Improved properties of TiAlN coating by combined Si-addition and multilayer architecture

Alloying a fourth element and multilayer architecture are efficient methods to tailor the structure and properties of aluminum-containing transition metal nitrides coatings. Here, we combine Si-addition and multilayer structure to improve the properties of TiAlN coating. Incorporation of Si into TiAlN leads to a nanocomposite structure with TiAlN nanocrystalline encapsulated by amorphous SiNx, and thereby an increased hardness from 29.1 +/- 1.0 GPa for Ti0.52Al0.48N to 33.1 +/- 1.2 GPa for Ti0.53Al0.38Si0.09N. In order to avoid the formation of undesired wurtzite (w) AlN in Ti0.53Al0.38Si0.09N, the c-Ti0.52Al0.48N template layer (similar to 5.2 nm) is used to stabilize Ti0.53Al0.38Si0.09N layer (similar to 7.5 nm) in its metastable cubic structure based on epitaxial growth. The Ti0.52Al0.48N/Ti0.53Al0.38Si0.09N multilayer with an overall cubic structure shows a hardness value of 35.6 +/- 0.7 GPa. All coatings exhibit an age-hardening ability due to the spinodal decomposition. A peak hardness value of 36.7 +/- 0.8 and 38.2 +/- 0.5 GPa is achieved by Ti0.53Al0.38Si0.09N and Ti0.52Al0.48N/Ti0.53Al0.38Si0.09N, respectively, upon annealing at 1000 degrees C. In contrast, Ti0.52Al0.48N coating exhibits a maximum hardness increase to 33.5 GPa at 800 degrees C. Furthermore, the Ti0.53Al0.38Si0.09N and Ti0.52Al0.48N/Ti0.53Al0.38Si0.09N coatings show oxide scales of similar to 2.1 and 1.0 mu m at 1000 degrees C for 10 h after exposure to air atmosphere, respectively, whereas the Ti0.52Al0.48N coating has already been completely oxidized at 850 degrees C. (C) 2019 Elsevier B.V. All rights reserved.