This paper describes details of the spinodal decomposition and coarsening in metastable cubic Ti0.33Al0.67N and Ti0.50Al0.50N coatings during isothermal annealing, studied by in-situ small angle x-ray scattering, in combination with phase field simulations. We show that the isostructural decomposition occurs in two stages. During the initial stage, spinodal decomposition, of the Ti0.50Al0.50N alloy, the phase separation proceeds with a constant compositional wavelength of ∼2.8 nm of the AlN- and TiN-rich domains. The time for spinodal decomposition depends on annealing temperature as well as alloy composition. After the spinodal decomposition, the coherent cubic AlN- and TiN-rich domains coarsen. The coarsening rate is kinetically limited by diffusion, which allowed us to estimate the diffusivity and activation energy of the metals to 1.4 × 10−6 m2 s−1 and 3.14 eV at−1, respectively.

In the present work, we have studied the decomposition of arc-evaporated Ti 0.55 Al 0.45 N and Ti 0.36 Al 0.64 N during heat treatments in vacuum by in situ synchrotron wide-angle X-ray scattering primarily to characterize the kinetics of the phase transformation of AlN from the cubic (c) NaCl structure to the hexagonal (h) wurtzite structure. In addition, in situ small-angle X-ray scattering measurements were conducted to explore details of the wavelength evolution of the spinodal decomposition, thus providing information about the critical size of the c-AlN-rich domains prior to the onset of the transformation to h-AlN. We report the fractional cubic to hexagonal transformation of AlN in Ti 1Àx Al x N as a function of time and extract activation energies between 320 and 350 kJ mol À1 depending on the alloy composition. The onset of the hexagonal transformation occurs $50 K lower in Ti 0.36 Al 0.64 N compared to Ti 0.55 Al 0.45 N where the high Al content alloy also has a significantly higher transformation rate. A critical wavelength for the cubic domains of $13 nm was observed for both alloys. Scanning transmission electron microscopy shows a c-TiN/h-AlN microstructure with a striking morphology resemblance to the c-TiN/c-AlN microstructure present prior to the hexagonal transformation.

No abstract

No abstract

No abstract