Tribological phenomena and tool wear mechanisms during machining of hard-to-cut TiAl6V4 aerospace alloy have been investigated in detail. Since cutting tool wear is directly affected by tribological phenomena occurring between the surfaces of the workpiece and the cutting tool, the performance of the cutting tool is strongly associated with the conditions of the machining process. The present work shows the effect of different machining conditions on the tribological and wear performance of TiB 2 -coated cutting tools compared to uncoated carbide tools. FEM modeling of the temperature profile on the friction surface was performed for wet machining conditions under varying cutting parameters. Comprehensive characterization of the TiB 2 coated vs. uncoated cutting tool wear performance was made using optical 3D imaging, SEM/EDX and XPS methods respectively. The results obtained were linked to the FEM modeling. The studies carried out show that during machining of the TiAl6V4 alloy, the efficiency of the TiB 2 coating application for carbide cutting tools strongly depends on cutting conditions. The TiB 2 coating is very efficient under roughing at low speeds (with strong buildup edge formation). In contrast, it shows similar wear performance to the uncoated tool under finishing operations at higher cutting speeds when cratering wear predominates.

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In the aluminum die casting process, erosion, corrosion, soldering, and die sticking have a significant influence on tool life and product quality. A number of coatings such as TiN, CrN, and (Cr,Al)N deposited by physical vapor deposition (PVD) have been employed to act as protective coatings due to their high hardness and chemical stability. In this study, the wear performance of two nanocomposite AlTiN and AlCrN coatings with different structures were evaluated. These coatings were deposited on aluminum die casting mold tool substrates (AISI H13 hot work steel) by PVD using pulsed cathodic arc evaporation, equipped with three lateral arc-rotating cathodes (LARC) and one central rotating cathode (CERC). The research was performed in two stages: in the first stage, the outlined coatings were characterized regarding their chemical composition, morphology, and structure using glow discharge optical emission spectroscopy (GDOES), scanning electron microscopy (SEM), and X-ray diffraction (XRD), respectively. Surface morphology and mechanical properties were evaluated by atomic force microscopy (AFM) and nanoindentation. The coating adhesion was studied using Mersedes test and scratch testing. During the second stage, industrial tests were carried out for coated die casting molds. In parallel, tribological tests were also performed in order to determine if a correlation between laboratory and industrial tests can be drawn. All of the results were compared with a benchmark monolayer AlCrN coating. The data obtained show that the best performance was achieved for the AlCrN/Si3N4 nanocomposite coating that displays an optimum combination of hardness, adhesion, soldering behavior, oxidation resistance, and stress state. These characteristics are essential for improving the die mold service life. Therefore, this coating emerges as a novelty to be used to protect aluminum die casting molds.

This paper presents experimental investigations of various interrelated multi-scale cyclic and temporal processes that occur on the frictional surface under severe tribological conditions during cutting with buildup edge formation. The results of the finite element modeling of the stress/temperature profiles on the friction surface are laid out. This study was performed on a multilayer coating with the top alumina ceramic layer deposited by CVD (chemical vapor deposition) on a WC/Co carbide substrate. A detailed analysis of the wear process was conducted by 3D wear evaluation, scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDS) and electron backscattered diffraction (EBSD), as well as X-ray photoelectron spectroscopy (XPS) methods. The following cyclic phenomena were observed on the surface of the tribo-system during the experiments: a repetitive formation and breakage of buildups (a self-organized critical process) and a periodical increase and decrease in the amount of thermal barrier tribo-films with a sapphire structure (which is a self-organization process). These two processes are interrelated with the accompanying progression of cratering, eventually resulting in the catastrophic failure of the entire tribo-system.

Optimization of the composition of a new generation of bi-nano-multilayered TiAlCrSiN/TiAlCrN-based coatings is outlined in this study for the machining of direct aged (DA) Inconel 718 alloy. Three types of TiAlCrSiN/TiAlCrN-based bi-nano-multi-layer coatings with varying chemical compositions were investigated: (1) a previous state-of-the-art Ti0.2Al0.55Cr0.2Si0.03Y0.02N/Ti0.25Al0.65Cr0.1N (coating A); (2) Ti0.2Al0.52Cr0.2Si0.08N/Ti0.25Al0.65Cr0.1N with increased amount of Si (up to 8 at.%; coating B); (3) a new Ti0.18Al0.55Cr0.17Si0.05Y0.05N/Ti0.25Al0.65Cr0.1N coating (coating C) with an increased amount of both Si and Y (up to 5 at.% each). The structure of each coating was evaluated by XRD analysis. Micro-mechanical characteristics were investigated using a MicroMaterials NanoTest system and an Anton Paar-RST3 tester. The wear performance of nano-multilayered TiAlCrSiN/TiAlCrN-based coatings was evaluated during the finish turning of direct aged (DA) Inconel 718 alloy. The wear patterns were assessed using optical microscopy imaging. The tribological performance was evaluated through (a) a detailed chip characteristic study and (b) XPS studies of the worn surface of the coated cutting tool. The difference in tribological performance was found to correspond with the type and amount of tribo-films formed on the friction surface under operation. Simultaneous formation of various thermal barrier tribo-films, such as sapphire, mullite, and garnet, was observed. The overall amount of beneficial tribo-films was found to be greater in the new Ti0.18Al0.55Cr0.17Si 0.05Y0.05N/Ti0.25Al0.65Cr0.1N nano-bi-multilayer coating (coating C) than in the previous state-of-the-art coatings (A and B). This resulted in over two-fold improvement of this coating’s tool life compared with those of the commercial benchmark AlTiN coating and coating B, as well as a 40% improvement of the tool life of the previous state-of-the-art coating A. Multi-scale self-organization processes were observed: nano-scale tribo-film formation on the cutting tool surface combined with micro-scale generation of strain-induced martensite zones as a result of intensive metal flow during chip formation. Both of these processes are strongly enhanced in the newly developed coating C.