Short-time high-temperature oxidation behavior of nanocrystalline Ta coating at 850 °C

Short-time oxidation behavior of nanocrystalline Ta coating is studied at 850 °C in comparison with that of the Ta sheet. Owing to the large PBR value and insufficient expansion space, the oxide scale on Ta sheet is dramatically cracked, delaminated and pulverized, resulting in rapid deterioration. For nanocrystalline Ta coatings with columnar structures and quantitative grain boundaries, a rapid oxygen diffusion rate causes no initial Ta2O5 to form. The gap between columns provides spaces for bulk expansion, resulting in few opening cracks and delamination. Ta oxidation experiences a crystallization course from amorphous Ta oxide, leading to in situ temperature surging and thus pulverization.