Nikolay Sitnikov

Melt-spun thin ribbons of shape memory TiNiCu alloy for micromechanical applications

The development of micromechanical devices (MEMS and NEMS) on the basis of nanostructured shape memory alloys is reported. A Ti50Ni25Cu25 (at. %) alloy fabricated by the melt spinning technique in the form of a ribbon with a thickness around 40 μm and a width about 1.5 mm was chosen as a starting material. Technological parameters were optimized to produce the alloy in an amorphous state. The thickness of the ribbon was reduced to 5–14 μm by means of electrochemical polishing. A nanostructural state of the thin ribbons was obtained via the dynamic crystallization of the amorphous alloy by application of a single electric pulse with duration in the range of 300–900 μs. A microtweezers prototype with a composite cantilever of 0.8 μm thick and 8 μm long was developed and produced on the basis of the obtained nanostructured thin ribbons by means of the focused ion beam technique. Controlled deformation of the micromanipulator was achieved by heating using semiconductor laser radiation in a vacuum chamber of scanning ion-probe microscope.

Study of Properties of Nanostructured Multilayer Composite Coatings of Ti-TiN-(TiCrAl)N and Zr-ZrN-(ZrNbCrAl)N

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.

Study of Two-Way Shape Memory Behavior of Amorphous-Crystalline TiNiCu Melt-Spun Ribbons

Recently we reported on the development of a composite material exhibiting reversible shape memory effect. A Ti–25Ni–25Cu (at.%) alloy was obtained by the melt spinning technique as amorphous–crystalline ribbons with a thickness of approximately 40 μm. The thickness of the amorphous and crystalline layers (dа and dc, respectively) was varied by electrochemical polishing. It has been ascertained that with varying the relationship dc/dа the martensite transformation and shape-recovery temperatures do not actually change, while the minimum radius of the ribbon bending decreases from 8.0 mm to 2.4 mm with increasing the relationship dc/dа from 0.33 to 1.40. The maximum reversible strain comprises 0.4% at dc/dа = 0.82. On the basis of experimental data obtained the phenomenological description, providing an explanation for nature of the phenomena taking place in the rapidly quenched amorphous-crystalline ribbon composite, has been proposed.

Control of Structure and Properties of Nanostructured Multilayer Composite Coatings Applied to Cutting Tools as a Way to Improve Efficiency of Technological Cutting Operations

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.

Improvement of structure and quality of nanoscale multilayered composite coatings, deposited by filtered cathodic vacuum arc deposition method

This article studies the specific features of cathode vacuum arc deposition of coatings used in the production of cutting tools. The detailed analysis of the major drawbacks of arc-Physical Vapour Deposition (PVD) methods has contributed to the development of the processes of filtered cathodic vacuum arc deposition to form nanoscale multilayered composite coatings of increased efficiency. This is achieved through the formation of nanostructure, increase in strength of adhesion of coating to substrate up to 20%, and reduction of such dangerous coating surface defects as macro- and microdroplets up to 80%. This article presents the results of the studies of various properties of developed nanoscale multilayered composite coating. The certification tests of carbide tool equipped with cutting inserts with developed nanoscale multilayered composite coating compositions in longitudinal turning (continuous cutting) and end symmetric milling, and intermittent cutting of steel C45 and hard-to-cut nickel alloy of NiCr20TiAl showed advantages of tool with nanoscale multilayered composite coating as compared to the tool without coating. The lifetime of the carbide inserts with developed NMCC based on the system of Ti–TiN–(NbZrTiCr)N (filtered cathodic vacuum arc deposition) was increased up to 5–6 times in comparison with the control tools without coatings and up to 1.5–2.0 times in comparison with nanoscale multilayered composite coating based on the system of Ti–TiN–(NbZrTiCr)N (standard arc-PVD technology).

Study of Mechanism of Failure and Wear of Multi-Layered Composite Nano-Structured Coating Based on System Ti-TiN-(ZrNbTi)N Deposited on Carbide Substrates

The aim of this paper is to study physical and chemical properties of nanostructured multi-layered composite coating based on three-layered architecture of Ti-TiN-(ZrNbTi)N, deposited to a carbide substrate, as well as to study the mechanism of wear and failure of carbide tools with coatings under the conditions of stationary cutting. The coating obtained by the method of filtered cathodic vacuum arc deposition (FCVAD). The microstructure of carbide cubstrate with coating on transverse cross-section were investigated, as well as its hardness, strength of the adhesive bond to the substrate, chemical composition and phase composition. The studies of cutting properties of the carbide inserts with developed coating was conducted on a lathe in longitudinal turning of steel C45 (HB 200). Analysis of mechanisms of coated tool wear and failure was carried out, as well as - the study of processes of diffusion and oxidation in the surface layers of the coated substrate.

Specifics of Application of Cutting Ceramics with Functional Coating in Turning of High-Strength Materials

This paper reviews some of the features of application of cutting ceramics with Ti-TiN-(TiAlZr)N coating for machining of high-strength hardened alloy steel. The study has revealed the conceptual role of coatings on ceramic cutting tools, which can serve as a scientific and technological basis for further improvement of the ceramic tool. It has been found out that the coating increases the antifriction properties of ceramics both due to lower coefficient of friction of the coating material and to reduction of roughness of rake face of the tool, and that is the main cause of 25% reduction in cutting force components for the coated tool, wherein the difference in cutting forces for the coated and uncoated tools is inversely proportional to the thickness of the slice. On the basis of the analysis of the studies on the issues of cutting with coated tools of ceramic material and the results of research presented in this paper, the conceptual role of the coating on the working surfaces of the ceramic tool was formulated, and it can serve as a scientific and technological basis for further improvement of the ceramic tool.

The formation of the two-way shape memory effect in rapidly quenched TiNiCu alloy under laser radiation

The effect of pulsed laser radiation (λ = 248 nm, τ = 20 ns) on structural properties and shape memory behavior of the rapidly quenched Ti50Ni25Cu25 alloy ribbon was studied. The radiation energy density was varied from 2 to 20 mJ mm−2. The samples were characterized by means of scanning electron microscopy, x-ray diffraction, microhardness measurements and shape memory bending tests. It was ascertained that the action of the laser radiation leads to the formation of a structural composite material due to amorphization or martensite modification in the surface layer of the ribbon. Two methods are proposed which allow one to generate the pronounced two-way shape memory effect (TWSME) in a local area of the ribbon by using only a single pulse of the laser radiation. With increasing energy density of laser treatment, the magnitude of the reversible angular displacement with realization of the TWSME increases. The developed techniques can be used for the creation of various micromechanical devices.

Forming the two-way shape memory effect in TiNiCu alloy via melt spinning

Thin ribbons of Ti50Ni25Cu25 (at %) alloy are produced by melt spinning in the amorphous, amorphous–crystalline, and crystalline states, depending on the melt cooling rate. It is shown that laminated amorphous–crystalline composite displays two-way shape memory behavior in bending with no additional thermomechanical treatment. It is established that a slower cooling rate results in a thicker crystalline layer and greater reversible bending deformation in this structural composite.

Deformation behavior of layered amorphous-crystalline Ti-Ni-Cu composite under different conditions of torsion in a bridgman chamber

Features of structural phase transitions under the high-pressure torsion of layered amorphouscrystalline Ti50Ni25Cu25 composite with 3 : 1 ratios of the layer thicknesses of the amorphous and crystalline phases, respectively, are analyzed by means of X-ray diffraction and transmission electron microscopy. The applied pressure is varied from 2 to 8 GPa. It is found that the structure of the layered Ti50Ni25Cu25 composite evolves in different ways in different parts of the material.