Structure, hardness and thermal stability of TiAlN and nanolayered TiAlN/CrN multilayer films

TiAlN films were deposited on silicon (1 1 1) substrates from a TiAl target using a reactive DC magnetron sputtering process in Ar+N2 plasma. Films were prepared at various nitrogen flow rates and TiAl target compositions. Similarly, CrN films were prepared from the reactive sputtering of Cr target. Subsequently, nanolayered TiAlN/CrN multilayer films were deposited at various modulation wavelengths (Λ). X-ray diffraction (XRD), energy dispersive X-ray analysis, nanoindentation and atomic force microscopy were used to characterize the films. The XRD confirmed the formation of superlattice structure at low modulation wavelengths. The maximum hardness of TiAlN/CrN multilayers was 3900 kg/mm2, whereas TiAlN and CrN films exhibited maximum hardnesses of 3850 and 1000 kg/mm2, respectively. Thermal stability of TiAlN and TiAlN/CrN multilayer films was studied by heating the films in air in the temperature range (TA) of 500-900 °C for 30 min. The XRD spectra revealed that TiAlN/CrN multilayers were stable up to 800 °C and got oxidized substantially at 900 °C. On the other hand, the TiAlN films were stable up to 700 °C and got completely oxidized at 800 °C. Nanoindentation measurements performed on the films after heat treatment showed that TiAlN retained a hardness of 2200 kg/mm2 at TA=700 °C and TiAlN/CrN multilayers retained hardness as high as 2600 kg/mm2 upon annealing at 800° C.