Effect of Si on the oxidation reaction of α-Ti(0 0 0 1) surface: ab initio molecular dynamics study

Somesh Kr Bhattacharya,Ryoji Sahara,Kyosuke Ueda,Takayuki Narushima

doi:10.1080/14686996.2017.1403273

Abstract

We present our ab initio molecular dynamics (MD) study of the effect of Si on the oxidation of α-Ti(0 0 0 1) surfaces. We varied the Si concentration in the first layer of the surface from 0 to 25 at.% and the oxygen coverage (θ) on the surface was varied up to 1 monolayer (ML). The MD was performed at 300, 600 and 973 K. For θ = 0.5 ML, oxygen penetration into the slab was not observed after 16 ps of MD at 973 K while for θ > 0.5 ML, oxygen penetration into the Ti slab was observed even at 300 K. From Bader charge analysis, we confirmed the formation of the oxide layer on the surface of the Ti slab. At higher temperatures, the Si atoms diffused from the first layer to the interior of the slab, while the Ti atoms moved from second layer to the first layer. The pair correlation function shows the formation of a disordered Ti-O network during the initial stage of oxidation. Si was found to have a strong influence on the penetration of oxygen in the Ti slab at high temperatures.

Highlights

Ti and its alloys are used for high-temperature components such as jet engines and automobile exhaust systems [1,2]
At 300 K, 75% of the oxygen atoms were observed to occupy the face centred cubic (FCC) sites, while the remaining ones occupied the hexagonal close-packed (HCP) sites. This is due to the fact that the binding between the adsorbate and the adsorbent is stronger at the FCC site compared to the HCP site [20]
When the temperature was raised to 600 K, very little change was observed during the molecular dynamics (MD) as the oxygen atoms remain trapped to their respective FCC or HCP sites

Summary

Introduction

Ti and its alloys are used for high-temperature components such as jet engines and automobile exhaust systems [1,2]. Schneider and Ciacchi used molecular dynamics (MD) to characterize the oxidation of Ti films [18] They performed simulations on microcanonical ensembles and the effect of temperature on the oxidation was not captured. Using DFT, we studied the oxygen adsorption on Si-segregated α-Ti(0 0 0 1) surface and the effect of Si on the penetration of oxygen [20]. From atomistic simulations point of view, little has been done to understand the effects of temperature and oxygen coverage on the oxide layer formation and oxygen penetration in Ti substrate. Our simulations revealed the effect of Si on the initial stages of the oxide layer formation as well as the penetration of the oxygen into the Ti substrate

Computational details

Results and discussion

Conclusion