How the wear of WC and PCBN inserts affects the surface integrity of Inconel 718 in dry, flood and cryogenic finish turning

Aerospace components must adhere to extremely stringent reliability standards, necessitating the use of high-performance alloys such as Inconel 718. While valued for its superior mechanical properties across a wide temperature range, Inconel 718 is notoriously difficult to machine, often resulting in rapid tool wear and compromised surface integrity. Furthermore, Inconel 718 is usually machined using conventional flood lubrication, which poses sustainability challenges and high disposal costs. This study has the twofold objective of (i) evaluating the feasibility of dry and cryogenic finishing turning as eco-friendly alternatives to traditional flood lubrication, and (ii) assessing the performance of polycrystalline cubic boron nitride (PCBN) inserts compared to traditional coated tungsten carbide (WC) ones. Tool wear and surface roughness were continuously monitored until the inserts’ end-of-life, while surface integrity was evaluated at the end of the inserts’ life for each cutting condition investigated. Results indicate that the dominant wear mechanisms of WC inserts were abrasion and adhesion under all tested lubrication-cooling conditions, although cryogenic cooling slightly extended their life, yielding smoother, higher-quality surfaces with reduced severe deformation layer at the same time. Although PCBN inserts exhibited shorter tool life than WC inserts, they showed comparable lifetimes under dry and flood conditions, with cryogenic cooling yielding the highest surface quality and the thinnest SPD layer. While lubrication strategies and cutting speeds significantly influenced surface characteristics, all tested conditions met aerospace standards, confirming the industrial viability of sustainable machining strategies for Inconel 718.