Cutting performance and wear mechanism of Ti-Al-N/Al-Cr-O coated silicon nitride ceramic cutting inserts

In the present work, Ti-Al-N/Al-Cr-O coating was deposited on silicon nitride cutting inserts by PVD technique. The micro-structure, chemical composition, hardness and coating/substrate adhesion were studied by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), micro-indentation and scratch tests, respectively. The cutting performance of the Ti-Al-N/Al-Cr-O coated silicon nitride cutting inserts were investigated in turning HT250 gray cast iron and AISI 4340 steel under dry environment. The uncoated inserts were applied for turning tests as comparison. The results revealed that higher hardness was obtained by covering Ti-Al-N/Al-Cr-O coating on silicon nitride cutting inserts with acceptable coating/substrate adhesion. The cutting performance of the Ti-Al-N/Al-Cr-O coated silicon nitride inserts was higher than that of the uncoated inserts for both gray cast iron and steel turning. The wear of the coated inserts was a combination of abrasion and adhesion under given cutting conditions, both in cast iron turning and steel turning. It can be concluded that the obtained Ti-Al-N/Al-Cr-O coated silicon nitride inserts perform better than uncoated inserts in cast iron and steel turning and are capable of reducing machining costs.