Dislocations and Plasticity in Silicon Crystals by 3-D Mesoscopic Simulations

1998 ◽  
Vol 538 ◽  
Author(s):  
L.P. Kubin ◽  
A. Moulin ◽  
P. Pirouz
Keyword(s):  
Dislocation Density ◽  
Yield Stress ◽  
Low Temperatures ◽  
Mechanical Twinning ◽  
Mesoscopic Simulation ◽  
Brittle To Ductile Transition ◽  
Silicon Crystals ◽  
Partial Dislocations ◽  
Yield Point Phenomenon ◽  
Dislocation Sources

AbstractSeveral problems related to the dynamics of dislocation sources and the plasticity of silicon crystals are investigated with the help of a mesoscopic simulation. The questions successively examined are the dynamics of a source of perfect dislocations and the conditions under which perfect or partial dislocations are emitted by a source. This leads to a discussion of the initial steps of the model proposed by Pirouz for mechanical twinning and, further, to the suggestion that a relation may exist between several transitions experimentally observed at low temperatures in elemental or compound semi-conductors: a change in the slope of the yield stress vs. temperature curves, a brittle-to-ductile transition and a change in the nature of the mobile dislocations. Finally, simulations are presented of the yield point phenomenon that is a well-known feature of Si and Ge crystals. The results are discussed in terms of evolutionary laws for the total dislocation density during straining.

What Controls Temperature Dependence of Yield Stress in L12-Ordered Intermetallic Compounds?

2015 ◽  
Vol 1760 ◽  
Author(s):  
Haruyuki Inui ◽  
Norihiko L. Okamoto
Keyword(s):  
Temperature Dependence ◽  
Yield Stress ◽  
Intermetallic Compounds ◽  
Low Temperatures ◽  
Rapid Decrease ◽  
Partial Dislocations ◽  
Ordered Intermetallic ◽  
Image Position ◽  
Made In

ABSTRACTThe temperature dependence of yield stress and the associated dislocation dissociation in L12 intermetallic compounds are investigated in order to check the feasibility of the classification of L12 intermetallic compounds so far made in terms of the planarity of core structures of partial dislocations with b = 1/2<110> and 1/3<112> on {111} and {001} glide planes. In contrast to what is believed from the classification, the motion of APB-coupled dislocations is evidenced to give rise to the rapid decrease in yield stress at low temperatures for Pt3Al. In view of the fact that rapid decrease in yield stress at low temperatures is also observed in Co3(Al,W) and Co3Ti in which APB-coupled dislocations are responsible for deformation, the SISF-type dissociation is not a prerequisite for the rapidly decreasing CRSS for slip on (111) and the relative magnitudes of the APB energy on (111) and the SISF energy on (111) cannot be a primary factor that determines the type of the temperature dependence of CRSS for L12 compounds. The importance of the CSF energy as a factor determining the type of the temperature dependence of yield stress for L12 compounds through the changes in the planarity of the core structure of the APB-coupled partial dislocation with bp = ½[1$\overline 1$0] is discussed in the light of experimental evidence obtained from Pt3Al.

Temperature Dependence of Yield Stress and Dislocation Dissociation in L12-Ordered Intermetallic Compounds

2011 ◽  
Vol 1295 ◽  
Author(s):  
Haruyuki Inui ◽  
Norihiko L. Okamoto
Keyword(s):  
Solid Solution ◽  
Temperature Dependence ◽  
Yield Stress ◽  
Intermetallic Compounds ◽  
Low Temperatures ◽  
Solid Solution Hardening ◽  
Solution Hardening ◽  
Partial Dislocations ◽  
Ordered Intermetallic ◽  
Dislocation Dissociation

ABSTRACTThe temperature dependence of yield stress and the associated dislocation dissociation in L12 intermetallic compounds are investigated in order to check the feasibility of the classification of L12 intermetallic compounds so far reported in terms of the planarity of core structures of partial dislocations with b = 1/2<110> and 1/3<112> on {111} and {001} glide planes. In contrast to what is believed from the reported classification, the motion of APB-coupled dislocations is proved to give rise to the rapid decrease in yield stress at low temperatures for Co3Ti and Co3 (Al,W). The temperature dependence of yield stress at low temperatures is newly interpreted in terms of a thermal component of solid-solution hardening, at least, for these two L12 compounds. We have proposed a new way to describe the yield stress–temperature curves of L12 compounds with three parameters (the athermal and thermal components of solid-solution hardening and the anomalous strengthening component) when the dislocation dissociation scheme is of the APB-type.

Effect of Prestraining on the Brittle-To-Ductile Transition of NiAl Single Crystals

1996 ◽  
Vol 460 ◽  
Author(s):  
S. Shrivastava ◽  
F. Ebrahimi
Keyword(s):  
Fracture Toughness ◽  
Transition Temperature ◽  
Crack Initiation ◽  
Single Crystals ◽  
Low Temperatures ◽  
Crack Initiation And Propagation ◽  
Brittle To Ductile Transition ◽  
Initiation And Propagation ◽  
Toughness Testing ◽  
Dislocation Sources

ABSTRACTThe brittle-to-ductile transition (BDT) has been established for NiAl single crystals as evaluated by fracture toughness testing and also the effects of prestraining on the brittle-to-ductile transition temperature (BDTT) have been investigated. Specimens were prestrained to a 10% plastic strain level at 200°C under tension prior to toughness testing. The BDT of the prestrained specimens was compared to that of the as homogenized specimens. The results have revealed the occurrence of two competing effects upon prestraining: (1) an increase in dislocation sources causing a difficulty in micro-crack initiation and resulting in an increase in toughness at low temperatures, and (2) an increase in the flow stress resulting in an increase in BDT temperature. The crack initiation and propagation mechanisms were also analyzed and have been discussed.

scholarly journals The Influence Of The Rare Earth Metals Modification On The Fracture Toughness Of G17CrMo5-5 Cast Steel At Low Temperatures

2015 ◽  
Vol 60 (2) ◽  
pp. 773-777 ◽  
Author(s):  
I. Dzioba ◽  
J. Kasińska ◽  
R. Pała
Keyword(s):  
Mechanical Properties ◽  
Fracture Toughness ◽  
Rare Earth ◽  
Low Temperatures ◽  
Cast Steel ◽  
Rare Earth Metals ◽  
Positive Influence ◽  
Reference Temperature ◽  
Brittle To Ductile Transition ◽  
The Rare Earth

Abstract This paper presents the influence of the rare earth metals (REM) modification on mechanical properties and fracture toughness of G17CrMo5-5 cast steel at low temperatures. The REM was in the form of mishmetal. The research has been performed on serial (several) industrial melts. The fracture toughness values of unmodified and modified cast steel at the temperature range from −80°C to 20°C were tested. The reference temperatures of the brittle-to-ductile transition, TQ, for both unmodified and modified cast steel were determined. The positive influence of the modification by REM on the fracture toughness and the reference temperature TQ are shown.

Tailoring Microstructures Under Strong Non-Equilibrium Conditions: A Feasible Path Towards High JC in Melt Textured YBa2Cu3O7

2000 ◽  
Vol 659 ◽  
Author(s):  
Felip Sandiumenge ◽  
Jérôme Plain ◽  
Teresa Puig ◽  
Xavier Obradors ◽  
Jacques Rabier ◽  
...  
Keyword(s):  
Dislocation Density ◽  
Partial Dislocation ◽  
Enhancement Factor ◽  
Stacking Faults ◽  
Equilibrium Conditions ◽  
Pinning Centers ◽  
Partial Dislocations ◽  
High Oxygen Pressure ◽  
Density Analysis ◽  
Feasible Path

ABSTRACTMelt textured YBa2Cu3O/Y2BaCuO5 were post processed by high oxygen pressure for different periods and temperatures. This process permits the control of the microstructure, in particular the growth and shape of the stacking faults and thereby the partial dislocation density. Analysis of the Jc(H,T) behavior allow to separate the contribution of Y2BaCuO5 interface from that of dislocations. It is shown that the in-plane partial dislocations act as point-like pinning centers increasing Jc up to 180% but this enhancement factor is counterbalanced by the effect of the stacking faults associated to the partial dislocations.

Atomistic simulation for configuration evolution and energetic calculation of crack in body-centered-cubic iron

2006 ◽  
Vol 21 (10) ◽  
pp. 2542-2549 ◽  
Author(s):  
Li-Xia Cao ◽  
Chong-Yu Wang
Keyword(s):  
Low Temperatures ◽  
Crack Tip ◽  
Dislocation Nucleation ◽  
Effect Of Temperature ◽  
Body Centered Cubic ◽  
Partial Dislocations ◽  
Higher Temperature ◽  
Crack Blunting ◽  
Increasing Temperature ◽  
Extended Dislocation

The molecular dynamics method has been used to simulate mode I cracking in body-centered-cubic iron. Close attention has been paid to the process of the atomic configuration evolution of the cracks. The simulation shows that at low temperatures, partial dislocations are emitted before the initiation of crack propagation, subsequently forming the stacking faults or multilayer twins on {112} planes, and then brittle cleavage and extended dislocation nucleation are observed at the crack tip accompanied by twin extension. These results are in agreement with the experimental observation that twinning and fracture processes cooperate at low temperatures. Furthermore, an energetics analysis has been made on the deformation behavior observed at the crack tip. The effect of temperature on the fracture process is discussed. At the higher temperature, plastic deformation becomes easier, and crack blunting occurs. With increasing temperature, the fracture resistance increases, and the effect of the lattice trapping can be weakened by thermal activation.

scholarly journals Low-temperature rheology of calcite

2019 ◽  
Vol 221 (1) ◽  
pp. 129-141 ◽  
Author(s):  
Michael K Sly ◽  
Arashdeep S Thind ◽  
Rohan Mishra ◽  
Katharine M Flores ◽  
Philip Skemer
Keyword(s):  
Low Temperature ◽  
Yield Stress ◽  
Low Temperatures ◽  
Focused Ion Beam ◽  
Ion Beam ◽  
Polycrystalline Sample ◽  
Small Scale ◽  
Indentation Hardness ◽  
Micropillar Compression ◽  
Flow Laws

SUMMARY Low-temperature plastic rheology of calcite plays a significant role in the dynamics of Earth's crust. However, it is technically challenging to study plastic rheology at low temperatures because of the high confining pressures required to inhibit fracturing. Micromechanical tests, such as nanoindentation and micropillar compression, can provide insight into plastic rheology under these conditions because, due to the small scale, plastic deformation can be achieved at low temperatures without the need for secondary confinement. In this study, nanoindentation and micropillar compression experiments were performed on oriented grains within a polycrystalline sample of Carrara marble at temperatures ranging from 23 to 175 °C, using a nanoindenter. Indentation hardness is acquired directly from nanoindentation experiments. These data are then used to calculate yield stress as a function of temperature using numerical approaches that model the stress state under the indenter. Indentation data are complemented by uniaxial micropillar compression experiments. Cylindrical micropillars ∼1 and ∼3 μm in diameter were fabricated using a focused ion beam-based micromachining technique. Yield stress in micropillar experiments is determined directly from the applied load and micropillar dimensions. Mechanical data are fit to constitutive flow laws for low-temperature plasticity and compared to extrapolations of similar flow laws from high-temperature experiments. This study also considered the effects of crystallographic orientation on yield stress in calcite. Although there is a clear orientation dependence to plastic yielding, this effect is relatively small in comparison to the influence of temperature.

The plasticity and cleavage of polycrystalline beryllium I. Yield and flow stresses

1980 ◽  
Vol 370 (1740) ◽  
pp. 17-27 ◽  
Keyword(s):  
Grain Size ◽  
Flow Stress ◽  
Dislocation Density ◽  
Temperature Dependence ◽  
Yield Stress ◽  
Dislocation Motion ◽  
Orientation Factor ◽  
High Rigidity ◽  
Rigidity Modulus

The dependence of the yield and flow stresses of vacuum-cast and extruded polycrystalline beryllium on the grain size, d, is studied over 20-400 °C. Both follow the standard d -1/2 relationship. The Taylor orientation factor in the deformation of the poly crystal is ca. 4.3. The marked temperature dependence of the yield stress between 20 and 200 °C arises primarily from the intragranular resistance to dislocation motion, in particular on prismatic planes. The variation of the flow stress with d1/2 increases progressively with strain and this is attributed to the effect of grain size on the dislocation density at a given strain; the increase is particularly marked for beryllium because of its high rigidity modulus.

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