Thermal Stability of Structure and Properties of Gradient and Gradient-Layered Coatings of the Ti–Al–Si–Cu–N System

Using the methods of dark-field electron microscopy analysis, energy-dispersive X-ray microanalysis, hardness measurements and scratch testing, the variations of elemental composition, structure and mechanical properties of gradient and gradient-layered coatings of the Ti–Al–Si–Cu–N system are investigated during annealing in vacuum at the temperatures within the range 973–1373 K. It is found out that at the annealing temperatures up to 1173 K such structural changes as equalization of the nitride-phase lattice parameter throughout the coating thickness and decreased lattice bending are due to the diffusion-induced redistribution followed by a drop in the concentration of the nitride-doping elements and precipitation of the nanosized copper crystals. For the annealing temperature 1373 K, a several-fold (compared to the state after deposition) decrease in the nitride-phase crystal lattice bending and a change in the concentration of the elements of a few tens of percent are revealed, as well as the formation of heterophase nanocrystalline structure during their localization at the interfaces. A similarity of the defect microstructure in the crystals of both coatings after annealing at 1373 K is determined. The influence of the structural-phase transformations on the variations in the hardness and adhesion strength values of the coatings is discussed.