Thin films of metastable NaCl-structure Ti1-xAlxN, with excellent high-temperature oxidation resistance and high hardness (typically ~30 GPa), are employed in different applications from cutting tools to mechanical aerospace components as they prevent wear. At high temperatures, alloy films with high AlN content demonstrate improved performance. For the entire composition range, the calculated Ti1-xAlxN enthalpy of mixing is positive, and its maximum is achieved at x = 0.68. As a result of , Metastable NaCl-structure alloys can be achieved through physical vapor deposition, a direct result of kinetically-limited low-temperature growth and dynamic low-energy ion-irradiation-induced mixing in the near-surface region.
In this experiment, the growth of polycrystalline Ti1-xAlxN films deposited by magnetron co-sputtering from separate elemental metal targets, Al and Ti was studied. The investigation was carried out using a hybrid approach that combines both high-power pulsed magnetron sputtering (HIPIMS) and dc magnetron sputtering (DCMS). HIPIMS is known to create significant ionization of the metal ion flux incident at the growing film surface, while DCMS was found to produce only a few metal ions. Therefore, the hybrid concept ensures selective control of the composition of metal ion fluxes during ion-assisted growth.
Figure 1. Ion energy distribution functions (IEDFs) obtained with PSM003 mass spectrometer from Hiden Analytical, UK. Data are presented for Al and Ti targets operated in both DCMS and HIPIMS modes.
The researchers performed two separate sets of experiments, in the first Al target is powered with HIPIMS and Ti target is employed with DCMS. The target positions were then swapped for the second set of experiments. By doing this, the researchers could individually analyze the effect of intense Tin+ and Aln+ ion fluxes (n = 1,2) from HIPIMS-powered targets on different parameters. This includes; physical properties over a wide range in metastable alloy compositions, microstructure and film growth kinetics.
The ion flux distribution functions are measured in situ using the PSM 003 Hiden Analytical Mass Spectrometer. The distinct flux distributions gained from targets operated in HIPIMS vs. DCMS modes (Figure 1) enable separate investigation of the effects of Aln+ and Tin+ (n = 1, 2) ion irradiation on film growth kinetics, and resulting properties.
During film growth, bombardment with Aln+ ions (primarily Al+ in the Al-HIPIMS/Ti-DCMS configuration) resulted in NaCl-structure Ti1-xAlxN (0.53 ≤ x ≤ 0.60) films which show signs of high hardness (> 30 GPa) with low stress (0.2 - 0.7 GPa tensile.) However, films with corresponding AlN concentrations, developed under Tin+ metal ion irradiation in the Ti-HIPIMS/Al-DCMS mode, exhibit high compressive stress in the range of up to 2.7 GPa and a lower hardness of 18 to 19 GPa.
The wide variation in mechanical properties is due to the fact that the kinetic AlN solubility limit in Xmax in Ti1-xAlxN rely on the target power configuration during growth, and the ion flux composition. When compared to ~40 mol% for growth with Tin+ flux, the NaCl structure can accommodate AlN with Xmax ~64 mol% under Aln+ ion flux. The doubly ionized metal ion flux is about two orders of magnitude greater from the Ti target, than from Al, powered by HIPIMS. This causes a strong asymmetry in film growth reaction paths.
This information has been sourced, reviewed and adapted from materials provided by Hiden Analytical.
For more information on this source, please visit Hiden Analytical.