scholarly journals Чувствительность дислокационных розеток к форме индентора Берковича на кристаллах LiF и MgO

2020 ◽  
Vol 62 (8) ◽  
pp. 1232
Author(s):  
Д. Грабко ◽  
К. Пырцак ◽  
О. Шикимака
Keyword(s):  
Single Crystals ◽  
Orientation Effect ◽  
Berkovich Indenter ◽  
Cubic Crystals ◽  
Micro Scale ◽  
Vickers Indenter ◽  
Load Growth ◽  
The Asymmetry

A peculiar effect, namely, the sensitivity of the shape of dislocation rosettes to the indenter type under indentation of the (001) face of LiF and MgO single crystals has been revealed. It was shown that the dislocation rosettes forming around the Vickers indenter are symmetrical, while the rosettes around the Berkovich one are asymmetric, the edge beams of the dislocation rosettes vary in length, and the screw ones do not show such asymmetry. An orientation effect was found during the penetration of the Berkovich indenter: the shape of the dislocation rosettes and the length of the edge beams change with a change in the orientation of the indenter relative to the crystallographic directions of the sample. It was also shown that the asymmetry of dislocation rosettes is more visible on harder crystals and increases with load growth on the indenter. The factors responsible for the anomaly in the development of dislocation rosettes under indentation in nano and micro scale by the Berkovich indenter of the (001) plane of cubic crystals are established

Accommodation of constrained deformation in f. c. c. metals by slip and twinning

1969 ◽  
Vol 309 (1499) ◽  
pp. 433-456 ◽  
Keyword(s):  
Shear Stress ◽  
Single Crystals ◽  
Plane Strain ◽  
Plane Strain Compression ◽  
Orientation Factor ◽  
Cubic Crystals ◽  
Constrained Deformation ◽  
Critical Resolved Shear Stress ◽  
Good Agreement ◽  
External Strain

The problem of accommodation of constrained deformation by slip and twinning has been analysed. The analysis is based on Taylor’s least work hypothesis. In this analysis, the operative combination of slip and twinning systems is found by minimizing the orientation factor M = (∑ i s i +α∑ i t i )/ ε , where s i and t i are the simple shears resulting from slip and twinning respectively, α is the ratio of the critical resolved shear stress for twinning against slip, and Ɛ is the external strain. Detailed calculations have been made for face-centred cubic crystals deformed by plane strain compression. Experimental observations on deformed single crystals of a Co–8% Fe alloy indicate good agreement with the analysis. Implications of the present study to the twinning observations of Heye & Wassermann on rolled Ag crystals are discussed.

Preparation and Characterization of Wurtzitic Gan Single Crystals in Nano and Micro Scale

1996 ◽  
Vol 423 ◽  
Author(s):  
San Yu ◽  
Hongdong Li ◽  
Haibin Yang ◽  
Dongmei Li ◽  
Haiping Sun ◽  
...  
Keyword(s):  
Single Crystals ◽  
Crystal Size ◽  
Arc Discharge ◽  
Short Wave ◽  
Wurtzite Structure ◽  
Light Emitters ◽  
X Ray ◽  
Lattice Constants ◽  
Micro Scale ◽  
Transmission Electron

AbstractGallium nitride and its alloys are the most promising materials for short wave light emitters. If high quality GaN single crystals can be prepared, the GaN base light emitters should be fabricated directly on the lattice-matched GaN substrate.In this work, GaN crystals in nano and micro scale with definite faces have been prepared by dc arc discharge using gallium and N2+NH3 as starting materials. Transmission electron microscope, selected area diffraction, x-ray microanalysis of energy dispersive spectroscopy, and x-ray diffraction investigation of the as grown GaN crystals show that the well faceted crystals are single crystalline GaN in wurtzite structure having lattice constants a0=3.18Å and c0=5.18Å. The crystal size of stoichoimetric GaN in wurtzite structure depends on the partial pressure of nitrogen in the plasma. The maximum crystal size in this work is about several micrometers.

The asymmetry of cyclic hardening in Ni3(Al,Nb) single crystals

1985 ◽  
Vol 19 (6) ◽  
pp. 741-745 ◽  
Author(s):  
Salah S. Ezz ◽  
D.P. Pope
Keyword(s):  
Single Crystals ◽  
Cyclic Hardening ◽  
The Asymmetry

scholarly journals Novel micro-scale specimens for mode-dependent fracture testing of brittle materials: A case study on GaAs single crystals

2020 ◽  
Vol 193 ◽  
pp. 108765 ◽  
Author(s):  
J. Ast ◽  
J.J. Schwiedrzik ◽  
N. Rohbeck ◽  
X. Maeder ◽  
J. Michler
Keyword(s):  
Single Crystals ◽  
Brittle Materials ◽  
Fracture Testing ◽  
Micro Scale

scholarly journals The glide elements of body-centred cubic crystal, with special reference to the effect of temperature

1940 ◽  
Vol 175 (962) ◽  
pp. 290-315 ◽  
Keyword(s):  
Special Reference ◽  
Single Crystals ◽  
Effect Of Temperature ◽  
Cubic Crystal ◽  
Cubic Crystals ◽  
Different Temperatures ◽  
Sodium And Potassium

In a previous paper from this laboratory (Andrade and Tsien 1937) the particular interest of body-centred cubic crystals was pointed out, and the glide elements for single crystals of sodium and potassium at atmospheric temperatures were determined, viz. glide plane (123) and glide direction [111]. Another paper (Tsien and Chow 1937) describes the determination of the glide elements for molybdenum, for which the glide direction was again [111], but the glide plane was different at different temperatures, viz. (110) at 1000° C and (112) at 300 and 20° C. Planes (123), (110) and (112) have all been given as glide planes for α -iron by different workers (Taylor and Elam 1926; Gough 1928; Fahrenhorst and Schmid 1932), while for tungsten (Goucher 1924) the glide plane has been given as (112) and for β -brass under certain conditions (G. I. Taylor 1928) as (110).

scholarly journals An equivalent dipole analysis of PZT ceramics and lead-free piezoelectric single crystals

2016 ◽  
Vol 06 (02) ◽  
pp. 1650010
Author(s):  
Andrew J. Bell
Keyword(s):  
Phase Boundary ◽  
Single Crystals ◽  
Effective Charge ◽  
Force Constants ◽  
Lead Free ◽  
Electromechanical Coupling Coefficient ◽  
Ionic Charge ◽  
Pzt Ceramics ◽  
Equivalent Dipole ◽  
The Asymmetry

The recently proposed Equivalent Dipole Model for describing the electromechanical properties of ionic solids in terms of 3 ions and 2 bonds has been applied to PZT ceramics and lead-free single crystal piezoelectric materials, providing analysis in terms of an effective ionic charge and the asymmetry of the interatomic force constants. For PZT it is shown that, as a function of composition across the morphotropic phase boundary, the dominant bond compliance peaks at 52% ZrO2. The stiffer of the two bonds shows little composition dependence with no anomaly at the phase boundary. The effective charge has a maximum value at 50% ZrO2, decreasing across the phase boundary region, but becoming constant in the rhombohedral phase. The single crystals confirm that both the asymmetry in the force constants and the magnitude of effective charge are equally important in determining the values of the piezoelectric charge coefficient and the electromechanical coupling coefficient. Both are apparently temperature dependent, increasing markedly on approaching the Curie temperature.

Orientation effect on recovery and recrystallization of cold rolled niobium single crystals

2009 ◽  
Vol 507 (1-2) ◽  
pp. 179-189 ◽  
Author(s):  
R. Srinivasan ◽  
G.B. Viswanathan ◽  
V.I. Levit ◽  
H.L. Fraser
Keyword(s):  
Single Crystals ◽  
Orientation Effect ◽  
Cold Rolled
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