Mechanical response and plastic deformation of coherent twin boundary with perfect and defective structures

2020 ◽  
Vol 141 ◽  
pp. 103266 ◽  
Author(s):  
Liang Zhang ◽  
Wei Mao ◽  
Mao Liu ◽  
Yasushi Shibuta
Keyword(s):  
Plastic Deformation ◽  
Twin Boundary ◽  
Mechanical Response ◽  
Coherent Twin Boundary

Construction of plastic contact deformation maps on ceramics: a case study on aluminum nitride

1996 ◽  
Vol 54 ◽  
pp. 636-637
Author(s):  
D. L. Callahan
Keyword(s):  
Plastic Deformation ◽  
Aluminum Nitride ◽  
Mechanical Response ◽  
Three Dimensional ◽  
Bright Field Image ◽  
Perfectly Plastic ◽  
Contrast Analysis ◽  
Deformation Patterns

Modern polishing, precision machining and microindentation techniques allow the processing and mechanical characterization of ceramics at nanometric scales and within entirely plastic deformation regimes. The mechanical response of most ceramics to such highly constrained contact is not predictable from macroscopic properties and the microstructural deformation patterns have proven difficult to characterize by the application of any individual technique. In this study, TEM techniques of contrast analysis and CBED are combined with stereographic analysis to construct a three-dimensional microstructure deformation map of the surface of a perfectly plastic microindentation on macroscopically brittle aluminum nitride.The bright field image in Figure 1 shows a lg Vickers microindentation contained within a single AlN grain far from any boundaries. High densities of dislocations are evident, particularly near facet edges but are not individually resolvable. The prominent bend contours also indicate the severity of plastic deformation. Figure 2 is a selected area diffraction pattern covering the entire indentation area.

Molecular Dynamics Modeling the Nano-Identation of Titanium

2021 ◽  
Author(s):  
Peiqiang Yang ◽  
Xueping Zhang ◽  
Zhenqiang Yao ◽  
Rajiv Shivpuri
Keyword(s):  
Molecular Dynamics ◽  
Plastic Deformation ◽  
Titanium Alloys ◽  
Large Scale ◽  
Mechanical Response ◽  
Pure Titanium ◽  
Dynamics Modeling ◽  
Dynamics Model ◽  
Nano Indentation ◽  
Molecular Dynamics Modeling

Abstract Titanium alloys’ excellent mechanical and physical properties make it the most popular material widely used in aerospace, medical, nuclear and other significant industries. The study of titanium alloys mainly focused on the macroscopic mechanical mechanism. However, very few researches addressed the nanostructure of titanium alloys and its mechanical response in Nano-machining due to the difficulty to perform and characterize nano-machining experiment. Compared with nano-machining, nano-indentation is easier to characterize the microscopic plasticity of titanium alloys. This research presents a nano-indentation molecular dynamics model in titanium to address its microstructure alteration, plastic deformation and other mechanical response at the atomistic scale. Based on the molecular dynamics model, a complete nano-indentation cycle, including the loading and unloading stages, is performed by applying Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS). The plastic deformation mechanism of nano-indentation of titanium with a rigid diamond ball tip was studied under different indentation velocities. At the same time, the influence of different environment temperatures on the nano-plastic deformation of titanium is analyzed under the condition of constant indentation velocity. The simulation results show that the Young’s modulus of pure titanium calculated based on nano-indentation is about 110GPa, which is very close to the experimental results. The results also show that the mechanical behavior of titanium can be divided into three stages: elastic stage, yield stage and plastic stage during the nano-indentation process. In addition, indentation speed has influence on phase transitions and nucleation of dislocations in the range of 0.1–1.0 Å/ps.

Shear Properties of Polymer Films Within Confined Contacts

2005 ◽  
Author(s):  
E. Gacoin ◽  
C. Fretigny ◽  
A. Chateauminois
Keyword(s):  
Plastic Deformation ◽  
Hydrostatic Pressure ◽  
Polymer Films ◽  
Mechanical Response ◽  
Contact Stiffness ◽  
Shear Moduli ◽  
Lateral Contact ◽  
Contact Models ◽  
Film Substrate ◽  
Material Compressibility

Approximate contact models for film/substrate systems have been developed and validated in order to determine the shear moduli of mechanically confined films using lateral contact stiffness measurements. This approach allowed to discuss the effects of material compressibility, hydrostatic pressure and plastic deformation on the mechanical response of thin polymers films within macroscopic contacts.

scholarly journals Plastic Deformation Behavior of Bi-Crystal Magnesium Nanopillars with a { 10 1 ¯ 2 } Twin Boundary under Compression: Molecular Dynamics Simulations

Materials ◽  
2019 ◽  
Vol 12 (5) ◽  
pp. 750
Author(s):  
Xiaoyue Yang ◽  
Shuang Xu ◽  
Qingjia Chi
Keyword(s):  
Molecular Dynamics ◽  
Plastic Deformation ◽  
Molecular Dynamics Simulations ◽  
Twin Boundary ◽  
Basal Slip ◽  
Boundary Migration ◽  
Plastic Deformation Process ◽  
Plastic Deformation Behavior ◽  
Schmid Factor ◽  
Dynamics Simulations

In this study, molecular dynamics simulations were performed to study the uniaxial compression deformation of bi-crystal magnesium nanopillars with a { 10 1 ¯ 2 } twin boundary (TB). The generation and evolution process of internal defects of magnesium nanopillars were analyzed in detail. Simulation results showed that the initial deformation mechanism was mainly caused by the migration of the twin boundary, and the transformation of TB into (basal/prismatic) B/P interface was observed. After that, basal slip as well as pyramidal slip nucleated during the plastic deformation process. Moreover, a competition mechanism between twin boundary migration and basal slip was found. Basal slip can inhibit the migration of the twin boundary, and { 10 1 ¯ 1 } ⟨ 10 1 ¯ 2 ⟩ twins appear at a certain high strain level ( ε = 0.104). In addition, Schmid factor (SF) analysis was conducted to understand the activations of deformation modes.

Mechanical and Optical Properties Characterization of C-Plane (0001) and M-Plane (10−10) GaN by Nanoindentation and Luminescence

2015 ◽  
Vol 1792 ◽  
Author(s):  
Toshiya Yokogawa ◽  
Masaki Fujikane ◽  
Shijo Nagao ◽  
Roman Nowak
Keyword(s):  
Plastic Deformation ◽  
Shear Stress ◽  
Dislocation Density ◽  
Twin Boundary ◽  
Boundary Energy ◽  
Dynamics Simulation ◽  
Dark Spot ◽  
Yield Shear Stress ◽  
Gan Crystal

ABSTRACTYield shear stress dependence on dislocation density and crystal orientation was studied in bulk GaN crystals by nanoindentation examination. The yield shear stress decreased with increasing dislocation density which is estimated by dark spot density in cathodoluminescence, and it decreased with decreasing nanoindentation strain-rate. It reached and coincided at 11.5 GPa for both quasi-static deformed c-plane (0001) and m-plane (10-10) GaN. Taking into account theoretical Peierls–Nabarro stress and yield stress for each slip system, these phenomena were concluded to be an evidence of heterogeneous mechanism associated plastic deformation in GaN crystal. Transmission electron microscopy and molecular dynamics simulation also supported the mechanism with obtained r-plane (-1012) slip line right after plastic deformation, so called pop-in event. The agreement of the experimentally obtained atomic shuffle energy with the calculated twin boundary energy suggested that the nucleation of the local metastable twin boundary along the r-plane concentrated the indentation stress, leading to an r-plane slip. This nanoindentation examination is useful for the characterization of crystalline quality because the wafer mapping of the yield shear stress coincided the photoluminescence mapping which shows increase of emission efficiency due to reduction of non-radiative recombination process by dislocation.

Atomic and Electronic Structure Analysis of Σ=3, 9 and 27 Boundary, and Multiple Junction in β-SiC

1999 ◽  
Vol 589 ◽  
Author(s):  
K. Tanaka ◽  
M. Kohyama
Keyword(s):  
Electronic Structure ◽  
Energy Loss ◽  
Twin Boundary ◽  
Structural Unit ◽  
High Resolution Electron Microscopy ◽  
Coherent Twin Boundary ◽  
Atomic Structures ◽  
Resolution Electron ◽  
Electron Energy Loss ◽  
Atomic And Electronic Structure

AbstractThe atomic structures of σ=3, 9 and 27 boundaries, and multiple junctions in β-SiC were studied by high-resolution electron microscopy (HREM). Especially, the existence of the variety of structures of σ=3 incoherent twin boundaries and σ=27 boundary was shown by HREM. The structures of σ=3, 9 and 27 boundary were explained by structural unit models. Electron energy-loss spectroscopy (EELS) was used to investigate the electronic structure of grain boundaries. The spectra recorded from bulk, {111}σ=3 coherent twin boundary (CTB) and {1211}σ=3 incoherent twin boundary (ITB) did not show significant differences. Especially, the energy-loss corresponding to carbon 1s-to Φ* transition was not found. It indicates that C atoms exist at grain boundary on the similar condition of bulk

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