Selection of metal ion irradiation for controlling Ti1−xAlxN alloy growth via hybrid HIPIMS/magnetron co-sputtering

We demonstrate, for the first time, the growth of metastable single-phase NaCl-structure high-AlN-content Ti_1−xAl_xN alloys (x ≤ 0.64) which simultaneously possess high hardness and low residual stress. The films are grown using a hybrid approach combining high-power pulsed magnetron (HPPMS/HIPIMS) and dc magnetron sputtering of opposing metal targets. With HIPIMS applied to the Al target, Alⁿ⁺ ion irradiation (dominated by Alⁿ⁺) of the growing film results in alloys 0.55 ≤ x ≤ 0.60 which exhibit hardness H ∼ 30 GPa and low stress σ = 0.2-0.7 GPa, tensile. In sharp contrast, films with corresponding AlN concentrations grown with HIPIMS applied to the Ti target, giving rise to Tiⁿ⁺ ion irradiation (with a significant Ti²⁺ component), are two-phase - cubic (Ti,Al)N and hexagonal AlN - with low hardness, H = 18-19 GPa, and high compressive stress ranging up to 2.7 GPa. Annealing alloys grown with HIPIMS applied to the Al target results in age hardening due to spinodal decomposition; the hardness of Ti_0.41Al_0.59N increases from 30 to 33 GPa following a 900 °C anneal.