The effect of Si content on microstructure and mechanical properties of Ti-Al-Ta-Si-N coatings

The evolution of the microstructure and mechanical properties of magnetron-sputtered Ti 1-x-y-zAlxTaySizN coatings with increasing the Si content from z = 0 to 0.3 is studied. Based on the results of the X-ray photo-electron spectroscopy and X-ray diffraction investigations, it is shown that the nanocomposite structure consisting of Ti-Al-Ta-Si-N crystallites and the Si3N4 amorphous tissue phase is formed in the coatings at z = 0.1. The evolution of the coating microstructure with increasing the Si content from the pronounced columnar morphology to the featureless nanocomposite morphology is demonstrated using scanning electron microscopy and transmission electron microscopy. The formation of the amorphous tissue phase in the coatings with z >= 0.12 is clearly shown by high-resolution transmission electron microscopy investigations. Variations of the mechanical properties of the coatings with the Si content are studied by nanoindentation. The Ti0.36Al0.44Ta0.10Si0.10N coating is found to have a maximum hardness of 41 GPa coupled with the highest H/E* and H3/E*2 ratios.