Influence of residual stresses and grain size on the spinodal decomposition of metastable Ti1 − xAlxN coatings

At elevated temperatures, the metastable Ti1 − xAlxN solid solution decomposes in cubic AlN and cubic TiN. Within this work, the effect of residual stresses on the decomposition of sputtered Ti1 − xAlxN coatings was investigated. Using different bias voltages, a series of Ti1 − xAlxN coatings (x = 0.63) with stresses ranging from + 630 to − 2500 MPa was synthesized on Si (100) substrates. Vacuum annealing treatments and subsequent X-ray diffraction measurements showed that tensile stresses foster the formation of more volume consuming cubic TiN domains, while compressive stresses promote the formation of smaller cubic AlN domains. The influence of the grain size has been considered by investigations of free standing films using differential scanning calorimetry. Smaller grains lead to faster decomposition and earlier precipitation of wurtzite AlN.

► Effect of tensile/compressive stresses on decomposition of sputtered Ti0.37Al0.63N.
► Tensile stresses promote the formation of more volume consuming fcc-TiN domains.
► Compressive stresses foster the formation of smaller fcc-AlN domains.
► Smaller grains lead to earlier precipitation of w-AlN and faster decomposition.
► Tensile stresses cause higher hardness after decomposition.