Electronic theory study on high temperature oxidation mechanism of Nb-Ti-Al alloy

The electronic structure parameters of density of electronic states, atoms embedding energy, affinity energy and cluster energy of Nb alloy have been calculated using the recursive method. The high-temperature oxidation mechanism of Nb alloy was investigated. Studies show that the oxygen adsorption on Nb alloy surface can lower the adsorption energy, so oxygen is easily adsorbed on the alloy surface, and gradually diffuses into the Nb alloy matrix. Oxygen has a high solubility in the Nb alloy matrix because of the negative atom embedding energy, and it has similar density of states to Nb. Because the atom embedding energies of Ti and Al in the alloy matrix are higher than that on the alloy surface, Ti and Al atoms diffuse from the alloy matrix to the alloy surface and segregate on the alloy surface, ultimately making the Nb surface rich in Ti and Al. The clustering energy calculation shows that Ti and Al atom tend to gather on their own area, forming Ti and Al atom clusters respectively. Oxygen can interact with Nb, Ti and Al because of the negative affinity energy with Nb, Ti and Al on Nb alloy surface, to generate the Nb2O5, TiO2 and Al2O3 mixed oxide film which has protective effect on Nb alloy.