Titanium Deposition Processes

Electronic energy modelling in DSMC simulations

In the Experimental Testing Facility (ETF) at the Lawrence Livermore National Laboratory (LLNL) various metals are vaporized to study the production of surface coatings on substrates. The flow under consideration here is titanium evaporated into an argon background gas. Titanium from a liquid pool is vaporized using the energy from an electron beam and the vapor plume is expanded through a chamber to be deposited on a substrate.

Figure 1
Figure 2

Figure 1 shows the contours of number density and absolute velocity in the flowfield. The titanium atoms that vaporize from the surface of the molten pool, at the bottom of the figure, quickly undergo expansion to hypersonic speeds in the deposition chamber.

Figure 2 shows the contours of the electronic and translational temperatures in the flowfield. These provide a measure of the energy in the electronic and translational modes in the flow. The modelling of electronic energy plays a crucial role in the analysis of this problem.

Due to the high temperature of the molten pool, a large proportion of the titanium atoms are electronically excited. Hence, a significant part of the energy is in the electronic mode and it would not be possible to account for the total energy content of the flow without taking the electronic energy of the titanium atoms into consideration. The energy transferred between the electronic and the translational modes can significantly affect the velocity of the flow, and hence the flux. This becomes especially important at the substrate where deposition takes place.

Acknowledgements

This work was funded by the Lawrence Livermore National Laboratory.