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Effect of adhesion and tribological properties of modified composite nanostructured multi-layer nitride coatings on WC-Co tools life http://researchonline.ljmu.ac.uk/id/eprint/9965/ Article LJMU has developed LJMU Research Online for users to access the research output of the University more effectively. Citation (please note it is advisable to refer to the publisher's version if you intend to cite from this work) Vereschaka, A, Aksenenko, A, Sitnikov, N, Migranov, M, Shevchenko, S, Sotova, C, Batako, ADL and Andreev, N (2018) Effect of adhesion and tribological properties of modified composite nano-structured multi-layer nitride coatings on WC-Co tools life. Tribology International, 128. pp. 313-Abstract:The paper presents the results of the comparative tests of carbide samples with multilayered nano-structured coatings based on titanium nitrides (Ti-TiN-(Ti,Cr,Al,Si)N) and zirconium nitrides (Zr-ZrN-(Nb,Zr,Cr,Al)N and Zr-ZrN-(Zr,Al,Si)N). The phase composition and microstructure of these coatings were studied. The scratch test method was applied to study the adhesion bond strength to the substrate and the coating fracture patterns. The tribological parameters of the coated samples were studied at temperatures of 450°C-900 °C. The cutting properties of the tools with the coatings under study were investigated in turning AISI 321 steel. Various coating parameter effects on the cutting tool life were studied.

The structures of surface layers of the tool material, adapted to the conditions of the thermomechanical loading during the cutting process, can be formed with the use of different processing methods, the most effective of which is to deposit functional coatings on working surfaces of the cutting tool. During the studies, two nanostructured multilayer composite coatings (NMCCs) were considered: Ti-TiN-(TiCrAl)N and Zr-ZrN-(ZrNbCrAl)N. Metallographic studies were conducted, and the phase compositions of the coatings were determined by X-ray crystal analysis. The efficiency of tools made of carbide T14K8 with developed coatings was determined by comparative evaluation of tool life of a tool without coating, a tool with standard coating (TiN), and a tool with elaborated coatings (Ti-TiN-(TiCrAl)N and Zr-ZrN-(ZrNbCrAl)N) in turning structural steel 45. These tests allow noting the increase in tool life of a tool with elaborated NMCCs by up to 4 times as compared with tool life of an uncoated tool and by up to 2 times as compared with tool life of standard coating TiN. Meanwhile, NMCC of Ti-TiN-(TiCrAl) showed lifetime about 10% longer than NMCC of Zr-ZrN-(ZrNbCrAl)N). The longer lifetime of NMCC of Ti-TiN-(TiCrAl) conforms to its better adhesion characteristics and thinner nanosublayers of its wear-resistant layer.

The study considers the challenge of improving the efficiency of dry finishing and semi-finishing turning of (P10-P20) steel with carbide tools with complex composition coatings by directed selection of the composition and properties of the coatings through the control of the parameters of the filtered cathodic vacuum-arc deposition (FCVAD). The conducted tests have confirmed the feasibility and effectiveness of the control of compositions, structures, and properties of complex composite coatings of Ti-TiN-TiAlN type by varying the parameters of the FCVAD process. In particular, it has been found out that the ratio of Ti/Al, which greatly affects the important properties of the coating (grain size, lattice parameter, microhardness, fracture toughness, etc.), can be changed at constant compositions of cathodes by varying such parameters of coating synthesis as titanium cathode arc current, nitrogen pressure, and substrate shear stress. It has been shown that Ti-TiN-TiAlN coating produced at different values of the parameters of synthesis significantly changes the cutting properties of carbide tool and thus allows optimizing the coating composition for a variety of machining conditions.The developed methods are also applicable for multi-component complex composite coatings.

Within the last few years topological insulators (TIs) have attracted a lot of interest due to their unique electronic structure with spin-polarized topological surface states (TSSs), which may pave the way for these materials to have a great potential in multiple applications. However, to enable consideration of TIs as building blocks for novel devices, stability of TSSs towards oxidation should be tested. Among the family of TIs with tetradymite structure, Sb 2 Te 3 is of p-type and appears to be the least explored material since its TSS is unoccupied in the ground state, a property that allows the use of optical excitations to generate spin currents relevant for spintronics. Here, we report relatively fast surface oxidation of Sb 2 Te 3 under ambient conditions. We show that the clean surface reacts rapidly with molecular oxygen and slowly with water, and that humidity plays an important role at the stage of the oxide-layer growth. In humid air, we show that Sb 2 Te 3 oxidizes in a time scale of minutes to hours, and much faster than other tetradymite TIs. The high surface reactivity revealed by our experiments is of critical importance and must be taken into account for the production and exploitation of novel TI-based devices using Sb 2 Te 3 as working material. Our results provide a fundamental and comprehensive understanding of the universal trend underlying the chemical reactivity of TIs.2