Ti2AlN and Ti4AlN3 are MAX phases that exhibit a unique combination of the characteristics of both ceramics and metals coupled with an unusual combination of mechanical, electrical and thermal properties. Such unique properties make these materials ideally suited for a wide range of engineering and high-temperature applications. However, MAX phases are generally unstable and undergo phase dissociation in vacuum at elevated temperature, but the underlying causes are still poorly understood. Hitherto, no work has been reported on the phase stability of ternary nitrides. This project aims to investigate the effects of porosity and high-temperature vacuum-annealing on the thermal stability of Ti2AlN and Ti4AlN3. This information is vital for understanding the underlying chemistry and kinetics of decomposition susceptibility, as well as providing new strategies for stabilizing MAX phases.