Analytic model of dislocation density evolution in fcc polycrystals accounting for dislocation generation, storage, and dynamic recovery mechanisms

2022 ◽  
pp. 103178
Author(s):  
Abigail Hunter ◽  
Dean L. Preston
Keyword(s):  
Dislocation Density ◽  
Dynamic Recovery ◽  
Analytic Model ◽  
Density Evolution ◽  
Dislocation Generation ◽  
Recovery Mechanisms

A Dislocation Density Based Constitutive Model for Cyclic Deformation

1996 ◽  
Vol 118 (4) ◽  
pp. 441-447 ◽  
Author(s):  
Y. Estrin ◽  
H. Braasch ◽  
Y. Brechet
Keyword(s):  
Cyclic Loading ◽  
Dislocation Density ◽  
Constitutive Model ◽  
Constitutive Equations ◽  
Cyclic Deformation ◽  
Internal Variables ◽  
Density Evolution ◽  
Alloy 800H ◽  
Material Response ◽  
Dislocation Densities

A new constitutive model describing material response to cyclic loading is presented. The model includes dislocation densities as internal variables characterizing the microstructural state of the material. In the formulation of the constitutive equations, the dislocation density evolution resulting from interactions between dislocations in channel-like dislocation patterns is considered. The capabilities of the model are demonstrated for INCONEL 738 LC and Alloy 800H.

Effect of N/Ga Flux Ratio in GaN Buffer Layer Growth by MBE on (0001) Sapphire on Defect Formation in the GaN Main Layer

1999 ◽  
Vol 572 ◽  
Author(s):  
S. Ruvimov ◽  
Z. Liliental-Weber ◽  
J. Washburn ◽  
Y. Kim ◽  
G. S. Sudhir ◽  
...  
Keyword(s):  
Dislocation Density ◽  
Buffer Layer ◽  
Defect Formation ◽  
Flux Ratio ◽  
Growth Conditions ◽  
Buffer Layers ◽  
Simultaneous Increase ◽  
Growth Stages ◽  
Dislocation Generation ◽  
Gan Buffer Layer

ABSTRACTTransmission electron microscopy was employed to study the effect of N/Ga flux ratio in the growth of GaN buffer layers on the structure of GaN epitaxial layers grown by molecular-beamepitaxy (MBE) on sapphire. The dislocation density in GaN layers was found to increase from 1×1010 to 6×1010 cm−2 with increase of the nitrogen flux from 5 to 35 sccm during the growth of the GaN buffer layer with otherwise the same growth conditions. All GaN layers were found to contain inversion domain boundaries (IDBs) originated at the interface with sapphire and propagated up to the layer surface. Formation of IDBs was often associated with specific defects at the interface with the substrate. Dislocation generation and annihilation were shown to be mainly growth-related processes and, hence, can be controlled by the growth conditions, especially during the first growth stages. The decrease of electron Hall mobility and the simultaneous increase of the intensity of “green” luminescence with increasing dislocation density suggest that dislocation-related deep levels are created in the bandgap.

The Influence of Mobile Dislocation Density on the Fracture Toughness of B2-Based Ni-Fe-Al Alloys

1994 ◽  
Vol 350 ◽  
Author(s):  
A. Misra ◽  
R. D. Noebe ◽  
R. Gibala
Keyword(s):  
Fracture Toughness ◽  
Dislocation Density ◽  
Tensile Ductility ◽  
Growth Direction ◽  
Mobile Dislocation ◽  
Second Phase ◽  
Mobile Dislocation Density ◽  
Dislocation Generation ◽  
Multiphase Materials ◽  
Β Phase

AbstractThe deformation and fracture behaviors of two directionally solidified multi-phase Ni-Fe-Al ordered alloys were investigated. One alloy consisted of continuous β+γ lamellae with fine γ precipitates within the γ phase. The NiAl-based β phase of this alloy exhibited <100> slip even when deformed parallel to the [001] growth direction. This material exhibited an initiation fracture toughness of ∼ 30 MPa √m and tensile ductility of 10%. The second alloy consisted of aligned but discontinuous γ lamellae within a continuous β phase. Again, the γ phase contained γ precipitates, but unlike the previous alloy, the β phase also contained a fine dispersion of bcc precipitates due to spinodal decomposition. The β phase of this alloy deformed by <111> slip. This four-phase alloy exhibited a fracture toughness of ∼ 21 MPa √m and tensile ductility of 2%. Observations of the plastic zone in both alloys indicated significant plasticity in the β phase due to easy slip transfer from the ductile second phase. The enhanced fracture resistance of these multiphase materials compared to single phase β alloys is attributed in large part to intrinsic toughening of the β phase by an increased mobile dislocation density due to efficient dislocation generation from the β/γ interfaces.

scholarly journals Age–depth correlation, grain growth and dislocation-density evolution, for three ice cores

2009 ◽  
Vol 55 (190) ◽  
pp. 345-352 ◽  
Author(s):  
L.W. Morland
Keyword(s):  
Dislocation Density ◽  
Evolution Equation ◽  
Grain Growth ◽  
Ice Cores ◽  
Density Evolution ◽  
Depth Profiles ◽  
Growth Profiles ◽  
The Given ◽  
Theoretical Analyses

AbstractTwo previous theoretical analyses of data from the GRIP, Vostok and Byrd ice cores, presenting age–depth correlations, grain growth and dislocation-density evolution, are re-examined. It is found that the age–depth correlations are inconsistent with the idealized flow with unchanging history adopted, but that good correlations can be obtained by relaxing those restrictions. A modified grain-growth relation is proposed, consistent with the distinct growth profiles of the Vostok and other two cores, which can be solved simultaneously with the given dislocation-density evolution equation. These are solved for all three cores with the given parameters, and the depth profiles of grain diameter and dislocation density at the present time are determined with the new age–depth correlation and with that shown empirically in the papers. The varying flow history influences the age–depth correlation, and hence the depth profiles, which is important both for the interpretation of core data, and for the determination of constitutive variables at each depth at the present time.

scholarly journals A Unified Model for Plasticity in Ferritic, Martensitic and Dual-Phase Steels

Metals ◽  
2020 ◽  
Vol 10 (6) ◽  
pp. 764
Author(s):  
Shuntaro Matsuyama ◽  
Enrique I. Galindo-Nava
Keyword(s):  
Grain Size ◽  
Dislocation Density ◽  
Carbon Content ◽  
Grain Boundaries ◽  
Uniform Elongation ◽  
High Strength Steels ◽  
High Strength ◽  
Dual Phase ◽  
Dual Phase Steels ◽  
Dislocation Generation

Unified equations for the relationships among dislocation density, carbon content and grain size in ferritic, martensitic and dual-phase steels are presented. Advanced high-strength steels have been developed to meet targets of improved strength and formability in the automotive industry, where combined properties are achieved by tailoring complex microstructures. Specifically, in dual-phase (DP) steels, martensite with high strength and poor ductility reinforces steel, whereas ferrite with high ductility and low strength maintains steel’s formability. To further optimise DP steel’s performance, detailed understanding is required of how carbon content and initial microstructure affect deformation and damage in multi-phase alloys. Therefore, we derive modified versions of the Kocks–Mecking model describing the evolution of the dislocation density. The coefficient controlling dislocation generation is obtained by estimating the strain increments produced by dislocations pinning at other dislocations, solute atoms and grain boundaries; such increments are obtained by comparing the energy required to form dislocation dipoles, Cottrell atmospheres and pile-ups at grain boundaries, respectively, against the energy required for a dislocation to form and glide. Further analysis is made on how thermal activation affects the efficiency of different obstacles to pin dislocations to obtain the dislocation recovery rate. The results are validated against ferritic, martensitic and dual-phase steels showing good accuracy. The outputs are then employed to suggest optimal carbon and grain size combinations in ferrite and martensite to achieve highest uniform elongation in single- and dual-phase steels. The models are also combined with finite-element simulations to understand the effect of microstructure and composition on plastic localisation at the ferrite/martensite interface to design microstructures in dual-phase steels for improved ductility.

Modelling Dynamic Recovery and Recrystallization of Metals by a New Non-Equilibrium Thermodynamics Approach

2007 ◽  
Vol 558-559 ◽  
pp. 517-522
Author(s):  
Ming Xin Huang ◽  
Pedro E.J. Rivera-Díaz-del-Castillo ◽  
Sybrand van der Zwaag
Keyword(s):  
Steady State ◽  
High Temperature ◽  
Flow Stress ◽  
Dislocation Density ◽  
Dynamic Recovery ◽  
High Temperature Deformation ◽  
Temperature Deformation ◽  
Equilibrium Thermodynamics ◽  
Burgers Vector ◽  
Non Equilibrium

A non-equilibrium thermodynamics-based approach is proposed to predict the dislocation density and flow stress at the steady state of high temperature deformation. For a material undergoing dynamic recovery and recrystallization, it is found that the total dislocation density can be expressed as ( )2 ρ = λε& b , where ε& is the strain rate, b is the magnitude of the Burgers vector and λ is a dynamic recovery and recrystallization related parameter.

Bulk Growth of SiC

2008 ◽  
Vol 1069 ◽  
Author(s):  
Peter Wellmann ◽  
Ralf P. Müller ◽  
Sakwe A. Sakwe ◽  
Ulrike Künecke ◽  
Philip Hens ◽  
...  
Keyword(s):  
Dislocation Density ◽  
X Rays ◽  
Dislocation Generation ◽  
Thermally Induced ◽  
Bulk Crystal Growth ◽  
Bulk Growth ◽  
Single Defect ◽  
Process Visualization ◽  
Continuous Feeding

ABSTRACTThe paper reviews the basics of SiC bulk growth by the physical vapor transport (PVT) method and discuss current and possible future concepts to improve crystalline quality. In-situ process visualization using x-rays, numerical modeling and advanced doping techniques will be briefly presented which support growth process optimization. The “pure” PVT technique will be compared with related developments like the so called Modified-PVT, Continuous-Feeding-PVT, High-Temperature-CVD and Halide-CVD concepts. Special emphasis will be put on dislocation generation and annihilation and concepts to reduce dislocation density during SiC bulk crystal growth. The dislocation study is based on a statistical approach. Rather than following the evolu-tion of a single defect, statistic data which reflect a more global dislocation density evolution are interpreted. In this context a new approach will be presented which relates thermally induced strain during growth and dislocation patterning in networks.

scholarly journals Boundary conditions for dislocation dynamics simulations and stage 0 of BCC metals at low temperature

2001 ◽  
Vol 677 ◽  
Author(s):  
Meijie Tang ◽  
Ladislas P. Kubin
Keyword(s):  
Low Temperature ◽  
Dislocation Density ◽  
Boundary Conditions ◽  
Dislocation Dynamics ◽  
Body Centered Cubic ◽  
Density Evolution ◽  
Bcc Metals ◽  
Effective Boundary ◽  
Effective Boundary Condition ◽  
Dynamics Simulations

ABSTRACTIn order to study the dislocation density evolution of body centered cubic (bcc) crystals at low temperature by dislocation dynamics (DD) simulations, we investigated carefully three different boundary conditions (BC) for DD, i.e., the quasi-free surface BC, the flux-balanced BC, and the periodic BC. The latter two BCs can account for the dislocation loss from the boundary of the finite simulation box. PBC can also eliminate the influence of surfaces and improve the line connectivity. We have found that the PBC provides a convenient and effective boundary condition for DD simulations and have applied it to the study of dislocation density evolution of bcc metals during stage 0 deformation at low temperature.

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