Initial oxidation on 12 grain boundaries in pure TiN coating and on (Al,Si,Cr) doped Σ3 (111) grain boundaries: A first-principles calculations

In this work, using first-principles calculation method, the effect of twelve <110> symmetric tilt grain boundaries (GBs) on the initial oxidation behavior of TiN was studied. Firstly, the calculated GB energies show that for the TiN (1–10) surface with GBs from Σ3 to Σ27, Σ3 (111) GB possesses an extremely small GB energy (0.404 J/m2), while the other GBs possess a high energy (2.681∼4.834 J/m2). The electronic structure results show that the intrinsic characteristic of GB with high energy is well associated with the extra DOS peak existing in high energy region. Secondly, the oxygen adsorption results show that for TiN surfaces without GB, the order of adsorption energy of O is (100) > (110) > (111). When TiN (1–10) surface with different GBs, the sites at GBs are chemically more favorable sites for oxygen. The degree of weakening of oxidation resistance varies depending on the type of GBs, due to the apparent difference in oxygen adsorbability. Moreover, an interesting discovery is that Σ3 (111) GB provides a possibility to enhance the oxidation resistance of TiN, attributed to the easy introduction of Σ3 (111) GBs and suppressed inward progression of oxidation. Finally, the doping investigation in Σ3 (111) GB shows that among the three doping elements (Al, Si, and Cr), Si doping can further improve the oxidation resistance of (1–10) surface with Σ3 (111) GB in TiN, owing to the easy introduction of Si and formation of diffusion barrier layer of silicon oxides.