scholarly journals The critical shear stress of mercury single crystals

1937 ◽  
Vol 163 (912) ◽  
pp. 34-53 ◽  
Keyword(s):  
Plastic Deformation ◽  
Shear Stress ◽  
Melting Point ◽  
Single Crystal ◽  
Single Crystals ◽  
Critical Shear Stress ◽  
Impurity Content ◽  
Thermal Agitation ◽  
Plastic Yield ◽  
Metal Single Crystals

The influence of very small quantities of impurity on the critical shear stress of metal single crystals has an important bearing on the mechanism of their plastic deformation. For investigations in this field, mercury is a very suitable metal: its impurity content can easily be reduced to an extremely low level (Hulett 1911) and it contains no dissolved gases (Hulett 1911). Also, as first pointed out by Andrade (1914), single crystal wires of this metal can be prepared without difficulty. The low melting point of mercury (-38∙8° C.) is far from being a disadvantage. The crystals can be maintained at -60° C., and at a temperature so near the melting point the thermal agitation may be expected to accentuate phenomena not observable at lower temperatures, if such agitation plays the important part in the mechanism of glide ascribed to it (Taylor 1934; Polanyi 1934; Orowan 1934). As a possible instance of this, the experiments to be described have revealed the existence of a preliminary “set” preceding the true plastic yield. Widely differing forms of slip band have also been observed, and are described elsewhere (Greenland 1937). It is hoped that these results will throw further light on the mechanism of glide.

The Characteristic of the La3Ga5SiO14 Single Crystal Grown by Vertical Bridgman Method in Ar Atmosphere

2006 ◽  
Vol 510-511 ◽  
pp. 842-845 ◽  
Author(s):  
Noriko Bamba ◽  
Kentaro Kato ◽  
Toshinori Taishi ◽  
Takayuki Hayashi ◽  
Keigo Hoshikawa ◽  
...  
Keyword(s):  
Melting Point ◽  
Single Crystal ◽  
Single Crystals ◽  
Room Temperature ◽  
Color Change ◽  
Piezoelectric Materials ◽  
Lead Free ◽  
Piezoelectric Constant ◽  
Interstitial Oxygen ◽  
Vertical Bridgman

Langasite (La3Ga5SiO14: denoted by LGS) single crystal is one of the lead free piezoelectric materials with high piezoelectricity that is maintained up to its melting point (1470°C). Although LGS single crystals have usually been grown by Czochralski (CZ) method in oxygen contained atmosphere to prevent evaporation of Ga, they were grown by the vertical Bridgman (VB) method in Ar atmosphere without oxygen, and their properties were evaluated in this work. Transparent and colorless LGS single crystals were successfully obtained without Ga evaporation by the VB method in Ar atmosphere, and their resistivity at room temperature was much higher than that grown by conventional CZ method. Piezoelectric constant d11 of the crystal grown by the VB method was 6 x 10-12 C/N, which was close to that of the crystal grown by CZ method. The colorless transparent LGS single crystal turned to orange and its resistivity decreased by annealing in air. Since an orange-colored transparent LGS single crystal has been grown by conventional CZ method, this indicates that color change and the resistivity decrease of LGS crystal is caused by extra interstitial oxygen atoms in the crystal.

scholarly journals Molecular Dynamics Simulation of Crack Propagation in Single-Crystal Aluminum Plate with Central Cracks

2017 ◽  
Vol 2017 ◽  
pp. 1-12 ◽  
Author(s):  
Jun Ding ◽  
Lu-sheng Wang ◽  
Kun Song ◽  
Bo Liu ◽  
Xia Huang
Keyword(s):  
Molecular Dynamics ◽  
Plastic Deformation ◽  
Crack Propagation ◽  
Strain Rate ◽  
Single Crystal ◽  
Crack Length ◽  
Crack Growth ◽  
Plastic Yield ◽  
Model Size ◽  
Dislocation Multiplication

The crack propagation process in single-crystal aluminum plate (SCAP) with central cracks under tensile load was simulated by molecular dynamics method. Further, the effects of model size, crack length, temperature, and strain rate on strength of SCAP and crack growth were comprehensively investigated. The results showed that, with the increase of the model size, crack length, and strain rate, the plastic yield point of SCAP occurred in advance, the limit stress of plastic yield decreased, and the plastic deformability of material increased, but the temperature had less effect and sensitivity on the strength and crack propagation of SCAP. The model size affected the plastic deformation and crack growth of the material. Specifically, at small scale, the plastic deformation and crack propagation in SCAP are mainly affected through dislocation multiplication and slip. However, the plastic deformation and crack propagation are obviously affected by dislocation multiplication and twinning in larger scale.

scholarly journals The Stress Induced Martensite-Austenite Interface in Fe-15Ni-15Cr Single Crystals

1973 ◽  
Vol 31 ◽  
pp. 110-111
Author(s):  
G. A. Stone ◽  
G. Thomas
Keyword(s):  
Shear Stress ◽  
Slip System ◽  
Single Crystal ◽  
Single Crystals ◽  
Habit Plane ◽  
Maximum Shear Stress ◽  
Crystal Axis ◽  
Surface Study

A single crystal stressed in the [3]𝛄 direction at 185°K was transformed to 5% 𝛂 martensite and 2% Ɛ martensite by volume. The austenite slip system of maximum shear stress is the (11)𝛄 [01)𝛄. Fig. 1 shows a two surface study using the electron and optical microscopes. The a martensite is confined between £martensite plates with the (0001)Ɛ ∥ (11)𝛄. The size of the acicular martensite crystals is controlled by the spacing of the £ martensite plates. These £ martensite plates are seen in Fig. 1A as dark vertical bands. The axes of the acicular crystals lie in the (11)𝛄 plane. The £ martensite habit plane is defined as the plane perpendicular to the (11)𝛄 containing the vector defining the crystal axis.

The Effect of Solid Solution Impurities on Dislocation Nucleation in a (001) Mo – 1.5 at.% Ir Single Crystal

2010 ◽  
Vol 662 ◽  
pp. 85-93
Author(s):  
Sergey Dub ◽  
Igor Zasimchuk ◽  
Leonid Matvienko
Keyword(s):  
Mechanical Properties ◽  
Solid Solution ◽  
Shear Stress ◽  
Elastic Modulus ◽  
Single Crystal ◽  
Single Crystals ◽  
Free Volume ◽  
Dislocation Nucleation ◽  
Initial Portion ◽  
G 12

Mechanical properties of (001) Mo and (001) Mo – 1.5 at.% Ir single crystals have been studied by nanoindentation. It has been found that the iridium addition to molybdenum leads to an increase in both hardness and elastic modulus. An abrupt elasto-plastic transition (pop-in) at a depth of about 20 - 40 nm caused by dislocation nucleation in previously dislocation-free volume has been observed in the initial portion of the loading curve. It has shown that the Ir addition essentially affects the dislocation nucleation. Mean shear stress required for the dislocation nucleation increased from 10.8 GPa (G/12) for a Mo single crystal to 18.2 GPa (G/8) for the Mo – 1.5 at% Ir solid solution. Thus, the Ir solution in a Mo single crystal affects not only the resistance to the motion of dislocations (hardness) but the nucleation of them as well. The latter is likely to occur as a result of an increase in the structure perfection of the Mo – 1.5 at% Ir solid solution as compared to the pure Mo single crystal.

Influence of the Crystallographic Orientation of CuZn30 Single Crystal on the Portevin-Le Chatelier Effect

2013 ◽  
Vol 203-204 ◽  
pp. 406-410 ◽  
Author(s):  
Barbara Grzegorczyk ◽  
Wojciech Ozgowicz ◽  
Elżbieta Kalinowska-Ozgowicz
Keyword(s):  
Plastic Deformation ◽  
Strain Rate ◽  
Single Crystal ◽  
Single Crystals ◽  
Crystallographic Orientation ◽  
Stress And Strain ◽  
Complex Process ◽  
Orientation Axis ◽  
Chatelier Effect ◽  
Stress And Strain Rate

Plastic deformation of solid crystals is a complex process, mostly heterogeneous, due to the simultaneous effect of several deformation mechanisms. A dominating deformation mechanism depends on the properties of the material and external coefficients, viz. temperature, stress and strain rate. The applied Bridgman method permitted to obtain single crystal of the CuZn30 alloy adequate for plastic deformation investigations. Single crystal are characterized by selected crystallographic orientations from various areas of the basic triangle. In order to determine the influence of the crystallographic orientation on the Portevin-Le Chatelier effect selected single crystals were compressed at a temperature of 300°C at a strain rate of 10-3 s-1. Experiments confirmed the effect of the crystallographic orientation axis of CuZn30 single crystals on the observed differences in the intensity of stress oscillation on stress-strain curves.

The mechanical behaviour of single crystals of metals, in particular copper

1957 ◽  
Vol 240 (1222) ◽  
pp. 304-320 ◽  
Keyword(s):  
Shear Stress ◽  
High Temperature ◽  
Single Crystals ◽  
Mechanical Behaviour ◽  
Critical Shear Stress ◽  
Deformation Bands ◽  
Hexagonal Metals

With single crystals of copper, measurements have been made on the variation of the amount of easy glide with the orientation of the crystal axes relative to the direction of tension. At —180° C it has been shown that this variation can be quantitatively expressed by a specific hardening on the active glide planes, which does not exist for the latent glide planes, and a general hardening which applies to both active and latent glide planes. This is compared with the behaviour of hexagonal metals. The occurrence of double glide is analyzed. The variation of glide properties with temperature has been measured for one particular orientation, and the coefficient of specific hardening shown to be roughly independent of temperature. The critical shear stress is also very little affected by temperature, but depends somewhat on orientation. The glide behaviour at high temperature has been found to be influenced largely by the occurrence of deformation bands. A few measurements have been made on gold.

Twinning in Ti-48%Ni-2%Fe Single Crystals under Rolling

2013 ◽  
Vol 738-739 ◽  
pp. 118-122
Author(s):  
Margarita Isaenkova ◽  
Yuriy Perlovich ◽  
Vladimir Fesenko ◽  
Tatyana Dementyeva
Keyword(s):  
Plastic Deformation ◽  
Single Crystal ◽  
Single Crystals ◽  
Stereographic Projection ◽  
Rolling Temperature ◽  
Main Mechanism ◽  
Geometrical Analysis ◽  
Pole Figures

Under rolling of Ti-48%Ni-2%Fe single crystals in the phase B2 at 350oC the twinning is the main mechanism of plastic deformation by many initial orientations of these single crystals, as texture data show clearly. Splitting of initial maxima in the stereographic projection of single crystal into several new ones is an evident manifestation of twinning. But this mode of reorientation is observed only at initial stages of rolling, when deformation degrees do not exceed ~10-15%. A geometrical analysis of pole figures for rolled single crystals showed, that at the used rolling temperature the preferable twinning planes there were {114} and {118}.

The mechanical behaviour of single crystals of certain face-centred cubic metals

1951 ◽  
Vol 244 (880) ◽  
pp. 177-203 ◽  
Keyword(s):  
Single Crystal ◽  
Single Crystals ◽  
Room Temperature ◽  
Critical Shear Stress ◽  
Crystal Form ◽  
Surface Contamination ◽  
Cube Root ◽  
Impurity Atoms ◽  
Gold Silver ◽  
Normal Diffusion

Single crystal rods of gold, silver and nickel have been prepared from the melt by a modified cooling method. The three metals differ in that the gold is very pure and has no surface contamination; the silver is very pure and the surface normally shows contamination; the nickel is markedly less pure. These three features find expression in the results. The stress-glide relationship has been investigated over the whole range to fracture, special attention being paid to the region of small glide. At very small glides the results show certain variations attributed to metastable conditions. For pure metals at low temperatures a region of easy glide has been established, which is absent in nickel. Considerations of the variation of hardening with temperature at constant glide show that, at moderate glide, rise of temperature at low temperature promotes hardening, but rise of temperature at high temperature leads to decrease of hardening. From these results it is concluded that in metals without notable impurity glide is due to two distinct processes, first the initiation of glide planes, which temperature agitation tends to check, and secondly to glide proceeding on planes already initiated, which temperature agitation tends to promote. The surface contamination of silver single crystals which takes place by exposure to air at room temperature raises the critical shear stress somewhat, but has a much more marked effect on the hardening after some tens of per cent of glide has taken place, which is attributed to diffusion of the impurity atoms, probably oxygen, taking place during the travel of the dislocations. This is distinct from normal diffusion, which is negligible at room temperature. The results on the effect of surface contamination explain abnormalities previously noted with silver. The close connexion of asterism and hardening is exhibited in the results obtained with gold and silver. In particular, silver in the region of easy glide shows very small asterism, even at large glide. The cube root of the breaking stress of all metals in single-crystal form has been found to show a linear relationship with temperature.

scholarly journals The mechanism of plastic deformation of crystals. Part I.—Theoretical

1934 ◽  
Vol 145 (855) ◽  
pp. 362-387 ◽  
Keyword(s):  
Plastic Deformation ◽  
Single Crystal ◽  
Shear Strain ◽  
Single Crystals ◽  
Rock Salt ◽  
Theory Of Elasticity ◽  
Crystal Plane ◽  
Lateral Movement

Experiments on the plastic deformation of single crystals, of metals and of rock salt have given results which differ in detail but possess certain common characteristics. In general the deformation of a single crystal in tension or compression consists of shear strain in which sheets of the crystal parallel to a crystal plane slip over one another, the direction of motion being some simple crystal-lographic axis. The measure of this strain, which will be represented by s , is the ration of the relative lateral movement of two parallel planes of slip to the distance between them. Thus it is defined in the same way as the shear strain considered in the theory of elasticity.

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