scholarly journals Две стадии формирования повреждения при ударном воздействии на поликристаллические соединения ZnS и ZnSe

2018 ◽  
Vol 60 (4) ◽  
pp. 760
Author(s):  
И.П. Щербаков ◽  
А.А. Дунаев ◽  
А.Е. Чмель
Keyword(s):  
Crack Nucleation ◽  
Synthesis Method ◽  
Barrier Properties ◽  
Interatomic Bond ◽  
Dislocation Motion ◽  
Local Deformation ◽  
Boundary Structure ◽  
Bond Rupture ◽  
Dislocation Glide ◽  
Excitation Mechanisms

AbstractMechanoluminescence (ML) in ductile solids is caused by the motion of charged dislocations in the deformable material. Interatomic bond ruptures followed by electronic structure reconfiguration are the main source of ML in brittle bodies. We studied ML in ceramics composed of mixed ionic/covalent ZnS and ZnSe compounds, which are generated during impact loading higher than the limit deformation. Depending on synthesis method and thermal treatment, the resulting ceramics had different size and geometry of grains and intergrain boundary structure, which presumably may have a significant effect on the dislocation glide. In both materials, the time sweeps of ML pulses have two well-resolved peaks. The position of the peaks along the time axis is substantially dependent on the size of ceramic-forming grains and, to a smaller extent, on the barrier properties of intergrain boundaries. The first peak is associated with plastic deformation preceding disintegration of the crystal structure. The second peak emerges upon crack nucleation as interatomic bonds are ruptured and the material is undergoing local deformation in tips of propagating cracks. The distributions of ML pulse amplitudes (the dependences between the number of pulses and their amplitude) calculated for both peaks individually follow the power law, which demonstrates that the electronic processes having different excitation mechanisms (dislocation motion vs bond rupture) are correlated.

Effect of Interface Conditions on Yield Behavior of Passivated Copper Thin Films

2002 ◽  
Vol 17 (7) ◽  
pp. 1863-1870 ◽  
Author(s):  
Richard P. Vinci ◽  
Stefanie A. Forrest ◽  
John C. Bravman
Keyword(s):  
Thin Films ◽  
Driving Force ◽  
Copper Film ◽  
Dislocation Motion ◽  
Yield Behavior ◽  
Dislocation Glide ◽  
Preferential Diffusion ◽  
Continuous Vacuum ◽  
And Diffusion ◽  
Induced Dislocation

Wafer curvature was used to study the thermal–mechanical behavior of 1-μm Cu thin films capped with a 100-nm-thick Si3N4 layer. These films were grown with either a Ta or a Si3N4 underlayer. Films on Si3N4 that were exposed to oxygen at the film/capping layer interface or at the center of the copper layer exhibited Bauschinger-like yielding at low stress. Stacks deposited under continuous vacuum, with a Ta underlayer, with carbon exposure at the upper surface of the copper film, or with oxygen exposure of only the underlayer did not demonstrate the anomalous yielding. Preferential diffusion of oxygen into copper grain boundaries or interfaces is the likely cause of the early yield behavior. Possible mechanisms include an increase in interface adhesion due to the presence of oxygen in solution and diffusion-induced dislocation glide as an additional driving force for dislocation motion at low applied stress.

Irradiation-Induced Grain Growth: Role of Dislocations

1989 ◽  
Vol 157 ◽  
Author(s):  
Charles W. Allen ◽  
Lynn E. Rehn
Keyword(s):  
Grain Growth ◽  
Point Defects ◽  
Ion Irradiation ◽  
Boundary Migration ◽  
Dislocation Motion ◽  
Boundary Structure ◽  
Thermal Growth ◽  
Growth Phenomenon

ABSTRACTExisting theories of irradiation-induced grain growth assume that growth occurs by the boundary migration mechanism commonly observed for thermal growth and that it is only the point defects generated si boundaries during the irradiation which are responsible for boundary migration. In contrast, in situ observations during ion irradiation of Au films at temperatures less than 20 K even have clearly demonstrated that growth occurs both by boundary migration and by grain coalescence. Here we present further evidence for the latter. Furthermore, the substantial defect cluster activity observed during irradiation suggests that dislocations play a significant role in the growth phenomenon. Here, we also demonstrate qualitatively that glide of such dislocations to or “through” a boundary can produce essentially the same effect on boundary position or structure that the original point defects would have had if they had migrated individually to or through the boundary. Via dislocation motion, point defects originating far from a boundary may induce boundary migration or boundary structure change, and hence, grain growth.

Atomistic Simulation of Flow Stress and Dislocation-Interface Interaction in Thin Metal Films

2003 ◽  
Vol 778 ◽  
Author(s):  
E. S. Ege ◽  
Y.-L. Shen
Keyword(s):  
Free Surface ◽  
Flow Stress ◽  
Tensile Stress ◽  
Atomistic Simulation ◽  
Dislocation Motion ◽  
Metal Films ◽  
Strain Response ◽  
Metallic Films ◽  
Free Standing ◽  
Dislocation Glide

AbstractThis study focuses on the atomistics of interface-mediated plasticity in thin metallic films. Molecular statics simulations are carried out to model the tensile stress-strain response of the free-standing and substrate-bonded films. In the free-standing film dislocation glide readily occurs, inducing slip steps at both surfaces of the film. The existence of an interface with the substrate constrains the dislocation motion in the film and restricts the slip steps to only the free surface. The propensity of film plasticity is dictated by the capability of atoms to slide along the interface. The flow stress of the film can be correlated with the dislocation activities obtained from the simulation. The propensity of spreading of relatively energetic atoms associated with the dislocation near the interface is also discussed.

Semi-brittle transient creep in Carrara marble: Hardening and Twinning-induced Plasticity

2020 ◽  
Author(s):  
Erik Rybacki ◽  
Lu Niu ◽  
Brian Evans
Keyword(s):  
Inelastic Strain ◽  
Dislocation Motion ◽  
Mechanical Twinning ◽  
Strain Rates ◽  
Dislocation Glide ◽  
Functional Relationships ◽  
Different Temperatures ◽  
Confining Pressures ◽  
Almost All ◽  
Hardening Coefficient

<p>Abundant observations of field- and micro-structures in marble rocks in both natural and laboratory settings indicate that these rocks have deformed by various combinations of mechanical twinning, dislocation motion, and dilatant fracturing. To better constrain the systematics of this semi-brittle flow, we performed a set of about 80 experiments at eight different temperatures (20°C<T<800°C). At each T, deformation conditions included different confining pressures (50 < P<sub>C </sub><300 MPa) and strain rates (10<sup>-6</sup> < ε’ <10<sup>-4 </sup>s<sup>-1</sup>). Under almost all these conditions, both the strength (σ) and the hardening coefficient (Θ=∂σ/∂ε) are affected by changes in P<sub>C</sub> and ε’, but the functional relationships of σ(P<sub>C</sub>, ε’) and Θ(P<sub>C</sub>, ε’) are unique. For example, at 20°C, σ is a non-linear function of both P<sub>C</sub> and ε’, while Θ depends on P<sub>C</sub> alone. In contrast, at 600°C, the dependence of σ on P<sub>C</sub> is very weak, and Θ depends on ε’ alone.</p><p>At T<650°C (less than half the absolute melting point of calcite), and P<sub>C</sub> greater than 50 MPa, the hardening coefficients are substantial (1% or more of the shear modulus), similar to steels and hexagonal metals that deform in a regime called twinning induced plasticity (TWIP). During TWIP, deformation proceeds with “easy” mechanical twinning, combined with dislocation glide on several slip systems whose glide planes are at high angles to the twin plane. In the calcite rocks, depending on conditions, the hardening resulting from twinning may be reduced by dilation and failure owing to brittle processes (at low pressures and temperatures), or by recovery and recrystallization (at higher temperatures or slower strain rates). Thus, both microstructural observations and mechanical deformation data are consistent with the interpretation that the hardening coefficient and strength are determined by the relative partitioning of inelastic strain amongst mechanical twinning, dislocation mechanisms, and dilatant fracturing. One important aspect is the nature of the mechanism that accommodates of discontinuous inelastic strain at the termination of twins at grain boundaries.</p>

Effect of Hydrogen on Dislocation Emission from a Crack Tip in Nickel

1992 ◽  
Vol 291 ◽  
Author(s):  
Richard G. Hoagland
Keyword(s):  
Barrier Height ◽  
Slip Plane ◽  
Crack Tip ◽  
Dislocation Motion ◽  
Dislocation Emission ◽  
Intrinsic Resistance ◽  
Dislocation Glide ◽  
Atomic Models ◽  
Work Done

ABSTRACTA method for determining the intrinsic resistance to dislocation emission and glide in atomic models is presented and applied to EAM models of nickel containing a single-ended crack tip. The method is an adaptation of the Peierls approach in which the work done on the glide plane is computed as a function of dislocation position and its derivative is the intrinsic resistance to dislocation motion. The results indicate that there are two parts to the resistance dislocation glide from the crack tip: a distinct barrier to injection of the dislocation from the crack tip and a periodic resistance associated with the lattice. When a hydrogen interstitial is placed on the slip plane near the crack tip the barrier height is reduced but its width is increased.

scholarly journals Ударное и "задержанное" повреждение поверхности керамики ZnS-CVD

2019 ◽  
Vol 45 (22) ◽  
pp. 39
Author(s):  
И.П. Щербаков ◽  
А.А. Дунаев ◽  
А.Б. Синани ◽  
А.Е. Чмель
Keyword(s):  
Time Series ◽  
Crack Nucleation ◽  
Chemical Vapor ◽  
Active Phase ◽  
Dislocation Motion ◽  
Energy Yield ◽  
Time Domains ◽  
Weak Points ◽  
The Difference ◽  
The Impact

Impact and impeded damage of ZnS-CVD ceramics surface I.P. Shcherbakov, A.A. Dunaev, A.B. Sinani, A.E. Chmel Localized damage of the surface of ductile ZnS ceramics synthesized by the chemical vapor deposition (CVD) method was performed by either impact of a pointed striker or by the impeded indenting of a Vickers pyramid. In both cases, the time series of acoustic emission pulses were recorded. The duration of the impact-induced sound emission was of 0.3-0.5 ms, while the indenting-produced active phase of emission was of 3-5 ms in length. The primary emission followed by the irradiation of weak acoustic signals during 80-100 ms. The statistical analysis of the time series showed the exponential (poissonian) energy distribution in impact-induced pulses, while in indented specimens, the distribution function followed a power law of the Gutenberg-Richter type. Considering that dislocation clusters serve as weak points for the crack nucleation, the difference in the mode of energy yield was explained by varying temporal pattern characteristics of the strain-stimulated dislocation motion in different time domains.

Investigating the local deformation and transformation behavior of sintered X3CrMnNi16-7-6 TRIP steel using a calibrated crystal plasticity-based numerical simulation model

2020 ◽  
Vol 111 (5) ◽  
pp. 392-404
Author(s):  
Faisal Qayyum ◽  
Sergey Guk ◽  
Stefan Prüger ◽  
Matthias Schmidtchen ◽  
Ivan Saenko ◽  
...  
Keyword(s):  
Trip Steel ◽  
Material Model ◽  
Local Deformation ◽  
Physical Parameters ◽  
Dislocation Glide ◽  
Material Optimization ◽  
Compressive Loads ◽  
Static Tensile ◽  
Dislocation Pinning ◽  
Transformation Stress

Abstract In this study, DAMASK was used to model and elucidate the microstructural deformation behavior of sintered X3CrMnNi16-7-6 TRIP steel. The recently developed TRIP-TWIP material model was used within the DAMASK framework. Material optimization was performed using the least computationally expensive method, which yielded the desired results. The physical parameters of the material model were identified and tuned to fit the experimental observations. This tuned material model was used to run simulations utilizing 2D EBSD data. The local deformation, transformation, and twinning behaviors of the material under quasi-static tensile and compressive loads were analyzed. The results of this are in good agreement with previous experimental observations. The phenomena of dislocation glide, twinning, martensitic transformation, stress evolution, and dislocation pinning in different deformation stages are discussed.

Micromechanical Analysis of Dislocation and Precipitate Interactions in Aluminum Alloys

2020 ◽  
Vol 985 ◽  
pp. 23-28
Author(s):  
Shinji Muraishi ◽  
Jianbin Liu
Keyword(s):  
Aluminum Alloys ◽  
Dislocation Line ◽  
Elastic Field ◽  
Type A ◽  
Interaction Force ◽  
Misfit Strain ◽  
Dislocation Motion ◽  
Type B ◽  
Burgers Vector ◽  
Dislocation Glide

Misfit precipitates greatly contribute to precipitation hardening in wrought aluminum alloys, where attractive and repulsive interactions are expected by stress-strain field of fine misfit precipitates. There are two types of dislocation cutting manner of {001} GP-zone and θ’ phase in Al-Cu alloys; one is dislocation burgers vector intersects (001) variant by 0 deg. (Type A), the other is dislocation Burgers vector intersects (001) variant by 60 deg. (Type B). In order to simulate the interaction of dislocation and fine misfit precipitates, internal stress fields by dislocation and precipitate are computed by Micromechanics based Green’s function method. The elastic field inside and outside a precipitate is deduced from Eshelby’s inclusion theory, where misfit strain of a (001) precipitate is assumed by unidirectional eigenstrain across the disk shaped inclusion. Dislocation motion under three different kinds of dislocation Burgers vector is tested by computing interaction force acted on the discretized dislocation line elements. The interaction force caused by (001) misfit precipitate is varied with types of dislocation cutting manner, magnitude of the interaction force associated with dislocation glide is increased by Type B variant (60 deg.), whereas that is minutely zero for Type A variant (parallel).

The Interaction Between Dislocations and Lamellar Grain Boundaries in Pst γ Tiai

1993 ◽  
Vol 319 ◽  
Author(s):  
S. Rao ◽  
C. Woodward ◽  
P.M. Hazzledine
Keyword(s):  
Grain Boundaries ◽  
Soft Mode ◽  
Dislocation Core ◽  
Dislocation Motion ◽  
Core Structure ◽  
Interface Plane ◽  
Atomic Step ◽  
Screw Dislocations ◽  
Dislocation Glide ◽  
Eam Potential

AbstractIn lamellar TiAl the flat-plate geometry of the grains, the barriers to deformation across the grain boundaries and the coherency stresses all contribute to a marked anisotropy in the yield and fracture stresses of the material. Both yield and fracture occur at low stresses when the deformation is within the lamellae (soft mode) and they occur at high stresses when the deformation crosses the lamellae (hard mode). The anisotropy is enhanced by a new effect which can soften the soft mode and harden the hard mode: the geometry of the lamellar boundary produces degeneracies in the planar fault energies at the interfaces which enhance the mobilities of dislocations on these interfaces. These degeneracies modify the core structure of dislocations on or near the interfaces, consequently soft mode dislocations can dissociate widely and move more easily when their glide plane is contained in the interface. Hard mode dislocations can substantially reduce their core energies when intersecting a γ/γ interface, and subsequently become immobilized, by cross slipping on to the interface plane. This paper presents a discussion of the geometry and relative energies of the γ/γ interfaces using elements of Bollman O-lattice theory. In order to investigate the influence of the interfaces on dislocation core structure we have fit an empirical Embedded Atom Method (EAM) potential to the structural and elastic properties of bulk L10 TiAl. The mobility and core structure of the twinning dislocation at the 180° interface and the perfect, 1/2<110] screw dislocation at the 60° and 120° interfaces were calculated using molecular statics within the EAM. We have also studied the influence of one and two atomic step ledges on dislocation mobility in the 120° interface. We find in general that dislocations are more glissile on the γ/γ interfaces, as compared to bulk TiAl and that ledges are weak barriers to dislocation glide. The interfaces themselves are strong barriers to dislocation motion in the hard mode. We find that the 1/2<110] screw dislocations gliding on conjugate {111} planes are trapped at these interfaces, as a result of lower core energies for screw dislocations lying in the interface.

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