Effects of solutes on dislocation nucleation and interface sliding of bimetal semi-coherent interface

Atomistic simulation studies of dislocation nucleation and propagation in nanoscale multilayered metallic systems (Cu-Ni and Cu-Nb) are performed. Nanoindentation model is used to generate dislocations at and near the surface. Interaction of the propagating dislocations with two types of interfaces (coherent and incoherent) is analyzed. In the case of coherent interface, Cu(111)-Ni(111), dislocations that initiate in Cu layer propagate through the interface into Ni. However, the interface acts as an obstacle for dislocation propagation and leads to a higher dislocation density near the interface. In the case of incoherent interface, Cu(111)-Nb(110), dislocations that initiate in Cu do not propagate into Nb and tend to accumulate in copper near the interface. In both cases, the interfaces provide mechanisms for strengthening the nanoscale multilayered metallic systems.

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HREM observation of dislocations near room temperature fractures in silicon

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100106521 ◽

1988 ◽

Vol 46 ◽

pp. 892-893

Author(s):

M. H. Rhee ◽

W. A. Coghlan

Keyword(s):

Cross Section ◽

Room Temperature ◽

Single Crystal Silicon ◽

Dislocation Nucleation ◽

Back Side ◽

Ion Milling ◽

Crystal Silicon ◽

Flat Surfaces ◽

Induced Fractures ◽

Vicker’S Microhardness

Silicon is believed to be an almost perfectly brittle material with cleavage occurring on {111} planes. In such a material at room temperature cleavage is expected to occur prior to any dislocation nucleation. This behavior suggests that cleavage fracture may be used to produce usable flat surfaces. Attempts to show this have failed. Such fractures produced in semiconductor silicon tend to occur on planes of variable orientation resulting in surfaces with a poor surface finish. In order to learn more about the mechanisms involved in fracture of silicon we began a HREM study of hardness indent induced fractures in thin samples of oxidized silicon.Samples of single crystal silicon were oxidized in air for 100 hours at 1000°C. Two pieces of this material were glued together and 500 μm thick cross-section samples were cut from the combined piece. The cross-section samples were indented using a Vicker's microhardness tester to produce cracks. The cracks in the samples were preserved by thinning from the back side using a combination of mechanical grinding and ion milling.

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A study of interface sliding at F.C.C.-B.C.C. boundaries in a Cu-Zn alloy

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100109252 ◽

1978 ◽

Vol 36 (1) ◽

pp. 422-423

Author(s):

F. Monchoux ◽

A. Rocher ◽

J.L. Martin

Keyword(s):

Face Centered Cubic ◽

Creep Tests ◽

High Voltage Electron Microscopy ◽

Diffusion Treatment ◽

Voltage Electron ◽

The Face ◽

Face Centered ◽

Interface Sliding ◽

Zn Alloy ◽

Made In

Interphase sliding is an important phenomenon of high temperature plasticity. In order to study the microstructural changes associated with it, as well as its influence on the strain rate dependence on stress and temperature, plane boundaries were obtained by welding together two polycrystals of Cu-Zn alloys having the face centered cubic and body centered cubic structures respectively following the procedure described in (1). These specimens were then deformed in shear along the interface on a creep machine (2) at the same temperature as that of the diffusion treatment so as to avoid any precipitation. The present paper reports observations by conventional and high voltage electron microscopy of the microstructure of both phases, in the vicinity of the phase boundary, after different creep tests corresponding to various deformation conditions.Foils were cut by spark machining out of the bulk samples, 0.2 mm thick. They were then electropolished down to 0.1 mm, after which a hole with thin edges was made in an area including the boundary

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The Strain Rate Sensitivity and Creep Behavior for the Tripler Plane of Potassium Dihydrogen Phosphate Crystal by Nanoindentation

Micromachines ◽

10.3390/mi12040369 ◽

2021 ◽

Vol 12 (4) ◽

pp. 369

Author(s):

Jianhui Mao ◽

Wenjun Liu ◽

Dongfang Li ◽

Chenkai Zhang ◽

Yi Ma

Keyword(s):

Strain Rate ◽

Strain Rate Sensitivity ◽

Creep Deformation ◽

Potassium Dihydrogen Phosphate ◽

Rate Sensitivity ◽

Dislocation Nucleation ◽

Machining Process ◽

Dihydrogen Phosphate ◽

Potassium Dihydrogen ◽

Kdp Crystals

As an excellent multifunctional single crystal, potassium dihydrogen phosphate (KDP) is a well-known, difficult-to-process material for its soft-brittle and deliquescent nature. The surface mechanical properties are critical to the machining process; however, the characteristics of deformation behavior for KDP crystals have not been well studied. In this work, the strain rate effect on hardness was investigated on the mechanically polished tripler plane of a KDP crystal relying on nanoindentation technology. By increasing the strain rate from 0.001 to 0.1 s−1, hardness increased from 1.67 to 2.07 GPa. Hence, the strain rate sensitivity was determined as 0.053, and the activation volume of dislocation nucleation was 169 Å3. Based on the constant load-holding method, creep deformation was studied at various holding depths at room temperature. Under the spherical tip, creep deformation could be greatly enhanced with increasing holding depth, which was mainly due to the enlarged holding strain. Under the self-similar Berkovich indenter, creep strain could be reduced at a deeper location. Such an indentation size effect on creep deformation was firstly reported for KDP crystals. The strain rate sensitivity of the steady-state creep flow was estimated, and the creep mechanism was qualitatively discussed.

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Dislocation-mediated shear amorphization in boron carbide

Science Advances ◽

10.1126/sciadv.abc6714 ◽

2021 ◽

Vol 7 (8) ◽

pp. eabc6714 ◽

Cited By ~ 1

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.

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