Poster contributions

abstract: 1.2
Fundamental Behavior of Dislocation Loops in Fe
EIICHI KURAMOTO, KAZUHITO OHSAWA, Research Institute for Applied Mechanics, Kyushu University, Japan; JUNICHI IMAI, KIYOKAZU OBATA, Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, Japan; TETSUO TSUTSUMI, Research Institute for Applied Mechanics, Kyushu University, Japan.
One dimensional motion of dislocation loops (bundle of crowdions) has recently become very important in the field of radiation damage of materials because of its contribution to void swelling. In the cascade formation of radiation damage small dislocation loops (bundle of crowdions) are emitted outwards and make one dimensional motion and are absorbed into sinks like dislocations, assisting vacancies left to form voids in the matrix, that is, to contribute to the so-called production bias. Since this one dimensional motion of a dislocation loop is caused by the slip motion of the peripheral dislocation segments of edge character, detailed information of the slip of a dislocation loop must be obtained as a function of loop size, applied shear stress and temperature. From the viewpoint of lattice defects this is also very important because the largest limit of a dislocation loop is a straight edge dislocation and the smallest limit is a single crowdion. Hence the study of the interrelation between these two limits will give us the new feature on the relation between a point defect and a dislocation. In the present study dislocation loops of various sizes are formed in the model Fe lattice constructed by using Finnis-Sinclair potential and the core structures of the edge dislocation segments of the hexagonal shaped loops and the response to the applied shear stress, that is, Peierls stress of loops are obtained. A straight edge dislocation makes a slip motion overcoming Peierls potential which has an effective periodicity of b/3, but dislocation loops have a changing tendency of this period into b. This must be one of the reasons that Peierls force increases with decreasing of loop size.

abstract: 1.7
Dislocations in C60 crystals
NATSUKO AOTA, MASARU TACHIBANA, KENICHI KOJIMA, Graduate School of Integrated Science,Yokohama City University, Japan.
C60 single crystals are well known as molecular crystals with face-centered-cubic (fcc) structure. The magnitude of Burgers vector in C60 crystals is 1.001 nm at room temperature and is quite longer than that of the typical fcc metal crystals. Therefore, we are interested in whether the characteristics of dislocations in the C60 crystals are the same as those of fcc metals. In this work, we investigated the characteristics of dislocations in the C60 crystals by X-ray topography and etching method. C60 single crystals with $\{111\}$ habit faces were grown by vapor deposition method. Dislocations were introduced by an indentation method. The dislocation structures were investigated by X-ray topography and etching method. The X-ray topography experiments were carried out by using white-beam synchrotron radiation at KEK-PF and SPring-8. We also observed the motion of dislocations after indentation by thermal annealing. The X-ray topography indicated that Burgers vector of dislocations in C60 crystals which was introduced by indentation method was $1/2<110>$ as same as that in fcc metals. These slip dislocations were straight along the $<110>$ directions as if they tended to lie along deep valleys of the Peierls potential. After the indentation, moreover, the $\{111\}$ habit faces were etched. We observed the well developed rosette patterns of dislocation pits around the indentation. These rosette pattern distributions were developed after annealing. The activation energy of dislocation motions in rosette pattern was estimated by changing annealing temperature. These results will be discussed in the conference.


abstract: 1.8
Dislocations in orthorhombic lysozyme crystals using synchrotron X-ray topography
MIKI SHIMIZU, HARUHIKO KOIZUMI, MASARU TACHIBANA, KENICHI KOJIMA, Graduate School of Integrated Science, Yokohama City University, 22-2 Seto, Kanazawa-ku, Yokohama 236-0027 Japan.
The characterization of dislocations in protein crystals is very important for an understanding of their crystallization. X-ray topography using synchrotron radiation is one of the most powerful methods to characterize dislocations because a large number of topographs with different reflections can be obtained by one short exposure for short exposure time. We have succeeded in observation of X-ray topographs of tetragonal hen egg-white lysozyme (HEWL) crystals. However, dislocations in orthorhombic HEWL have not observed using X-ray topography yet. We would like to report the first observation of the topographic images of dislocations in orthorhombic HEWL crystals using synchrotron radiation. Orthorhombic HEWL crystals were grown at 313 K by the two-liquid interface method. Millimeter-size crystals (the maximum size is about 18 mm) were obtained after about 1 month. X-ray topographs of these crystals were taken at KEK-PF and SPring-8. Recently, we succeed in taking very clear X-ray topography of orthorhombic HEWL crystals. Several straight dislocations from center parts of crystals to the surface were observed. The distribution of the dislocations was similar to that of grown-in dislocations commonly observed in solution-grown crystals. These images were decided to be dislocations because they satisfied the extinction criterion (g.b=0). We will discuss the details of the characteristics of the dislocations at the conference.


abstract: 1.10
Formation of dislocation dipole by knock-on process in irradiated graphite
KEISUKE NIWASE, Hyogo University of Teacher Education, 942-1 Yashiro, Hyogo, Japan 673-1494, Japan.
The planar structure of graphite transforms to a disordered structure under high energy particle irradiation. Recently, we have proposed a kinetic model to explain irradiation-induced amorphization of graphite (Niwase, Phil. Mag. Lett. 82 (2002) 401). The model assumes the formation of dislocation dipoles by knock-on process and the existence of a barrier inhibiting the mutual annihilation of an interstitial and a vacancy. Calculated results for the change in a sample dimension along the c-axis up to a high dose of amorphization and the Raman intensity ratio in a low damage range compare favorably with the experimental results and reveal a very small value of $5.0 x 10^{-4}$ on the recombination probability between an interstitial and a vacancy. Here, we discuss the structure of the dislocation dipole, which contains fivefold, sevenfold or eightfold rings at the ends.


abstract: 1.12
On the mobility of partial dislocations in silicon
G. VANDERSCHAEVE, CEMES/CNRS, 29 rue Jeanne Marvig,, BP 94347, 31055 Toulouse, France and INSA Toulouse, Physics Department, 135 av. de Rangueil, 31077 Toulouse, France. DANIEL CAILLARD, CEMES/CNRS, 29 rue Jeanne Marvig,, BP 94347, 31055 Toulouse, France.
Dislocations in covalent materials such as semiconductors are subjected to a high lattice friction. At low temperatures they align themselves along the low energy $<110>$ Peierls valleys. Then perfect dislocations have either 60° or screw characters and partial dislocations have either 90° or 30° characters, each with a specific core structure. From their TEM investigation of the dislocation microstructure in high-stress deformed silicon, Wessel and Alexander(1) came to the conclusion that partial dislocations have different mobilities, depending not only on their character (90° or 30°), but also on their position (leading or trailing) with respect to the sense of dislocation motion. This latter point was rather unexpected because the core structure of a given partial does not depend of its position. To account for this effect, it was suggested that the velocity of a given partial could depend on the climb component of the Peach-Köhler force. The histograms of experimental data on dissociation widths present a rather wide scatter with an asymmetrical distribution. We have reexamined the data by considering that metastable dissociation configurations could be observed, because the partial dislocations are not entirely mobile in their dissociation plane(2). From a theoretical analysis of the distribution of dissociation distances for dislocations moving in a periodic Peierls potential, it is shown that the experimental results can be interpreted in a consistent way without the assumption of different mobilities for leading or trailing partials. This analysis shows that the Schmid law is obeyed and that it is not necessary to consider the climb forces acting on the different partials. The mobility ratio between 90° and 30° partials is estimated to be about 5, independently of their leading or trailing position., in agreement with an experimental ratio of about 2 between the mobilities of 60° and screw perfect dislocations, as determined by X-Ray topography(3). Implications of this result on particular dislocation mechanisms (e. g. twin formation) in silicon will be discussed.

References:
(1) K. Wessel, H. Alexander, Phil. Mag. 35, 1523 (1977)
(2) V. Paidar, D. Caillard, Phil. Mag. Letters 69, 305 (1994)
(3) M. Imai, K. Sumino, Phil.Mag. A, 47, 599 (1983)


abstract: 1.13
Dislocations in brittle materials activated at room temperature and 77K
HIROYASU SAKA, Deparment of Quantum Engineering, Nagoya University, Japan.
Dislocations introduced into Si, Ge, GaAs, Al$_{2}$O$_{3}$ by Vickers indentation at room temperature and 77K were examined by transmission electron microscopy. In elemental semiconductor such as Si and Ge, those dislocations activated at these temperatures were identified as shuffle sets, while those in GaAs are dissociated into two Shockley partials. Thermal stability of the shuffle dislocations was investigated by in-situ and ex-situ heating experiments.


abstract: 1.18
Atomistic Insights into Dislocations: Coupling Ab Initio, Classical Potential, Dislocation Dynamics and Finite Element Simulations into a Single Framework
F. TAVAZZA, A. M. CHAKA, S. M. A. KHAN, L. MA, L. E. LEVINE, National Institute of Standards and Technology, USA.
Dislocation phenomenology is extremely complex and covers length scales ranging from the nanoscale to the continuum. In this work, we introduce a new simulation methodology that directly bridges these length scales. At the atomistic level, a hybrid ab initio-classical potential methodology has been developed that allows us to conduct large-scale atomistic simulations with a simple classical potential (embedded atom method (EAM), for instance) while simultaneously using the more accurate ab initio approach for critical embedded regions. The coupling is made through shared atomic shells where the two atomistic modeling approaches are used in an iterative, self-consistent manner. The small, critical region is relaxed using density functional theory and the much larger cell in which this is embedded is relaxed using a Monte-Carlo algorithm with EAM potentials. The initial positions and boundary conditions for the EAM simulation cell come from elastic displacement fields provided by either multi-scale discrete dislocation plasticity simulations or conventional finite element modeling. Applications of this method will be discussed, including the variation of vacancy and solute atom formation energies at different distances from a dislocation core, and an analysis of dislocation nucleation during nanoindentation.


abstract: 1.19
Motion of dislocation kinks in a simple model crystal
HIROKAZU KOIZUMI, Meiji University, Kawasaki, Japan. TAKAYOSHI SUZUKI, Professor Emeritus, The University of Tokyo, Japan.
A dislocation glides between adjacent Peierls valleys by nucleation of a pair of kinks which subsequently glide apart. The lattice periodicity along the dislocation line produces a periodic potential for a kink, that is, the Peierls potential of second kind. If the kinks move sufficiently fast, the kink-pair formation process determines the dislocation velocity. If the kinks move slowly on the second kind Peierls potential, the dislocation velocity is determined not only by the formation rate of kink-pairs but also by the velocity of kinks. This work investigates the effects of lattice periodicity on the kink motion by a molecular dynamics simulation for a simple model.

The model crystal of the diamond structure contains a screw dislocation with a kink pair on a shuffle plane. The Stillinger-Weber potential is assumed between atoms. In this system the dislocation does not extend and kinks are abrupt, which enables unambiguous determination of the kink position applying the Burgers circuit method.

The Peierls stress for a perfect screw dislocation in this model crystal is 0.04G[1], where G is the shear modulus on (111) plane. Because two kinks are not symmetric under the applied stresses, the stresses necessary to move a positive and a negative kink are different: The Peierls stress of second kind for a positive kink is 0.0035G, while that of a negative kink is 0.0027G. However, the two kinks attain nearly the same terminal velocity except at very low stresses. When the kink velocity is about 0.2 times the shear wave velocity, the velocity-stress relation shows discontinuous jump. Similar velocity-stress relation is observed for an infinitely long straight dislocation and attributed to abrupt change in the spectrum of emitted waves [2]. The kink velocity exceeds the shear wave velocity at high stresses as in the case of a straight dislocation.

References:
1. H. Koizumi, H. O. K. Kirchner and T. Suzuki, Philos. Mag. A80(2000)609.
2. H. Koizumi, H. O. K. Kirchner and T. Suzuki, Phys. Rev. B65(2002)214104.


abstract: 1.20
Limiting Speeds of Fast Moving Edge Dislocations
Z-H. JIN, IZBS, Uni. Karlsruhe (TH), Kaiserstr. 12, 76131 Karlsruhe, Germany; P. GUMBSCH, IZBS, Uni. Karlsruhe (TH), Kaiserstr. 12, 76131 Karlsruhe, Germany and Fraunhofer IWM, Woehlerstr. 11, 79108 Freiburg, Germany.
The dynamics of single edge dislocations was studied using microcanonical molecular dynamics (MD) and the Finnis-Sinclair potentials for tungsten, tantalum and niobium. Full edge dislocations (b=$<111>$/2) are confined within an otherwise perfect lattice with fixed borders perpendicular to the glide plane normal ($<112>$//y). Periodic boundary conditions are applied along the $<111>$ direction (x) and the dislocation line direction ($<110>$//z). Driven by an applied homogeneous simple shear strain in the x-y plane, the dislocations can move uniformly at subsonic, transonic or supersonic velocities. The velocity-strain relation of fast moving dislocations was mapped-out and limiting speeds of moving dislocations across subsonic, transonic and supersonic regimes were clarified and analyzed by linear elasticity theory. In the subsonic regime, the work required to propagate dislocations has to be released from the dislocation by lattice waves emitted from the dislocation core and increases the faster the dislocation moves. The limiting speeds of transonic dislocations depend on the anisotropic nature of the material. Dislocations in tungsten show nearly ideal isotropic behavior; in tantalum and niobium, however, the full anisotropic solution is required for the interpretation of the observed velocity strain relation. Supersonic dislocations leave all lattice waves behind, characterized by Mach cones of both longitudinal type and transverse type. The patterns of the Mach cones are again related to the anisotropic nature of the material. In essentially all limiting properties of the fast moving dislocations the (anisotropic) continuum elasticity analysis was found to be applicable and sufficient. However, transitions between different velocity regimes and the required driving forces for sustained motion require atomistic analyses including non-linear effects and the discrete and periodic nature of lattices.


abstract: 1.23
Transition path study of the motion of dissociated dislocations in FCC metals
YASUSHI KAMIMURA, KEIICHI EDAGAWA, Institute of Industrial Science, University of Tokyo, Meguro, Tokyo, Japan.
In general, a dislocation in face-centered-cubic (FCC) metal is dissociated into two parallel Shockley partial dislocations connected by a stacking fault. Motion of such dissociated dislocations has not been fully clarified yet, especially in the case of the fault-width being several atomic distances, as in copper. In such a case, we cannot treat the motion of each partial independently but must consider a correlative motion. Here, assuming only a fixed Peierls potential for each partial is not appropriate because of the interaction between the two partials and the attractive force due to the stacking fault. Such a complicated situation makes it difficult to understand the correlative motion and the kink-pair formation process of the partials. This fact is one of the causes of the controversy on the inconsistency between the Bordoni peak and the flow stress of FCC metals. In the present study, we examined the slip motion of dissociated dislocations in a model FCC metal using a transition-path calculation.

A model FCC crystal of 42x42x50 atoms was prepared. First, the partial dislocations with a given fault-width were introduced by giving atomic displacements of elastic solution. Then, the system was relaxed by use of an empirical potential for copper by derived by Ackland. For different initial fault-width, we found a few (meta-) stable configurations. Of them, we selected the most stable configuration as the initial state for the transition-path calculation. As the final state, we constructed the structure in which the two partials proceed by a lattice period from those in the initial state. The minimum energy path (MEP) between the initial state and the final state was determined by a numdged-elastic band method. Here, we started from a straight line in the 3N dimensional configuration space as the initial trial transition path and arranged about 20 points (replicas) on it. Then, each replica was relaxed perpendicularly to the path to find the MEP.

The MEP obtained consists of two successive processes. First, the trailing partial proceeds to the next stable position with the leading partial position unchanged to form a transient metastable configuration. Then, the leading partial proceeds to the next stable position to reach the final state. The energy at the transient state was evaluated to be 0.02eV. The activation energy from the initial state to the transient state and that from the transient state to the final state were 0.14 and 0.12eV, respectively. Further calculations, such as those under applied stress and those for different stable fault-width are now in progress.


abstract: 1.26
Metadislocation reactions and networks in the complex metallic alloy xi´-Al-Pd-Mn
MARC HEGGEN, MICHAEL FEUERBACHER, KNUT URBAN, IFF, Forschungszentrum Jülich, 52425 Jülich, Germany.
The mechanisms of plastic deformation of complex metallic alloys (CMAs) and the defects mediating plastic deformation are largely unknown. Due to the large lattice parameters encountered in these materials, the concepts that are used to describe the plastic deformation of simple crystalline materials fail. The introduction of a perfect dislocation into in a CMA would lead to a high elastic line energy. Recently, a novel mechanism of plastic deformation involving a new type of structural defect called metadislocation (Klein et al. 1999) was found in the complex intermetallic phase xi´-Al-Pd-Mn.

In the present work we present a TEM study on metadislocation networks and reactions. We demonstrate that metadislocations (MDs) can dissociate into MDs with smaller Burgers vectors, which leads to a decrease of the elastic line energy. Connected groups of MDs can assume large and complex network structures. Examples of networks of MDs are presented and their properties are analysed. These networks may play an important role for the plastic deformation mechanism. Although single MDs possess a Burgers vector with an irrational Burgers vector modulus to lattice parameter ratio, it is shown that networks of MDs can be perfect dislocations in the xi´-Al-Pd-Mn-structure. By this mechanism, effective large Burgers vectors, contributing massively to plastic strain, can be distributed over a large portion of the material.

Klein, H., Feuerbacher, M., Schall, P., und Urban, K., (1999) Phys. Rev. Lett. 82, 3468.


abstract: 1.27
Dislocation glide in model Ni(Al) solid solutions by molecular dynamics
LAURENT PROVILLE, SRMP CEA-Saclay, Gif-sur-Yvette, France. DAVID RODNEY, GPM2/ENSPG, St Martin d'Hères, France. YVES BRéCHET, LTPCM/ENSEEG, St Martin d'Hères, France. GEORGES MARTIN, SRMP CEA-Saclay, Gif-sur-Yvette, France.

The glide of an edge dislocation, in a random solid solution, Ni (1 to 8at% Al), is simulated by Molecular Dynamics. An Embedded Atom Method potential has been optimized to reproduce the relevant properties of the face centered cubic solid solution and of the L12 Ni3Al phase. Glide is studied at fixed temperature and applied stress. We find that the obstacles are made of specific configurations of the Al atoms, which are brought in positions of strong mutual repulsion in course of the glide process. The solute-solute short range repulsion, rather than the usually assumed dislocation-solute interaction, is thus argued to be the main mechanism responsible for chemical hardening in the present concentrated random solid solution.


abstract: 1.28
Metastability of Undissociated State of Dissociated Dislocation
S. TAKEUCHI, Department of Materials Science and Technology, Tokyo University of Science.

Undissociated metastable dislocations have often been observed in addition to stable dissociated dislocation in various crystals by high resolution electron microscopy. The origin of the metastability of the undissociated state has been discussed specifically for the dissociation into Shockley partial dislocations in the fcc or hcp lattice. It is shown that the metastability is due either to a high Peierls-Nabarro stress of the partial dislocations larger than a few percent of the shear modulus and/or to increase of the total core energy by an amount larger than 0.04Gb2 per unit length (G: shear modulus, b:the strength of the total Burgers vector) with an increase of the dangling bonds. The metastability of undissociated dislocations in zincblend III-V compounds is concluded to be due to the latter contribution.


abstract: 1.29
Peierls-Nabarro relation in the Peierls stress of different slip systems
KEIICHI EDAGAWA, IIS, Univ. Tokyo, Komaba, Meguro-ku, Tokyo 153-8505 Japan; SHIN TAKEUCHI, Dept. of Mat. Sci. and Tech., Tokyo Univ. of Science, Noda, Chiba 278-8510 Japan.
The Peierls stress $\tau_{P}$ is defined as the minimum external stress necessary for a lattice dislocation to move without any assistance from thermal vibration of the lattice. Using a continuum approximation, Peierls and Nabarro [1] first derived a relation (P-N relation) giving this fundamental quantity of a dislocation. The relation has the form: $\tau_P$/G=2/(1-$\nu$)exp-2$\pi$/(1-$\nu$)(h/b), where G is the shear modulus, $\nu$ is the Poisson's ratio, h is the spacing across the slip plane and b is the length of the Burgers vector. Experimentally, the values of $\tau_P$ can be estimated by extrapolating the yield stress at a finite temperature to zero absolute temperature. It has been shown that the data of $\tau_P$ for various kinds of crystals are in good agreement with those expected from the P-N relation [2]. Because the lattice discreteness should play an essential role in determining the Peierls stress, it is useful to reexamine the validity of the P-N relation, which was derived from a continuum approximation, by use of full lattice models. Here, the calculations of $\tau_P$ for different lattice structures are not suitable for this purpose because we have no reasonable way to compare them. In the present study, to avoid this problem, we have attempted the calculations of $\tau_P$ for different slip systems in a single model lattice.

An edge dislocation with a selected Burgers vector was introduced into a model bcc lattice by giving atomic displacements according to the elastic solution. It was relaxed using an interatomic potential constructed by Vitek et al.[3] The shear stress was applied to the model crystal and it was subsequently relaxed. The stress application and relaxation were repeated with increasing applied stress gradually to find the Peierls stress at which the structure loses stability. The calculation was done for various slip systems: $<111>-\{110\}$, $<100>-\{100\}$, $<100>-\{110\}$ and $<110>-\{110\}$, whose h/b values are 0.82, 0.5, 0.71 and 0.5, respectively. We found that the evaluated $\tau_P$ values satisfactorily agree with the P-N relation with nyu=0.3. Further calculations for other slip systems are now underway to confirm the result.

References:
1. R.E. Peierls, Proc. Phys. Soc., 52 (1940) 34; F.R.N. Nabarro, Proc. Phys. Soc. 59 (1947) 256.
2. T. Suzuki and S. Takeuchi, Rev. Phys. Appl. 23 (1988) 405.
3. V. Vitek et al., Philos. Mag. 21 (1970) 1049.


abstract: 1.30
Dislocation defect interaction in irradiated Cu
R. SCHAEUBLIN, Z. YAO, CRPP-EPFL, Villigen PSI, Switzerland ; D. RODNEY, GPM2 - ENSPG, Saint Martin d'Heres, France; P. SPAETIG, CRPP-EPFL, Villigen PSI, Switzerland.
Irradiation generally leads to significant hardening and loss of ductility in alloys and in pure metals. In order to study the relationship between the mechanical properties and the radiation induced microstructure pure Cu single crystals have been deformed by uniaxial tensile testing and in-situ deformation in transmission electron microscopy has been used to identify the basic mechanisms at the origin of hardening. Cu was irradiated with 590 MeV protons to a dose of 0.01 dpa at room temperature. It appears that the irradiation induces a hardening that increases the yield strength from 14 MPa in the unirradiated case to 37 MPa, and that the radiation induced microstructure consists at 90% in 2 nm stacking fault tetrahedra, the remaining being dislocation loops or undefined clusters. The activation volume, deduced from successive stress relaxation experiments performed at 77, 173, 233 and 293 K, strongly decreases with increasing strain in the unirradiated case while in the irradiated case it remains nearly constant, at values between 60 to 150 b3 for the lowest ones obtained at the lowest temperature of 77 K. In-situ deformation reveals that dislocation defect interaction can take several forms. One of the most significant at low temperature can be described by the strong pinning of dislocations by defects that leads to the formation of elongated debris. Molecular dynamics simulations were performed to understand these mechanisms and are presented together with the experimental results.


abstract: 1.31
Core structure, dislocation energy and Peierls stress for $1/3 \langle 11\overline{2}0 \rangle$ edge dislocation with $(0001)$ and $\{1\overline{1}00\}$ slip planes in $\alpha-$Zr
R.E. VOSKOBOINIKOV, The University of Liverpool, Liverpool, United Kingdom ; Y.N. OSETSKY, Oak Ridge National Laboratory, Oak Ridge, TN, USA; D.J. BACON, The University of Liverpool, Liverpool, United Kingdom.
Atomic-scale simulations have been carried out for two edge dislocations with the same Burgers vector $\textbf{b}=1/3 \langle 11\overline{2}0 \rangle$ but different glide planes, $(0001)$ and $\{1\overline{1}00\}$, in the hcp structure. An equilibrium short-range Finnis-Sinclair type many-body potential was applied for the simulations. Both dislocations were relaxed at $T=0K$ using the conjugate gradients method.

The distribution of atomic displacements in the dislocation core was studied. It is shown that the edge dislocation in the basal slip plane splits into two partials whereas the one in the prism plane remains undissociated. The core structures for both dislocations were visualized. The effective core radius and core energy were estimated, and the effect of the anisotropy of the shear modulus on dislocation energy was revealed.

Dislocation behaviour under increasing applied shear strain was investigated, and the stress-strain curve, shear modulus and critical stress for dislocation glide (Peierls stress) were determined for both slip systems.


abstract: 1.32
Interaction of $1/3 \langle 11\overline{2}0 \rangle (0001)$ edge dislocation with point defect clusters created in displacement cascades in $\alpha-$Zr
R.E. VOSKOBOINIKOV, The University of Liverpool, Liverpool, United Kingdom ; Y.N. OSETSKY, Oak Ridge National Laboratory, Oak Ridge, TN, USA; D.J. BACON, The University of Liverpool, Liverpool, United Kingdom.
Interaction of an edge dislocation with Burgers vector $\textbf{b}=1/3 \langle 11\overline{2}0 \rangle$ and $(0001)$ glide plane with vacancy and self-interstitial atom (SIA) clusters found in displacement cascades was investigated by atomic-scale modelling at $T=0K$ using an equilibrium short-range Finnis-Sinclair type many-body potential. The dislocation of this type dissociates in $(0001)$ plane into two partials with formation of $I_2$ intrinsic stacking fault.

Interaction of the extended dislocation with two typical SIA clusters and two typical vacancy clusters was simulated. Several different interaction mechanisms were detected. (i) A 5-SIAs triangular cluster consisting of 15 atoms sharing 10 vacant sites and lying exactly in the dislocation glide plane was not absorbed by the dislocation. Instead, the leading partial pushes it in the glide direction of the dislocation while the cluster itself also moves along the dislocation line. (ii) Irregular 3D SIA cluster lying across the dislocation slide plane was completely absorbed by the dislocation with creation of a corresponding super-jog. (iii) Interaction of the dislocation with a prismatic vacancy cluster occurred in a similar way, i.e. the dislocation was constricted and created a super-jog, but only the half of the vacancy cluster above the glide plane was absorbed by the dislocation. (iv) There was an elastic interaction of the dislocation with a pyramidal vacancy cluster but the cluster recovered its initial configuration and the dislocation did not climb.

Strain-stress curves have been obtained for all the simulated cases.


abstract: 1.33
Climbing and pinning of $1/3 \langle 11\overline{2}0 \rangle \{1\overline{1}00\}$ edge dislocation in $\alpha-$Zr due to interaction with self-interstitial and vacancy clusters
R.E. VOSKOBOINIKOV, The University of Liverpool, Liverpool, United Kingdom ; Y.N. OSETSKY, Oak Ridge National Laboratory, Oak Ridge, TN, USA; D.J. BACON, The University of Liverpool, Liverpool, United Kingdom.
Atomic-scale details of the interaction between a $1/3 \langle 11\overline{2}0 \rangle \{1\overline{1}00\}$ edge dislocation and clusters of point defects in pure $\alpha$-Zr were investigated at zero temperature with an equilibrium short-range Finnis-Sinclair type many-body potential. Clusters in the form of a triangular self-interstitial atom (SIA) cluster, an immobile irregular SIA cluster and two glissile SIA loops with Burgers vector making angle of $60$ and $120$ degrees with the Burgers vector of the dislocation were simulated. The triangular SIA cluster pins the dislocation line but remains undamaged by the interaction. Part of the irregular SIA cluster is absorbed by the dislocation and creates a super-jog on the dislocation line, whereas the other part is turned into a triangular SIA cluster. The interaction mechanism of the dislocation with a glissile SIA loop depends on the orientation. The loop with Burgers vector at $120^o$ to the Burgers vector of the dislocatio! n effectively pins the dislocation line. Interaction of the dislocation with SIA loop with Burgers vector at $60^o$ to the Burgers vector of the dislocation produces an immobile segment due to dislocation reaction. This segment strongly pins the dislocation line.

Interaction of the dislocation with two typical vacancy clusters was also considered. A prismatic vacancy cluster was completely absorbed by the dislocation, which climbs by formation of a super-jog. A pyramidal vacancy cluster, that is an embryo of a vacancy loop in the basal plane, was not destroyed or absorbed although the dislocation line was pinned. However, its strength is less then that of SIA dislocation loops of comparable size.

Strain-stress curves have been obtained for all the simulated cases.