TiCx/Al bilayer thin films were synthesized using combinatorial magnetron sputtering to study the influence of C content on the reaction products at different annealing temperatures. Based on energy-dispersive X-ray analysis calibrated by elastic recoil detection analysis data, x in TiCx was varied from 0.4 to 1.0. Film constitution was studied by X-ray diffraction before and after annealing at temperatures from 500 to 1000°C. The formation of TiCx and Al in the as-deposited samples over the whole C/Ti range was identified. Upon annealing, TiCx reacts with Al to form Ti–Al-based intermetallics. At temperatures as low as 700°C, the formation of MAX phases (space group P63/mmc) is observed at x⩽0.7. Based on the comparison between the C content induced changes in the lattice spacing of TiCx and Ti2AlC as well as Ti3AlC2, we infer the direct formation of MAX phases by Al intercalation into TiCx for x⩽0.7.