High-temperature thermal stability of Ti2AlN and Ti4AlN3: A comparative diffraction study

The susceptibility of Ti2AlN and Ti4AlN3 to high-temperature thermal dissociation in a dynamic environment of high-vacuum has been investigated using in situ neutron diffraction. Under high vacuum, these ternary nitrides decomposed above 1400 °C through the sublimation of Al, and possibly Ti, to form a surface coating of TiNx (0.5 ≤ x ≤ 0.75). The kinetics of isothermal phase decomposition were modelled using the Avrami equation and the Avrami exponents (n) of isothermal decomposition of Ti2AlN and Ti4AlN3 were determined to be 0.62 and 0.18, respectively. The characteristics of thermal stability and phase transitions in Ti2AlN and Ti4AlN3 are compared in terms of the rate of decomposition, phase relations and microstructures.