Microstructure of TiAlN and CrAlN coatings and cutting performance of coated silicon nitride inserts in cast iron turning

Ti0.5Al0.5N and Cr0.3Al0.7N coatings were produced by cathodic arc evaporation (CAE) on silicon nitride cutting inserts. The microstructure and phase composition of the coatings were investigated by SEM and XRD, respectively. The hardness of the coatings was evaluated by applying micro-hardness tester. Turning tests were carried out on both uncoated and coated inserts in gray cast iron turning under dry environment. Wear behavior and cutting performance of the uncoated and coated inserts were investigated. The results showed that Ti0.5Al0.5N coating had higher hardness than Cr0.3Al0.7N coating owing to its smaller grain size. Cutting performance of the silicon nitride inserts was improved with the covering of Ti0.5Al0.5N and Cr0.3Al0.7N coatings with at least 2 times of the cutting life. No spalling was occurred after the cutting tests for both Ti0.5Al0.5N and Cr0.3Al0.7N coated inserts. Ti0.5Al0.5N coating performed better cutting performance and tool life than Cr0.3Al0.7N coating. The dominant wear mechanism of Ti0.5Al0.5N and Cr0.3Al0.7N coated inserts was abrasion with grooves on the worn faces.