An investigation of the effect of a new tool treatment technique on the machinability of Inconel 718 during the turning process

Though Inconel 718 alloy possesses excellent material properties and has various key applications in different industries, it still suffers from severe machinability issues and is considered one of the most difficult-to-cut materials. In this paper, a new and simple method is proposed to improve the machinability of Inconel 718 by forming different ductile and lubricious layers at the tool tip prior to its application for machining. Previous research showed that this method is very successful at improving the tool performance. In the current study, an enhancement of the proposed method is presented. Prior to the actual machining of Inconel, very short cuts of around two seconds were performed on an Al-Si and/or cast iron workpiece to form very thin layers of these materials on the tool rake face. During the subsequent machining of Inconel, the built-up material on the tool face has melted and the excess material was pushed out of the contact zone, with just a thin film remaining on the tool. This thin film protected the tool from chipping and considerably improved the tool life and the integrity of the machined surface. Results indicate that the tool treated with both cast iron and aluminum possessed a maximum tool life increase of 204%, a 45% lesser cutting force, and a 59% reduction in machining-induced work-hardening compared to the uncoated tool. All of the treatments displayed significantly reduced chipping. The following mechanisms contributed to these improvements: filling of the tool microcracks and prevention of their propagation, friction reduction enabling greater control over adhesion, seizure and built-up edge formation, improvement of the running-in stage of tool wear by preconditioning the tool surface prior to its main application, formation of various lubricious and thermal barrier tribofilms on the tool tip, control of different tool wear mechanisms such as adhesion, abrasion, and oxidation. All these mechanisms are discussed in details using various characterization techniques.