Increasing tool life is a significant objective in production. Achieving this objective in a machining process poses a significant challenge, especially during cutting hard-to-cut materials such as superalloys, due to the severe tool chipping/failure at the beginning of the cut. Although numerous attempts have been carried out to improve tool performance and prolong tool life during the machining of difficult-to-cut materials over the past several years, researchers have not obtained sufficient control over sudden tool failure/chipping. The focus of this study is to prolong tool life and control tool chipping by developing an ultra-soft deposited layer on the cutting tool that can protect it during the machining of difficult-to-cut materials such as Inconel 718. In the current study, an ultra-soft layer of material is deposited on the tool through two different techniques; a typical physical vapor deposition (PVD) technique and a novel developed method called “pre-machining”. In the PVD method, the soft layer is deposited under a high vacuum environment using a PVD coater. In the novel pre-machining method, the soft layer is deposited through a very short machining process involving Al-Si. It should be mentioned that soft coatings have never been used before for machining applications of difficult-to-cut materials including Inconel 718. This study shows that in contrast to what is expected, depositing an ultra-soft layer on the cutting tool significantly improves tool performance, by reducing chipping, and improving the machined surface integrity during cutting of Inconel 718. The obtained results show up to a 500% ± 10% improvement in tool life and around a 150% ± 10% reduction in cutting forces. Significant reductions in work hardening, residual stress, and surface roughness on the machined surface were other main achievements of the current study. / Thesis / Doctor of Philosophy (PhD) / Inconel 718 is considered to be a difficult-to-cut material due to its poor machinability. Significant tool failure at the early stage of cutting is the main challenge of machining this material and is the most significant contributing factor to its high manufacturing costs. Studies show that the common methods used to tackle this issue have not been completely successful. The goal of the present study is to tackle the machining challenges of Inconel 718 by developing tool coatings that meet the specific needs of the material to eliminate tool failure and thereby improve overall machining performance. For this purpose, a new tool coating material and a novel deposition technique that can be used as an alternative for commonly used coatings were developed in this study to improve the tool performance during the machining of Inconel 718. In addition, thorough studies have been carried out to gain a better understanding of the dominant wear phenomena and tool surface treatments that result in an improvement in the machinability of Inconel 718.

Inconel 718 has widespread use in critical industries like aerospace, marine, and power generation. However, its challenging machinability, characterized by tool chipping/failure, and poor surface quality, remains a significant concern. Despite numerous efforts to enhance tool performance in machining hard-to-machine materials, the issue of sudden tool failure and chipping persists. This study presents an innovative in-situ tool treatment method, complemented by an optimized recoating strategy, aimed at tackling these challenges. The approach involves the application of a lubricating soft metallic Al-Si alloy coating to the tool’s faces, which can be recoated when needed. During subsequent Inconel machining, the Al-Si layer deposited on the tool melts due to high temperatures. The molten material fills microcracks on the tool surface, preventing their propagation. Moreover, the tool can slide on the beneficial tribo-films Al-Si layer which reduces friction, sticking, seizure, and built-up edge formation, resulting in decreased tool wear and chipping. The newly developed pre-machined recoating method has yielded promising outcomes, reducing cutting force and significantly improving tool lifespan compared to the PVD benchmark and uncoated tools. Additionally, this novel method enhances surface quality and minimizes undesirable microstructural alterations induced by machining. / Thesis / Master of Applied Science (MASc) / Chipping and excessive tool wear pose significant challenges in machining high-strength alloys like Inconel 718, limiting their applicability across various industries. According to research, conventional strategies used to deal with the machining challenges posed by Inconel 718 have not produced the best results. The goal of this research is to overcome the machining issues associated with such a difficult-to-cut material innovatively by depositing soft metallic coatings as a solid lubricant to enhance the machining performance. In this study, a cost-effective novel in-situ deposition technique with recoating capability as an alternative to conventional coatings is presented to achieve this goal. This innovative approach aims to improve tool performance during Inconel 718 machining significantly. This study also provides a thorough insight into the application of solid lubricants in machining, discussing their mechanisms, effectiveness, constraints, and potential to boost productivity and environmental sustainability. Furthermore, comprehensive investigations have been conducted to gain deeper insights into the prevalent wear mechanisms and surface treatments that can lead to improved machining performance for Inconel 718.