Determination of the critical content of Al for selective oxidation of Ti3AlC2 at 1100 °C

The critical Al content required to form protective Al2O3 scale on Ti3AlC2 at 1100 °C in air has been investigated by using a scale removal cyclic oxidation method. During the first five cycles, Al2O3 scale forms predominantly, and Ti3AlC2 keeps a similar low mass-gain rate. With increasing the cycle number, the Al content in Ti3AlC2 decreases. During the sixth cycle, the breakaway oxidation happens, and non-protective multilayer oxide forms. It is determined that the critical value of Al/Ti mole ratio is in the range of (0.970-0.977)/3 for the selective oxidation of Ti3AlC2, the corresponding atomic percent of Al is in the range of 16.25-16.34 at.%. Meanwhile, a part of Ti3AlC2 substrate decomposes to TiCx because of de-intercalation of enough Al from Ti3AlC2 during the sixth cyclic oxidation.