Papers by Keyword: Interatomic Potentials

Abstract: Titanium additions suppress the radiation swelling in vanadium alloys, but the mechanism of the suppression is debatable. It is claimed that interactions of Ti atoms with vacancies in vanadium are crucial in the suppression. In this paper we study clustering of excess vacancies in pure V and V-4Ti by molecular dynamics simulations at 700 K based on our interatomic potentials constructed earlier for the Ti-V system. For pure V the process results in the formation of a Frank sessile dislocation while the clustering in V-4Ti ends with the formation of the Ti-vacancies complexes with a specific structure. This allows us to discuss a possible mechanism of the swelling reduction in V caused by Ti alloying.

Abstract: There is a need to choose appropriate interatomic empirical potentials for the molecular dynamics (MD) simulation of nanomachining, so as to represent chip formation and other cutting processes reliably. Popularly applied potentials namely; Lennard-Jones (LJ), Morse, Embedded Atom Method (EAM) and Tersoff were employed in the molecular dynamics simulation of nanometric machining of copper workpiece with diamond tool. The EAM potentials were used for the modelling of the copper-copper atom interactions. The pairs of EAM-Morse and EAM-LJ were used for the workpiece-tool (copper-diamond) atomic interface. The Tersoff potential was used for the carbon-carbon interactions in the diamond tool. Multi-pass simulations were carried out and it was observed that the EAM-LJ and the EAM-Morse pair potentials with the tool modelled as deformable with Tersoff potential were best suitable for the simulation. The former exhibit the lowest cutting forces and the latter has the lowest potential energy.

Abstract: Based on the phase field theory, the long-range order (LRO) parameter related interatomic potentials equations were utilized to calculate the interatomic potentials of L1₀-Ni₃(Al,V), L1₂-Ni₃Al and L1₂-Ni₃(Al,V) phases varying with temperature and concentrations. Using these potentials, the simulated microstructure evolution and the order parameter with the time of Ni₇₅Al₂₀V₅ ternary alloy are simulated at temperature 1000K during the early stage of the precipitation process in this research. Results testify that the precipitation sequence during the early stage of Ni₇₅Al₂₀V₅ alloy is the disordered phase →L1₀ pre-precipitation phase →L1₂ equilibrium phase. Firstly, the nonstoichiometric L1₀ pre-precipitation phase formed by congruent ordering precipitation mechanism; secondly, the nonstoichiometric L1₂ phase formed by transforming from L1₀ phase; thirdly, the stoichiometric equilibrium L1₂ phase formed by spinodal decomposition precipitation mechanism. It is discovered that the precipitation mechanism (congruent ordering+ spinodal decomposition) process was closely related to free energy and interatomic potentials: L1₀ pre-precipitation phase’s free energies are higher and interatomic potentials are smaller than those of L1₂ equilibrium phase.

Abstract: The structural properties of GdFe_2-xT_x (T=Ti, Al) and their hydrides are studied by using inter-atomic potentials based on Chens lattice inversion technique. The results show that GdFe_2-xAl_x crystallizes with the MgZn₂ type phase in the range 0.35x0.7. And GdFe2-xTix crystallizes with the MgZn₂ type phase has the lowest energy for 0x<0.17 and="" the="" tolerance="" is="" acceptable="" gdfe="" sub="">2-xTi_x compounds are stabilized in MgZn₂ type phase with different Ti atoms content in the range 0.17<x0.6. Moreover, the calculated lattice constants coincide quite well with experimental values. All the results indicate the potentials are valid for studying the structural properties of the intermetallics.

Abstract: An atomistic simulation of the structural properties of the Rh7-xTxB3 series, where T is Fe, Cr, Mn, has been carried out using interatomic pair potentials based on the lattice inversion method. Calculated results show T atoms can stabilize Rh7-xTxB3 with Th7Fe3-type structure, and T atoms substitute for Rh with a strong preference for the 2b sites. The phase stability of the intermetallics Rh7-xTxB3 is tested by many means including random atom shift, global deformation and high temperature disturbance under the control of the pair potentials. Calculated unit-cell parameters for Rh7-xTxB3 agree with the experimental data very well. All the above results indicate that the potentials are valid for studying the structural properties of these kinds of complex structure of transition metal boride.

Abstract: The effect of interatomic potentials on the onset of plastic deformation in the nanometric machining of a crystalline diamond tool on a crystalline copper workpiece, was investigated by using the MD simulation. Three potential pairs were used for the copper-copper (workpiece) and the copper-carbon (tool-workpiece interface) atomic interactions. For case 1, the Morse potential was used for both the copper-copper and the copper-carbon interactions; for case 2, the Embedded Atom Method (EAM) potential was used for the copper-copper interactions and the Morse potential was used for the copper-carbon interactions; and for case 3, the EAM potential was used for the copper-copper interactions and the Lennard-Jones (LJ) potential was used for the copper-carbon interactions. The diamond tool was modelled as a deformable body and the Tersoff potential was applied for the carbon-carbon interactions. From the simulation results, pile-up volume and the force ratio appear to indicate the onset of plasticity during the machining. The pile-up volume shows that ploughing starts from 0.25nm, 0.20 and 0.30nm depth of cut for case 1, case 2 and case 3 respectively and the formation of chips starts to occur from the depth of cut of 1.5nm for case 3. The force ratio also indicate the onset of ploughing at different depths of cut from 0.10nm-0.3nm.

Abstract: The phase stability and site preference of transition metal carbides Cr in Fe7-xCrxC3 are studied based on the pair potentials obtained by the lattice inversion method. The lattice constants and cohesive energy of Fe7-xCrxC3 with the content x are calculated. The results show that Cr atoms substitute for Fe with a strong preference for the 6c1 sites and the order of site preference is 6c1, 6c2 and 2b. Calculated lattice parameters are in good agreement with the experimental data. Moreover, the total and partial phonon densities of states are first evaluated for the Fe7-xCrxC3 compounds with the hexagonal structure. We also provide some information on the vibrational properties of transition metal carbides, such as the specific heat and Debye temperature were also evaluated.

Abstract: The effect of cobalt on the structural properties of intermetallic Tb₃(Fe_28-xCo_x)V_1.0 with Nd₃(Fe,Ti)₂₉ structure has been studied by using interatomic pair potentials obtained through the lattice inversion method. Calculated results show that the order of site preference of cobalt is 8j(Fe8), 4e(Fe11) and 2c(Fe1) which is in good agreement with experimental results. And the calculated lattice constants coincide quite well with experimental values. All these prove the effectiveness of interatomic pair potentials obtained through the lattice inversion method in the description of rare-earth materials.

Abstract: An atomistic simulation is presented on the phase stability and lattice parameters of the new actinide intermetallic compounds A₃Ni₅Al₁₉ (A = Th, U). Calculations are based on a series of interatomic pair potentials related to the actinides and transition metals, which are obtained by lattice inversion method. Calculated lattice constants are found to agree with a report in the literature. It is noted that, the total and partial phonon densities of states are first evaluated for the A₃Ni₅Al₁₉ (A = Th, U) compounds. The analysis for the inverted potentials explains qualitatively the contributions of different atoms to the vibrational modes.

Abstract: Helmholtz free energy functional for generalized lattice model is reduced to Ginzburg- Landau-like form. Connections between interatomic potentials characteristics and parameters of Ginzburg-Landau-like functional are established. Equations for equilibrium distributions of species in multicomponent systems are derived. Equations of rearrangement kinetics of multicomponent systems are obtained. Description of the rearrangement processes via non-classical partial differential equations is proposed.