Oxidation Behaviors of TiB_2-TiC_x and TiB_2-TiC_x/15SiC Ceramics

摘要

Fully dense samples of TiB_2-TiC_X and TiB_2-TiC_X/15SiC ceramic composites were fabricated by in-situ synthesis under hot isostatic pressing from TiH_2, B_4C and SiC powders. Their oxidized behaviors at different temperatures were tested. Optical micrograph studies and thermo-gravimetric analyses show that the highest effective temperature of oxidation resistance is 700°C for TiB_2-TiC_x, and 1100°C for TiB_2-TiC_x/15SiC. The weight gain of TiB_2-TiC_x/15SiC below 1100°C is quite low, and it rises up suddenly when the temperature reaches 1200°C. Thus, the highest effective temperature of oxidation resistance is 1100°C for TiB_2-TiC_x/15SiC. The oxidation dynamic curves of TiB_2-TiC_x/15SiC ceramics accord with the parabola's law. The activation energy of TiB_2-TiC_X/15SiC (189.87kJ.mol~(-1)) is higher than that of TiB_2-TiCx (96.44kJ.mol~(-1)). In the oxidation process of TiB_2-TiCx/15SiC, TiB_2 reacts with oxygen and generates TiO_2 and B_2O_3 at first. A layer of whole homogeneous oxide film cannot be formed, in the mean time, the oxidation of TiC begins. When temperature goes up to 1000°C, TiC phase is totally oxidized. SiC is oxidized to SiO_2 at about 900°C, Meanwhile, TiO_2 forms denser film than B_2O_3, which grows and covers the surface of the material, and gives better property of oxidation resistance.