Tribological and high speed turning performance in Ti_1-xAl_xN coatings prepared by close-field unbalanced magnetron sputtering

Titanium-aluminium-nitride (Ti_1-xAl_xN) coatings were deposited by close-field unbalanced magnetron sputtering on M42 steel substrates and WC-6wt%Co inserts at 450°C. The tribological behavior was analyzed by sliding against steel and WC-6wt%Co balls, while the turning performance was evaluated by a conventional turning machine at high cutting speeds without using coolants. In the tribological tests, the formation of transfer layer and the variations of hardness of the coatings played an important role for sliding against steel balls. For the coatings sliding against WC-6wt%Co balls, the Ti-Al-N coatings showed a similar friction coefficient, but the TiN coating exhibited a lower value. The difference could be explained by the tri-oxidation wear mechanism. In the turning tests, a superior cutting performance of the coating was found at x=0.45, which endured 38 minutes before the tool flank wear reached the maximum value of 0.3 mm, whereas only 20 minutes were endured for the TiN coating. The excellent performance of the coatings in the turning tests could be explained by the enhanced mechanical properties and oxidation/diffusion resistance of the coatings.