Nanocrystalline TiN coatings with improved toughness deposited by pulsing the nitrogen flow rate

Nanocrystalline titanium nitride (TiN) coatings were deposited on Si (100) substrates using reactive pulsed direct current magnetron sputtering where nitrogen flow rate was pulsed during the deposition. The pulse on time for nitrogen flow rate was 5, 20, 40, 50 and 60 s. X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy (TEM), micro-Raman spectroscopy and proton elastic backscattering spectroscopy (PEBS) techniques were employed to study the structure and microstructure of the as-deposited coatings. Complete nano-mechanical characterization of the coatings was carried out using nanoindentation, nanoscratch and wear testing techniques. TEM studies revealed the nanocrystalline nature of the coatings with column size between 25 and 30 nm. PEBS analysis revealed an increase in N/Ti ratio from 0.79 to 0.90 in the coatings with increasing pulse on time of nitrogen flow rate. Nanoindentation hardness was found to vary from 17 to 27 GPa and fracture toughness values varied from 2.75 MPa m1/2 to 1.19 MPa m1/2 with increase in pulse on time. The coating deposited at a pulse on time of 20 s was found to exhibit optimal nanoindentation hardness and fracture toughness values of around 18 GPa and 2.12 MPa m1/2, respectively. It is concluded that the pulsing of nitrogen flow rate during reactive deposition of TiN coatings allows one to obtain encouraging combinations of moderate hardness and high toughness.