Influence of Substrate Biasing on (Al, Ti)N Thin Films Deposited by a Hybrid HiPIMS/DC Sputtering Process

(Al, Ti)N coatings were reactively cosputtered using a hybrid process in Ar/ N₂ atmosphere, where aluminum and titanium targets were supplied via classical pulsed-dc and HiPIMS power units, respectively. Aiming to study the influence of substrate biasing on the properties of the coatings, all other parameters were kept constant. Unexpectedly, the titanium content seems to remain unchanged, whereas the deposition rate, the morphology, the structure, and the mechanical properties of the coatings strongly depend on the applied voltage on the samples. Increasing the negative bias voltage leads to a slight decrease in the deposition rate of up to -100 V, and for a higher bias voltage, the deposition rate drops drastically. The compressive stresses show similar evolution. These behaviors depend on the attraction of highly energetic metallic and Ar⁺ ions, which strongly impinge the biased substrates. Finally, all the films synthesized below a negative bias of -100 V are crystallized in hcp-AIN form, whereas those deposited above -130 V exhibit the c-TiN structure. This induces a hardness enhancement, but combined to poor adhesion due to a too high level of internal stresses, this induces the characteristic of a brittle and rigid character.