Wear Mechanisms in Cutting Tools for Machining Applications: Interfacial Phenomena, Characterization, and Relation to Performance

Metal cutting technology plays an important role in the automotive and aeronautic sectors, both of which
are important for the Swedish economy. Both make use of traditional grey cast iron and difficult-to-
machine materials like titanium alloys and compacted graphite iron. The tools used to machine these
materials wear at varying rates depending on factors such as contact temperature, pressure, and the
relative motion of the workpiece material and the tool surface. Given that the machining process and the
production of tool and workpiece materials are energy intensive and generate waste, it is important to
improve the process sustainability. This can be achieved by improving machining conditions and tooling
solutions, and by developing more wear-resistant tooling. Doing so requires knowledge of the wear
mechanisms that contribute to tool degradation.
The aim of this work is to expand knowledge of wear mechanisms in commercial tooling during
machining, to explore the phenomena occurring at the tool-chip/workpiece interface, and to explore the
driving forces that govern their intensity and relation to performance. Tools worn in turning and milling
applications and the related interfacial phenomena were explored after controlled variations in the cutting
environment. The methods used included freezing the cutting action, imitational experiments, and to a
lesser extent simulations or models of the wear processes. Samples generated by these experimental
methods were studied using scanning electron microscopy, X-ray energy-dispersive spectroscopy,
electron backscatter diffraction, ion channeling contrast, transmission electron microscopy, and X-ray
diffraction.
The major tool wear mechanisms include diffusional dissolution and formation of reaction products that
are either easily removed with the chip flow or that work as diffusion barriers. Additional chemical wear
through oxidation may occur in milling operations. Tool coatings are subject to mechanical wear and also
to some degree to diffusional dissolution. The combination of several titanium alloys including
commercially pure titanium, near-α Ti-6Al-2Sn-4Zr-2Mo, α+β Ti-6Al-4V, α+β Ti-6Al-2Sn-4Zr-6Mo, and
near-β Ti-5Al-5V-5Mo-3Cr, compacted graphite iron, and grey cast iron with tooling including
polycrystalline diamond, polycrystalline cubic boron nitride, uncoated cemented carbide grades and
coated versions including physical vapor deposition applied Ti 0.45Al 0.55N with or without NbN overlayer
and chemical vapor deposition applied Ti(C,N)-Al 2O3 makes for many variants of reaction products,
intensity of wear mechanisms, performance, and ways to decrease the wear rate.