Oxidation behavior of Nb-coated Zirconium Diboride

Abstract

Metallic Nb-coatings were deposited on top of ZrB2 by means of magnetron sputtering to improve its oxidation resistance. High temperature oxidation tests have revealed that the metallic Nb-coatings lead to the formation of a dense solid and protective reaction zone in addition to a more stable B2O3 liquid solution at the surface. Compared to baseline ZrB2, a reduction in the oxidation kinetics, as well as the thickness of the porous zirconia layer by 71%, has been achieved with the help of Nb-coatings. A liquid phase sintering by molten Nb2O5 mechanism was responsible for the formation of the dense reaction zone under the boria layer, resulting in the improved oxidation resistance. Furthermore, the experiments revealed the need for an annealing process of Nbcoated specimens, in vacuum, to improve the adhesion of the coatings with ZrB2 and to avoid spallation during oxidation.