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Molecular Dynamics Simulation Of Electric Pulse Explosion Of Metal Wires
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21st European Conference on Fracture, ECF21, 20-24 June 2016, Catania, Italy 21st European Conference on Fracture, ECF21, 20-24 June 2016, Catania, Italy
Molecular Dynamics Simulation Of Electric Pulse Explosion Of Molecular Dynamics Simulation Of 10-12 Electric Pulse Of XV Portuguese Conference on Fracture, PCF 2016, February 2016,Explosion Paço de Arcos, Portugal Metal Wires Metal Wires K.P. Zolnikova,∗, D.S. Kryzhevicha , E.V. Shilkoa , A.V. Korchuganova Thermo-mechanical modeling ofa a high pressure turbine blade of an a a K.P. Zolnikova,∗ISPMS , D.S. Kryzhevich , E.V. Tomsk, Shilko , A.V. SB RAS, 2/4, pr. Akademicheskii, 634021, Russia Korchuganov airplane gas turbine engine ISPMS SB RAS, 2/4, pr. Akademicheskii, Tomsk, 634021, Russia a a
Abstract
P. Brandãoa, V. Infanteb, A.M. Deusc*
a Abstract Department Mechanicalof Engineering, Instituto Superior Universidade Av. Rovisco Pais, 1,explosion 1049-001 of Lisboa, Molecular dynamicsofsimulation the bicomponent particle Técnico, formation as a resultdeofLisboa, simultaneous electric copper Portugal and nickel wires is carried out. The influence of the internal structure of exploding metal wires and the distance between them on b Molecular dynamics simulation of the bicomponent particle formation asUniversidade a result of de simultaneous electricPais, explosion of copper IDMEC, Department of Mechanical Engineering, Instituto Superior Técnico, Av. Rovisco 1, 1049-001 the dynamics of their dispersion, the size and phase composition of the formed particles isLisboa, investigated. It is shown that the Lisboa, basic and nickel wires is carried out. The influence of the internal structure of exploding metal wires and the distance between them on Portugal mechanism of particle synthesis is the agglomeration of smaller clusters, and the minor one is the deposition of atoms from the c CeFEMA, Department of Mechanical Engineering, Instituto SuperiorofTécnico, Universidade Av. Rovisco 1, 1049-001 Lisboa, the dynamics of their dispersion, the size and phase composition the formed particlesdeisLisboa, investigated. It isPais, shown that the basic gas phase on the particle surfaces. The distribution of chemical Portugal elements is non-uniform over the cross section of the synthesized mechanism of particle synthesis is the agglomeration of smaller clusters, and the minor one is the deposition of atoms from the particles. The concentration of copper atoms in the subsurface region is higher than in the particle volume. Varying the loading gas phase on the particle surfaces. The distribution of chemical elements is non-uniform over the cross section of the synthesized parameters (temperature, distance between the wires) allows controlling the size and phase composition of the synthesized particles. particles. The concentration of copper atoms in the subsurface region is higher than in the particle volume. Varying the loading c Abstract 2016 The Authors. Published by Elsevier B.V. parameters distance betweenElsevier the wires) allows thearticle size and phase oflicense the synthesized particles. Copyright © (temperature, 2016 The Authors. Published This iscontrolling an access under the composition CC BY-NC-ND Peer-review under responsibility of theby Scientific B.V. Committee ofopen ECF21. c 2016 The Authors. Published by Elsevier B.V. (http://creativecommons.org/licenses/by-nc-nd/4.0/). During their operation, modern aircraft engine components are subjected to increasingly demanding operating conditions, Peer-review under responsibility of Scientific the Scientific Committee of ECF21. Peer-review under responsibility ofNanoparticles; the Committee of ECF21. explosion; Keywords: especiallyMolecular the high dynamics; pressure turbine (HPT)Electrical blades. Such conditions cause these parts to undergo different types of time-dependent degradation, one ofdynamics; which isNanoparticles; creep. A model using explosion; the finite element method (FEM) was developed, in order to be able to predict Molecular Electrical Keywords: the creep behaviour of HPT blades. Flight data records (FDR) for a specific aircraft, provided by a commercial aviation company, were used to obtain thermal and mechanical data for three different flight cycles. In order to create the 3D model for the FEM analysis, a HPT blade scrap was scanned, and its chemical composition and material properties were 1. needed Introduction obtained. The data that was gathered was fed into the FEM model and different simulations were run, first with a simplified 3D 1. rectangular Introduction block shape, in order to better establish the model, and then with the real 3D mesh obtained from the blade scrap. The The electric metallic wires is onewas ofobserved, the mostinperspective forofthe synthesis of partioverall expectedexplosion behaviourof in terms of displacement particular at technologies the trailing edge the blade. Therefore such a cles of given composition. As shown by Jonson and Siegel (1970), Bennett (1968), Psakhie (2010) and Abdrashitov model can be useful in the goal of predicting life,most given perspective a set of FDR technologies data. The electric explosion of metallic wiresturbine is oneblade of the for the synthesis of parti-
(2010) this technology enables the synthesis of and composite particlesBennett consisting of crystallites of several metallic or cles of given composition. As shown by Jonson Siegel (1970), (1968), Psakhie (2010) and Abdrashitov non-metallic phases, due to which their properties can change considerably and they can possess required perfor© 2016 The Authors. Published by Elsevier B.V. (2010) this technology enables the synthesis of composite particles consisting of crystallites of several metallic or 6 9 2 Peer-review under responsibility of of thewires Scientific Committee of PCF 2016. mance characteristics. Dispersion occurs as follows: when a high-density electric pulse (10 -10 Å/cm ) is non-metallic phases, due to which their properties can change considerably and they can possess required perforsent through a metallicDispersion wire, it isofrapidly heated, melted andwhen then aexplodes. The electric explosion products disperse 9 mance characteristics. wiresFinite occurs as follows: high-density pulse (106 -10 Å/cm2into ) is Keywords: High Pressure Turbine Blade; Creep;of ElementThe Method; 3D Model; Simulation. allows synthesizing a wide range of gaseous atmosphere with the formation particles. explosive technology sent through a metallic wire, it is rapidly heated, melted and then explodes. The explosion products disperse into metal, nitride and powders with complex The internal structure. In Zol’nikov (2001), Psakhie a(1995), Psakhie gaseousoxide, atmosphere withother the formation of particles. explosive technology allows synthesizing wide range of (1998), Psakhie (2012) it was shown that the internal structure of nanopowders influences their physical, chemical metal, oxide, nitride and other powders with complex internal structure. In Zol’nikov (2001), Psakhie (1995), Psakhie and mechanical It should that thestructure use of the of particles in itstheir various representations (1998), Psakhie properties. (2012) it was shown be thatnoted the internal of method nanopowders influences physical, chemical is promising for description of structural and phase transformations, generation of charged clusters, formation of gas and mechanical properties. It should be noted that the use of the method of particles in its various representations phase and dispersion particles under the electric explosion of the wires, i.e. see Shilko (2015), Psakhie (2013), Psakhie is promising for description of structural and phase transformations, generation of charged clusters, formation of gas (2008). phase and dispersion particles under the electric explosion of the wires, i.e. see Shilko (2015), Psakhie (2013), Psakhie (2008).
* Corresponding author. Tel.: +351 218419991. Corresponding author. Tel.: +7-382-228-6972; fax: +7-382-249-2576. E-mail address: [email protected] address: [email protected] ∗ E-mail Corresponding author. Tel.: +7-382-228-6972; fax: +7-382-249-2576. 2452-3216 © 2016 The Authors. Published by Elsevier B.V. E-mail address: [email protected] c 2016 2452-3216 The Authors. Published by Elsevier B.V. Peer-review under responsibility of by the Scientific Committee of PCF 2016. Copyright © 2016 The Authors. Published Elsevier B.V. This is an open access article under the CC BY-NC-ND license Peer-review under responsibility of the Scientific Committee of ECF21. c 2016 The Authors. Published by Elsevier B.V. 2452-3216 (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer reviewunder under responsibility of the Scientific Committee of ECF21. Peer-review responsibility of the Scientific Committee of ECF21. 10.1016/j.prostr.2016.06.180 ∗
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a)
b)
Fig. 1. The dependencies of the cluster number (a) and number of atoms in the gas phase (b) on time. The distance between the wires before detonation was 80 lattice parameters.
The purpose of this work is the investigation of the bicomponent particles synthesis as a result of simultaneous electric explosion of copper and nickel wires. The influence of the distances between metal wires on characteristics of the synthesized particles and the distribution of chemical elements inside of them are studied. 2. Results and discussion Investigations in the paper were carried out using the molecular dynamics method (Psakhie (2008), Psakhie (2009)). The potentials calculated in the framework of the embedded atom method were used to describe interatomic interaction (Bonny (2009)). These potentials allow calculating with good accuracy the surface properties, energy of structural defects, elastic characteristics and other properties that are necessary for a correct simulation of electric explosion. Copper and nickel specimens of cylindrical shape were chosen as conductors for explosion. Each simulated wire consisted of 110 000 atoms, the height of a cylindrical crystallite was about 50÷60 and the diameter was about 25÷30 lattice parameters. Each specimen consisted of two grains. In view of the small size of the simulated wires, they had a shape of rectangular prisms. Periodic boundary conditions were used along the cylinder axis, and the free surface was simulated in other directions. Loading was applied in the following steps: the system was kept at temperature 1000 K, and then copper and nickel wires were rapidly heated up to 7000 K and 9000 K, respectively. The thermostat was applied to the simulated system 100 ps after explosion. The distance between the wires in different calculations varied within the range from 40 to 260 Å. The high-rate heating resulted in explosive failure of the wires accompanied by the formation of nanosized particles (atomic clusters) and a gaseous phase. The cluster size was determined by assuming that atoms belong to one cluster if the distance between them is shorter than the radius of the second coordination sphere in a perfect lattice close to the melting point. The cluster size was defined by the number of atoms in it. The cluster of minimum size was assumed to contain no less than 13 atoms because the first coordination sphere in the fcc lattice consists of 12 atoms. The analysis of simulation results shows that after the simulated wire has been heated, the process of dispersion occurs by stages. At the first stage of dispersion process the average interatomic distance rapidly increases; however, the thermal expansion of the specimens causes no loss of continuity. At the next stage fast fracture processes occur in the specimens, which involve formation of clusters of different sizes and intensive surface evaporation of atoms. The fracture leads to abrupt decrease in the temperature of the simulated system. This is due to the fact that a significant part of the kinetic energy of the specimens is expended to break atomic bonds. The change of the number of clusters and the number of atoms in the gas phase in the simulated system as a function of time is shown in Fig. 1. The figure shows that the number of the synthesized clusters in 70 ps starts to go to saturation. The fraction of the gas phase in the simulated system grows continuously until the beginning of cooling (100 ps), and then decreases due to deposition of atoms on the surface of forming clusters. Note that setting a high temperature heating allowed for “reasonable” computational time (using molecular dynamics method) to describe the dispersion of the simulated wires and the particle synthesis. The structure of simulated
K.P Zolnikov et al. / Procedia Structural Integrity 2 (2016) 1421–1426 K.P. Zolnikov et al. / Structural Integrity Procedia 00 (2016) 000–000
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a)
b)
Fig. 2. Structure of dispersed copper-nickel system at different time points after explosion: a) 30 ps; b) 100 ps. The distance between the wires before the explosion was 80 lattice parameters.
a)
b)
Fig. 3. The total number of formed clusters (a) and bicomponent clusters (b) versus the distance between the wires (a – lattice parameter).
copper-nickel system at different points in time after the explosion is shown in Fig. 2. The figure shows that the bicomponent particles were formed in the process of dispersing (copper atoms are shown in red, nickel – in blue). The results show that the distance between the dispersing wires has a significant influence on the number of generated clusters, their composition and structure, as well as the fraction of gas phase, which is formed in the process of explosion. The total number of formed clusters and number of bicomponent clusters as a function of the distance between the wires after relaxation process are shown in Fig. 3. The figure clearly shows that for the simulated system there is optimal distance interval, at which maximum number of bicomponent particles is synthesized. This interval corresponds to 80-160 lattice parameters between the wires before loading. It can be assumed that the optimum distance between the wires for the synthesis of bicomponent particles will depend largely on the wire thickness, their form and, to a lesser extent on the mode of heating and environmental properties, at which dispersion takes place. A more detailed picture of the cluster distribution by their size and component composition depending on the distance between the wires at the end of the calculations is shown in Fig. 4. The figure shows that a large number of clusters with a high concentration of the second component is formed for small distances between the dispersing wires. It is obvious that the evolution of the simulated system closer to equilibrium state and particle formation will continue with the slowing rates for a longer time intervals. In view of the limited computing resources, the evolution of the system towards equilibrium cannot be described within the framework of molecular dynamic approach without using some approximations. A quite efficient approach is the use of viscoelastic boundary conditions that simulate the properties of the environment in which metal wires are dispersed, and the increase of the integration step at lowering the temperature of the simulated system.
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a)
b)
Fig. 4. The number of formed clusters N versus: their size n and distance d between the wires (a); copper concentration in them f and distances between the wires (b).
Fig. 5. Structure of dispersed copper-nickel system in 150 ps. The distance between the wires before the explosion was 80 lattice parameters.
Typical particle distribution after the application of viscoelastic boundary conditions and cooling the dispersed system up to 2000 K is shown in Fig. 5. The calculations showed that the basic mechanism of particle formation is the agglomeration of smaller clusters, but not the deposition of atoms from the gas phase on the particle surface. It is seen in Fig. 5 that the chemical composition of the formed particles varies in a wide interval. Moreover, the chemical composition along the cross section of the bicomponent particles varies strongly. The concentration of copper atoms near the surface of bicomponent particles is much higher than in bulk (Fig. 6). It should be noted that temperature dynamics of the simulated system has the feature. The temperature abruptly decreases after high-rate heating. This behavior of the simulated system is connected with fracture processes of the wires and particle formation. The process of the wire fracture is accompanied by an increase in the free surface area of the simulated system and leads to the transition of a significant part of the kinetic energy into potential energy. The decrease in the intensity of the thermal pulse loading leads to the formation of particles of larger size. The calculations showed that the wire heating at high-rate electric pulse can lead to a significant increase in their volume without
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Fig. 6. The structure of the bicomponent cluster (the copper atoms are marked in red, the nickel atoms in blue).The cluster contains around 15 000 atoms, the concentration of copper in it is 9.5 %.
discontinuity (the jump of the atomic volume was about 9 %). Such behavior of the crystalline wires might be related to a lower rate of accommodation processes in the internal structure as compared to the heating rate. 3. Conclusion It is shown that there are two mechanisms of particle formation at metal wires explosion. The first one is agglomeration of small clusters and it prevails over the process of atom deposition from the gas on the free surface of the particles. The chemical composition of the formed particles is heterogeneous along their cross section. So, the concentration of copper atoms near the particle surface is higher than in the volume. It is found that the distance between dispersing wires greatly affects the process of particle formation. On the basis of the performed calculations one can conclude that the molecular dynamics approach can be used effectively to determine the optimal loading conditions of wire dispersion to obtain particles with desired composition and size. Acknowledgements The work was carried out at the support of RFBR Project No. 15-01-06585. References Jonson, R., Siegel, B. 1970. Chemical Reactor Utilising Successive Multiple Electrical Explosions of Metal Wires. Rev. Sci. Instr. 42, 854–859. Bennett, F.D., 1968. High-temperature Exploding Wires. Progress in High-temperature Physics and Chemistry. V. 2. Pergamon Press, N.Y. pp. 463. Psakhie, S.G., Zolnikov, K.P., Kryzhevich, D.S., Abdrashitov, A.V., Lerner, M.I. 2010. Stage character of cluster formation in metal specimens in electrothermal pulse dispersion. Physical Mesomechanics 13, 184-188. Abdrashitov, A.V., Kryzhevich, D.S., Zolnikov, K.P., Psakhie, S.G. 2010. Simulation of nanoparticles with block structure formation by electric dispertion of metal wire. Procedia Engineering 2, 1589-1593. Zol’nikov, K.P., Uvarov, T.Y., Psakh’e, S.G. 2001. Anisotropy of the plastic deformation and fracture processes in a dynamically loaded crystallite. Technical Physics Letters 27, 263-265. Psakhie, S.G., Zolnikov, K.P., Korostelev, S.Y. 1995. Nonlinear response of materials under the high-speed deformation. Atomic level. Pisma v Zhurnal Tekhnicheskoi Fiziki 21, 1-5.
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Psakh’e, S.G., Zol’nikov, K.P., Saraev, D.Y. 1998. Nonlinear effects in dynamic loading of a material with defect zones. Technical Physics Letters 24, 99-101. Psakhie, S.G., Kryzhevich, D.S., Zolnikov, K.P. 2012. Local structural transformations in copper crystallites under nanoindentation. Technical Physics Letters 38, 634-637. Shilko, E.V., Psakhie, S.G., Schmauder, S., Popov, V.L., Astafurov, S.V., Smolin, A.Yu. 2015. Overcoming the limitations of distinct element method for multiscale modeling of materials with multimodal internal structure. Computational Materials Science 102, 267-285. Psakhie, S.G., Smolin, A.Yu., Shilko, E.V., Anikeeva, G.M. Pogozhev, Yu.S., Petrzhik, M.I., Levashov, E.A. 2013. Modeling nanoindentation of TiCCaPON coating on Ti substrate using movable cellular automaton method. Computational materials science 76, 89-98. Psakhie, S.G., Zolnikov, K.P., Skorentsev, L.F., Kryzhevich, D.S., Abdrashitov, A.V. 2008. Structural features of bicomponent dust Coulomb balls formed by the superposition of fields of different origin in plasma. Physics of plasmas 15, 053701. Psakhie, S.G., Zolnikov, K.P., Kryzhevich, D.S., Zheleznyakov, A.V., Chernovb, V.M. 2009. Atomic collision cascades in vanadium crystallites with grain boundaries. Physical Mesomechanics 12, 20-28. Bonny, G., Pasianot, R.C., Castin, N., MalerbaTernary, L. 2009. Fe-Cu-Ni many-body potential to model reactor pressure vessel steels: First validation by simulated thermal annealing. Philosophical Magazine 89, 3531-3546.
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21st European Conference on Fracture, ECF21, 20-24 June 2016, Catania, Italy 21st European Conference on Fracture, ECF21, 20-24 June 2016, Catania, Italy
Molecular Dynamics Simulation Of Electric Pulse Explosion Of Molecular Dynamics Simulation Of 10-12 Electric Pulse Of XV Portuguese Conference on Fracture, PCF 2016, February 2016,Explosion Paço de Arcos, Portugal Metal Wires Metal Wires K.P. Zolnikova,∗, D.S. Kryzhevicha , E.V. Shilkoa , A.V. Korchuganova Thermo-mechanical modeling ofa a high pressure turbine blade of an a a K.P. Zolnikova,∗ISPMS , D.S. Kryzhevich , E.V. Tomsk, Shilko , A.V. SB RAS, 2/4, pr. Akademicheskii, 634021, Russia Korchuganov airplane gas turbine engine ISPMS SB RAS, 2/4, pr. Akademicheskii, Tomsk, 634021, Russia a a
Abstract
P. Brandãoa, V. Infanteb, A.M. Deusc*
a Abstract Department Mechanicalof Engineering, Instituto Superior Universidade Av. Rovisco Pais, 1,explosion 1049-001 of Lisboa, Molecular dynamicsofsimulation the bicomponent particle Técnico, formation as a resultdeofLisboa, simultaneous electric copper Portugal and nickel wires is carried out. The influence of the internal structure of exploding metal wires and the distance between them on b Molecular dynamics simulation of the bicomponent particle formation asUniversidade a result of de simultaneous electricPais, explosion of copper IDMEC, Department of Mechanical Engineering, Instituto Superior Técnico, Av. Rovisco 1, 1049-001 the dynamics of their dispersion, the size and phase composition of the formed particles isLisboa, investigated. It is shown that the Lisboa, basic and nickel wires is carried out. The influence of the internal structure of exploding metal wires and the distance between them on Portugal mechanism of particle synthesis is the agglomeration of smaller clusters, and the minor one is the deposition of atoms from the c CeFEMA, Department of Mechanical Engineering, Instituto SuperiorofTécnico, Universidade Av. Rovisco 1, 1049-001 Lisboa, the dynamics of their dispersion, the size and phase composition the formed particlesdeisLisboa, investigated. It isPais, shown that the basic gas phase on the particle surfaces. The distribution of chemical Portugal elements is non-uniform over the cross section of the synthesized mechanism of particle synthesis is the agglomeration of smaller clusters, and the minor one is the deposition of atoms from the particles. The concentration of copper atoms in the subsurface region is higher than in the particle volume. Varying the loading gas phase on the particle surfaces. The distribution of chemical elements is non-uniform over the cross section of the synthesized parameters (temperature, distance between the wires) allows controlling the size and phase composition of the synthesized particles. particles. The concentration of copper atoms in the subsurface region is higher than in the particle volume. Varying the loading c Abstract 2016 The Authors. Published by Elsevier B.V. parameters distance betweenElsevier the wires) allows thearticle size and phase oflicense the synthesized particles. Copyright © (temperature, 2016 The Authors. Published This iscontrolling an access under the composition CC BY-NC-ND Peer-review under responsibility of theby Scientific B.V. Committee ofopen ECF21. c 2016 The Authors. Published by Elsevier B.V. (http://creativecommons.org/licenses/by-nc-nd/4.0/). During their operation, modern aircraft engine components are subjected to increasingly demanding operating conditions, Peer-review under responsibility of Scientific the Scientific Committee of ECF21. Peer-review under responsibility ofNanoparticles; the Committee of ECF21. explosion; Keywords: especiallyMolecular the high dynamics; pressure turbine (HPT)Electrical blades. Such conditions cause these parts to undergo different types of time-dependent degradation, one ofdynamics; which isNanoparticles; creep. A model using explosion; the finite element method (FEM) was developed, in order to be able to predict Molecular Electrical Keywords: the creep behaviour of HPT blades. Flight data records (FDR) for a specific aircraft, provided by a commercial aviation company, were used to obtain thermal and mechanical data for three different flight cycles. In order to create the 3D model for the FEM analysis, a HPT blade scrap was scanned, and its chemical composition and material properties were 1. needed Introduction obtained. The data that was gathered was fed into the FEM model and different simulations were run, first with a simplified 3D 1. rectangular Introduction block shape, in order to better establish the model, and then with the real 3D mesh obtained from the blade scrap. The The electric metallic wires is onewas ofobserved, the mostinperspective forofthe synthesis of partioverall expectedexplosion behaviourof in terms of displacement particular at technologies the trailing edge the blade. Therefore such a cles of given composition. As shown by Jonson and Siegel (1970), Bennett (1968), Psakhie (2010) and Abdrashitov model can be useful in the goal of predicting life,most given perspective a set of FDR technologies data. The electric explosion of metallic wiresturbine is oneblade of the for the synthesis of parti-
(2010) this technology enables the synthesis of and composite particlesBennett consisting of crystallites of several metallic or cles of given composition. As shown by Jonson Siegel (1970), (1968), Psakhie (2010) and Abdrashitov non-metallic phases, due to which their properties can change considerably and they can possess required perfor© 2016 The Authors. Published by Elsevier B.V. (2010) this technology enables the synthesis of composite particles consisting of crystallites of several metallic or 6 9 2 Peer-review under responsibility of of thewires Scientific Committee of PCF 2016. mance characteristics. Dispersion occurs as follows: when a high-density electric pulse (10 -10 Å/cm ) is non-metallic phases, due to which their properties can change considerably and they can possess required perforsent through a metallicDispersion wire, it isofrapidly heated, melted andwhen then aexplodes. The electric explosion products disperse 9 mance characteristics. wiresFinite occurs as follows: high-density pulse (106 -10 Å/cm2into ) is Keywords: High Pressure Turbine Blade; Creep;of ElementThe Method; 3D Model; Simulation. allows synthesizing a wide range of gaseous atmosphere with the formation particles. explosive technology sent through a metallic wire, it is rapidly heated, melted and then explodes. The explosion products disperse into metal, nitride and powders with complex The internal structure. In Zol’nikov (2001), Psakhie a(1995), Psakhie gaseousoxide, atmosphere withother the formation of particles. explosive technology allows synthesizing wide range of (1998), Psakhie (2012) it was shown that the internal structure of nanopowders influences their physical, chemical metal, oxide, nitride and other powders with complex internal structure. In Zol’nikov (2001), Psakhie (1995), Psakhie and mechanical It should that thestructure use of the of particles in itstheir various representations (1998), Psakhie properties. (2012) it was shown be thatnoted the internal of method nanopowders influences physical, chemical is promising for description of structural and phase transformations, generation of charged clusters, formation of gas and mechanical properties. It should be noted that the use of the method of particles in its various representations phase and dispersion particles under the electric explosion of the wires, i.e. see Shilko (2015), Psakhie (2013), Psakhie is promising for description of structural and phase transformations, generation of charged clusters, formation of gas (2008). phase and dispersion particles under the electric explosion of the wires, i.e. see Shilko (2015), Psakhie (2013), Psakhie (2008).
* Corresponding author. Tel.: +351 218419991. Corresponding author. Tel.: +7-382-228-6972; fax: +7-382-249-2576. E-mail address: [email protected] address: [email protected] ∗ E-mail Corresponding author. Tel.: +7-382-228-6972; fax: +7-382-249-2576. 2452-3216 © 2016 The Authors. Published by Elsevier B.V. E-mail address: [email protected] c 2016 2452-3216 The Authors. Published by Elsevier B.V. Peer-review under responsibility of by the Scientific Committee of PCF 2016. Copyright © 2016 The Authors. Published Elsevier B.V. This is an open access article under the CC BY-NC-ND license Peer-review under responsibility of the Scientific Committee of ECF21. c 2016 The Authors. Published by Elsevier B.V. 2452-3216 (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer reviewunder under responsibility of the Scientific Committee of ECF21. Peer-review responsibility of the Scientific Committee of ECF21. 10.1016/j.prostr.2016.06.180 ∗
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K.P Zolnikov et al. / Procedia Structural Integrity 2 (2016) 1421–1426 K.P. Zolnikov et al. / Structural Integrity Procedia 00 (2016) 000–000
a)
b)
Fig. 1. The dependencies of the cluster number (a) and number of atoms in the gas phase (b) on time. The distance between the wires before detonation was 80 lattice parameters.
The purpose of this work is the investigation of the bicomponent particles synthesis as a result of simultaneous electric explosion of copper and nickel wires. The influence of the distances between metal wires on characteristics of the synthesized particles and the distribution of chemical elements inside of them are studied. 2. Results and discussion Investigations in the paper were carried out using the molecular dynamics method (Psakhie (2008), Psakhie (2009)). The potentials calculated in the framework of the embedded atom method were used to describe interatomic interaction (Bonny (2009)). These potentials allow calculating with good accuracy the surface properties, energy of structural defects, elastic characteristics and other properties that are necessary for a correct simulation of electric explosion. Copper and nickel specimens of cylindrical shape were chosen as conductors for explosion. Each simulated wire consisted of 110 000 atoms, the height of a cylindrical crystallite was about 50÷60 and the diameter was about 25÷30 lattice parameters. Each specimen consisted of two grains. In view of the small size of the simulated wires, they had a shape of rectangular prisms. Periodic boundary conditions were used along the cylinder axis, and the free surface was simulated in other directions. Loading was applied in the following steps: the system was kept at temperature 1000 K, and then copper and nickel wires were rapidly heated up to 7000 K and 9000 K, respectively. The thermostat was applied to the simulated system 100 ps after explosion. The distance between the wires in different calculations varied within the range from 40 to 260 Å. The high-rate heating resulted in explosive failure of the wires accompanied by the formation of nanosized particles (atomic clusters) and a gaseous phase. The cluster size was determined by assuming that atoms belong to one cluster if the distance between them is shorter than the radius of the second coordination sphere in a perfect lattice close to the melting point. The cluster size was defined by the number of atoms in it. The cluster of minimum size was assumed to contain no less than 13 atoms because the first coordination sphere in the fcc lattice consists of 12 atoms. The analysis of simulation results shows that after the simulated wire has been heated, the process of dispersion occurs by stages. At the first stage of dispersion process the average interatomic distance rapidly increases; however, the thermal expansion of the specimens causes no loss of continuity. At the next stage fast fracture processes occur in the specimens, which involve formation of clusters of different sizes and intensive surface evaporation of atoms. The fracture leads to abrupt decrease in the temperature of the simulated system. This is due to the fact that a significant part of the kinetic energy of the specimens is expended to break atomic bonds. The change of the number of clusters and the number of atoms in the gas phase in the simulated system as a function of time is shown in Fig. 1. The figure shows that the number of the synthesized clusters in 70 ps starts to go to saturation. The fraction of the gas phase in the simulated system grows continuously until the beginning of cooling (100 ps), and then decreases due to deposition of atoms on the surface of forming clusters. Note that setting a high temperature heating allowed for “reasonable” computational time (using molecular dynamics method) to describe the dispersion of the simulated wires and the particle synthesis. The structure of simulated
K.P Zolnikov et al. / Procedia Structural Integrity 2 (2016) 1421–1426 K.P. Zolnikov et al. / Structural Integrity Procedia 00 (2016) 000–000
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a)
b)
Fig. 2. Structure of dispersed copper-nickel system at different time points after explosion: a) 30 ps; b) 100 ps. The distance between the wires before the explosion was 80 lattice parameters.
a)
b)
Fig. 3. The total number of formed clusters (a) and bicomponent clusters (b) versus the distance between the wires (a – lattice parameter).
copper-nickel system at different points in time after the explosion is shown in Fig. 2. The figure shows that the bicomponent particles were formed in the process of dispersing (copper atoms are shown in red, nickel – in blue). The results show that the distance between the dispersing wires has a significant influence on the number of generated clusters, their composition and structure, as well as the fraction of gas phase, which is formed in the process of explosion. The total number of formed clusters and number of bicomponent clusters as a function of the distance between the wires after relaxation process are shown in Fig. 3. The figure clearly shows that for the simulated system there is optimal distance interval, at which maximum number of bicomponent particles is synthesized. This interval corresponds to 80-160 lattice parameters between the wires before loading. It can be assumed that the optimum distance between the wires for the synthesis of bicomponent particles will depend largely on the wire thickness, their form and, to a lesser extent on the mode of heating and environmental properties, at which dispersion takes place. A more detailed picture of the cluster distribution by their size and component composition depending on the distance between the wires at the end of the calculations is shown in Fig. 4. The figure shows that a large number of clusters with a high concentration of the second component is formed for small distances between the dispersing wires. It is obvious that the evolution of the simulated system closer to equilibrium state and particle formation will continue with the slowing rates for a longer time intervals. In view of the limited computing resources, the evolution of the system towards equilibrium cannot be described within the framework of molecular dynamic approach without using some approximations. A quite efficient approach is the use of viscoelastic boundary conditions that simulate the properties of the environment in which metal wires are dispersed, and the increase of the integration step at lowering the temperature of the simulated system.
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a)
b)
Fig. 4. The number of formed clusters N versus: their size n and distance d between the wires (a); copper concentration in them f and distances between the wires (b).
Fig. 5. Structure of dispersed copper-nickel system in 150 ps. The distance between the wires before the explosion was 80 lattice parameters.
Typical particle distribution after the application of viscoelastic boundary conditions and cooling the dispersed system up to 2000 K is shown in Fig. 5. The calculations showed that the basic mechanism of particle formation is the agglomeration of smaller clusters, but not the deposition of atoms from the gas phase on the particle surface. It is seen in Fig. 5 that the chemical composition of the formed particles varies in a wide interval. Moreover, the chemical composition along the cross section of the bicomponent particles varies strongly. The concentration of copper atoms near the surface of bicomponent particles is much higher than in bulk (Fig. 6). It should be noted that temperature dynamics of the simulated system has the feature. The temperature abruptly decreases after high-rate heating. This behavior of the simulated system is connected with fracture processes of the wires and particle formation. The process of the wire fracture is accompanied by an increase in the free surface area of the simulated system and leads to the transition of a significant part of the kinetic energy into potential energy. The decrease in the intensity of the thermal pulse loading leads to the formation of particles of larger size. The calculations showed that the wire heating at high-rate electric pulse can lead to a significant increase in their volume without
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Fig. 6. The structure of the bicomponent cluster (the copper atoms are marked in red, the nickel atoms in blue).The cluster contains around 15 000 atoms, the concentration of copper in it is 9.5 %.
discontinuity (the jump of the atomic volume was about 9 %). Such behavior of the crystalline wires might be related to a lower rate of accommodation processes in the internal structure as compared to the heating rate. 3. Conclusion It is shown that there are two mechanisms of particle formation at metal wires explosion. The first one is agglomeration of small clusters and it prevails over the process of atom deposition from the gas on the free surface of the particles. The chemical composition of the formed particles is heterogeneous along their cross section. So, the concentration of copper atoms near the particle surface is higher than in the volume. It is found that the distance between dispersing wires greatly affects the process of particle formation. On the basis of the performed calculations one can conclude that the molecular dynamics approach can be used effectively to determine the optimal loading conditions of wire dispersion to obtain particles with desired composition and size. Acknowledgements The work was carried out at the support of RFBR Project No. 15-01-06585. References Jonson, R., Siegel, B. 1970. Chemical Reactor Utilising Successive Multiple Electrical Explosions of Metal Wires. Rev. Sci. Instr. 42, 854–859. Bennett, F.D., 1968. High-temperature Exploding Wires. Progress in High-temperature Physics and Chemistry. V. 2. Pergamon Press, N.Y. pp. 463. Psakhie, S.G., Zolnikov, K.P., Kryzhevich, D.S., Abdrashitov, A.V., Lerner, M.I. 2010. Stage character of cluster formation in metal specimens in electrothermal pulse dispersion. Physical Mesomechanics 13, 184-188. Abdrashitov, A.V., Kryzhevich, D.S., Zolnikov, K.P., Psakhie, S.G. 2010. Simulation of nanoparticles with block structure formation by electric dispertion of metal wire. Procedia Engineering 2, 1589-1593. Zol’nikov, K.P., Uvarov, T.Y., Psakh’e, S.G. 2001. Anisotropy of the plastic deformation and fracture processes in a dynamically loaded crystallite. Technical Physics Letters 27, 263-265. Psakhie, S.G., Zolnikov, K.P., Korostelev, S.Y. 1995. Nonlinear response of materials under the high-speed deformation. Atomic level. Pisma v Zhurnal Tekhnicheskoi Fiziki 21, 1-5.
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