Effect of microstructure on mechanical and tribological properties of TiAlSiN nanocomposite coatings deposited by modulated pulsed power magnetron sputtering

•TiAlSiN nanocomposite coatings were prepared by MPPMS without heating and bias.•TiAlSiN compositions were almost constant with increasing nitrogen partial pressure.•TiAlN nanocrystallites were embedded in an amorphous Si3N4 matrix in TiAlSiN coatings.•TiAlSiN coatings had low compressive residual stress of about − 0.5 GPa.•Mechanical and tribological properties were related to the nanocomposite structure.

TiAlSiN nanocomposite coatings were deposited in a closed field unbalanced magnetron sputtering system by reactive sputtering from Ti0.475Al0.475Si0.05 targets using modulated pulsed power magnetron sputtering (MPPMS) under a floating substrate bias. The ratio of the nitrogen flow rate to the total gas flow rate (fN2) was varied from 0 to 40%. The application of MPPMS as sputtering sources was aimed at generating a high ionization degree of the sputtered material and a high plasma density by using a pulsed high power approach. When fN2 = 0%, an amorphous-like structure Ti0.479Al0.454Si0.066 coating was deposited with a hardness of 10 GPa. When nitrogen was added, an optimized nanocomposite structure of nc-TiAlN/a-Si3N4 formed in the TiAlSiN coating deposited at fN2 = 10%, in which 5–10 nm TiAlN nanocrystallites were embedded in a 2–3 nm thick amorphous Si3N4 matrix. As the fN2 was increased up to 40%, the elementary composition of the coatings remained almost the same, but the grain size of nanocrystallites approached to 10–20 nm and the AlN phase gradually precipitated. A maximum hardness (H) of 33.2 GPa, a hardness to the elastic modulus (E) ratio of 0.081 and an H3/E*2 ratio of 0.19 GPa were found in the coating deposited at fN2 = 10%. The friction coefficient of the TiAlSiN coatings was around 0.8–0.9 as sliding against a Si3N4 counterpart under a normal load of 0.5 N. A wear rate of 2.0 × 10− 5 mm3 N− 1 m− 1 was measured in the TiAlSiN coatings deposited at fN2 = 20–40%. As only a low residual stress is found in the TiAlSiN coatings, we consider the complete phase separation is responsible for the enhanced mechanical and tribological properties of the nc-TiAlN/a-Si3N4 nanocomposite coatings.