The Dislocation Structure and Deformation Mechanism of Tib2/Nial Composites

1990 ◽  
Vol 213 ◽  
Author(s):  
L. Wang ◽  
R.J. Arsenault
Keyword(s):  
Grain Size ◽  
Dislocation Density ◽  
Screw Dislocation ◽  
Dislocation Structure ◽  
Deformation Mechanism ◽  
Volume Fraction ◽  
Dislocation Generation ◽  
Screw Dislocations ◽  
Size Refinement ◽  
Dislocation Annihilation

ABSTRACTDislocation structures in 0, 10, and 20 V% TiB2/NiAl composites have been thoroughly investigated with a 1 MeV HVEM after compression testing at 760–1000° C. Samples with 0 and 10 V% TiBl2/NiAl additions have almost identical dislocation structures which can be described as a<100> screw dislocations with extensive jogs and superjoqs. Prismatically punched dislocations were observed in all of the deformed composites and deformed samples of 20 V% TiB2/NiAl had extensive dislocation generation around the particles. Dislocation density, grain size, and the tendency for dislocation reactions or networks forming during deformation decrease as the volume fraction of TiB2 increases. Also, since a predominance of screw dislocation was observed, the rate controlling process is not likely to be dislocation annihilation or climb, but dislocation generation. The grain size refinement could play an important role in the strengthening of the composites.

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.

A Model for the Critical Height for Dislocation Annihilation and Recombination in GaN Columns Deposited by Patterned Growth

2004 ◽  
Vol 831 ◽  
Author(s):  
M. E. Twigg ◽  
N. D. Bassim ◽  
C. R. Eddy ◽  
R. L. Henry ◽  
R. T. Holm ◽  
...  
Keyword(s):  
Grain Size ◽  
Dislocation Density ◽  
Column Height ◽  
Critical Height ◽  
Patterned Growth ◽  
Sapphire Substrates ◽  
Density Reduction ◽  
Vertical Leakage ◽  
Dislocation Annihilation ◽  
Gan Film

ABSTRACTIn order to reduce vertical leakage in III-nitride detectors, we have grown a patterned array of hexagonal GaN columns on masked heteroepitaxial GaN template layers using a-plane sapphire substrates. In addition to eliminating cracking, we have found that for GaN columns tens of microns in diameter and several microns high, the dislocation density is also significantly reduced. We have developed a simple closed-form analytical model for predicting the critical column height for the onset of the reduction in the dislocation density. Among the predictions of this model is that the critical column height for the onset of dislocation density reduction is proportional to the product of column width and the grain size of the GaN film.

scholarly journals Microstructure Evolution in Cu–0.5 wt% Zr Alloy Processed by a Novel Severe Plastic Deformation Technique of Rotational Constrained Bending

Metals ◽  
2020 ◽  
Vol 11 (1) ◽  
pp. 63
Author(s):  
Tomáš Krajňák ◽  
Miloš Janeček ◽  
Peter Minárik ◽  
Jenő Gubicza ◽  
Pham Tran Hung ◽  
...  
Keyword(s):  
Grain Size ◽  
Dislocation Density ◽  
Microstructure Evolution ◽  
Coarse Grained ◽  
Strong Increase ◽  
Heterogeneous Distribution ◽  
Size Refinement ◽  
Elongation To Failure ◽  
Constrained Bending ◽  
Zr Alloy

In the present study, a coarse-grained Cu–0.5 wt% Zr alloy was repeatedly processed by a novel technique of rotational constrained bending (RCB). In this technique, the workpiece was deformed by bending in a channel with an angle of 90°, using a rotating roller. The influence of the number of passes (N) of RCB on strain distribution, microstructure evolution and mechanical properties of the alloy was investigated. The heterogeneous distribution of the microhardness in the billet cross-section after the first pass was transformed into a homogeneous one after twelve passes, due to the rotation of the sample by 90° clockwise between individual passes. In addition, the gradual refinement/homogenization of the microstructure and formation of strong (110) crystallographic texture were found with increasing N. The initial grain size of 180 μm decreased down to 3.4 μm after twelve passes. The dislocation density increased by two orders of magnitude after RCB processing. In accordance with the grain-size refinement and the strong increase of the dislocation density, RCB processing significantly enhanced the strength of the alloy, while the ductility considerably decreased. The yield stress increased from 63 to 524 MPa, while the elongation to failure decreased below 10% after twelve passes.

Research on Intercritical Rolling of 0.2C-1.5Si-1.5Mn TRIP Steels by Thermo-Mechanical Simulation

2005 ◽  
Vol 297-300 ◽  
pp. 1223-1228
Author(s):  
Zuo Cheng Wang ◽  
Sung Joon Kim ◽  
Chang Gil Lee ◽  
Tae Ho Lee
Keyword(s):  
Grain Size ◽  
Volume Fraction ◽  
Intercritical Annealing ◽  
Rolling Process ◽  
Isothermal Treatment ◽  
Trip Steels ◽  
Mechanical Simulation ◽  
Size Refinement ◽  
Multi Phase ◽  
Hot Rolled

In order to simplify the production routine and to save cost of hot-rolled TRIP steels, the intercritical rolling process was investigated using thermo-mechanical simulation technology. Both 0.2C-1.5Mn-1.5Si and 0.2C-1.5Mn-1.5Si-0.5Cu TRIP steels were chosen so as to study the effect of 0.5 pct Cu addition on microstructure and retained austenite volume fraction of 0.2C-1.5Mn-1.5Si TRIP steel. It is found that grain size refinement happened during intercritical deformation, and multi-phase microstructure could be achieved after isothermal treatment, so intercritical annealing can be eliminated to avoid grain size coarse and to keep the refine grain size in intercritical-deformed TRIP steels.

scholarly journals Shift of Creep Mechanism in Nanocrystalline NiAl Alloy

Materials ◽  
2019 ◽  
Vol 12 (16) ◽  
pp. 2508
Author(s):  
Zhihui Sun ◽  
Baoshu Liu ◽  
Chenwei He ◽  
Lu Xie ◽  
Qing Peng
Keyword(s):  
Grain Size ◽  
Dislocation Density ◽  
Grain Boundary ◽  
Boundary Diffusion ◽  
Volume Fraction ◽  
Grain Boundary Diffusion ◽  
Creep Mechanism ◽  
Creep Process ◽  
Nial Alloy ◽  
Coble Creep

We have examined the effects of temperature, stress, and grain size on the creep process including creep strain, crystal structure, dislocations and diffusions of nanocrystalline NiAl alloy through molecular dynamics simulations. A smaller grain size accelerates the creep process due to the large volume fraction of grain boundaries. Higher temperatures and stress levels also speed up this process in terms of dislocation changes and atom diffusion. In both primary creep and steady-state creep stages, atomic diffusion at the grain boundary could be seen and the dislocation density increased gradually, indicating that the creep mechanism at these stages is Coble creep controlled by grain boundary diffusion while accompanied by dislocation nucleation. When the model enters the tertiary creep stage, it can be observed that the diffusion of atoms in the grain boundary and in the crystal and the dislocation density gradually decreases, implying that the creep mechanisms at this stage are Coble creep, controlled by grain boundary diffusion, and Nabarro–Herring creep, controlled by lattice diffusion.

Influence of Austenite Grain Size on Martensite Start Temperature of Nb-V-Ti Microalloyed Ultra-High Strength Steel

2016 ◽  
Vol 848 ◽  
pp. 624-632 ◽  
Author(s):  
Ji Dong ◽  
Chen Xi Liu ◽  
Yong Chang Liu ◽  
Chong Li ◽  
Qian Ying Guo ◽  
...  
Keyword(s):  
Grain Size ◽  
Dislocation Density ◽  
High Strength Steel ◽  
Volume Fraction ◽  
High Strength ◽  
Austenite Grain Size ◽  
Microstructure Observation ◽  
Austenite Grain ◽  
Ultra High Strength Steel ◽  
Start Temperature

In order to investigate the effect of austenite grain size on martensite start temperature of Nb-V-Ti micro-alloyed ultra-high strength steel, the phase transformation features of Nb-V-Ti micro-alloyed steel was investigated. It has been found that martensite start temperature increased with the increase of austenite grain size as a consequence of the increase of austenitizing temperature. Based on microstructure observation, two types of MX carbonitrides with different compositions and morphologies have been identified. With the increase of the austenite grain size, both the volume fraction of precipitates and the dislocation density decreased, which may be induced by the strengthening of the austenite matrix directly and increasing the resistance of austenite to plastic deformation. Hence, the increase of martensite start temperature could be attributed to a decrease in volume fraction of precipitates and dislocation density.

Deformation Mechanism Map of Nanocrystalline Metallic Materials

2007 ◽  
Vol 539-543 ◽  
pp. 2816-2821
Author(s):  
Hyoung Seop Kim
Keyword(s):  
Grain Size ◽  
Deformation Mechanism ◽  
Size Dependence ◽  
Volume Fraction ◽  
Tensile Deformation ◽  
Boundary Phase ◽  
Metallic Materials ◽  
Adequate Description ◽  
Deformation Response ◽  
Phase Mixture

In this study, a deformation mechanism map of metallic nanocrystalline materials (NCMs) using the phase mixture model is proposed. It is based on recent modelling that appears to provide a conclusive description of the phenomenology and the mechanisms underlying the mechanical properties of NCMs. The proposed models adopted the concept of a ‘phase mixture’ in which the grain interior and the grain boundaries are treated as separate phases. The volume fraction of this grain boundary ‘phase’ may be quite appreciable in a NCM. Based on the theoretical model that provides an adequate description of the grain size dependence of plasticity covering all grain size range from coarse down to the nanoscale, the tensile deformation response of NCMs, especially focusing on the deformation mechanisms was investigated. The deformation mechanism map is newly proposed with axes of strain rate, grain size and temperature.

Observations of dislocation interactions with recrystallized grain boundaries

1988 ◽  
Vol 46 ◽  
pp. 628-629
Author(s):  
C. W. Price
Keyword(s):  
Dislocation Density ◽  
Grain Boundary ◽  
Strain Rate ◽  
Grain Boundaries ◽  
Dislocation Structure ◽  
Hot Deformation ◽  
Static Recrystallization ◽  
High Dislocation Density ◽  
High Angle ◽  
Dislocation Interactions

Little evidence exists on the interaction of individual dislocations with recrystallized grain boundaries, primarily because of the severely overlapping contrast of the high dislocation density usually present during recrystallization. Interesting evidence of such interaction, Fig. 1, was discovered during examination of some old work on the hot deformation of Al-4.64 Cu. The specimen was deformed in a programmable thermomechanical instrument at 527 C and a strain rate of 25 cm/cm/s to a strain of 0.7. Static recrystallization occurred during a post anneal of 23 s also at 527 C. The figure shows evidence of dissociation of a subboundary at an intersection with a recrystallized high-angle grain boundary. At least one set of dislocations appears to be out of contrast in Fig. 1, and a grainboundary precipitate also is visible. Unfortunately, only subgrain sizes were of interest at the time the micrograph was recorded, and no attempt was made to analyze the dislocation structure.

Observation of dislocations in dynamically loaded Cu-SiO2

1986 ◽  
Vol 44 ◽  
pp. 424-425
Author(s):  
D. S. Pritchard
Keyword(s):  
Electron Microscope ◽  
Strain Rate ◽  
Single Crystal ◽  
Transmission Electron Microscope ◽  
Volume Fraction ◽  
Screw Dislocations ◽  
Spherical Inclusions ◽  
Transmission Electron ◽  
Crystal Dispersion ◽  
Strain Rate Loading

The effect of varying the strain rate loading conditions in compression on a copper single crystal dispersion-hardened with SiO2 particles has been examined. These particles appear as small spherical inclusions in the copper lattice and have a volume fraction of 0.6%. The structure of representative crystals was examined prior to any testing on a transmission electron microscope (TEM) to determine the nature of the dislocations initially present in the tested crystals. Only a few scattered edge and screw dislocations were viewed in those specimens.

The effect of austenite grain size on deformation mechanism of Fe–17Mn steel

2021 ◽  
Vol 809 ◽  
pp. 140972
Author(s):  
Jin-Young Lee ◽  
Jin-Sung Hong ◽  
Seok-Hyeon Kang ◽  
Young-Kook Lee
Keyword(s):  
Grain Size ◽  
Deformation Mechanism ◽  
Austenite Grain Size ◽  
Austenite Grain
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