Effect of Si_3N_4 Dispersoids on the Cyclic Oxidation Resistance of TiAl Intermetallics

摘要

The oxidation kinetics of TiAi alloys with and without 3,5 and 10 wt. percent additions of Si_3N_4 particles were studied between 900 and 1100 deg C in atmospheric air. The Si_3N_4 dispersoids effectively increased the oxidation resistance of TiAl alloys, the more pronouncing the more Si_3N_4 dispersoids were added. The oxide scales formed on pure TiAl alloys were primarily composed of TiO_2 and some Al_2O_3, whereas those formed on TiAl- Si_3N_4 alloys consisted of TiO_2, Al_2O_3, and SiO_2. The increased oxidation resistance of TiAl- Si_3N_4 alloys compared with Si_3N_4-free TiAl alloys was mainly attributed to; (i) increased scale adherence via stabilized, refined oxide grains, (ii) thin scale formation owing to the presence of silica phase and the promotion of Al_2O_3-rich scale formation.