Atomistic simulation of fracture in Ni3Al

2008 ◽  
Vol 23 (6) ◽  
pp. 1597-1603 ◽  
Author(s):  
Hong-Xian Xie ◽  
Chong-Yu Wang ◽  
Tao Yu
Keyword(s):  
Atomistic Simulation ◽  
Crack Tip ◽  
Dislocation Core ◽  
Atomic Configuration ◽  
Close Attention ◽  
Shockley Partial ◽  
Simulation Process ◽  
Partial Dislocations ◽  
Higher Temperature ◽  
Dynamics Method

The molecular dynamics method has been used to simulate mode I cracking in Ni3Al. Close attention has been paid to the process of atomic configuration evolution of the cracks. The simulation results show that at low temperature, the Shockley partial dislocations are emitted before the initiation of the crack propagation, subsequently forming the pseudo-twins on (111) planes in crack-tip zone, and then the crack cleavage occurs. The emitting of the Shockley partial dislocations accompanies the crack cleavage during the simulation process. At the higher temperature, the blunting at the crack tip is caused by the [110] superdislocations emitted on (100) plane. The present work also shows that the dipole dislocations on (111) planes in the 1/2[110] dislocation core can be formed.

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 Effects of Re, W and Co on dislocation nucleation at the crack tip in the γ -phase of Ni-based single-crystal superalloys by atomistic simulation

2019 ◽  
Vol 6 (7) ◽  
pp. 190441 ◽  
Author(s):  
Dianwu Wang ◽  
Chongyu Wang ◽  
Tao Yu
Keyword(s):  
Activation Energy ◽  
Atomistic Simulation ◽  
Crack Tip ◽  
Dislocation Nucleation ◽  
Nucleation Process ◽  
Energy Landscapes ◽  
Alloying Element ◽  
Cleavage Process ◽  
Alloying Effects ◽  
Dynamics Method

The effects of Re, W and Co on dislocation nucleation at the crack tip in Ni have been studied by the molecular dynamics method. The results show that the activation energy of dislocation nucleation is lowered by the addition of Re, W and Co; moreover, the activation energy decreases when the alloying element increases from 1 at.% to 2 at.%. The energy landscapes of the atoms are studied to elucidate these effects. Quantification analyses of the bonding strength between Ni and X (X = Re, W or Co) reveal that strong bonding between Ni and X (X = Re, W or Co) in the dislocation nucleation process can suppress the cleavage process and enhance the ability of dislocation nucleation. The surface energy and unstable stacking fault energy are also calculated to understand the alloying effects on the dislocation nucleation process. The results imply that interaction between alloying elements and Ni atoms plays a role in promoting the dislocation nucleation process at the crack tip. The ability of Re, W and Co in improving the ductility of the Ni crack system is in the order W > Re > Co. The results could provide useful information in the design of Ni-based superalloys.

Extended Defects in 4H-SiC PiN Diodes

2002 ◽  
Vol 742 ◽  
Author(s):  
M. E. Twigg ◽  
R. E. Stahlbush ◽  
M. Fatemi ◽  
S. D. Arthur ◽  
J. B. Fedison ◽  
...  
Keyword(s):  
Elevated Temperatures ◽  
Compressive Strain ◽  
Pin Diode ◽  
Extended Defects ◽  
Pin Diodes ◽  
Plan View ◽  
Shockley Partial ◽  
Inhomogeneous Strain ◽  
Partial Dislocations ◽  
Transmission Electron

ABSTRACTUsing site-specific plan-view transmission electron microscopy (TEM) and lightemission imaging (LEI), we have identified SFs formed during forward biasing of 4H-SiC PiN diodes. These SFs are bounded by Shockley partial dislocations and are formed by shear strain rather than by condensation of vacancies or interstitials. Detailed analysis using TEM diffraction contrast experiments reveal SFs with leading carbon-core Shockley partial dislocations as well as with the silicon-core partial dislocations observed in plastic deformation of 4H-SiC at elevated temperatures. The leading Shockley partials are seen to relieve both tensile and compressive strain during PiN diode operation, suggesting the presence of a complex and inhomogeneous strain field in the 4H-SiC layer.

Recombination of Shockley partial dislocations by electron beam irradiation in wurtzite GaN

2019 ◽  
Vol 126 (16) ◽  
pp. 165702 ◽  
Author(s):  
I. Belabbas ◽  
I. G. Vasileiadis ◽  
J. Moneta ◽  
J. Smalc-Koziorowska ◽  
G. P. Dimitrakopulos
Keyword(s):  
Electron Beam ◽  
Electron Beam Irradiation ◽  
Beam Irradiation ◽  
Shockley Partial ◽  
Partial Dislocations

Effect of Ta on the Structure and Dynamics of γ/α2 Interfaces in Tial

1990 ◽  
Vol 213 ◽  
Author(s):  
S. R. Singh ◽  
J. M. Howe
Keyword(s):  
Partial Dislocation ◽  
Growth Mechanisms ◽  
Tial Alloys ◽  
Shockley Partial ◽  
Structure And Dynamics ◽  
Partial Dislocations ◽  
Α2 Phase ◽  
Atomically Flat ◽  
Ledge Mechanism ◽  
Image Simulations

ABSTRACTThe structure of γ/α interfaces in binary and Ta-containing TiAl alloys were analyzed by HRTEM and image simulations. Growth of α2 was found to be due to a ledge mechanism, consisting of Shockley partial dislocations on alternate (111)γ planes. The interface is atomically flat between the ledges and addition of Ta was found to transform arrays of growth ledges in the binary alloy into islands on the plate faces in the Ta-containing alloy. These islands of α2 on the γ/α2 interfaces were 4–7nm wide and increased in size with decreasing ageing temperature. The height of the ledges and islands were always a multiple of the c-parameter (0.46nm) of the α2 phase. The islands were bounded by 90°(edge) and 30° screw) Shockley partial dislocations. The 30° partial dislocation cores were localized whereas the 90° partial dislocation cores appeared to be highly delocalized due to presence of a high density of kinks, which in one case was found to be about 0.65nm−1.These results are interpreted in terms of the growth mechanisms and morphology of the α2 phase.

Simple Flexible Boundary Conditions for the Atomistic Simulation of Dislocation Core Structure and Motion

1992 ◽  
Vol 291 ◽  
Author(s):  
Roberto Pasianot ◽  
Eduardo J. Savino ◽  
Zhao-Yang Xie ◽  
Diana Farkas
Keyword(s):  
Atomistic Simulation ◽  
Dislocation Line ◽  
Dislocation Core ◽  
Dislocation Motion ◽  
Peierls Stress ◽  
Rigid Boundary ◽  
The Past ◽  
Structure And Motion ◽  
Linear Effects ◽  
Dislocation Core Structure

ABSTRACTFlexible boundary codes for the atomistic simulation of dislocations and other defects have been developed in the past mainly by Sinclair [1], Gehlen et al.[2], and Sinclair et al.[3]. These codes permitted the use of smaller atomic arrays than rigid boundary codes, gave descriptions of core non-linear effects and allowed fair assessments of the Peierls stress for dislocation motion. Green functions (continuum or discrete) or surface traction forces were used to relax the boundary atoms.A much simpler approach is followed here. Core and mobility effects at the boundary are accounted for by a dipole tensor centered at the dislocation line, whose components constitute six more parameters of the minimization process. Results are presented for [100] dislocations in NiAl. It is shown that, within the limitations of the technique, reliable values of the Peierls stress are obtained.

Some aspects of forces and fields in atomic models of crack tips

1991 ◽  
Vol 6 (12) ◽  
pp. 2565-2577 ◽  
Author(s):  
R.G. Hoagland ◽  
M.S. Daw ◽  
J.P. Hirth
Keyword(s):  
Crack Tip ◽  
Lattice Parameter ◽  
Crack Model ◽  
Dislocation Emission ◽  
Linear Elastic ◽  
Partial Dislocations ◽  
Atomistic Models ◽  
Crack Tips ◽  
Eam Potential ◽  
Crack Faces

This paper examines the stresses and displacement gradients in atomistic models of cracks based on an EAM potential devised for aluminum. Methods for computing these quantities are described. Results are presented for two models differing in terms of the orientations of the crack relative to the crystal, a [100] (010) orientation that behaves in a brittle fashion and a [111] (110) orientation that emits partial dislocations prior to extending. Both models display lattice trapping. The stresses in the brittle crack model are compared with the linear elastic prediction and found to be in remarkably good agreement to within distances of about one lattice parameter of the crack tip and at the free surface where contributions from sources other than strain energy (e.g., surface tension) influence the results. Similar results are observed for the ductile model until dislocation emission occurs. The largest stresses that develop just prior to crack extension or dislocation emission are used to estimate the ratio of theoretical tensile strength to shear strength in this material. Eshelby's conservation integrals, F and M, are also computed. F is found to be essentially contour independent and in agreement with the linear elastic prediction in both models until dislocation emission occurs, at which point a large screening contribution arises from the emitted partials. The contour size dependence of M reveals some interesting features of the crack tip including a slight wobble of the crack tip inside its potential well with changing applied K and the existence of forces acting to move the crack faces apart as blunting occurs.

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