Zh. G. Kovalevskaya

Effect of ultrasonic plastic treatment on the surface structure and phase state of nickel titanium

The influence of ultrasonic plastic treatment (UPT) on the relief, microstructure, and phase state of the surface of nickel titanium (TiNi) has been studied. The UPT leads to significant hardening, nanofragmentation, and a change in the phase state of the surface TiNi layer.

Effect of ultrasound treatment of the substrate on the formation of the coating in detonation spraying

The detonation spraying of coatings is characterized by the pulsed flow of the process determined by the application of gas explosion for accelerating and heating the particles of the sprayed powder material. The generation of heat in detonation spraying results in the heating and expansion of detonation products, and consequently they are discharged under high pressure from the barrel of equipment and carrying with them the particles of the powder at high speed, deposited on the surface of the component. The thermal and impact interaction of the powder particles with the substrate results in the ‘fixing’ of the main bulk of the powder and the formation of the coating layer. To activate the surface and ensure mechanical bonding of the coating with the substrate in the gas thermal spraying methods, it is necessary to prepare the surface by producing rough areas by sand blasting or by making grooves. In Kudinov et al., it has been reported that the coating particles can be microwelded to the substrate, and that welding areas usually form on the ridges of the rough surface. The highest efficiency of gas thermal spraying has been recorded in depositing coatings on the most important, highly stressed components of machines, mechanisms and equipments. At the same time, practical experience shows that there are a number of components in the structures of the forging–stamping equipment, where abrasive treatment that can reduce the fatigue strength of the component is not allowed. In addition to this, in the high-speed spraying methods that include detonation, surface preparation by sand blasting is not the main process. High-speed spraying creates special conditions for the deposition of the material particles on the substrate at super-high speeds, resulting in highdynamic pressure in the dispersion of particles, and this can lead to significant changes in the mechanism of bonding of the particles of the coating with the component surface. In this work, investigations were carried out on the possibilities of ultrasound modification of the surfaces of structural steels for detonation spraying of coatings. This method produces a specific surface morphology, refines the grain structure and activates and hardens the surface layer leading to a decrease in the extent of changes of the properties at the coating-based interface, and consequently, increases efficiency, especially the wear resistance of hard coatings. Spraying trials were carried out in detonation equipment developed at the M.A. Lavrent’ev Institute of Hydrodynamics, Siberian Division of the Russian Academy of Sciences. Fuel was in the form of gas mixtures consisting of acetylene and oxygen. The coatings were sprayed using powders of pure metals: nickel, chromium, molybdenum and also NR-N70Kh17SR4 nickel-based alloy. The equipment accelerates the powder particles to speeds of the order of 1000 m/s. The coatings were deposited without moving the specimen in relation to the barrel of the detonation equipment into a ‘spot’ with a thickness of 250mm. The sprayed surface was placed 100 mm from the outlet of the barrel of the equipment. The spraying conditions were selected to obtain the most extensive melting of the powder and ensure the highest quality of the deposited coating. Preliminary surface preparation for spraying after machining to the surface roughness, Rz 1⁄4 8.3mm, was carried out by several methods. Sand blasting was conducted in a special chamber with a pneumatic gun which directs the flow of the synthetic corundum particles to the treated surface using a compressed air jet. The surface of the substrate was ground using abrasive paper. Ultrasound treatment was carried out in UZGK-02 ultrasound-finishing equipment with a power of 200W, with the clamping force of the indentor of 70–75N, frequency of oscillations of the indentor of 24 kHz, and surface roughness parameter of Rz 1⁄4 4.1mm. Ultrasound treatment and grinding were conducted to obtain the same surface finish grade. The morphology and surface roughness of the substrate were investigated and the nature of bonding of the coating with the substrate after separation was analysed in a Micro Measure 3D station profile-measuring system. In this equipment, the surface roughness was measured by the contactless method using laser beam scanning the surface. In line scanning, the equipment produces the image (morphology) of the measured surface area with a high degree of accuracy given by the discreteness of movement of the laser beam on the surface of the measured component. The surface roughness of the specimens was investigated in accordance with the GOST 2789-73 standard over a length of 2.5 mm. Graph-plotting software was used for evaluating the area of the zones of bonding of the base with the coating, and the results were used for predicting adhesion strength. A Philips SEM 315

Investigation of high-energy external influences on structural heredity of the Ti-Nb alloy

The effects of high-energy external influences on structural heredity of Ti-Nb alloy is investigated in this paper. By the methods of XRD, SEM, EDX and optical microscopy it was founded that thermal treatment and severe plastic deformation lead to the phase transformations in the alloy, the dendritic segregation occurs and retains in the alloy under external influences.

Study of microstructure of surface layers of low-carbon steel after turning and ultrasonic finishing

Profilometry and optical and transmission electron microscopy are used to examine the microstructure of surface layers of a low-carbon ferrite-pearlite steel subjected to turning and ultrasonic finishing. It is shown that turning peaks and valleys have different microstructures, which stipulates manifestation of technological hereditary when processing surfaces of machined parts. Ultrasonic finishing causes the severe plastic deformation of the surface layer, which favors the elimination of a technological heredity that is acquired during turning.

Effect of ultrasonic surface treatment of steel 40Kh13 on the microstructure of nitrided layer formed by high-intensity low-energy implantation with nitrogen ions

X-ray diffraction and transmission electron microscopy were used to study the microstructure and phase composition of surface layers of steel 40Kh13 subjected to irradiation with high-intensity low-energy ion beams, ultrasonic surface modification, and combined treatment including ultrasonic surface modification and ion implantation. It was found that the ultrasonic modification of steel surface leads to changes in the structure of tempered martensite and the formation of grain structure with a grain size of 0.3 μm and nanosized special carbides Cr23C6 in the martensite lamellae. The ion implantation into this steel results in the formation of a nitrided layer consisting of a nitride region, which represents a mixture of several phases (α-, γ′-, ɛ, and ultrafine chromium nitrides), and a zone of internal nitriding (α″ and nitrogen-containing martensite αN). The preliminary ultrasonic modification causes an increase in the nanohardness and in the thickness of the nitrided layer, which is due to the more intense penetration of nitrogen atoms into the surface layer and an increase in the volume fraction of iron nitrides and density of ultrafine chromium nitrides in this layer.

Features of the microstructure of Ti–Nb alloy obtained via selective laser melting

Ti–Nb alloy with 40 wt % of Nb is obtained from a composite Ti–Nb powder by means of selective laser melting. The Ti–Nb alloy has a two-phase microstructure. The main β-phase of the solid titanium–niobium solution forms grains ranging in size from ~2 to 20 μm. A nonequilibrium α″-phase is found in the forms of lamellar, globular, and packet martensite inside the grains of the β-phase and along their boundaries.

The character of fracture of iron based thermal coating during fretting

The character of destruction of thermal coatings during fretting has been investigated. An iron based plasma coating has been tested with oscillation amplitude from 30 to 200 microns. The tests were conducted in air. It has been determined that the main factor influencing the rate of the wear of the coating during fretting corrosion is the size of the coating area involved into the wear process. The coating exhibits high wear resistance when the amplitude of the oscillation is commensurate with the size of the sprayed particles. During destruction of the coating the leading role belongs to fatigue-oxidation processes. The wear of the coating acquires a catastrophic character when coating macro defects - pores and interlayer boundaries - are involved into the wear process.

Features of the Ti-40Nb alloy prototype formation by 3D additive method

The structure of Ti-40Nb alloy prototype obtained by selective laser melting (SLM) on “VARISKAF 100MV” installation was considered by the methods of optical metallography, scanning and transmission electron microscopy. It was revealed that the most of the specimens’ surface is uniform flowed surface with typical banded structure formed by laying-on molten pools. The process of the individual layer formation was followed by drop formation. This leads to the porosity formation on the specimen’s surface. The structure of entire specimen is not homogeneous throughout the transverse section. The porosity of three kinds is observed. They are cavities of not full contact and melting of the layers, drawholes, gas pores. The porosity optimization requires more careful SLM modes selection. The alloy has a grain structure with anisotropy from small (2–8 µm) to medium (8–20 µm) grain size. The anisotropy of the specimen is formed in each layer and is retained during building of the specimen. The grains of microstruct...