Oxidation behavior of bulk Ti u3 SiC u2 at intermediate temperatures in dry air
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The isothermal oxidation behavior of bulk Ti3SiC2 at intermediate temperatures from 500 to 900 °C in flowing dry air was investigated. An anomalous oxidation with higher kinetics at lower temperatures was observed. This phenomenon resulted from the formation of microcracks in the oxide scales at low temperatures. The generation of these microcracks was caused by a phase change in the oxide products, i.e., the transformation of anatase TiO2 to rutile TiO2. This phase transformation resulted in tensile stress, which provided the driving force for the formation of the microcracks during oxidation. Despite the existence of microcracks, the intermediate-temperature oxidation of Ti3SiC2 generally obeyed the parabolic rate law and did not exhibit catastrophic destruction due to the fact that cracks occurring in the oxide layers were partially filled with amorphous SiO2. Therefore, further high oxidation kinetics was prevented.
I. INTRODUCTION
In recent years, materials scientists, physicists, and chemists have shown ever-increasing interest in a family of ternary layered compounds because of their striking combination of both ceramic and metal properties. These ternary layered compounds have the general formula of MN+1AXN (N ⳱ 1, 2, or 3), where M is a transition metal, A is an A-group (mostly IIIA and VIA) element, and X is either C or N. Titanium silicon carbide (Ti3SiC2) is a member of this family of layered ternary compounds. The outstanding properties of Ti3SiC2 include good high-temperature oxidation resistance, low density, high elastic modulus and strength, chemical stability, excellent thermal shock resistance, good machinability, and a high ratio of fracture toughness to strength. Thus, Ti3SiC2 is a promising structural material for high-temperature applications. The high-temperature oxidation behavior of Ti3SiC2 has been widely investigated1–3 because oxidation resistance is one of the most important properties for materials applied in hightemperature environments. The results showed that the oxidation of Ti3SiC2 followed the parabolic law and the resulting oxide layer had a stratified structure: the outer layer was TiO2, and the inner layer was a mixture of TiO2 and SiO2 at 1000–1300 °C. The oxidation process a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2006.0046 402
http://journals.cambridge.org
J. Mater. Res., Vol. 21, No. 2, Feb 2006 Downloaded: 13 Mar 2015
was controlled by the inward diffusion of oxygen and the outward diffusion of titanium and carbon, while silicon was immobile. Actually, materials in high-temperature applications are not immune to exposure to oxidizing conditions at intermediate temperatures. At times, intermediatetemperature oxidation can exert a significantly detrimental influence on the properties of materials. For example, MoSi2 possesses excellent oxidation resistance at temperatures of 1000–1700 °C; however, the applicability of this material is restricted by the occurrence of completely destructive oxidation at intermediate temperatu
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