Room Temperature Creep

The crystal orientation effect on mechanical heterogeneity of LiTaO3 single crystals is well known, whilst the time-dependent plastic behavior, i.e., creep is still short of understanding. Relying on nanoindentation technology, we systematically studied room-temperature creep flows at various holding depths (100 nm to 1100 nm) in three typical orientations namely the X-112°, Y-36° and Y-42° planes. Creep resistance was much stronger in the X-112° plane than the others. In the meanwhile, creep features were similar in the Y-36° and Y-42° planes. The orientation effect on creep deformation was consistent with that on hardness. The nanoindentation length scale played an important role in creep deformation that creep strains were gradually decreased with the holding depth in all the planes. Based on strain rate sensitivity and yield stress, the activation volumes of dislocation nucleation were computed at various nanoindentation depths. The activation volumes ranged from 5 Å3 to 23 Å3 for the Y-36° and Y-42° planes, indicating that a point-like defect could be the source of plastic initiation. In the X-112° plane, the activation volume was between 6 Å3 and 83 Å3. Cooperative migration of several atoms could also be the mechanism of dislocation activation at deep nanoindentation.

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