Dominant mechanisms of the sintering of copper nano-powders depending on the crystal misalignment (original) (raw)
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Atomistic Simulation of Sintering Mechanism for Copper Nano-Powders
Journal of Korean Powder Metallurgy Institute, 2015
The sintering mechanisms of nanoscale copper powders have been investigated. A molecular dynamics (MD) simulation with the embedded-atom method (EAM) was employed for these simulations. The dimensional changes for initial-stage sintering such as characteristic lengths, neck growth, and neck angle were calculated to understand the densification behavior of copper nano-powders. Factors affecting sintering such as the temperature, powder size, and crystalline misalignment between adjacent powders have also been studied. These results could provide information of setting the processing cycles and material designs applicable to nano-powders. In addition, it is expected that MD simulation will be a foundation for the multi-scale modeling in sintering process.
International Journal of Engineering Science, 2018
A molecular dynamics (MD) simulation is performed on the coalescence kinetics and mechanical behavior of a thermally sintered nanoporous copper (Cu) nanoparticulate system. To investigate the effect of particle size and sintering temperature on the coalescence of the nanoparticulate system, particles with sizes of 4, 5, and 6 nm are sintered at temperatures of 30 0, 50 0, and 70 0 K. To determine the thermal sintering process at elevated temperatures and ambient pressure, bulk periodic nanoparticle unit cells consisting of a finite number of nanoparticles are equilibrated through isothermal-isobaric ensemble simulations. In thermally sintered configurations, uniaxial tension/compression and shearing simulations are applied at a constant strain rate to derive stress-strain curves. It is found that stacking faults are actively generated in smaller nanoparticles even at a low sintering temperature, while local amorphization and surface and grain boundary diffusion are rather prominent in larger nanoparticles. Even at the same sintering temperature, the density of the sintered nanoparticle increases as the size of the nanoparticle decreases. In elastic moduli, the same particle size dependency is observed, while no obvious difference is observed in tension and compression. On the other hand, the yield strengths of the sintered nanoparticles in tension are larger than those in compression. The asymmetric yield strength of the sintered systems is clarified by addressing the surface stress and surface equilibrium strain of atoms on the surface of nanopores by the evolution of atomic virial stress in tension and compression.
Molecular dynamics simulation of the sintering of metallic nanoparticles
Journal of Nanoparticle Research, 2010
The sintering of two different-sized nickel nanoparticles is simulated by a molecular dynamics method in this work. The particles are partitioned into different regimes where tracing atoms are arranged to investigate the sintering kinetics. The detailed sintering process of two nanoparticles, 3.52 and 1.76 nm in diameter, respectively, is subsequently examined by the shrinkage ratio, gyration radius, mean square displacement, sintering diffusivity, and activation energy. A three-stage sintering scenario is established, and the layered structure shows a regime dependent behavior of diffusivity during the sintering process. Besides the surface diffusion, sintering of differentsized nanoparticles is found to be affected by a few other mechanisms.
A molecular dynamics study of sintering between nanoparticles
Computational Materials Science, 2009
The paper presents a molecular dynamics study on the interactions between nanoparticles at elevated temperatures. The emphasis is on the comparison between the molecular dynamics model and the continuum model using solid state physics. It is shown that the continuum model is unable to capture the sintering behaviour of nanoparticles. This is not because the continuum theory does not apply at the nano-scale but because the nanoparticles behave in so many different scenarios of the continuum theory that a meaningful model has to predict these scenarios, using the molecular dynamics for example. In the MD simulation, it is observed that the particles reorient their crystalline orientations at the beginning of the sintering and form different types of ''necks" between different particles. This leads to different mechanisms of matter redistribution at the different necks. It is also observed that the particles can switch the mechanism of matter transportation half-way through the sintering process. It would be very difficult, if not impossible, to handle these complexities using the continuum model. However assuming the right scenario, the continuum theory does agree with the MD simulation for particles consisting of just a few thousands atoms.
Scientific Reports
The paper presents results of a large-scale classical molecular dynamics study into the effect of ingrain defects on the grain growth rate of face centered cubic nanocrystalline material under thermal annealing. To do this, two types of virtual MD samples are used. The samples of the first type are constructed artificially by filling Voronoi cells with atoms arranged in fcc lattice essentially with no ingrain defects. The other samples are obtained by natural crystallization from melted material and contain numerous extended ingrain defects. These samples with a high concentration of ingrain defects imitate nanocrystalline material produced by severe plastic deformation via high pressure torsion or equal channel angular extrusion. The samples of both types are subjected to long-time zero pressure isothermal annealing at T\approx 0.9T_m$$ T ≈ 0.9 T m ($$T_m$$ T m is melting temperature) which leads to grain coarsening due to recrystallization. Direct molecular dynamics simulations ...
Fast Sintering of Nanocrystalline Copper
Metallurgical and Materials Transactions A, 2012
The behavior of nanocrystalline (nc) copper specimens obtained by high energy ball milling (HEBM) and electromagnetic field-assisted sintering under stress and mechanical compression is explored. High yield stress values combined with plastic behavior are observed. The basic densification mechanisms involved in the production process and the peculiar action on the dislocation network are discussed.
Computer Simulations of Nanoparticle Sintering
TechConnect Briefs, 2005
During the vapor-phase synthesis of titanium dioxide (TiO 2) nanoparticles, sintering of the nanoparticles is an important aspect of their behavior and an understanding of this phenomenon is therefore important. In this work, molecular dynamics (MD) simulations of the coalescence of TiO 2 nanoparticles have been carried out. The driving force for sintering of nanoparticles is the reduction in potential energy due to the decrease in surface area. The loss of potential energy manifests itself as an increase in the temperature of the sintering particles. This work concentrates on 3 and 4nm anatase and rutile nanoparticles. Dependence of particle orientation on sintering is reported along with ion mobility studies in the core and neck regions.
Journal of the American Ceramic Society, 2009
Collective particle behavior such as interparticle coordination and particle rearrangement plays a significant role in the sintering of heterogeneous powder systems. Those phenomena have been investigated by in situ X-ray microtomography and discrete element simulation (DEM). In situ 3D images of sintering copper-based systems have been obtained at the European Synchrotron Research Facilities. The sintered systems comprise a dense packing of atomized copper powder with a size range of 0-63 lm and the same powder including artificial pores. Quantitative analysis of these images provided valuable data on local strain, coordination number, and particle movement. The sintering of the same systems has been simulated with the discrete element code dp3D. From this set of information, the importance of collective behavior on densification and microstructural evolution is assessed and the relevance of DEM to describe it is discussed. II. Microtomography Experiments Microtomography experiments were carried out at the European Synchrotron Radiation Facilities (ESRF) in Grenoble,
Molecular dynamics simulations of the preparation and deformation of nanocrystalline copper
Acta Materialia, 2004
The molecular dynamics method is used here to simulate: (1) the preparation of full-density nanostructured copper by compacting copper nanoparticles and (2) the deformation behaviors of the nanostructured copper under compression. It is found that the packing arrangement, the size of the nanoparticles and the compaction temperature, affect the deformation behaviors of the nanostructured copper. Our simulation results also show that the synergy of the rotation and mass shedding of grains and the thickening and sliding of grain boundaries, prevents the formation of voids and cracks in the nanostructured copper under compression.
Journal of Computational and Theoretical Nanoscience, 2013
In the present work the effects of temperature and crystallographic orientation on the sintering behavior of Ni-Ni nanoparticles were investigated using molecular dynamic simulation modified embedded atom method (MEAM). The assumed systems contained two and 27 nanoparticles (4 nm in diameter) located in the (100) and (110) planes. The initial sintering temperatures were considered as 300 K and 800 K and the applied pressure for sintering is 0.1 GPa. The results show that, by sintering at 300 K, the nanoparticles are not joined perfectly due to insufficient temperature and pressure. At 800 K, however the sintering temperature is enough, applied pressure could not convert the nanoparticles to a unified particle and the volume of system would be increased. As a result, the system volume changes through the sintering process could be divided into two separate categories: first, decrease in volume due to applied pressure and secondly, increase in volume because of thermal expansion of nanoparticles. Regarding the effect of crystallographic direction, the sintered nanoparticles with different direction are deformed elastically and get oriented in a desirable crystallographic direction to minimize the interface energy as a driving force factor for sintering process.