Delamination and longitudinal cracking in multi-layered composite nanostructured coatings and their influence on cutting tool life

This paper presents the results of a study of the mechanisms of delamination and the formation of longitudinal cracks in the structure of multi-layered nano-structured coatings to predict the mechanisms for further improvement of tool life and the reliability of metal-cutting tools. Various mechanisms of formation of longitudinal cracks and delaminations in coatings on rake and flank tool surfaces, which vary based on the compositions and architectures of the coatings, are addressed. In addition, the influence of internal defects, including embedded microdrops and pores, on the formation of cracks and delaminations and the failure of coatings is discussed. The importance of ensuring a balance of the basic properties of coatings to achieve high wear resistance and maximum tool life of coated metal cutting tools is shown. The properties of coatings and the natures of their failures, as investigated during scratch testing and dry turning of steel C45, are provided

Comparative analysis of cutting properties and nature of wear of carbide cutting tools with multi-layered nano-structured and gradient coatings produced by using of various deposition methods

The aim of this work was to investigate mechanical and cutting properties, as well as the nature of wear and failure of carbide cutting tools with modifying coatings of two types: nano-structured multi-layered coating Zr-ZrN-(ZrCrAl)N, applied through the use of the technology of filtered cathodic vacuum arc deposition, and multi-layered nano-structured and gradient coating Ti-(TiAl)N-(TiAl)N, applied through the use of the technology of LARC® (lateral rotating cathodes). It is found out that the both types of coatings under test significantly improve tool life of a carbide cutting tool. The studies of mechanisms of wear and failure of carbide tools with coatings under test, conducted at macro and micro levels, have identified their major differences and revealed their most preferable field of application. The carbide tools, equipped with cutting inserts with the nano-structured multi-layered coating under study, provided a significant increase in cutting properties (tool life) of the tool in comparison with the uncoated carbide tool and in comparison with the reference carbide tool with TiN coating. The tool with the coating Ti-(TiAl)N-(TiAl)N under study demonstrated the increased wear resistance during 30–35 min of cutting, and then, the process of coating failure and tool wear was sharply intensified. For the tool with coating Zr-ZrN-(ZrCrAl)N, the tests revealed more evenly balanced wear during the whole operating time between failures. It should be noted that NMCC Zr-ZrN-(ZrCrAl)N are substantially thinner, and that fact predetermines their better resistance to failure because of crack formation, and the technology of its generation is more cost-effective. © 2016 Springer-Verlag Londo

Nano-scale multi-layered coatings for improved efficiency of ceramic cutting tools

This paper considers improving the efficiency of ceramic cutting tools using nano-scale multi-layered composite coatings deposited with an innovative arc-PVD processes with filtration of vapour-ion flow and diamond-like coating (DLC). Here a three-layered architecture of nano-structured multi-layered composite coatings is used, and the wear mechanism of the ceramic tool is examined. This approach allows implementing a direct control over the contact characteristics of the cutting process in order to reduce the normal and shear stresses that increase the probability of tool failure as a result of brittle fracture. This increases the adhesive strength of the coating with respect to the ceramic substrate. This resulted in an increase in tool life with reduced failure rate because of brittle fracture of the cutting edge. © 2016 Springer-Verlag Londo

Working efficiency of cutting tools with multilayer nano-structured Ti-TiCN-(Ti,Al)CN and Ti-TiCN-(Ti,Al,Cr)CN coatings: Analysis of cutting properties, wear mechanism and diffusion processes

The study investigated the performance properties of a carbide tool with multilayer composite nano-structured Ti-TiCN-TiAlCN and Ti-TiCN-TiAlCrCN coatings, obtained by filtered cathodic vacuum-arc deposition (FCVAD). The study considered the structure of these coatings and their basic mechanical properties (hardness, strength of adhesion bond to substrate, and elemental composition). The study included cutting tests of carbide tools with those coatings in comparison with uncoated tools and tools with Ti-TiN coating. The tests were carried out during the turning of steel C45 at various cutting speeds (300, 350, and 400 m/min). The study included research of the kinematics of tool wear and the nature of cracking in the structure of coatings. Diffusion processes in the system of substrate-coating tool material during machining were also studied

Development of wear-resistant coatings compounds for high-speed steel tool using a combined cathodic vacuum arc deposition

This article presents the work on wear-resistance coatings (WRC), formed on the working surfaces of HSS tools, in order to increase their efficiency. The wear-resistant complex includes nitride layer, which increases the plastic strength of the HSS tool cutting wedge and cutting tool wear resistance, as well as a three-layer nano-structured composite coating that increases tool life. The equipment for the processes of ion nitriding in the gas plasma and the formation of nano-structured multi-layer composite coatings in the filtered metal-gas plasma cathode vacuum arc discharge has been developed. Particular attention was paid to the regularities in the formation of the nitride layer and optimization of its parameters and structure, together with the study of the properties and structure of functional coating layers, depending on the parameters of the deposition process. The parameters of the combined cathodic vacuum arc processing (CCVAP), provides minimum intensity of tool wear during the cutting tests. Sample of coated tools were used to conduct a certification of the developed WRC. This allowed determining the optimal parameters WRC that provided the maximum increase in tool life for a variety of cutting conditions. The outcomes are compared with uncoated HSS tool and standard commercial coatings

New Synthetic Thrombin Inhibitors: Molecular Design and Experimental Verification

BACKGROUND: The development of new anticoagulants is an important goal for the improvement of thromboses treatments. OBJECTIVES: The design, synthesis and experimental testing of new safe and effective small molecule direct thrombin inhibitors for intravenous administration. METHODS: Computer-aided molecular design of new thrombin inhibitors was performed using our original docking program SOL, which is based on the genetic algorithm of global energy minimization in the framework of a Merck Molecular Force Field. This program takes into account the effects of solvent. The designed molecules with the best scoring functions (calculated binding energies) were synthesized and their thrombin inhibitory activity evaluated experimentally in vitro using a chromogenic substrate in a buffer system and using a thrombin generation test in isolated plasma and in vivo using the newly developed model of hemodilution-induced hypercoagulation in rats. The acute toxicities of the most promising new thrombin inhibitors were evaluated in mice, and their stabilities in aqueous solutions were measured. RESULTS: New compounds that are both effective direct thrombin inhibitors (the best K(I) was <1 nM) and strong anticoagulants in plasma (an IC(50) in the thrombin generation assay of approximately 100 nM) were discovered. These compounds contain one of the following new residues as the basic fragment: isothiuronium, 4-aminopyridinium, or 2-aminothiazolinium. LD(50) values for the best new inhibitors ranged from 166.7 to >1111.1 mg/kg. A plasma-substituting solution supplemented with one of the new inhibitors prevented hypercoagulation in the rat model of hemodilution-induced hypercoagulation. Activities of the best new inhibitors in physiological saline (1 µM solutions) were stable after sterilization by autoclaving, and the inhibitors remained stable at long-term storage over more than 1.5 years at room temperature and at 4°C. CONCLUSIONS: The high efficacy, stability and low acute toxicity reveal that the inhibitors that were developed may be promising for potential medical applications

First measurement of the |t|-dependence of coherent J/ψ photonuclear production

The first measurement of the cross section for coherent J/ψ photoproduction as a function of |t|, the square of the momentum transferred between the incoming and outgoing target nucleus, is presented. The data were measured with the ALICE detector in ultra-peripheral Pb–Pb collisions at a centre-of-mass energy per nucleon pair sNN=5.02TeV with the J/ψ produced in the central rapidity region |y|<0.8, which corresponds to the small Bjorken-x range (0.3−1.4)×10−3. The measured |t|-dependence is not described by computations based only on the Pb nuclear form factor, while the photonuclear cross section is better reproduced by models including shadowing according to the leading-twist approximation, or gluon-saturation effects from the impact-parameter dependent Balitsky–Kovchegov equation. These new results are therefore a valid tool to constrain the relevant model parameters and to investigate the transverse gluonic structure at very low Bjorken-x.publishedVersio