Coated cemented carbide tool life extension accompanied by comb cracks: The milling case of 316L stainless steel

Abstract Two typical commercial coatings were deposited on a cemented carbide substrate, including CVD multilayered TiN/MT-TiC 0.7 N 0.3 /TiCNO/α-Al 2 O 3 (cm-Al 2 O 3 based) and PVD nano-multilayered Al 0.55 Ti 0.45 N/TiN (pn-AlTiN based). Performance and mechanisms for tool failure and tool life extension were investigated for the face milling of 316L stainless steel under a tough milling condition. The results show that the pn-AlTiN based coating exhibits a strong ability against delamination, abrasion wear and comb crack widening. As a result, its tool life is 2.1 times as long as the one with the cm-Al 2 O 3 based coating. Edge chipping resulted from comb crack evolution is still the dominated fatigue failure mechanism for both the coatings. Internal formation of longitudinal submicron to nano-scaled cracks, accompanied by clear lattice fringes with a coherent relation between AlTiN and TiN was observed in a FIB-cut specimen with a size of 6.5 × 6.5 µm with a transmission electron microscope. For the pn-AlTiN based coating, the strong ability against comb crack widening stems from its strong self-adaptive ability to plastic deformation through the internal formation of submicron to nano-scaled cracks and the associated strong stress dissipation ability. A design concept for improving the milling tool life is discussed.