Element Vaporization of Ti-6Al-4V Alloy during Selective Laser Melting

The present study aims to reveal the mechanism of element vaporization of Ti-6Al-4V alloy during selective laser melting (SLM). The equations of Redlich–Kister and the thermodynamics principles were employed to calculate the vaporization thermodynamics, which contributes to the obtaining the vaporization kinetic based on the Chapman-Enskog theory and the diffusion model. According to the achieved vaporization model, the elements with the most prominent tendency and flux to vaporize were distinguished. Moreover, the effect of the process parameters on the vaporization of Al and Ti is experimentally investigated using inductively coupled plasma optical emission spectrometer (ICP) technology. The analyzed results of the chemical composition of the powders and builds show a great agreement with the kinetic results calculated by the vaporization model. Notably, the element vaporization can be curbed by regulating the laser energy input.

An efficient and accurate method to calculate diffusion coefficient of structured particles. A first case study of Pb diffusion in rare gases

Diffusion coefficient depends on temperature, pressure, reduced mass of colliding particles and collision cross section. The presented method is designed to calculate the diffusion coefficient in loose systems containing molecules with relatively complicated colliding trajectories. It is a combination of the Chapman-Enskog theory and the molecular dynamics calculation. The Chapman-Enskog theory provides the relation between the diffusion coefficient and the collision cross section which is the result of multiple integration of the scattering angle of all possible initial conditions of the collision. The scattering angle is obtained by numerical integration of the Newton’s equation of motion with previously selected initial conditions. The proposed method has been verified for the simple system of a lead atom diffusion in rare gases and the results were compared to those of two other theoretical methods.

DIRECT SIMULATION MONTE CARLO FOR DENSE HARD SPHERES

We propose a modified direct simulation Monte Carlo (DSMC) method, which extends the validity of DSMC from rarefied to dense system of hard spheres (HSs). To assess this adapted method, transport properties of hard-sphere (HS) systems have been predicted both at dense states as well as dilute, and we observed the excellent accuracy over existing DSMC-based algorithms including the Enskog theory. The present approach provides an intuitive and systematic way to accelerate molecular dynamics (MD) via mesoscale approach.

Calculation of Viscosity Coefficient of Moderately Dense Fluids from the Modified SAFT-BACK Equation of State

The viscosity of some simple fluids in the wide density and temperature ranges have been calculated by the modified Enskog theory (MET) and with the help of Kaplun equations. The thermal pressure, second virial coefficient and internal energy are calculated from the modified SAFT-BACK EOS. The proposed scheme was further examined for the prediction of the viscosity of some dense fluids, including Ar, N2, O2, CO2, CH4, C2H6, C3H8 and C4H10. A comparison of the calculated and experimental values of the viscosity yields an overall average deviation of 2.16%.

DIFFUSION IN A CONTINUUM MODEL OF SELF-PROPELLED PARTICLES WITH ALIGNMENT INTERACTION

In this paper, we provide the O(ε) corrections to the hydrodynamic model derived by Degond and Motsch from a kinetic version of the model by Vicsek and co-authors describing flocking biological agents. The parameter ε stands for the ratio of the microscopic to the macroscopic scales. The O(ε) corrected model involves diffusion terms in both the mass and velocity equations as well as terms which are quadratic functions of the first-order derivatives of the density and velocity. The derivation method is based on the standard Chapman–Enskog theory, but is significantly more complex than usual due to both the non-isotropy of the fluid and the lack of momentum conservation.