  Ti$_{1-x-y}$Al$_{x}$Zr$_{y}$N cubic alloys within the 25-70\% Al composition
range have high age-hardening capabilities due to metastable phase transition
pathways at high temperatures. They are thus ideal candidates for ultra-hard
nano-coating materials. There is growing evidence that this effect is
associated with the elasto-chemical field-induced phase separation into
compositionally-segregated nanocrystaline nitride phases. Here, we studied the
microstructural evolution in this pseudo-ternary system within spinodal regions
at 1200 $^\circ$C by using an elasto-chemical phase field model. Our
simulations indicate that elastic interactions between nitride nano-domains
greatly affect not only the morphology of the microstructure but also the local
chemical phase equilibria. In Al-rich regions of the composition space we
further observe the onset of the transformation of AlN-rich phases into their
equilibrium wurtzite crystal structure. This work points to a wide palette of
microstructures potentially accessible to these nitride systems and their
tailoring is likely to result in significant improvements in the performance of
transition metal nitride-based coating materials.
