Bulletin PNRPU. Mechanical engineering, materials science

The work is dedicated, foremost, to the prominent discover of great Russian scientist and engineer D. K. Chernov, that predetermined dividing of “Iron Age” by two epochs: “TILL CHERNOV” and “AFTER CHERNOV”. In 1868 D. K. Chernov in his lecture during the meeting of the Russian Technical Society showed that on the temperature scale of steel treatment two points have the special value: ‘ a ’ and ‘ b ’. Further they will enter science as “Chernov’s points". D. K. Chernov was the first to show that iron and steel are polymorphic solids and during hardening temperature higher than point ‘ a ’ they undergo phase transformations. Physical sense of point ‘ b ’ authors of the article connect with the temperature threshold of the recrystallization. It is shown that in an epoch “AFTER CHERNOV” civilization of iron attained quite surprising progress and essentially became the epoch of metals. However large group of metals (about a half) are not polymorphic from nature (Pd, Nb etc.). They can be subjected to polymorphic transformations with a help of hydrogen exposure - hydrogen treatment. The phenomenon of the hydrogen phase naklep (HPN) is described in detail. It is shown that HPN is a basis of hydrogen treatment of metallic materials (HTM), a basis of a new paradigm of materials science. This new area of materials science successfully works out the problems of reliability of such important areas of technique, as metallurgy, atomic energy, chemical and petrochemical productions, aviation and cosmonautics etc. In a long-term prospect practical task of hydrogen materials science on the whole and HTM, in particular, consists of that, to hold up-to-the-mark the materials providing of including the hydrogen energy in life, and in subsequent - to provide the materials base of humanity motion along an ecologically clean vector ‘Hydrogen energy ® Hydrogen economy ® Hydrogen civilization’.

Austenitic class alloy Cr-Ni-Al was investigated by transmission electron microscopy before and after electrolytic plasma treatment, i.e. carbonitriding. Carbonitriding was conducted in a water solution during 5 minutes under 700 °C. Phase composition of the alloy was determined, along with its sizes, volume ratios of present phases, as well as carbide and carbonitride phases and the areas of their localization; the type of dislocation substructure was defined in each of the phase components and scalar density of dislocations was estimated. It was concluded that prior to electrolytic plasma treatment Al0.7Cr0.3Ni3 f.c.c. phase comprised the alloy matrix. These are grains which differ largely in their size. Fine grains are placed along the edges of coarse grains. Inside the coarse grains of Al0.7Cr0.3Ni3 phase there are found to be particles of other phases: 1) NiAl plate-like particles (b.c.c. phase) and 2) AlCrNi2 circular-shapes particles (f.c.c. phase). Apart from that, NiAl and AlCrNi2 phases were observed as detached or grouped single-phased grains, having carbide particles Cr23C6 along their edges. In near-surface zone of the sample treated by plasma electrolytic carbonitriding as well as in the original state there are the following phases present: Al0.7Cr0.3Ni3, AlCrNi2 and NiAl. The alloy matrix is still Al0.7Cr0.3Ni3. However, carbonitriding resulted in partial segregation of solid solutions Al0.7Cr0.3Ni3 and AlCrNi2, which is demonstrated by failure of diffraction patterns in these areas of structure (appearance of satellites, heavies of the basic reflexes) and a distinctive contrast on the image of “salt-pepper” kind. Emission of Cr2N nano-sized particles took place inside the Al0.7Cr0.3Ni3 grains.

The reason for the destruction of flat hydrogen permeable membranes based on tantalum and niobium due to dilation caused by the dissolving hydrogen is considered. It is shown that the problem of increasing the period of their functioning can be solved in two ways: by using alloys of niobium and tantalum less prone to hydrogen embrittlement; reconstruction of membranes for more uniform distribution of stresses generating from dilatation. The results of experiments to study the effect of the step of spot contact welding of tantalum and niobium foil membranes with a thickness of 40 μm, welded to a steel substrate, for the period of their work and the value of hydrogen permeability are presented. Composite membranes were tested, and a Pd layer was deposited on their outer surface after welding by the method of magnetron sputtering. Measurements were carried out at 580 °C, an overpressure of 500 kPa of a mixed gas of 1 part Ar / 5 parts H2. The membrane area was 7.85·10-3 m2. It is shown that the provision of conditions for uniform stress distribution in the membrane by resistance spot welding with the substrate over the area allows significantly (up to 400 %) to increase the period of their work, by reducing the probability of cracking. The construction of integrated laboratory installation for the separation of hydrogen from mixed gas is described. The device is designed for simultaneous operation of up to 10 flat membranes with a total area of up to 0.6 m2. The device is designed with the possibility of dismantling the membrane module with a retort, which will allow for the industrial operation of such equipment to replace the failed modules without stopping the entire production. The results of its testswere carried out with a membrane module with a total area of 0.18 m2 of membranes using composite Ta (40 µm) / Pd (0.155 µm) and Nb (40 µm) / Pd (0.39 µm) membranes.

The aim of the study is to improve the quality of the surface of products made of titanium alloys, processed by the method of copy-piercing electrical discharge machining by selecting rational processing parameters using a mathematical model obtained by the method of factorial experiment. Copper grade M1 GOST 1173-2006 is selected as the material of the electrode tool. Processed material titanium alloy OT-4 GOST 19807-91. This materials have unique properties, such as high strength, low thermal conductivity, high resistance. The high physicomechanical properties of titanium alloys in combination with the constantly complicating surface profiles of products limit the use of blade processing. A widely used alternative method for obtaining complex profiles of materials with high hardness is the method of electrical-discharge machining. However, the question of predicting the quality of the surface obtained by this method has not been fully studied. The paper considers an empirical model obtained by the method of factor experiment, which allows to predict the roughness of the treated surface. The technique of experimental research is described, the equipment used is shown. Variable regression analysis parameters ( I , T on, U ) are presented, a planning matrix is compiled, regression coefficients are calculated, significant coefficients are determined, and an empirical model is obtained that has been tested for adequacy. The inverse replacement of matrix parameters was carried out, the final model was obtained. The images of the hypersurface of the response function in the coordinate space with constant parameters ( I , T on, U ) are shown. The nature of the change in the response function Ra with changing parameters is determined. The roughness limit values are revealed. An empirical model was obtained, which allows predicting the quality of the surface obtained by the method of KEEDM, depending on the processing parameters.

In accordance with the main criteria of efficiency for plasma metal cutting technologies - productivity, cutting quality and reliability of the equipment - the tasks of the study are set. They are in search of new design solutions to improve the efficiency of plasma cutting of metals. Since the main design factor is to ensure the gas-dynamic operation of the plasma torch, the main attention is paid to the search for new constructive ways of gas-dynamic stabilization of the plasma arc. Various methods of gas-vortex stabilization in plasma torches for metal cutting are investigated. Single- and double-flow plasma torches with different swirler designs were investigated. The influence of the angle of entry of the plasma-forming gas on the kinematic characteristics of the plasma jet is shown. The increase in the radial component of the velocity at the output from the swirler allows to increase the uniformity of the velocity distribution and the kinetic properties of the jet in the zone of influence on the cut metal, which in turn increases the quality and productivity of cutting. As a result of the use of the upgraded swirler, the maximum cutting speed increased by 25%. When cutting sheet metals it is advisable to use the technology of "narrow-jet plasma". This technology is based on the separation of the plasma-forming gas flow into two - plasma-forming and stabilizing - with separate gas supply to the nozzle unit for additional compression of the plasma arc at the outlet of the main nozzle of the plasma torch. At the result a jet of double-flow plasma torch has a higher kinetic properties (has a higher top speed) than a jet of the single-flow plasma torch, however, retains its properties over a short distance.

Stability of performance in magnetorheological systems has a significant dependence on the temperature characteristics of working environment; therefore the impact of thermodynamic parameters should be taken into account by consideration of the dynamics of processes in the magnetorheological systems. Magnetorheological system is inherent to the large heat dissipation in working environment’s volume by external electromagnetic fields and to processes of liquid friction which are sharply increased at growing the viscosity of working environment. New generation magnetorheological systems use combined method of flow rate control of working environment; it helps to avoid excessive viscosity growth due to redistribution of the contribution of various components of combined control signal, for example, it could increase the contribution of hydrodynamic or non-Newtonian rheological effects in management process of magnetorheological fluid. But the effects of turbulence increase the intensity of heat release by fluid friction too and lead to other new factors of instability in performance. In flow turbulence negatively affects the time of transients and increases the time to stationary modes. Therefore the main guarantor of the stability of work processes is temperature stability of working environment (effective temperature control). The largest time of transients in the magnetorheological systems’ dynamics also have the thermodynamic processes in working environment’s volume. Providing even more high quality thermostating of working environment could have distributed temperature gradient along the flow section; it leads to under regulation of the temperature parameters of the fluid at some point in time. This is due to the fact that the processes of liquid friction and heat release occur throughout the liquid volume but the cooling processes are organized over the surface of the liquid volume which indicates the need to take into account the thermodynamics of process in magnetorheological system. Developed original rheological-throttling thermostat construction with thermoelectric semiconductor elements can improve the efficiency of thermostating. The results of numerical simulation of control element’s performance for thermodynamic parameters of thermostating system for new generation magnetorheological drive are proposed.

Experimental data test of heat treatment are presented in conditions of shop production of increased hardness grinding balls on EVRAZ-NTMK, commissioned in 2018. On example of balls Ø 120 mm production from the 55G grade steel billet, by heat treatment changing temperature-time parametersm, was obtained products corresponding to 3 grade hardness according to GOST 7524-2015, with intended purpose 2 grade hardness steel. Particular attention is paid to possibility of making 5th grade hardness balls, with ensured surface and bulk hardness. Experimental studies were carried out on steel grades Ш-3Г and 75ХГФН. The most critical in terms of final properties formation are: the temperature and the nature of its distribution over workpiece surface at ball-rolling mill outlet, the cooling time, the workpiece temperature, before being fed into quenching drum, the cooler temperature and dwell time into quenching drum. It was obtained that all modes, which considered ones satisfy bulk hardness criterion, this indicates a sufficient all steels hardenability. However, on surface and macrosections of balls, which highers alloyed steel, cracks were discovered, that spread deep into the metal at 45 to 50 mm depth, which will inevitably lead grinding media during operation to destruction. The possibility of mass production 5th grade hardness balls is ensured by exact observance of heat treatment temperature-time parameters and is conditioned by equipment complex high automation, control and all technological parameters correction in the on-line mode. Conditions for implementation of grinding balls heat treatment technological modes on the new ball rolling shop of JSC "EVRAZ-NTMK" allows to obtain high grades hardness balls on the steel with lower proprties, which shows its significant potential.