Damage of PVD-Coated Cutting Tools Due to Interrupted Cutting of Ni-Based Superalloys

Abstract

Ni-based superalloys are typically difficult-to-cut materials. During machining, the cutting forces and temperatures of these superalloys are generally higher than those of other materials. Therefore, the tool life of the coated carbide cutting tools used for superalloy machining is shortened. This study evaluates the damage of the coated end mills during interrupted cutting of alloy 718 and finds the coating properties necessary for improved cutting of Ni-based superalloys. Damage of the PVD-TiN-coated cutting tools was observed by scanning electron microscopy and transmission electron microscopy of the surfaces and cross sections. In addition, friction forces were measured during turning for some coatings, and hardness of the coatings was measured after annealing. Plastic deformation of the coating and crack formation was shown to occur at the coating cross section. In addition, we determined that the major factor for the damage was high friction force between the coating surface and work material at high temperatures. In summary, coatings with stability at high temperatures and low friction forces during machining can reduce the damage of coated cutting tools, thus increasing the tool life.

Damage of physical vapor deposition coatings of cutting tools during alloy 718 turning

“…The crack was confirmed to produce a relatively large fracture. The cracks were caused by principal shear stresses from Hertzian contact stress between the cutting tool and workpiece [17,22,23]. From the above observation result, the damage to the coating is considered to be caused by plastic deformation, microfracturing, and crack formation in the middle of the coating .The observed damage phenomena is almost similar to the surface fatigue based on the delimitation theory proposed by N.P.Suh [24].…”

“…On the other hand, the AlCrSiN-SP coating retained its hardness after the 1000 °C heat treatment. The average cutting temperature measured by the tool-work thermocouple method was approximately 680 °C at 30 m/min cutting speed [17]. In practice, the local areas of the A c c e p t e d M a n u s c r i p t coating surface are exposed to temperatures as high as 1.2-1.4 times that of measured cutting temperatures [19].…”

A review on cutting tool technology in machining of Ni-based superalloys

“…Compared with the multilayer nanocomposite hard coating carbide cutting tool at cutting speed 30 m/min in milling of superalloys, the proposed treatment prolonged the tool life which was obtained by uncoated, TiN-, NC-, and TiAlN-coated ones, by 54%, 110%, 29%, and 30%, respectively. In addition, a thinner PVD TiN coating generated less damage morphology compared with a thicker one in interrupted machining of superalloys [45].…”

“…In interrupted machining, crack formation and plastic deformation at the coating were found on a PVD TiN-coated tool [45]. In addition, in a milling operation, a BUE was found at both tools by using a TiAlN tool and a CrN-coated carbide tool [46].…”