No 1 (2024)

Cover Page

Changes in the structure, mechanical and corrosion properties of the Mg–Zn–Zr system alloy subjected to equal channel angular pressing

Aksenov D.A., Fakhretdinova E.I., Asfandiyarov R.N., Raab A.G., Sharipov A.E., Shishkunova M.A., Sementeeva Y.R.

Abstract

Magnesium alloys are considered promising materials for the production of bioresorbable implants. Their main disadvantages are low strength and corrosion resistance in biological environment. In the work, the authors studied the effect of severe plastic deformation using the equal channel angular pressing (ECAP) method on the structure, mechanical properties, and corrosion resistance of the Mg–8.6Zn–1.2Zr magnesium alloy. It was identified that one ECAP cycle at 400 °C leads to a substantial hardening of the Mg–8.6Zn–1.2Zr alloy by ~10 %, up to 330 MPa. Structural studies showed that dynamic recrystallisation plays a significant role in the structure transformation. ECAP leads to the formation of a bimodal structure with large deformed grains with an average transverse size of 20±4 µm and recrystallised grains with an average transverse size of 6±2 µm. It was found that with a decrease in the strain temperature up to 250 °С, the process of deformation-induced decay of the supersaturated solid solution takes place. Electrical conductivity of a sample after ECAP at 400 °C amounted 29±2 % according to the International Annealed Copper Standard (IACS), while second ECAP cycles lead to an increase in the electrical conductivity up to 32±2 % IACS. Using the electrochemical corrosion method, the authors found that one ECAP cycle at 400 °C leads to a slight decrease in the corrosion resistance of the alloy under study compared to the initial state. The study showed that the corrosion current increases from 24 to 32 µA/cm2, while the subsequent ECAP cycle at 250 °С increases the corrosion current more than twice (up to 57 µA/cm2).

Frontier Materials & Technologies. 2024;(1):9-17
pages 9-17 views

Low-temperature superplastic deformation of the EK79 nickel-based superalloy with the mixed ultrafine-grained microstructure

Galieva E.V., Klassman E.Y., Valitov V.A.

Abstract

One of the most effective ways to increase the processing plasticity of advanced superalloys (heat-resistant nickel-based alloys) is the formation of an ultrafine-grained (UFG) microstructure in bulk semi-finished products. Such a microstructure is a necessary condition for the manifestation of the structural superplasticity effect in the technological processes of manufacturing products from such superalloys. One of the most promising methods for producing UFG microstructures is thermomechanical treatment (TMT) according to the multiple isothermal forging scheme. It has been shown that the EK79 superalloy after TMT, with a gradual decrease in the processing temperature from 0.88 to 0.62 Ts (where Ts is the strengthening phase dissolution temperature) leads to the transformation of the initial microduplex fine-grained microstructure into a mixed UFG microstructure. Such a mixed UFG microstructure consists of: 1) relatively coarse (inherited from the fine-grain microstructure) particles – γ'-phase with a size of 3.0±0.8 μm; 2) γ-grains, and incoherent γ'-phase particles with a size of 0.3–0.5 μm; 3) strengthening coherent intragranular γ'-phase particles with a size of 0.05–0.1 μm, released upon cooling from the TMT temperature to room temperature. During uniaxial compression tests, the EK79 superalloy with such microstructure, demonstrates low-temperature superplasticity in the temperature range of 800–1000 °C. It has been found that an increase in the deformation temperature up to 1000 °C, leads to the increase of γ-phase grains to micron size. The maintenance of superplastic properties in the presence of relatively coarse incoherent particles in the microstructure of the second phase (γ'-phase) is apparently related to the fact that the deformation is localised in the UFG component.

Frontier Materials & Technologies. 2024;(1):19-27
pages 19-27 views

The influence of hafnium on high-magnesium alloys doped with transition metals during heat treatment

Zorin I.A., Aryshenskiy E.V., Kudryavtsev E.A., Drits A.M., Konovalov S.V.

Abstract

The purpose of the work is to study the influence of hafnium additives on the mechanical properties and thermal stability of particles at elevated temperature during heat treatment of aluminum alloys with a high magnesium content. Two modifications of 1570 alloy were chosen for the study: without hafnium content and with its addition of 0.5 % by weight. Both alloys were subjected to homogenizing annealing at a temperature of 440 °C with different exposure modes, which ranged from 2 to 100 h. Microhardness was studied for various heat treatment modes, and the fine microstructure was studied as well using transmission microscopy. As a result, it was possible to identify that during annealing at a short exposure time (2–8 h), the alloy with the hafnium addition has higher microhardness values exceeding those of 1570 alloy by an average of 20 HV units. This is associated with the fact that in 1570 alloy with hafnium additives, during heat treatment, the number of precipitated particles increases while their average size decreases compared to the base alloy. At the same time, in 1570 alloy without hafnium content, when annealed at a temperature of 440 °C, there is no increase in microhardness. This is caused by the fact that in 1570 alloy without hafnium content, when cooled after casting, discontinuous decomposition occurs, which resulted in the fact that most of the scandium precipitates from the supersaturated solid solution in the form of dispersoids. This phenomenon is not observed in the alloy with hafnium additives, which indicates its ability to stop discontinuous decomposition during cooling the ingot after casting.

Frontier Materials & Technologies. 2024;(1):29-36
pages 29-36 views

Special aspects of the microstructure evolution at the temperature-speed deformation of a medical purpose magnesium alloy of the Mg–Zn–Y alloying system

Kudasheva K.K., Linderov M.L., Brilevskiy A.I., Danyuk A.V., Yasnikov I.S., Merson D.L.

Abstract

Biocompatibility makes magnesium alloys attractive functional materials in terms of their use as biodegradable implants. However, the technologies for manufacturing semi-finished products carry a possible diversity of the local strain rate and temperature within a rather wide range, which affects the processed material structure and properties. The purpose of the study is to determine the range of temperatures and resistance to deformation, at which there is no negative effect on the main structural characteristics of the processed material, using the example of a medical purposes alloy of the Mg–Zn–Y alloying system. The authors carried out mechanical tests of a biodegradable Mg–1Zn–2.9Y magnesium alloy at various temperatures and strain rates. The influence of temperatures in the range of 20...400 °C on the structure and properties of the Mg–Zn–Y system alloy is disclosed. Starting from a temperature of 350 °C, the process of dynamic recrystallization is accompanied both by the complete restoration (return) of the original microstructure and by coarsening of the grain size, which can adversely affect the material functional characteristics. The high thermal stability of the biodegradable Mg–1Zn–2.9Y magnesium alloy is revealed, which probably results from the presence of the LPSO phase in it. The study shows that the deformation process is accompanied by twinning. At a strain rate of 2∙10−2 s−1 over the entire temperature range, the grain size distribution slightly narrows and shifts towards smaller diameters. The application of the obtained results in technological processes for manufacturing medical semi-finished products will help to solve the issue of microstructure instability at the stage of transition from a semi-finished product to a finished product during subsequent thermomechanical treatments.

Frontier Materials & Technologies. 2024;(1):37-47
pages 37-47 views

Electrospark modification of the surface of additive VT6 alloy with high-entropy and amorphous electrodes

Mukanov S.K., Loginov P.A., Petrzhik M.I., Levashov E.A.

Abstract

Unsatisfactory quality of the surface layer of additive products, in particular increased surface roughness, prevents the widespread use of electron beam powder bed fusion (EBPBF). Electrospark treatment (EST) is one of the methods for smoothing and hardening the surface layer. The work shows the possibility of modifying the surface of additive VT6 alloy samples by reactive EST with multicomponent electrodes. For this purpose, the authors used electrodes made of the Fe48Cr15Mo14Y2C15B6 bulk metallic glass forming alloy and the FeCoCrNi2 high-entropy alloy. Based on the results of scanning electron microscopy, it was identified that after EST, both modified layers have a thickness of about 16 μm. X-ray diffraction phase analysis showed that in the case of treatment with an amorphous electrode they contain carboborides of the Ti(B,C) type, and in the case of treatment with a high-entropy electrode – intermetallic of the Ti2(Fe,Ni) type. The modified layers have average hardness values of 19 and 10 GPa and elastic modulus of 234 and 157 GPa, respectively, which significantly exceeds the values of these parameters for the EBPBF-grown VT6 alloy. Electric discharge modification of the surface with multicomponent electrodes led to a decrease in roughness by 8...11 times due to the melting of the protrusions and filling of the dimples with the melt to a depth of more than 50 μm. A comparative analysis of the results of tribological tests showed a change in the wear mechanism as a result of EST of the additive VT6 alloy. Wear resistance increased by 4 and 3 orders of magnitude when using electrodes made of a bulk metallic glass and high-entropy alloy, respectively.

Frontier Materials & Technologies. 2024;(1):49-60
pages 49-60 views

The study of end milling temperature of low-alloy steel in coarse-grained and ultrafine-grained states

Rastorguev D.A., Sevastyanov A.A., Klevtsov G.V.

Abstract

The paper presents the results of the study of the end milling temperature of low-alloy steel depending on the cutting modes and the type of crystalline structure. The experiment was carried out on a PROMA FHV-50PD universal milling machine. The blanks were processed using a 12-12D-30C-75L-4F HRC55 carbide milling cutter. No cooling was used during processing. The obtained data were statistically analyzed to identify the dependence of the end milling temperature of low-alloy steel on the processing modes and the steel crystalline structure. When creating a mathematical model of cutting temperature, the authors carried out a bootstrap analysis to identify the significance of the parameters of the processing modes. The mathematical model was chosen using the Akaike informative criterion. It was found that mathematical models of the temperature dependence on processing modes for both types of crystalline structure include the cutting depth in the second power. At the same time, for steel in an ultrafine-grained state, both the cutting depth and the feed are statistically significant. It was not possible to detect the influence of cutting speed on temperature in the studied range of processing modes. Thus, when milling this group of materials, the force component primarily determined by the cutting depth exerts the predominant influence on the temperature regime. The level of cutting temperature when processing steel in an ultrafine-grained state is generally higher than when processing steel in a coarse-grained state, which should be associated with the increased physical and mechanical properties of steel with an ultrafine-grained crystalline structure.

Frontier Materials & Technologies. 2024;(1):61-69
pages 61-69 views

On the possibility of local measurement of crack resistance of structural steels taking into account the structure

Sergeyev M.I., Pogorelov E.V., Dudarev A.A., Sokolovskaya E.A., Kudrya A.V.

Abstract

The scale of heterogeneity of the structures of steels and alloys can be rather large both within one sample and within a product. The procedure adopted in practice for determining the integral values of crack resistance characteristics cannot always reflect this circumstance. In this regard, it is necessary to develop methods for assessing the crack resistance of a medium with a heterogeneous structure. In this work, the authors determined the crack resistance of large forgings made of heat-hardenable 38KhN3MFA-Sh steel (0.38%C–Cr–3%Ni–Mo–V) based on the critical crack opening δс and the J-integral. The presence of critical stages in the development of a ductile crack during testing was assessed by acoustic emission measurements. In combination with the obtained methods of digital fractography of 3D images of fractures, this allowed relating the shape and position of the leading edge of each crack jump to the load-displacement diagram. Measuring the crack opening geometry during the test showed the possibility of determining directly the coefficient of crack face rotation when estimating δс. In general, this allowed constructing a map of the distribution of parameter δс values over the thickness of the sample and estimating the scale of the scatter in crack resistance within one sample – up to 30 %. Such a localization of measurements, primarily of the δc parameter, is comparable to the scale of heterogeneity in the morphology of various types of structures, which was assessed based on the measurement of digital images of the dendritic structure, the Bauman sulfur print, non-metallic inclusions on an unetched section, and ferrite-pearlite banding in the microstructure. This makes it possible to link local crack resistance values to various fracture mechanisms and their accompanying structural components.

Frontier Materials & Technologies. 2024;(1):71-81
pages 71-81 views

The influence of tungsten carbide and boride additives on the structure and microhardness of CrFeNi equiatomic coating formed by short-pulse laser cladding

Stepchenkov A.K., Makarov A.V., Volkova E.G., Estemirova S.K., Kharanzhevskiy E.V.

Abstract

A coating based on a single-phase medium-entropy CrFeNi alloy with a face centered cubic structure has good ductility, relatively high anti-corrosion properties, low cost, but insufficient strength for its widespread use. It is assumed that adding strengthening particles in the form of tungsten carbides and borides to the CrFeNi equiatomic coating will lead to an increase in its mechanical properties. This work studies the influence of tungsten carbide and boride additives on the structure and microhardness of a CrFeNi equiatomic coating. The coatings were formed by layer-by-layer short-pulse laser cladding with preplaced powder on a multifunctional laser installation equipped with a solid-state laser with a lamp pump based on an Nd:YAG crystal. The change in phase composition when adding strengthening particles was detected using X-ray diffraction analysis and transmission electron microscopy (TEM). Both methods confirmed the precipitation of Cr23C6 chromium carbide in the deposited coatings. TEM photographs indicate that the precipitated phase is distributed along the grain boundaries of the g-solid solution. The study found that the addition of 6 wt. % WC and 3 wt. % WB increases the level of microhardness of the CrFeNi coating by 26 % (from 340±6 to 430±12 HV 0.025). This occurs due to the presence of Cr23C6, WC particles in the structure and possible microdistortions of the crystal lattice of the g-phase as a result of doping with tungsten atoms released during the dissolution of tungsten borides and carbides in the process of high-temperature short-pulse laser heating.

Frontier Materials & Technologies. 2024;(1):83-94
pages 83-94 views

Digital measurements of non-metallic inclusions in steel

Stukalova N.A., Kodirov D.F., Alekseev V.I., Sokolovskaya E.A., Rodionova I.G.

Abstract

The experience of many-year research has shown that optimizing the steel chemical composition and microstructural characteristics, as well as reducing its contamination with non-metallic inclusions (NMI), it is possible to significantly increase the corrosion resistance of oilfield pipeline steels and increase the time of their trouble-free operation. The influence of complex NMIs on the steel corrosion resistance is determined by both the chemical composition of NMIs and their quantitative ratios. Therefore, obtaining metal products of the required quality is possible only when using the “control by structure” principle. In the work, based on the analysis of brightness fields of images (on a sample scale) in 256 shades of gray, the authors proposed digital, metrologically supported procedures for measuring the NMI heterogeneity of low-carbon oilfield steels: eliminating the heterogeneity of field illumination, justifying the criteria for binarization and noise filtering. For low-carbon steels of various types of melting, the authors identified the key role of dispersed non-metallic inclusions ranging in size from 5–10 μm2 to 2 nm2 in the formation of the corrosion resistance of steels. This may explain why, in some cases, there is no interrelation between the corrosion rate and the fracture resistance of steels, the formation of which is determined by larger particles. When representing the NMI as a set of random points on the plane, the distribution of distances between the nearest ones is estimated based on Voronoi polyhedra statistics. The study shows that an increase in the kurtosis coefficient of distributions of polyhedra areas is accompanied by an increase in the corrosion rate of the steels under study. This indicates the negative impact of heterogeneity in the arrangement of dispersed NMIs on the corrosion resistance of steels.

Frontier Materials & Technologies. 2024;(1):95-103
pages 95-103 views

The study of the effect of heat treatment on the properties of the AMg2–10%TiC and AMg6–10%TiC composite materials produced by self-propagating high-temperature synthesis

Sherina Y.V., Luts A.R.

Abstract

Dispersion-strengthened composite materials belong to the group of promising structural materials characterised by a diverse combination of properties. The paper considers examples of the creation and heat treatment of composite materials based on aluminium alloys strengthened by the titanium carbide dispersed phase characterised by high hardness, elastic modulus, and good melt wettability. At present, self-propagating high-temperature synthesis (SHS) is the most accessible, inexpensive and effective way to obtain them. The authors substantiate the expediency and show their successful experience of the formation in the composition of the AMg2 and AMg6 industrial alloys of a titanium carbide dispersed phase with a particle size of 130 nm in an amount of up to 10 wt. % using the SHS method, which makes it possible to increase the hardness of the alloys. Additional heating of the AMg2–10%TiC and AMg6–10%TiC samples after synthesis also contributes to the further increase in hardness. The complex of studies of physical, mechanical and operational characteristics presented in the paper was carried out to compare the properties of the work-hardened matrix alloys and the samples of composite materials before and after heating. The test results showed that heat treatment reduces the porosity of the composites and significantly increases their hardness and microhardness. A slight decrease in compressive strength at a significant increase in wear resistance is observed. It was found that composite materials are characterised by high corrosion resistance to carbon dioxide and hydrogen sulfide corrosion corresponding to the level of matrix alloys. The results obtained allow recommending the developed materials for the production of parts of the connecting rod and piston group, bearings and other wear-resistant parts of friction units.

Frontier Materials & Technologies. 2024;(1):105-112
pages 105-112 views

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