Ion-plated PVD TiN, TiCN, and high-ionization sputtered PVD TiAlN coatings were deposited on WC–6wt%Co hardmetal inserts. Microstructural and mechanical properties of the coatings and substrate were characterized. Coated tools were evaluated in turning of Inconel 718, medium carbon SAE 1045 steel, and ductile iron at low and high cutting speeds. TiAlN coated tools showed the best metalcutting performance, followed by the TiCN and TiN coated tools. The superior performance of the TiAlN coated tools, which was even greater at higher speeds, is related to the coating's higher resistance to abrasive and crater wear. These characteristics are a result of the higher hot hardness and oxidation resistance of TiAlN at the temperatures normally encountered at the tool tip during machining operations.

Performance of PVD TiN, TiCN, and TiAlN coated cemented carbide tools in turning

Titanium nitride (TiN) deposited by chemical vapor deposition (CVD) techniques has been the premier wear-resistant coating in many applications for the last several decades. This review presents a history of developments in the technology of CVD TiN coatings. The CVD processes and equipment are discussed and the current knowledge on the thermodynamics and kinetics of the deposition process is presented. Various properties of CVD TiN coatings, such as hardness, adhesion, morphology and frictional properties, are discussed in the context of applications where wear resistance is required. Particular emphasis is given to applications in metal cutting where TiN has remained the mainstay of the various new and recent developments in coating design for cutting tools. Recent results of correlation between machining performance, deposition parameters, coating morphology and properties are presented. Throughout the paper, gaps in the existing understanding of the technology are pointed out. Finally, the paper presents a glimpse into the future of CVD TiN technology for wear-resistant applications.

Review of CVD TiN coatings for wear-resistant applications: deposition processes, properties and performance*

The metalcutting process, which includes turning, milling, drilling, and other methods for shaping metals, generates large mechanical forces and high temperatures at the point of contact between the cutting tool and workpiece material. The cutting tool is damaged substantially in these severe service conditions and has to be replaced when the tool cannot produce the desired product at the specified tolerances. To improve the lifetime for which it functions properly, the cutting tool has to be protected, often by coatings that are specifically designed to prevent certain damage modes that occur in particular applications. In fact, over 90% of all cemented carbide inserts are currently coated using chemical vapor deposition, CVD, physical vapor deposition, PVD, or their combination. This paper will present PVD coatings that are specially designed to protect the cutting tool and extend its functionality (lifetime). The paper is organized in two parts. First, it will briefly describe the metalcutting process, the resulting challenges to the cutting edge and the components of a functional tool. The second and the main part will present and discuss the key PVD architectures employed to protect the tool: monolithic, multilayer and nanostructured coatings. The paper will conclude with a summary and outlook on the development of new PVD coatings for cutting tools.

Architecture of PVD coatings for metalcutting applications: A review

Provided is a coated cutting tool (10) having a binder enriched substrate (18). The coating includes at least one chemical vapor deposited (CVP) layer (30) and at least one physical vapor deposited (PVD) layer (34). The PVD layer contains residual compressive stresses.

Binder enriched cvd and pvd coated cutting tool

A series of CVD TiC1 − xNx coatings has been deposited on cemented carbide. The choice of precursors (CH4 or CH3CN) and deposition temperature (850–1000 °C) influenced the microstructure, crystallinity, microhardness and chemical composition. Laser Raman spectroscopy was used to investigate the coatings, since it has been shown to be a very sensitive technique regarding composition differences. Even small changes in the C:N ratio resulted in systematical Raman shifts. This frequency shift was found to be particularly pronounced in the range of the acoustical phonons, wherein the peaks shifted about 30 cm− 1 to higher frequencies with increasing carbon content. In order to gain better understanding of the tribochemical reactions and high temperature oxidation, Raman spectroscopy was used to determine oxidation processes of TiC, TiN and TiC1 − xNx coatings. Depending on the annealing temperature different amounts of anatase and rutile could be found, and a correlation between carbon content and oxidation product was observed. The extent of oxidation at 500 °C could be explained by decreasing oxidation resistance with increasing carbon content. The opposite behavior was obtained at 700 °C due to differences in the oxide layer composition and the formation of a denser oxide layer. We proved that Raman spectroscopy is a very useful non-destructive tool for a qualitative characterization of CVD TiCN coatings. However, effects of laser power had to be taken into account carefully.

Raman spectroscopy as a tool to study cubic Ti–C–N CVD coatings

The role of hard coatings in prolonging the life of cemented carbide tools is now well‐documented for continuous turning applications. In contrast, relatively few studies have elucidated the effect of such coatings in milling, where both mechanical and thermal cyclic loading impose special requirements on the tool cutting edge. This investigation describes the wear mechanisms observed in coated carbide milling tools which have been the object of recent commercial tool development. Coated carbide tools (by CVD and PVD) of varying cutting edge geometry, substrate, and coating composition were subjected to fly‐cutter milling tests under a nominal range of cutting conditions. Examination of the used cutting edges under optical and electron microscopy showed both thermal‐fatigue‐induced vertical cracks, perpendicular to the cutting edge, as well as lateral cracks parallel to the edge which result from mechanical cyclic stresses. The wear patterns and the sequential progression of these cracks were characterize...

C. J. Petrosky

Papers

The role of hard coatings in carbide milling tools