scholarly journals Stacking fault energy in concentrated alloys

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Mulaine Shih ◽  
Jiashi Miao ◽  
Michael Mills ◽  
Maryam Ghazisaeidi
Keyword(s):  
Elastic Interaction ◽  
Stacking Fault ◽  
Stacking Fault Energy ◽  
Force Balance ◽  
Positive Zero ◽  
Experimental Measurements ◽  
Dislocation Interaction ◽  
Partial Dislocations ◽  
Balance Of Forces ◽  
Experimental Values

AbstractWe revisit the meaning of stacking fault energy (SFE) and the assumptions of equilibrium dissociation of lattice dislocations in concentrated alloys. SFE is a unique value in pure metals. However, in alloys beyond the dilute limit, SFE has a distribution of values depending on the local atomic environment. Conventionally, the equilibrium distance between partial dislocations is determined by a balance between the repulsive elastic interaction between the partial dislocations and a unique value for SFE. This assumption is used to determine SFE from experimental measurements of dislocation splitting distances in metals and alloys, often contradicting computational predictions. We use atomistic simulations in a model NiCo alloy to study the dislocation dissociation process in a range of compositions with positive, zero, and negative average SFE and surprisingly observe a stable, finite splitting distance in all cases at low temperatures. We then compute the decorrelation stress and examine the balance of forces on the partial dislocations, considering the local effects on SFE, and observe that even the upper bound of SFE distribution alone cannot satisfy the force balance in some cases. Furthermore, we show that in concentrated solid solutions, the resisting force caused by interaction of dislocations with the local solute environment becomes a major force acting on partial dislocations. Here, we show that the presence of a high solute/dislocation interaction, which is not easy to measure and neglected in experimental measurements of SFE, renders the experimental values of SFE unreliable.

On effects of non-systematic reflections on weak-beam images of partial dislocations

1991 ◽  
Vol 49 ◽  
pp. 688-689
Author(s):  
K. Z. Botros ◽  
S. S. Sheinin
Keyword(s):  
High Precision ◽  
Stacking Fault ◽  
Important Application ◽  
Stacking Fault Energy ◽  
Sharp Peak ◽  
Weak Beam ◽  
Partial Dislocations ◽  
Deviation Parameter ◽  
Beam Diffraction

The main features of weak beam images of dislocations were first described by Cockayne et al. using calculations of intensity profiles based on the kinematical and two beam dynamical theories. The feature of weak beam images which is of particular interest in this investigation is that intensity profiles exhibit a sharp peak located at a position very close to the position of the dislocation in the crystal. This property of weak beam images of dislocations has an important application in the determination of stacking fault energy of crystals. This can easily be done since the separation of the partial dislocations bounding a stacking fault ribbon can be measured with high precision, assuming of course that the weak beam relationship between the positions of the image and the dislocation is valid. In order to carry out measurements such as these in practice the specimen must be tilted to "good" weak beam diffraction conditions, which implies utilizing high values of the deviation parameter Sg.

Dislocations and stacking faults in stainless steel

1957 ◽  
Vol 240 (1223) ◽  
pp. 524-538 ◽  
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Stainless Steel ◽  
Grain Boundaries ◽  
Stacking Faults ◽  
Stacking Fault ◽  
Stacking Fault Energy ◽  
Thin Sections ◽  
Partial Dislocations ◽  
Transmission Electron

Further experiments by transmission electron microscopy on thin sections of stainless steel deformed by small amounts have enabled extended dislocations to be observed directly. The arrangement and motion of whole and partial dislocations have been followed in detail. Many of the dislocations are found to have piled up against grain boundaries. Other observations include the formation of wide stacking faults, the interaction of dislocations with twin boundaries, and the formation of dislocations at thin edges of the foils. An estimate is made of the stacking-fault energy from a consideration of the stresses present, and the properties of the dislocations are found to be in agreement with those expected from a metal of low stacking-fault energy.

Stacking Faults in Crystals

1968 ◽  
Vol 26 ◽  
pp. 250-251
Author(s):  
P. C. J. Gallagher
Keyword(s):  
Stacking Faults ◽  
Elastic Equilibrium ◽  
Stacking Fault ◽  
Stacking Fault Energy ◽  
Major Influence ◽  
Face Centered Cubic ◽  
Degree Of Dissociation ◽  
Partial Dislocations ◽  
Layer Structures ◽  
Face Centered

Stacking faults are an important substructural feature of many materials, and have been widely studied in layer structures (e.g. talc) and in crystals with hexagonal and face centered cubic structure. Particular emphasis has been placed on the study of faulted defects in f.c.c. alloys, since the width of the band of fault between dissociated partial dislocations has a major influence on mechanical properties.Under conditions of elastic equilibrium the degree of dissociation reflects the balance of the repulsive force between the partials bounding the fault, and the attractive force associated with the need to minimize the energy arising from the misfits in stacking sequence. Examples of two of the faulted defects which can be used to determine this stacking fault energy, Υ, are shown in Fig. 1. Intrinsically faulted extended nodes (as at A) have been widely used to determine Υ, and examples will be shown in several Cu and Ag base alloys of differing stacking fault energy. The defect at B contains both extrinsic and intrinsic faulting, and readily enables determination of both extrinsic and intrinsic fault energies.

Localized Influence of Solute on the Stacking Fault Energy of Dilute Al-Based Solid Solutions

1993 ◽  
Vol 319 ◽  
Author(s):  
C. Lane Rohrer
Keyword(s):  
Solid Solutions ◽  
Partial Dislocation ◽  
Binary Systems ◽  
Stacking Fault ◽  
Stacking Fault Energy ◽  
Dislocation Dipole ◽  
Partial Dislocations ◽  
Pure Metals ◽  
Small Clusters ◽  
Dislocation Spacing

AbstractThe stacking fault energy (SFE) is widely used to classify the mechanical behavior of pure metals. In alloys, however, the experimentally observed SFE is strongly influenced by localized solute effects. To further understand these effects on dislocation structure and on the observed SFE, solute segregation to an extended edge dislocation dipole, delineating two stacking faults, was studied in dilute Al:Cu, Al:Ag, and Al:Cu, Ag solid solutions. Cu and Ag were chosen to isolate solute size and modulus effects, Cu being smaller than Al, while Ag and Al are essentially the same size. Atomistic Monte Carlo results showed little change in the partial dislocation spacing in the binary systems as compared to the spacing in pure Al, even though Cu was observed to segregate to the compressive regions of the dislocation dipoles, forming widespread atmospheres, while Ag formed randomly distributed Ag-rich zones. However, in ternary Al:Cu,Ag simulations, the Ag apparently inhibited the Cu from distributing across the width of the extended dislocations, both Ag and Cu forming small clusters near or on the partial dislocations which increased the partial dislocation spacing. Results will be discussed in light of interpretations of experimental SFE determinations, emphasizing the importance of the localized solute distribution on the SFE.

scholarly journals Nanoscale Twinned Ti-44Al-4Nb-1.5Mo-0.007Y Alloy Promoted by High Temperature Compression with High Strain Rate

Metals ◽  
2018 ◽  
Vol 8 (8) ◽  
pp. 619 ◽  
Author(s):  
Wenqi Guo ◽  
Haitao Jiang ◽  
Shiwei Tian ◽  
Guihua Zhang
Keyword(s):  
Strain Rate ◽  
High Strain ◽  
Aerospace Industry ◽  
Dynamic Strength ◽  
Stacking Fault ◽  
Stacking Fault Energy ◽  
Tial Alloys ◽  
Partial Dislocations ◽  
Dynamic Mechanical Behavior ◽  
Twin Spacing

In order to investigate the dynamic mechanical behavior of TiAl alloys and promote their application in the aerospace industry, uniaxial compression of Ti-44Al-4Nb-1.5Mo-0.007Y (at %) alloy was conducted at a temperature range from 25 to 400 °C with a strain rate of 2000 s‒1. Twinning is found to be the dominating deformation mechanism of the γ phase at all temperatures, and the addition of Nb and Mo has a chemical impact on the alloy and reduces the stacking fault energy of the γ phase. The decreased stacking fault energy increases the twinnability; thus, the deformation is dominated by twinning, which increases the dynamic strength of the alloy. With the temperature increasing from 25 to 400 °C, the average spacing of twins in the γ phase increases from 32.4 ± 2.9 to 88.1 ± 9.2 nm. The increased temperature impedes the continuous movement of partial dislocations and finally results in an increased twin spacing in the γ phase.

HREM Observations of Deformation Recovery on and Near Surfaces of Eu2O3

1990 ◽  
Vol 48 (1) ◽  
pp. 344-345
Author(s):  
X.G. Ning ◽  
H.Q. Ye
Keyword(s):  
Surface Science ◽  
Electron Irradiation ◽  
Surface Deformation ◽  
Stacking Fault ◽  
Stacking Fault Energy ◽  
Partial Dislocations ◽  
Resolution Electron ◽  
High Resolution Electron Microscope ◽  
The Right ◽  
Deformation Recovery

Profile imaging technigue has been achieved very much in the field of surface science since it was first proposed. This work will show the deformation recovery on and near the surfaces of Eu2O3 under electron irradiation. The experiment was carried out in a JEOL-200CX high-resolution electron microscope. The Eu2O3 phase has a complex cubic structure with a=1.087 nm. A projected unit cell has been marked in Fig. la. It has been indicated that only Eu3+ ions , which are located in f.c.c. sublattice, appeared in HR images under certain defocus and in the thin areas of specimen. The structural character of Eu2O3 shown by HR images may be analyzed based upon comparing with that of simple f.c.c. structure.It can be seen from Fig. la that the surfaces of Eu2O3 are clean and Eu3+ ions on the (111) surfaces S1 and S2 moved /12 towards to the right (it is actually surface stacking fault). In Fig.lb the stacking fault on S2 was removed under electron irradiation but remained on S1. The stacking fault energy of Eu2O3 is high in the bulk. From Fig.l it can be known that the stacking fault energy may become lower on the (111) surface due to less constrained factors there. This kind of surface stacking fault is related to surface partial dislocations, and both of them may act as the main forms of surface deformation under electron irradiation.

The dissociated properties of dislocation in two-dimensional triangular lattice

Open Physics ◽  
2008 ◽  
Vol 6 (3) ◽  
Author(s):  
Wu Xiaozhi ◽  
Wang Shaofeng ◽  
Zhang Huili
Keyword(s):  
Triangular Lattice ◽  
Lattice Theory ◽  
Energy Criterion ◽  
Stacking Fault ◽  
Stacking Fault Energy ◽  
Two Dimensional ◽  
Partial Dislocations ◽  
Core Width ◽  
Equilibrium Separation ◽  
The Relationship

AbstractThe dissociated core structure of dislocation in two-dimensional triangular lattice is determined by the variational method within lattice theory. The dissociation effect leads to a narrower core width of partial dislocations than the compact one. The equilibrium separation between two partial dislocations is not very sensitive to the intrinsic stacking fault energy and there exists deviation from the intrinsic stacking fault energy criterion in the continuous elastic theory of dislocation. The relationship between the equilibrium separation and intrinsic stacking fault energy is analogous in lattice theory and the Peierls-Nabarro model. But the equilibrium separation obtained in lattice theory is wider than that obtained in the Peierls-Nabarro model for the same intrinsic stacking fault energy.

Stacking Fault Energy of Cu-Ga Alloys from First Principles

2007 ◽  
Vol 561-565 ◽  
pp. 1915-1918
Author(s):  
S. Fujita ◽  
Tokuteru Uesugi ◽  
Yorinobu Takigawa ◽  
Kenji Higashi
Keyword(s):  
Equilibrium State ◽  
First Principles ◽  
Input Parameter ◽  
Stacking Fault ◽  
Numerical Results ◽  
Stacking Fault Energy ◽  
Segregation Energy ◽  
Experimental Values ◽  
Good Agreement

The segregation energy of solute Ga in the staking fault in Cu-Ga alloy was calculated from the first principles. Then, we presented numerical results of the stacking fault energy for Cu-Ga alloy using the value of the segregation energy as a input parameter to a expression in the equilibrium state. The numerical results of the stacking fault energy were in good agreement with the experimental values.

The dissociation of dislocations in silicon

1971 ◽  
Vol 325 (1563) ◽  
pp. 543-554 ◽  
Keyword(s):  
Electron Microscopy ◽  
Dislocation Line ◽  
Anisotropic Elasticity ◽  
Stacking Fault ◽  
Stacking Fault Energy ◽  
Weak Beam ◽  
Partial Dislocations ◽  
A Value ◽  
Beam Method ◽  
Stacking Fault Energies

The weak-beam method of electron microscopy (Cockayne, Ray & Whelan 1969, 1970) has been used to investigate the dissociation of dislocations in silicon. Total dislocations with a/2<110> Burgers vectors were found to be dissociated into Shockley partial dislocations, with a separation of 7.5 +0.6 nm (75 + 6 Å) for the pure edge orientation and 4.1 +0.6 nm (41+ 6 Å) for the pure screw orientation. The intrinsic stacking-fault energy, calculated from the measured dissociation width using anisotropic elasticity theory, is 51 + 5 mJ m -2 (51 + 5 erg cm -2 ). The method has also been used to image partial dislocations at threefold dislocation nodes in silicon. All nodes in the specimens examined were found to be extended, and of about the same size, indicating that the intrinsic and extrinsic stacking-fault energies are comparable. Measurements of the radii of curvature of partial dislocations at the nodes gave a value of 50+15 mJ m -2 (50+15 erg cm -2 ) for the intrinsic stacking fault energy, using the method of Whelan (1959) as modified by Brown & Thölén (1964). Dislocations in silicon specimens annealed at a high temperature were found to be constricted along segments of the dislocation line. Evidence is presented which suggests that the constricted segments have climbed out of the slip plane.

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