Microstructure-oxidation resistance relationship in Ti3AlC2 MAX phase

Spark Plasma Sintering and Hot Isostatic Pressing were used to synthesize coarse-grained and fine-grained Ti3AlC2 specimens. Moreover, Spark Plasma Sintering processing parameters were modified in order to vary the TiC, Al2O3 and TixAly impurity and the porosity contents in the fine-grained samples. The influence of the Ti3AlC2 microstructure on the oxidation resistance was assesed. It is demonstrated that the grain size can drastically modify the oxidation resistance. The higher density of grain boundaries, in fine-grained specimens, increases the number of Al diffusion paths and leads to the formation of a protective alumina scale. In coarse-grained sample, Al diffusion is the rate limiting step of the α−Al2O3 formation and TiO2 is formed simultaneously to alumina. TiC impurities and porosity are demonstrated to be detrimental to the oxidation resistance in the 800 °C–1000 °C temperature range by favouring TiO2 formation. Finally, it is also shown that, for fine-grained specimens, the oxide scale grows very slowly for oxidation times in the range 20–40 days.