In aerospace engineering, high temperature alloys such as titanium are the preferred choice. However, machining of such materials remains a major challenge due to high process forces and process temperatures. Currently, machining is performed almost entirely in the presence of oxygen. This results in a process-inherent oxidation of the metal surface, which leads to higher tool wear during machining. By means of an oxygen-free machining undesirable oxidation reactions will be avoided and thus results in an extension of tool life. In addition, oxygen-free machining in an extreme high vacuum (XHV) adequate environment can influence the resulting workpiece surface and subsurface properties due to change in process forces and chip formation. In the present work, the influence of machining under air and XHV-adequate atmosphere is examined with regard to chip formation, workpiece surface topography and residual stresses. Significant differences can be seen in resulting surface integrity depending on the machining atmosphere.

Titanium and titanium alloys have high strength at low density, good corrosion resistance and excellent biocompatibility. Therefore, the use of titanium materials is well established in high-performance applications such as aerospace and biomedical. However, titanium and titanium alloys such as Ti–6Al–4 V have low thermal conductivity, exhibit unfavorable chip formation with typical segmented chips and have high chemical affinity to surrounding elements such as oxygen. Tool wear and the properties of the component surface and sub-surface are significantly influenced by the presence of oxygen and resulting chemical interactions. Among other things, chemical reactions such as oxidation occur due to the high temperatures and presence of oxygen. In this work, the chip formation of Ti–6Al–4 V at different cutting speeds in discontinuous orthogonal cutting process under different atmospheres is investigated. A conventional air atmosphere, a pure argon atmosphere and a silane-doped atmosphere were used. The oxygen content of the silane-doped argon atmosphere corresponds to an extremely high vacuum (XHV), which is practically oxygen-free. It was found that chip formation is affected by the surrounding atmosphere. At the cutting speed vc = 80 m/min, non-periodic segmentation is present under oxygen-free atmosphere, while segmental chip formation occurs under air. This is accompanied by up to 16.5% lower feed force under inert gas atmosphere, which is due to reduced friction caused by the use of an oxygen-free atmosphere.