Long-time Oxidation of Ti3(Al,Si)C2 Carbides at 400-800 oC

Junhee Hahn, Sang Whan Park, Dong Bok Lee
2020 Korean Journal of Metals and Materials  
Quarternay carbides of Ti<sub>3</sub>Al<sub>x</sub>Si<sub>1-x</sub>C<sub>2</sub> (x=0.3, 0.5, and 0.7) were oxidized at 400, 600, and 800 °C for 0.5-6 months in order to study their long-time oxidation behavior in air. When they were oxidized at 400-600 <sup>o</sup>C for 0.5-3 months, oxidation proceeded relatively slowly with moderate weight gains. However, further oxidation at 400-600 <sup>o</sup>C for 6 months resulted in the oxidation-induced microcracking of oxide scales due to large
more » ... expansion and large stress induced owing to the formation of Al<usb>2</sub>O<sub>3</sub>, SiO<sub>2</sub>. TiO<sub>3</sub>, and TiO<sub>2</sub> in oxide scales. However, at 800 <sup>o</sup>C, microcracking of oxide scales, which could lead to pulverization of Ti<sub>3</sub>Al<sub>x</sub>Si<sub>1-x</sub>C<sub>2</sub>, did not occur due to stress relaxation in oxide scales. Instead, at 800 <sup>o</sup>C, Ti<sub>3</sub>Al<sub>x</sub>Si<sub>1-x</sub>C<sub>2</sub> oxidized rapidly to form thick, somewhat porous oxide scales, which consisted primarily of an outer TiO<sub>2</sub> layer with some Al<sub>2</sub>O<sub>3</sub>, an intermediate Al<sub>2</sub>O<sub>3</sub> layer with some TiO<sub>2</sub>, and an inner TiO<sub>2</sub> layer with some (SiO<sub>2</sub>+Al<sub>2</sub>O<sub>3</sub>). The overall longtime oxidation resistance of Ti<sub>3</sub>Al<sub>x</sub>Si<sub>1-x</sub>C<sub>2</sub> at 400-800 °C was considered to be poor. Factors that determined the oxidation rates of Ti<sub>3</sub>Al<sub>x</sub>Si<sub>1-x</sub>C<sub>2</sub> were; (1) How fast titanium oxidized to semi-protective titanium oxides, (2) How fast Al and Si oxidized to Al<sub>2</sub>O<sub>3</sub> and SiO<sub>2</sub> barrier oxides, and (3) Whether oxidation-induced microcracking occurred in oxide scales or not. The ratio of Al/Si in Ti<sub>3</sub>Al<sub>x</sub>Si<sub>1-x</sub>C<sub>2</sub> and the matrix grain size were apparently not dominant factors, because the basic oxidation mode of Ti<sub>3</sub>Al<sub>0.3</sub>Si<sub>0.7</sub>C<sub>2</sub>, Ti<sub>3</sub>Al<sub>0.5</sub>Si<sub>0.5</sub>C<sub>2</sub>, and Ti<sub>3</sub>Al<sub>0.7</sub>Si<sub>0.3</sub>C<sub>2</sub> was similar under the identical oxidation condition.
doi:10.3365/kjmm.2020.58.3.182 fatcat:p5rkhqz6evgzjdignmpht63v3y