Ing. Martin Daněk, Ph.D.

Increasing requirements on high speed and dry cutting applications open up new demands on the quality of cutting tool materials. In this study, we evaluated the effect of Cr additions on the properties of Ti(Al)N/Cr(Al)N multilayered films deposited be magnetron sputtering. In particular, we studied the high temperature tribological properties and the cutting performance in real service drilling tests and compared the results with a monolayer Ti0.47Al0.46N reference film. Dry sliding experiments were performed using a pin-on-disc tribometer at room temperature and at 650 °C with Al2O3 balls as counterparts. The drilling performance of the coatings was evaluated at cutting speeds in the range 50–200 m/min. Wear of the drills in different zones (chisel edge and flank edge) was mapped after each 15 holes.

Ti1 - xAlxN coatings with NaCl-type structure have been widely used in advanced machining and other high temperature applications due to their excellent mechanical, thermal and tribological properties. Here, we investigated the influence of Cr additions on the structure, mechanical properties and oxidation resistance, including the oxide scale characterization, of multilayered TiAlN/CrAlN coatings deposited by magnetron sputtering. The properties of Cr rich coatings were compared to a TiAlN film deposited as reference. XRD diffraction analysis revealed that all coatings showed an fcc NaCl-type structure. However, for the TiAlN monolayer Ti and Al are forming a solid solution whilst, for Cr rich coatings, a multilayer structure alternating TiAlN and CrAlN layers, also forming solid solutions, was grown as a result of the geometry of the targets distribution inside the deposition chamber in combination with a slow rotation of the sample holder and a sufficiently high deposition rate. TGA measurements showed that Cr additions increased the oxidation performance of the coatings. For Ti0.47Al0.46N, dual oxide layers occur when tested at 800 degrees C, being the porous inner one of TiO2 and the outer a compact and continuous layer of Al-oxide which protects the coating from the oxidation. At 900 degrees C the oxidation resistance of this film degraded due to the fast Ti ions diffusion to the surface which impedes the formation of the continuous and protective Al oxide layer.

The effects of Ni-Ti(-Cu) interlayers on the mechanical and tribological behaviour of W-S-C/Ni-Ti(-Cu) and W:DLC/Ni-Ti(-Cu) bilayer coatings have been investigated. The mechanical properties of the bilayers, measured at different depths by nanoindentation, exhibited a clear dependence on the combination between different Ni-Ti(-Cu) interlayers and top layers. The tribological performance of the bilayers was evaluated by pin-on-disk under different load conditions. The use of Ni-Ti(-Cu) interlayers improved the adhesion of the top layers and the resistance against surface damage such as delamination and cracking. Transmission electron microscopy analyses performed in the wear tracks of W-S-C/Ni-Ti and W:DLC/Ni-Ti bilayers tested with high load revealed that the formation of stabilised martensite was limited when a much harder top functional layer was employed.

Improvement of the durability and cutting performance of coatings designed for tools is an ongoing engineering challenge. There are two main paths to achieve such ambitious goal: to enhance oxidation resistance and/or to decrease friction. In this investigation we is focused on laboratory and industrial performance of TiAlN coating with higher oxidation resistance due to various content of chromium. The objective of the work is to increase the cutting speed of drillers. TiAlCrN coatings with different content of chromium were deposited by unbalanced pulsed magnetron sputtering CemeCon 880 MLT industrial apparatus. TiAlN coatings were deposited as reference. The coatings were deposited on WCCo standard drills and cutting inserts to test their performance either in laboratory by drilling high-speed steel and Inconel as in real production by industrial partner. To measure oxidation resistance, oxidation speed was measured by thermogravimetric analysis (TGA); in this case fecralloy substrates were used. Tribological measurements were performed on CSM tribometer at temperatures up to 800 degrees C. The worn surfaces, both from tribometer and real tools, were investigated by scanning electron microscopy equipped with Energy-dispersive X-ray spectroscopy (EDX) and by Raman spectroscopy. The wear was measured by 3D white light optical profilometry. Oxidation tests and tribological properties obtained in laboratory were compared with the behavior of the coatings deposited on tools.

In this work, self-lubricant W-S-C films were alloyed with Cr by co-sputtering chromium and composite WS2-C targets. Besides the usual physical, chemical and mechanical characterization, including the evaluation of the chemical composition, the structure, the morphology, the hardness and the cohesion/adhesion, special attention was paid to the friction and wear analyses of the film deposited on intentionally roughened surfaces. The substrates were steel polished disks with different types of patterns produced by micromachining. To analyze the sliding process, in-situ techniques were applied, such as optical microscopy and Raman spectroscopy monitoring of the wear track. The surfaces in the contact were then analyzed by scanning electron microscopy (SEM) and 3D profilometry. The results showed that W-S-C-Cr coating exhibited remarkable ability to reduce the detrimental effect of deep grooves with irregular shape. For specific patterns on the substrate the friction and wear was even slightly lower compared to a polished sample. The grooves were filled with self-lubricant material and acted as reservoirs supporting formation of a low-friction tribolayer.