Zagulyaev, Dmitriy Valeryevich

Shlyarova Y.A., Shlyarov V.V., Panchenko I.A., Ivanov Y.F., Zagulyaev D.V., Prudnikov A.N.

Serebryakova A.A., Zaguliaev D.V., Shlyarov V.V., Gromov V.E., Aksenova K.V.

The microhardness of samples of technically pure lead was measured with and without exposure to an external magnetic field with inductions of 0.3, 0.4, and 0.5 T. Dependences of the microhardness of the C2 lead surface on the exposure time in a magnetic field were obtained reflecting the influence of the magnetic field on the plastic characteristics of lead. The exposure time during which the effect on microhardness is maximum was identified. Microhardness tests were carried out in addition on samples of technically pure lead without and under the influence of an external magnetic field with inductions of 0.3, 0.4, and 0.5 T and exposure times of 0.25, 0.5, and 1 h. Based on the microhardness data thus obtained, the plasticity parameter of lead in the original state and after exposure to an external magnetic field was calculated and the dependences of the plasticity parameter on the exposure time are shown. The nature of the plasticity parameter variation during lead exposure to a magnetic field with an induction of up to 0.5 T was identified. The percentage changes in microhardness values depending on the magnetic field induction are shown.

Serebryakova A.A., Zaguliaev D.V., Shlyarov V.V., Shliarova Y.A., Ivanov Y.F., Ustinov A.M.

Serebryakova A.A., Shlyarov V.V., Zaguliaev D.V.

Serebryakova A.A., Shlyarov V.V., Zaguliaev D.V., Gromov V.E.

Mechanical tests of commercially pure lead grade C2 were carried out, cylindrical samples of lead were destroyed in the process of creep with a constant tensile force. The tests were carried out initially without the inclusion of a magnetic field during deformation, then with the inclusion of a magnetic field with an induction of 0.5 T. Based on the data obtained, characteristic curves of the creep process were constructed. A change in the nature of the curve is revealed. At the discovered linear stage of the process, the creep rate was calculated. A decrease in the creep rate is shown compared to the process without the action of an external magnetic field. The duration of the creep process is analyzed depending on the induction and the percentage of residual relative elongation of the samples. Analysis of the fractograms showed a difference in the morphology of fractures in the studied samples. With the use of a magnetic field during the destruction of the sample, the number of pits on the surface decreased, the fibrous zone increased, and the fracture morphology changed.

Aksenova K.V., Shlyarov V.V., Zagulyaev D.V., Ivanov Y.F., Mohan H.M.

High-cycle fatigue tests of VT1-0 titanium samples were carried out under conditions of exposure to a constant magnetic field of various magnitudes and without it. It is shown that the use of a constant magnetic field with induction B = 0.3, 0.4, and 0.5 T leads to a multiple increase in the average number of cycles before the destruction of titanium samples VT1-0 by 64, 123, and 163%, respectively. Using scanning electron microscopy, it was found that the structure of a sample destroyed under fatigue testing conditions, regardless of the test mode, has three characteristic zones: a fatigue crack growth zone, an accelerated crack growth zone, and a fracture zone. It was found that the width of the fatigue crack growth zone depends on the magnetic field induction and reaches its maximum values (h = 264 μm) at B = 0.4 T, and during fatigue tests without a magnetic field, h = 182 μm. This indicates an increase in the critical crack length (the width of the fatigue crack growth zone) by a factor of 1.45. It is shown that the average distance between fatigue striations in titanium samples depends on the value of the magnetic induction of the magnetic field and decreases from 0.78 μm in the absence of a field to 0.49 μm at B = 0.5 T. The formation of a subgrain (fragmented) structure in the zone of fatigue crack growth in a titanium sample was established. The subgrain sizes correspond to the distance between the fatigue striations, which has a retarding effect on the movement of a microcrack. Taken together, the revealed facts indicate a higher resistance of the material to the propagation of a fatigue crack and an increase in its service life during fatigue tests in a magnetic field.

Suresh G., Zaguliaev D., Shlyarov V., Ivanov Y., Shliarova Y.

The present study aims to study the effect of change in beam energy density on microstructural features and mechanical behavior. The results show that the beam energy density value influences Ti coating layer particles. The microstructural studies indicate the presence of nanocrystalline columnar structure and eventually lead to the transformation of cellular structure with the increase of beam energy density. With the increase of beam energy density, metallurgical defects on the original surface, including micropores and elemental segregations, were eliminated, and a remelted layer consisting of the high density of cross slips and nanostructures was obtained. At lower beam energy density, Al-based solid solution was formed, but the decrease of the lattice parameter of Al was observed with the increase of beam energy density, which may be attributed to the doping of Al with Si and Cu atoms. Lower yield strength among all samples was obtained for a sample treated at 50 J/cm2, which is 40 % less than the as-fabricated alloy. The ultimate tensile strength was initially increased for the sample treated at 20 J/cm2, but ultimate tensile strength was decreased for all remaining samples on an average of about 6–8 %.

Shliarova Y.A., Shlyarov V.V., Zaguliaev D.V., Ivanov Y.F., Gromov V.E.

In this study, an integrated treatment approach was employed to modify hypereutectic silumin. This method involved electroexplosive alloying of the surface layer with yttrium oxide powder, followed by irradiation with a pulsed electron beam. The experimental data obtained demonstrate that this integrated treatment results in the formation of a submicron-nanocrystalline structure characterized by high-speed cellular crystallization of aluminum within the surface layer. This structure is composed of crystallization cells enriched with aluminum atoms, indicating the creation of a solid solution based on aluminum. The nanocrystalline layers, formed by silicon particles and yttrium oxide, are positioned at the cell boundaries. The study reveals that, as a consequence of integrated treatment with an electron beam energy density of 25 J/cm2 , the wear parameter of the modified samples increases by 7.9±0.6-fold, and the friction coefficient decreases by 1.7±0.15-fold compared to the initial state. Additionally, the microhardness of the modified silumin surface layer increases by 1.5±0.12-fold compared to the initial state. When the electron beam energy density is elevated to 35 J/cm2, the wear parameter of silumin is enhanced by 2.1±0.21-fold, while the friction coefficient increases by 1.13±0.1-fold. However, the microhardness decreases by 1.3±0.13-fold, while still surpassing the specified characteristics of untreated silumin. This investigation postulates that the substantial increase in the wear parameter during integrated treatment may be attributed to the presence of silicon inclusions in the surface layer that did not dissolve during the modification process. These inclusions are surrounded by the high-speed cellular crystallization structure mentioned earlier. 

Zaguliaev D., Ivanov Y., Gudala S., Tolkachev O., Aksenova K., Konovalov S., Shlyarov V.

Fatigue strength tests of Ti-coated aluminum alloys with a thickness of 1 µm, 3 µm, and 5 µm were conducted to investigate the effect of the coating thickness on fatigue strength. Under the same applied stress amplitude, the optimum thickness with the most-extended fatigue life was around the coating thickness of 5 µm. This may be attributed to the good resistance to surface cracks under repeated loads. The results suggested that a lower fatigue life of a coating thickness of 1 µm results from the fracture of the coating layer under the strong influence of the deformation of the substrate. This could be due to the higher tensile residual stress induced in the substrate near the coating layer and substrate interface. The titanium coating restricted the initiation of offsets and cracks beneath the surface of the specimen, which may be attributed to the high strength of the Al–5%Si substrate, good flexibility, and strong adhesion, which provided sufficient compressive stress to suppress slip band protrusions. The fatigue life and fatigue limit increased proportionally to the thickness of the titanium coating due to changes in the surface roughness and adhesion capability.

SURESH G., Zagulyaev D., Shlyarov V., Ivanov Y.F.

Abstract This study aims to investigate the effects of titanium coatings on aluminum alloy’s tribological and fatigue properties. In this investigation, aluminum alloy samples were coated with 1 μm, 3 μm, and 5 μm using the vacuum arc melting method. The morphological and mechanical features of the samples were characterized with SEM, microhardness, contact nanoprofilometer, and calotest methods. The increase in coating thickness resulted in improved adhesion properties and achieved better surface hardness. Further, hard sub-surface layers on the aluminum alloy substrate increased fatigue resistance. The superior mechanical properties, such as microhardness, lower surface roughness, and good bonding at the interface, are critical factors in increasing the fatigue and wear resistance of the aluminum alloy. No traces of defects, such as microcracks and porosity, were found on the coated samples. The microhardness of the coated sample increased by 3.69 times that of the AK5M2 aluminum alloy. The fatigue lifetime of the 5 μm coated samples was increased by 21%. The wear resistance of titanium-coated samples showed better wear resistance against the steel counter body than other coated and uncoated samples.

Aksenova K.V., Zaguliaev D.V., Ivanov Y.F., Klopotov A.A., Yakupov D.F., Ustinov A.M.

Shlyarov V.V., Aksenova K.V., Zaguliaev D.V., Osintsev K.A., Ivanov Y.F.

Шляров В.В., Загуляев Д.В., Серебрякова А.А.

В работе отражены результаты исследований воздействия внешнего магнитного поля (МП) на деформационные характеристики диамагнитного материала свинца марки С2. Первоначально, были проведены исследования процесса ползучести и микротвердости в исходном состоянии, затем производились исследования данных характеристик с применением постоянного магнитного поля. Для более качественной оценки влияния магнитного поля на динамику микротвердости и процесс ползучести в работе варьировали индукцией магнитного поля (0,3 Тл, 0,4 Тл и 0,5 Тл). В качестве материала исследования применялся свинец С2 технически чистый (99,98 %). Результаты испытаний на ползучесть свидетельствуют о наличии неоднозначного характера влияния магнитного поля на скорость ползучести, обнаружен знакопеременный эффект при увеличении значения индукции магнитного поля до 0,4 Тл и 0,5 Тл. Также, знакопеременный характер влияния магнитного поля установлен и при исследовании микротвердости. Кроме того, было обнаружено, что применение магнитного поля в процессе ползучести образца, количественно влияет на процент относительного остаточного удлинения при разрушении и продолжительность процесса ползучести. Выявлено рациональное время выдержки в магнитном поле при испытаниях на микротвердость, обнаружено, что максимальный эффект влияния магнитного поля проявляется при выдержке в течении 1 часа, в связи с чем дополнительно исследованы 2 режима выдержки в этом диапазоне (0,25 ч и 0,5 ч).

Serebryakova A.A., Zaguliaev D.V., Shlyarov V.V., Shliarova Y.A., Ivanov Y.F., Ustinov A.M.

Dhar J.C., Murdoch H., Smith P., Mishra S., Lewis D., Samuel J.

P. Mphasha N., S. Rabothata M.

Advanced surface modification (ASM) refers to the diverse range of surface treatment processes and techniques used to change the surface properties of materials, thereby enhancing their performance, durability, and functionality for various industrial applications. The surface of materials plays a critical role in determining their overall behaviour and application suitability. This chapter reviews the principles of various ASM techniques, with a focus on laser surface treatment (LST), plasma surface treatment (PST), ion implantation, and electron beam surface treatment (EBST). An overview of the effects of surface modification on mechanical and tribological properties is outlined. The chapter also describes the prospects and challenges of ASM in the aerospace, automotive, and medical fields. Despite the appreciable adoption and application of ASM techniques in various industries, several challenges persist that limit their full potential. It is envisioned that the integration of multiple surface treatments or hybrid surface treatments could provide an opportunity in advancing the development and effective application of ASM techniques. However, the successful application of these techniques is reliant on the understanding of processing parameters in relation to diverse materials as well as challenges innate to each technique.

Xv T., Cong M., Lei W., Han Z., Zhong H., Yang S.

Gudala S., Shlyarov V., Aksenova K., Zaguliaev D., Serebryakova A.

Chen X., Lu Z., Chen S., Gao Y., Tian X., Duan R., Liu Z., Dong J.

Bibik N., Metel A., Cherenda N., Sotova C., Astashynski V., Kuzmitski A., Melnik Y., Vereschaka A.

The structure and phase composition of a eutectic silumin surface layer modified by compression plasma flow impact were investigated in this work. Plasma flows were generated by a magnetoplasma compressor of a compact geometry in a nitrogen atmosphere. The energy density absorbed by the surface layer was varied in the range of 10–35 J/cm2. X-ray diffraction analysis, scanning electron microscopy, transmission electron microscopy and X-ray microanalysis were used as investigation techniques. It was found that the plasma impact led to the formation of a molten layer with a thickness of up to 50 μm. The layer thickness increased with the growth of the absorbed energy density. Dissolution of the intermetallic compounds and primary silicon crystals occurred as a result. The modified surface layer contained grains of a supersaturated solid silicon solution in aluminum. Grains with sizes of 100–500 nm were separated by interlayers of hypereutectic silumin containing nanocrystalline silicon precipitates. The doping elements of the alloy were concentrated mainly in these interlayers. The plasma impact resulted in a 1.5-fold microhardness increase.

Gao S., Du Y., Cong M., He Y., Lei W.

Banerjee A., Mondal A.K., Haldar B., Chatterje S., Alsaleh N.A.

Materials development has always been a major concern for scientists due to the growing need for advanced materials for severe conditions in automobile, aerospace, energy, and other high-performance sectors where there is always a need for innovative, tailored materials to create complex structures. Multi-component alloy, particularly high entropy alloy (HEA), has proven to be a promising candidate due to its superior mechanical property and unique composition consisting of nearly equal multiple principal components, leading to a high configurational entropy. Additive manufacturing, primarily developed as a 3D manufacturing technique, can be an option to produce the HEAs in bulk for a part. This study designed and developed a novel multi-wire-based retrofitted additive manufacturing setup to produce Fe38Al26Cu16Ni13Cr6. It comprises three wires fed together through a nozzle to produce a wall of multilayer deposit. Mechanical and microstructural characterisation was performed. The thin walls of HEA deposits reveal superior material properties than the base metals. The characterisation of the additive manufacturing process showed that a minimum of 327.57 J/mm2 energy density is required to deposit continuous beads. The novel Fe38Al26Cu16Ni13Cr6 HEA exhibited the best mechanical properties at 1008 J/mm heat input. The material has a microhardness of 385 Hv, an ultimate tensile strength of 1313 MPa at 62% elongation, and an average grain size of 11.1 µm.

Lucchini Huspek A., Akdogan B., Akhmadeev Y.H., Petrikova E.A., Ivanov Y.F., Moskvin P.V., Koval N.N., Bestetti M.

Al–Si alloys are among the most common aluminium based materials for cast products due to their high strength-to-weight ratio, excellent processability and relatively low cost. The presence of Si in the molten Al phase improves the castability and decreases the solidification shrinkage. Hard anodic oxidation is largely employed to improve their surface mechanical properties and corrosion resistance. However, the presence of high Si contents (>3%) and the size of Si particles in the alloy make the process challenging or even not possible. The surface pretreatment of Al–Si alloys with intense pulsed electron beams (EB) can effectively overcome the aforementioned limitations. Electron beam sources can be employed to reduce Si content and to refine and disperse Si particles, and effectively create an Al substrate that is more prone to oxidization. In the present work, two electron beam equipment were used, RITM-SP and SOLO, to modify the surface properties of hypoeutectic, eutectic and hypereutectic Al–Si alloys, by investigating the effect of energy density and number of pulses. The electron beam treated substrates were hard anodized and characterized in term of microstructure, elemental distribution, corrosion resistance and surface mechanical properties.

Cagirici M., Guo S., Ding J., Ramamurty U., Wang P.

Agrawal P., Gupta S., Reeder J., Toll M.P., Mishra R.S.

The regained interest in using the externally applied magnetic field (MF) to engineer properties in the solid state has opened a new lane and expanded the existing paradigm to control the microstructure and improve the performance of materials. One area to explore is the enhancement in corrosion resistance of an intricately shaped component for structural applications. This work evaluated the corrosion resistance of paramagnetic Ti alloy, Ti–6Al–4V, treated in a static MF of 2 T. To investigate the magnetically induced microstructural evolution in terms of α-phase fraction and dislocation density and its effect on corrosion behavior, the material was studied in three conditions: as-received (hot rolled) plate, 5% cold-rolled, and 5% cold-rolled + annealed. Experiments involved performing corrosion tests and evaluating phases and dislocation density via X-ray diffraction and electron microscopy. A decrease in dislocation density was observed for magnetic exposure of 2 T for all conditions, with a drastic decrease of ~ 38.5% for the cold-rolled sample. An evident improvement in corrosion resistance of magnetically treated paramagnetic alloy as a result of the negative magneto-plasticity effect paves new pathways for tailoring the properties.

Konovalov S., Gudala S., Panchenko I., Osintsev K., Chen X.

In the present study, the microstructure and mechanical properties of various CoCrFeMnNi high-entropy alloys were investigated. Analytical studies were conducted to determine the optimal chemical composition, mixing entropy, mixing enthalpy, atomic radii, valence electron concentration (VEC), dimensionless parameter, and melting point on the Co-Cr-Fe-Mn-Ni system. The microstructure of the alloys was analyzed using FESEM, XRD, and TEM. The results showed that the microstructure of all HEAs had dendritic and interdendritic regions, with secondary precipitations detected along the grain boundaries of the alloy, mainly composed of Mn and Ni. High-density dislocation structures and nano-precipitates were predominantly present in the alloy. The mechanical characteristics such as microhardness and tensile properties are conducted at room temperature. The HEA Co25Cr25Fe10Mn30Ni10 exhibited the highest average microhardness, while the Co20Cr20Fe30Mn10Ni20 HEA had the lowest mean hardness value. This significant difference of 7.2 % may be attributed to the hard phases composed of Mn and Ni. The results of the tensile experiments indicate that the Co20Cr20Fe20Mn20Ni20 alloy has the most favorable overall properties, with an ultimate tensile strength of 441 MPa. This represents a significant increase of 37.8 % compared to 20Cr20Fe20Mn20Ni20. Furthermore, the study examines the instability of the solid-solution state caused by differences in the valence electron concentrations of the constituent elements and phase stability.

Cerny A., Grabner F., Arnoldt A.R., Kunschert G., Mayr J., Zickler G.A., Österreicher J.A.

Aluminum-magnesium wrought alloys are well known for their advantageous properties and their application in various industries. However, the occurrence of the Portevin–Le Chatelier (PLC) effect leads to the formation of bands on the surface, thereby restricting the application of parts from Al–Mg alloys, primarily due to aesthetic concerns. Applying electrical pulses during deformation may not only improve the mechanical properties, moreover, it also affects the PLC effect. In this work, the properties of AA5083-H111 were investigated using standardized and electrically assisted tensile tests. Tensile behavior was assessed at room temperature, 250 °C, cryogenic conditions, and at two distinct electrically assisted conditions. We found that electrically assisted tensile testing leads to increased fracture strain compared to standard room temperature and cryogenic conditions. Furthermore, there was a transformation in PLC phenotypes, which included a partial suppression of the PLC effect. A spatio-temporal analysis of strain rate and strain highlights considerable differences in the occurrence of PLC bands and prolonged necking compared to standard room temperature testing. Furthermore, a modified dislocation pattern was observed using transmission electron microscopy.

Ivanov Y.F., Efimov M.O., Teresov A.D., Gromov V.E., Shliarova Y.A., Panchenko I.A.

Using the technology of wire-arc additive manufacturing (WAAM – wire arc additive manufacture), a high-entropy alloy (HEA) of non-equiatomic composition Al, Cr, Fe, Co, Ni was manufactured. Using the methods of modern physical materials science, an analysis of the elemental and phase composition, defective substructure, mechanical and tribological properties of the HEA surface layer, formed as a result of complex modification, combining the deposition of a film (B + Cr) and irradiation with a pulsed electron beam in an argon medium, was carried out. In the initial state, the alloy has a simple cubic lattice with a lattice parameter of 0.28795 nm; the average grain size of the HEA is 12.3 µm. Chemical elements (at. %) 33.4 Al; 8.3 Cr, 17.1 Fe, 5.4 Co, 35.7 Ni, which form HEA, are distributed quasi-periodically. The irradiation regime was revealed (energy density of the electron beam ES = 20 J/cm2, pulse duration 200 µs, number of pulses 3 pulses, frequency 0.3 s more than 5 times), allowing to increase microhardness (almost 2 times) and wear resistance (more than 5 times), reduce the coefficient of friction by 1.3 times. Regardless of the value of ES, HEA is a single-phase material and has a simple cubic crystal lattice. High-speed crystallization of the surface layer leads to the formation of a subgrain structure (150–200) nm. It is shown that an increase in the strength and tribological properties of HEA is due to a significant (4.5 times) decrease in the average grain size, the formation of particles of chromium and aluminum oxyborides, and the incorporation of boron atoms into the crystal lattice of HEA.

Wittenburg J., Ehle L., Küpper U., Petersen T., Klink A., Herrig T., Richter S., Bergs T.

Yetim A.F., Kovacı H., Uzun Y., Tekdir H., Çelik A.

This study aims to investigate the effects of duplex surface treatment consisting of plasma nitriding and DLC coating on the fatigue properties of Ti6A4V alloy. For this investigation, Ti6Al4V samples were plasma nitrided at 650 °C, 700 °C and 750 °C for 1, 2 and 4 h and then DLC films were produced on the plasma nitrided samples. The structural, mechanical and morphological features of the samples were characterized by XRD, SEM, micro hardness tester and scratch tester. Fatigue tests were performed on the samples by using stress life method. On the surface and sub-surface of the samples, a compound layer and a diffusion zone were formed by plasma nitriding, respectively and XRD results revealed that these layers consisted of Ti2N and TiN phases. The raising process time and temperature caused to increase the thickness of these layers and they also increased the surface hardness of the samples. On the other hand, DLC coated samples exhibited more surface hardness than untreated and all the plasma nitrided samples. Fatigue analyses revealed that plasma nitriding reduced the fatigue strength of the material in all process conditions. Although plasma nitriding formed hard surface and sub-surface layers, the brittle structure of the layers and the great difference of elastic modulus between the substrate and nitride layers caused to decrease the fatigue strength of the material. Although DLC coating increased the fatigue strength of untreated and plasma nitrided samples at 650 °C for 1 h, 700 °C and 750 °C for 4 h), the fatigue strength of duplex treated samples (plasma nitrided at 650 °C for 1 h, 700 °C and 750 °C for 4 h and DLC coated) was lower than the fatigue strength of untreated material, similar to only plasma nitrided materials. This showed that the fatigue strength of duplex treated Ti6Al4V was controlled by plasma nitriding.

Veshchunov M.S.

The theory of dislocation loop nucleation in irradiated crystals is critically analysed and revised. The key parameters of the nucleation model are reassessed within the traditional (mean field) rate theory for irradiation defects. In the new approach, it is shown that at relatively low irradiation temperatures all interstitial loops are supercritical (due to the absence of a critical nucleus) and grow until they coalesce with other loops or with the dislocation network. In the transition temperature range, a large critical size of interstitial loops arises and the nucleation rate decreases significantly. At higher temperatures, all interstitial loops become subcritical and shrink, in qualitative agreement with experimental observations in irradiated steels. The vacancy loops are shown to be subcritical at all irradiation temperatures and thus shrink and disappear, in agreement with observations. To further improve the predictions of the nucleation theory, possible modifications of the mean field rate theory for irradiation defects are discussed.

Ivanov K.V., Voronov A.V.

Using X-ray diffraction, scanning and transmission electron microscopy we studied the evolution of the morphology, microstructure and phase composition in the near-surface layer of copper covered with thin (2.8 μm) ZrO2 coating induced by low-energy high-current pulsed electron beam irradiation (the surface energy density was in the interval of 5.0–18.0 J/cm2, the accelerating voltage was 30 kV, the pulse duration was 3.2 μs, the number of pulses was 10). The variation of adhesion of the coating to substrate was evaluated using scratch testing. The evaporation of the upper part of the coating during irradiation was found and the thickness of the coating nonlinearly decreased with the increase of the energy density. We discussed the reasons for the surface cracking taking into account microstructural changes in the near-surface layer of the material. The irradiation was found to transfer most of monoclinic ZrO2 phase in the as-deposited coating to tetragonal and, possibly, cubic one. The factors influencing the adhesive strength of the coating were revealed and a potential for the increase of adhesion was demonstrated. We showed that irradiation with enhanced surface energy density was required to obtain copper-based composite hardened with zirconia nanoparticles in the near-surface layer. The thickness of the composite layer may be as much as 6 μm.

Cabello Mendez J.A., Arguelles Rojas A., Pérez Bueno J.D., Meas Vong Y.

AbstractThis study shows a multilayer system based on samarium compounds as a corrosion inhibitor and a continuous SiO2 layer by atmospheric pressure plasma jet (APPJ) as a protective barrier for aluminim alloy AA3003. One of the main advantages of this new coating is that it does not require vacuum chambers, which makes it easy to incorporate into production lines for automotive and aeronautical components, etc. The deposit of samarium corrosion inhibitor was carried out by two methods for comparison, the immersion method and a novel method to deposit corrosion inhibitor by APPJ. The multilayer system generated was homogeneous, continuous, adherent, and dense. The electrochemical behavior shows that the samarium compound was completely oxidized on coatings by the immersion method and favors corrosion. The APPJ deposition method shows a protective behavior against corrosion by both samarium compounds and silica depositions. XPS analyses show that the amount of Sm(OH)3 increases by the APPJ method compared with the immersion method since the spectrum of O1s is mainly controlled by OH. It was determined that the best processing times for the electrochemical study of the multilayer system were 40 min for the immersion method and 30 s for the APPJ method for the layer of corrosion inhibitor. In the case of the SiO2 barrier layer by APPJ, the best time was 60 s of exposure to the plasma jet and this coating could reduce the corrosion of AA3003 by 31.42%.

Serebryakova A.A., Zaguliaev D.V., Shliarova Y.A., Ivanov Y.F., Ustinov A.M.

The surface layer of AK5M2 alloy is modified with a Ti film by the vacuum-arc method. The modified samples are irradiated by the method of electron-beam processing using five modes. The dependences of the crystal-lattice parameter and the phase composition of samples of the AK5M2 alloy with surface-modified Ti alloy on the beam energy density during electron-beam processing are determined. The defect substructure of the samples is studied by scanning electron microscopy. The dependence of the coating thickness on the energy density of the electron beam is revealed. The modes are determined, in which the electron-beam energy density is insufficient for the formation of a homogeneous coating. The most rational mode of electron-beam processing is established, in which a homogeneous layer with the least number of surface defects is formed.

Yue H., Liang Z., Zhang F., Fang L., Chen P., Xu L., Xiao S., Li R.

This study investigated the effect of heat treatment on the microstructure and creep behavior of Ti–48Al–2Cr–2Nb alloy prepared by selective electron beam melting. The microstructure of the as-built and annealed TiAl alloys exhibited near γ structure and fully (α 2 /γ) lamellar structures , respectively. The creep properties were evaluated on the as-built and annealed TiAl alloys under a 250–300 MPa creep stress at 800 °C. The results showed that the creep property was improved significantly by post-heat treatment. The creep rupture life of heat-treated TiAl alloy was 1.6, 2.2, and 2.4 times that of as-built TiAl alloy under the stress of 250, 275, and 300 MPa at 800 °C, respectively. The creep stress exponents of the as-built TiAl alloy and heat-treated alloy were calculated and they were 8.94 and 5.96, respectively. Characterizing the fracture surfaces and deformed microstructure after the creep tests, the as-built alloy exhibited ductile fracture characteristics with numerous dimples. Whereas the heat-treated TiAl alloy displayed brittle fracture characteristics. Finally, the creep fracture behavior was discussed in detail.

Aksenova K., Zaguliaev D., Konovalov S., Shlyarov V., Ivanov Y.

Cyclic tests of the multicycle fatigue of commercially pure titanium were performed under normal conditions (without a magnetic field) and after exposure to a constant magnetic field of varying density (B = 0.3, 0.4, 0.5 T). It was shown that the application of the constant magnetic field of varying density led to a fold increase in the average number of cycles to destruction of the VT1-0 titanium samples by 64, 123, and 163%, respectively. Scanning electron microscopy revealed that the magnetic field led to a 1.45-fold increase in the critical length of the fracture (the width of the fatigue crack growth zone) and a 1.6-fold decrease in the distance between the fatigue striations in the accelerated crack growth zone of the destroyed titanium samples. It was established that a subgrain (fragmented) structure formed in the area of the fatigue growth of the fracture of the titanium samples. The size of the subgrains corresponded to the spaces between the fatigue striations, which had an inhibitory influence on the microcrack propagation. Collectively, the revealed facts are indicative of a higher material resistance to fatigue fracture propagation and increased operation resources under the fatigue tests in the magnetic field, which correlates with the data on the growth of the average number of cycles to fracture of the VT1-0 titanium samples.

Zhang L., Shao M., Wang Z., Zhang Z., He Y., Yan J., Lu J., Qiu J., Li Y.

Little work has been reported directly compared to the tribological behavior of plasma nitrided pure titanium and those coated with TiN coatings. This work prepared the compound layers and coatings with the same thickness on TA2 pure titanium by plasma nitriding and multi-arc ion plating. The tribological behaviors of sliding against ZrO 2 balls under lubricant conditions were investigated using a UMT-5 tribo-tester. The results reveal that nitrided and coating samples showed the friction coefficients (0.11–0.12) were significantly decreased compared to that (~0.33) of the TA2 pure titanium matrix. It was also found that the wear mechanism is different after nitriding or coating, which is caused by the surface phases, chemical composition, and surface roughness under other processes.

Shlyarov V.V., Zagulyaev D.V., Gromov V.E., Glezer A.M., Serebryakova A.A.

The deformation behavior and structure of commercial-purity titanium is studied under creep in a dc magnetic field. The action of a magnetic field is found to increase the strain rate at the steady-state creep stage. Failure occurs via a ductile dimple mechanism. The dimple size depends on the deformation conditions, namely, in a dc magnetic field or without the field.

Dai W., Li Q., Guo C., Zhang J., Yang X., Zhao L., Li C.

Ambiguous fatigue failure mechanism of micro-arc oxidation (MAO) coated samples was an urgent issue to be solved. In this paper, the influence mechanism of coating defects on the fatigue property of the samples with thin MAO coating was studied. Based on the stress analysis of the MAO coated 2024-T3 Al alloy, the effect of the MAO coatings produced using 8%, 10%, 15%, and 20% duty cycles on fatigue behavior was discussed. Fatigue fracture and strain under cyclic stress were measured with SEM and extensometer, respectively. The results showed that the maximum cyclic stress affected the initiation of fatigue cracks. With the increase in the external loading, stress variation of the coatings was the critical issue that caused the changes in the fatigue performance under the high and low cyclic stresses. Furthermore, the fatigue failure mechanism of the samples with the thin MAO coatings was revealed. This study provided a method basis for further exploring the fatigue property of the samples with the thick MAO coatings.

Aksenova K.V., Zagulyaev D.V., Klopotov A.A., Ivanov Y.F., Ustinov A.M., Yakupov D.S.

Silumin AK10M2N is studied in a cast condition and after irradiation with a pulsed electron beam (17 keV, 50 J/cm2, 3 pulses, 100 sec, 0.3 sec –1). Elemental and phase compositions of the alloy are determined. Structure and the fracture surfaces after uniaxial tension of flat specimens in an INSTRON 3386 machine at a constant rate are studied by scanning electron microscopy and transmission electron diffraction microscopy. It is shown that irradiation of alloy AK10M2N with a pulsed electron beam is accompanied by fusion of a comparatively thin (up to 100 μm) surface layer. Subsequent high-speed crystallization yields a multiphase submicro- and nanocrystalline structure of cellular crystallization. Cast alloy irradiation with an electron beam increases ultimate strength by a factor of 1.8 and elongation by a factor of 2.2. The main causes of this effect are determined.

Li G., Sun C.

• Internal crack initiation with nanograins is found in TC17 alloy at 400 °C. • Oxygen-rich layer formed at high temperature affects surface crack initiation. • Fatigue strength of notched specimens is insensitive to high temperature. • A fatigue strength model is proposed including effect of temperature and defect. Crack initiation is an essential stage of fatigue process due to its direct effect on fatigue failure. However, for titanium alloys in high-temperature high cycle fatigue (HCF), the crack initiation mechanisms remain unclear and the understanding for the defect sensitivity is also lacking. In this study, a series of fatigue tests and multi-scale microstructure characterizations were conducted to explore the high-temperature failure mechanism, and the coupled effect of temperature and defect on TC17 titanium alloy in HCF. It was found that an oxygen-rich layer (ORL) was produced at specimen surface at elevated temperatures, and brittle fracture of ORL at surface played a critical role for surface crack initiation in HCF. Besides, internal crack initiation with nanograins at high temperatures was a novel finding for the titanium alloy. Based on energy dispersive spectroscopy, electron backscatter diffraction and transmission electron microscope characterizations, the competition between surface and internal crack initiations at high temperatures was related to ORL at surface and dislocation resistance in inner microstructure. The fatigue strengths of smooth specimens decreased at elevated temperatures due to the lower dislocation resistance. While the fatigue strengths of the specimens with defect were not very sensitive to the temperatures. Finally, a fatigue strength model considering the coupled effect of temperature and defect was proposed for TC17 titanium alloy.

Liang R., Huang C., Liu F., Liu F., Lin X.

The role of the line energy density of electron beam remelting in repairing damaged 34CrNiMo6 parts was investigated. Remelting technology can be used to rapidly repair defects with superior performance, but the value of the heat input during operation was difficult to control, which has a substantial impact on the microstructure and mechanical properties of the parts. The line energy density Q was introduced to calculate the experimental parameters. The microstructure was observed at different regions of the sample, and its mechanical properties were analyzed. From the results, the following conclusion was drawn. An appropriate increase of line energy density could increase the depth and width of remelting to improve the remelting efficiency. Under a low line energy density ( Q1 ), the mainly thermal cycle on 34CrNiMo6 steel was tempering rather than the preheating. With the increase of energy density, the preheating effect of ex-remelting came into sight, and the martensite of repaired zone with energy density Q2 and Q3 became coarse. As to the enhanced diffusion of carbon, the amount and size of carbides precipitated from ferrite increased. The microhardness decreased with the increase of energy density, the max value was about 660 HV ( Q1 ) and the min was 330 HV ( Q3 ). Tensile properties in different Q were similar, the max tensile strength σ b was 845 MPa by remelting. The samples after quenching and tempering (QT) exceeded the forging standard even for the lowest strength value (1013 MPa). The fracture mode of remelted samples was brittle fracture in low energy density ( Q1 ), and changed to quasi-cleavage fracture at energy density Q2 and Q3 . All the modes of the QT samples were ductile fractures.

Zhang G., Liu Y., Liu J., Lan S., Yang J.

Bridge failure, which is generally associated with serious economic and life losses, is defined as the incapacity of a constructed bridge or its components to perform as specified in the design and construction requirements. This paper presents an overview of current researches on the typical characteristics and causes of bridge failures based on 10 former investigations. Principal causes can be divided into internal causes and external causes or natural factors and human factors. Design error, construction mistakes, hydraulic, collision, and overload are the top 5 leading causes of bridge failures, resulting in more than 70% of the bridge failures. Causes of bridge failures are closely related to regional economy, structural type, type of use, material type, and service age. The failure rate is very high for steel bridges, which is inseparable from excessive emphasis on structure strength but lack of consideration on structure stability and fatigue in early years. Researchers need to strengthen their research on the stability and fatigue of steel bridges, as well as inspection and maintenance. Extreme loads such as flood, collision, and overload contribute to a large number of bridge failures because of the lack of extreme loads data and design theory defects. It is critical for such bridges to have sufficient redundancy and capacity protection measures to reduce the probability of bridge failure due to extreme loads. Previous statistical methods and classification methods for the characteristics and causes of bridge failures lack unified standards, and a more scientific method needs to be established. A comprehensive electronic database on bridge damage and failures needs to be developed to establish damage models and conduct forensic studies to improve the design theory and specifications. • Statistical characteristics and causes of bridge failure are reviewed. • Standard for classification of causes and characteristics of bridge failure is needed. • The causes of bridge failures are related to the regional economy, structural type, type of use, material type, and service age. • Design error, construction mistakes, hydraulic, collision and overload are the top 5 leading causes of bridge failures. • It is critical for bridges to have sufficient redundancy and capacity protection measures to reduce the probability of bridge failure due to extreme loads.

Liu W., Man Q., Li J., Liu L., Zhang W., Wang Z., Pan H.

The effects of nitrogen ion implantation on the microstructures and the vibration fatigue properties of the 7075-T651 aluminum alloy were investigated. Nitrogen ions were implanted into 7075-T651 aluminum alloy by metal vapor vacuum arc (MEVVA) at the dose of 3 × 10 17 ions/cm 2 at room temperature. The trajectory distribution range and the introduced defects of nitrogen ion-implanted 7075-T651 aluminum alloy were simulated using the Stopping and Range of Ions in Matter software. The phase composition was tested by X-ray diffraction (XRD), the microstructures were characterized using a transmission electron microscope (TEM), and the fracture morphologies of vibration samples were observed using a scanning electron microscope (SEM). Experimental results indicate that the fatigue life of the ion-implanted vibration samples increased by 75% compared with the untreated samples. The ion implantation caused the microscopic strain，which increased the density of dislocation structure and reduced the grain size. The gradient microstructure and fracture properties of the sample were analyzed. The results show that the high-density dislocation and fine grains induced by ion implantation are beneficial to prolong the vibration fatigue life. • Ion implantation enhances anti-vibration fatigue properties of 7075-T651 aluminum alloy. • The damage induced by ion implantation leads to high-density dislocations. • High-density dislocations and grain refinement are the main factors to prolong the vibration fatigue life.