Synthesis and microstructural characterization of nanoscale multilayer TiAlN/TaN coatings deposited by DC magnetron sputtering

Abstract

(Ti,Al)N coatings have become the most used option for the protection of different industrial tools due to their excellent properties like high hardness and low wear rate, which is maintained until temperatures of 700 °C are achieved by the formation of a dense and stable layer of Al2O3. Additionally, TaN coatings have proved to be an appropriate alternative to conventional coatings with great potential in different applications, due to their high chemical stability and corrosion resistance. These aspects motivated the combination of both coatings in a multilayer structure at the nanometric scale. In this work, novel coatings of (Ti,Al)N/TaN were deposited on AISI H13 hot work tool steel by a self-manufactured DC magnetron sputtering vacuum chamber without target shutter. In order to obtain coatings with different decreasing periods, four substrate rotation speeds were used: 0.2 rpm, 0.5 rpm, 1.0 rpm, and 3.0 rpm. In addition to the multilayer coatings, the monolayers of (Ti,Al)N and TaN were deposited for comparison purposes. Using AFM, it was possible to observe that both the roughness and the grain size decreased from 17 to 13 nm and from 165 to 137 nm, respectively, as the substrate rotation speed increased. The monolayer coatings (Ti,Al)N and TaN exhibited an fcc crystal structure with growth directions (111) and (200), respectively. On the other hand, for the multilayer coating (Ti,Al)N/TaN, a change in the preferential direction corresponding to the TaN from [200] to [111] was identified. In the SEM images of the multilayers, a microstructure of columnar growth was observed, which is densified with an increased rotation speed of the substrates, and the multilayers are no longer observed for the highest speeds and the smallest periods. Using plan-view TEM images and selected area EDS, it was possible to suggest the formation of a nanoscale-structured multilayer with a well-defined interface between TiAlN and TaN. Regarding the residual stresses of the coatings, it was possible to observe that with the increase in the substrate rotation speed during the deposition, the stresses decreased progressively, reaching values up to − 1.51 GPa, significantly lower than both TiAlN (− 7.09 GPa) and TaN (− 8.66 GPa) monolayer coatings.