Influence of Si content on phase stability and mechanical properties of TiAlSiN films grown by AlSi-HiPIMS/Ti-DCMS co-sputtering

Ti1-x(AlySi1-y)(x)N coatings covering a wide compositional range, 0.38 < x < 0.76 and 0.68 <= y <= 1.00, are deposited to investigate the influence of Al+/Si+ ion irradiation on microstructural and mechanical properties. The samples are grown in Ar/N-2 atmosphere by the hybrid high-power impulse and dc magnetron co-sputtering (HiPIMS/DCMS) method with substrate bias synchronized to the Al+/Si+-rich portion of the HiPIMS pulses. Two Ti targets are operated in DCMS mode, while one AlSi target is operated in HiPIMS mode. Four different AlSi target compositions are used: Al1.0Si0.0, Al0.9Si0.1, Al0.8Si0.2, and Al0.6Si0.4. X-ray diffractometry reveals that films without Si (i.e., y = 1.0) have high Al solubility in NaCl-structure, c-TiAlN, up to x <= 0.67 no w-AlN is detected. Once Si (y < 1.0) is introduced the Al solubility limit decreases, but remains higher than other PVD techniques, along with grain refinement and the formation of a SiNz rich tissues phase, as shown by transmission electron microscopy. The nanoindentation hardness is high (similar to 30 GPa) for all films that do not contain the w-AlN phase. All the coatings have compressive stresses lower than -3 GPa. Interestingly, a range of films with different compositions displayed both high hardness (similar to 30 GPa) and low residual stress (sigma < 0.5 GPa). Such a unique combination of properties highlights the benefits of using HiPIMS/DCMS configuration with metal-ion-synchronized substrate bias, which utilizes the Al+/Si+ supplantation effect and minimizes the Ar+ incorporation.