Date of Award
Master of Science
The study presented here describes an investigation of an oxidation scale of a fully-sintered Y2O3-ZrB2-TiC composite exposed in air at 1173K. Upon oxidation of the boride/carbide, a ZrO2-TiO2 was expected to form similar to the ZrO2-SiO2 dual scale of an oxidized ZrB2-SiC. The 47wt% Y2O3-38wt%ZrB2-16wt%TiC composite formed a dual scale consisting primarily of an Y2O3-ZrO2-TiC inner scale with an outer scale of ZrO2-TiO2-Y2O3.
The samples oxidized with a parabolic layer growth allowing the calculation of the effective diffusion coefficient indicating that the oxidation was controlled by oxygen ingress through primarily the ZrO2-Y2O3 phase. The oxygen potential between the inner layer and the Y2O3-ZrB2-TiC core was estimated by a thermodynamically calculated phase diagrams of TiC-ZrB2 and Ti-ZrB2-O2.
For comparison purposes, a sample composed of HfB2 - TiC - Y2O3 - Ta sample was also oxidized at a temperature of 1773K. In this case, tantalum does not seem to react with any of the borides/carbides present in the sample. In fact, it is protected by a Y2O3 scale. The rest of the sample oxidizes very similar to the ZrB2 - TiC - Y2O3 sample; exhibiting the same oxidation mechanism.
Received from ProQuest
Salvador Manuel Rodriguez
Rodriguez, Salvador Manuel, "Oxidation of Borides and Carbides with Y2O3 and Ta Additions" (2012). Open Access Theses & Dissertations. 2177.