Influence of multilayer architecture on microstructure and fracture properties of arc evaporated TiAlTaN coatings

Abstract

The incorporation of a fourth element in Ti1-xAlxN, like Ta, and a multilayer architecture are possible concepts to further enhance the coating performance in cutting applications. In the present study, both concepts are combined, focusing on the investigation of the microstructure and the fracture properties of two Ti1-x-yAlxTayN single layer coatings (Ti0.55Al0.44Ta0.01N and Ti0.33Al0.54Ta0.13N) and two corresponding multilayer coatings with the same bilayer thickness but an inverse layer sequence with different layer thicknesses. Energy dispersive X-Ray spectroscopy was utilized to determine the average composition of the coatings, confirming that the Al and Ta contents increase from single layer Ti0.55Al0.44Ta0.01N via the two multilayers to single layer Ti0.33Al0.54Ta0.13N. The residual stress and microstructure were studied using X-ray diffraction and scanning electron microscopy revealing higher compressive stress and grain refinement with higher Al and Ta content, which provoked an increasing hardness as evidenced by nanoindentation experiments. In contrast, the contribution of the multilayer architecture to the hardness increase is only minor. Additionally, micromechanical bending tests revealed a trend of higher fracture stress with increasing Al and Ta content. The fracture toughness was constant for all coatings as different toughening mechanisms occur.