A Comparative Study of TiAlN and CrAlN Coatings Deposited on Sialon Ceramic Cutting Inserts by Physical Vapor Deposition

Abstract

TiAlN and CrAlN coatings were prepared by physical vapor deposition (PVD) on Sialon ceramic cutting tools. The results illustrated that the surface morphology of TiAlN coating was smoother than that of CrAlN coating. The thickness of TiAlN coating was about 1 µm, which was thicker than that of CrAlN coating (about 0.5µm). However, the hardness of TiAlN coating was lower (30.1 GPa) than that of CrAlN coating (37.5 GPa). Also the elastic modulus of TiAlN coating (346.9 GPa) was also lower than that of CrAlN coating (430.7 GPa), indicating that the stiffness of CrAlN coating was better than that of TiAlN coating. According to scratch tests, the adhesion force of TiAlN and CrAlN coatings were 31 N and 45 N, respectively, which revealed that the CrAlN coating exhibited better adhesion than the TiAlN coating. Cutting performance of the TiAlN coated and CrAlN coated Sialon ceramic cutting inserts were investigated by turning nickel-based alloys under dry conditions. For comparison, uncoated Sialon ceramic cutting inserts were also used for turning tests under the same conditions. The results indicated that the cutting performance of the inserts was considerably improved by the TiAlN and CrAlN coatings on the surfaces. The dominant failure mechanisms of the CrAlN coated inserts were abrasive and adhesive wear, whereas adhesive wear and spalling were the main failure mechanisms of the TiAlN coated inserts. The service life of TiAlN and CrAlN coated inserts were much longer than that of the uncoated inserts, indicating that the two coatings could effectively protect the inserts from wear.