Intermediate-temperature oxidation behavior of Ti2AlC in air

The isothermal oxidation behavior of Ti2AlC at intermediate temperatures of 500, 600, 700, 800, and 900 degreesC in flowing air was investigated by means of thermogravimetric analysis, x-ray diffraction (XRD), Raman spectroscopy, and scanning electron microscopy (SEM)/energy dispersive spectroscopy. An anomalous oxidation with higher kinetics at lower temperatures of 500 and 600 degreesC was observed although Ti2AlC exhibited good oxidation resistance at higher temperatures. As revealed by SEM scale morphology observation, oxidation-induced cracks present at temperatures of 500 and 600 degreesC resulted in poor protectivity of scales and accounted for the anomalous oxidation. The weight gain data for the remaining temperatures were analyzed with an instantaneous parabolic rate constant method by assuming a parabolic rate law. The variations of instantaneous parabolic rate constant with time reflected the complexity of the oxidation behavior of Ti2AlC at intermediate temperatures. These variations were discussed from the viewpoint of phase transformation of oxidation products on the basis of XRD, Raman spectroscopy, and SEM scale morphology observation. As indicated by XRD and Raman spectra, the scale formed on Ti(2)AIC at higher temperature was stable alpha-Al2O3 and rutile TiO2, while transition aluminas of gamma-Al2O3, delta-Al2O3, theta-Al2O3, and TiO2 (anatase) were detected at lower temperatures. The whisker morphology of theta-Al2O3 at 800 degreesC and ridged morphology of alpha-Al2O3 at 800 and 900 degreesC were confirmed by SEM.