Tribological behavior of differently deposited Al-Si layer in the improvement of Inconel 718 machinability

Inconel 718 suffers from very poor machinability which limits its application and causes very high machining costs. Therefore, maximizing the tool performance is of prime importance for improving its machinability and reducing the high costs. Physical vapor deposition (PVD), of coatings on the tool material, is the common method, suggested by many studies, to improve the tool performance during cutting of difficult-to-cut materials. Previously, authors have introduced an easy and cost-effective process for depositing the target material on the tool as an alternative for PVD coatings. In the novel proposed process, referred to by the authors as the “pre-machining” method, the material is deposited on the tool surface during a few seconds of machining of the target workpiece. In the current study, the performance of the new proposed technique is compared with the conventional PVD method. The target material used for deposition is a very soft material (Al-Si) which itself has not been used before for coatings used for difficult-to-cut materials. Thus, for this study, a single layer of soft Al-Si material is deposited on the tool through two different techniques; a typical PVD technique under a high vacuum environment in a coater chamfer and the “pre-machining” technique. The comprehensive machinability analysis performed on the tools showed that application of Al-Si as the target materials through both techniques is very beneficial for the cutting tools used for cutting Inconel 718. Moreover, results showed that the performance of the new, easy to perform, and cost-effective deposition technique is very similar to the performance of conventional PVD coatings and even outperforms a PVD coating in some respects. The results showed that the tool life of the Al-Si-coated tool with 1- and 0.7-μm thicknesses and Al-Si pre-machined tool are significantly higher than that of the uncoated tool by 321%, 231%, and 205% respectively. They also outperform the conventional TiAlN hard coating used for machining of this class of material. The study also demonstrated that the cutting force decreased significantly by using Al-Si-coated and pre-machined tools. Furthermore, chipping, abrasion wear, adhesion, BUE formation, and machining-induced work hardening of the workpiece material reduced significantly by using the Al-Si pre-machined/coated tools. Investigation of the chips produced during the machining process and coefficient of friction measurements also confirmed the friction reduction and better flow of the material at the tool-chip interface as a result of Al-Si deposition with both techniques.