Formation mechanism of Ti3AlC2 in TiO2–Al–C/TiC systems at high temperatures

Ti3AlC2/Al2O3 composites were synthesized by aluminothermic reduction of TiO2/Al/C and TiO2/Al/TiC. The effects of carbon sources (carbon black and TiC), steps heating-up profile, and Al-excess of raw materials composition on the Ti3AlC2 content in final products were investigated. The results showed that in contrast with carbon black, TiC used as a carbon source is beneficial to the formation of Ti3AlC2 at lower temperatures. However, Ti3AlC2 content in the product with carbon black was improved by the steps heating-up profile and Al-excess, promoting intermediate phases TiAl3 and TiC. Furthermore, the formation mechanisms of Ti3AlC2 with different carbon sources in aluminothermic reaction systems were also elucidated. For the TiO2/Al/C system, Ti3AlC2 is precipitated from the Ti–Al melt at high temperatures via the dissolution-precipitation mechanism, which has slower nucleation but faster growth. In contrast, in the TiO2/Al/TiC system, Ti3AlC2 is mainly growing from the intact TiC grains through the epitaxial nucleation mechanism, which has faster nucleation but lower growth.