Microstructure, mechanical properties and cutting performance of Cr1-yTayN single layer and Ti1-xAlxN/Cr1-yTayN multilayer coatings

Cr1-yTayN single-layer and Ti1-xAlxN/Cr1-yTayN multilayer hard coatings were deposited on cemented carbide substrates using magnetron sputter deposition and cathodic arc evaporation. For the sputtered coatings a bias voltage of −50V was applied, while arc evaporated coatings were deposited at three different bias voltages of −40, −60 and −80V. The coatings were grown from powder metallurgically produced CrTa targets with a composition of 75at% Cr and 25at% Ta, resulting in a Cr/Ta ratio of 71/29 in the sputtered coatings and 74/26 in the arc evaporated coatings, independent of the applied bias voltage. All coatings are characterized by a single-phase face centered cubic structure. The sputtered single- and multilayer coatings exhibited a hardness of ~22.2 and ~25.2GPa, respectively. For the arc evaporated coatings, a hardness of ~22.7 could be determined for the multilayer, while for the single-layers the hardness increased from ~21.6 to ~24.3GPa with increasing bias voltage. Ball-on-disk tests against alumina at room temperature, 500 and 700°C yielded wear rates comparable to conventional Ti1-xAlxN coatings, but significantly lower friction coefficients. The performed cutting tests also showed promising results, indicating the high application potential of Cr1-xTaxN-based hard coatings.