Study of initial notch wear during turning of stainless steel with CVD Al2O3/Ti(C,N) coated cemented carbide tools

Abstract

Notch wear often determines tool life when machining stainless steel. Chemical Vapour Deposited (CVD) Al₂O₃/Ti(C,N) coated cemented carbide tools are the first recommendation for turning of stainless steel. The CVD coating plays a vital role in reducing and delaying tool wear progress. Hence, it is essential to understand the interaction between the initiation of notch wear and the coating degradation. However, most publications have focused on studying the progression of notch wear rather than the initiation of notch. Thus, this work investigates the initial notch wear in two fundamentally different alumina-based CVD coatings. The first coating system is composed of κ-Al₂O₃ multilayers separated by thin TiN layers. The second coating system is a solid layer of textured (0001) α-Al₂O₃. Both coatings have a Ti(C,N) underlayer. The coated WC-Co cutting tools were assessed from 0.3 to 16 m of face turning in AISI 316Ti. The results showed that the notch wear started already at 0.3 m (equal to 0.3 s) of engagement length in the multilayer κ-Al₂O₃-TiN/Ti(C,N) coated tool and at 1 m (1 s) in the textured α-Al₂O₃/Ti(C,N) coated tool. The wear marks show signs of substantial mechanical and/or thermal loads in the notch region already after the first centimetres in cut. The initial notch wear occurred as a coating brittle fracture. Adhered stainless steel on the tools suggests that adhesion contributed to initial notch wear. The results of this work promote a better understanding and problem formulation of the fundamental mechanism of notch wear formation when using CVD-coated tools in stainless steel turning.