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Austenitic stainless steels are some of the most popular structural materials. This is explained by their chemical and mechanical properties among which one may particularly note their high ductility. Due this reason they are successfully subjected to cold working. One of the interesting phenomena of mechanical impact on the structure of austenitic stainless steels is a strain-induced martensitic transformation. The formation of martensite (α'-phase) is due to the metastable state of austenite (γ-phase) near the room temperatures. Such structural transformation can lead to both positive and negative effects. For instance, the increase in the fraction of α' leads to decrease in corrosion resistance. Therefore, consideration of the mechanism of deformation-induced transformation requires additional attention. In this paper, the first results of the analysis of AISI 321 stainless steel subjected to friction are presented. Operando studies using synchrotron radiation were carried out to identify the features of structural transformations. It was established that friction interaction leads to complete γ → α′ transformation. Strain hardening and fracture of subsurface layers were revealed with metallographic analysis. It was evaluated that a hardness of strain-induced phase more than twice higher than the hardness of austenite.

This paper presents a comparison between the “classical” and the modified Williamson–Hall and Warren–Averabach methods applied to an analysis of the microstructure of $$\alpha$$-titanium. The microstructural parameters of cold-rolled titanium specimens were retrieved from analysis of the X-ray diffraction (XRD) peaks. The high-quality XRD patterns were received at the P07 beamline (The High Energy Materials Science) at the German electron synchrotron. The dependence of the crystallite size, the inhomogeneous microstrains, the average dislocation density, the dislocation cut-off radius and some other parameters on the plastic strain were estimated. The results clearly indicate that, due to the consideration of the dislocation contrast effect, the modified models are a much better fit to the experimental data in comparison with the “classical” models. The results of hardness and corrosion resistance measurements of Ti samples can be explained based on the results obtained from the XRD analysis.

Metals 11(7), 1139 -1160 (2021). doi:10.3390/met11071139, Being one of the most high-demand structural materials, titanium has several disadvantages,including low resistance to high-temperature oxidation and wear. The properties of titaniumand its alloys can be improved by applying protective intermetallic coatings. In this study, 2 mm thickTi-Al-Ta and Ti-Al-Cr layers were obtained on titanium workpieces by a non-vacuum electron-beamcladding. The microstructure and phase compositions of the samples were different for variousalloying elements. The Cr-containing layer consisted of 2, , and B2 phases, while the Ta-containinglayer additionally consisted of !0 phase (P3m1). At the same atomic concentrations of aluminum andan alloying element in both layers, the volume fraction of the B2/! phase in the Ti-41Al-7Ta alloywas significantly lower than in the Ti-41Al-7Cr alloy, and the amount of phase was higher. The Ti-41Al-7Cr layer had the highest wear resistance (2.1 times higher than that of titanium). The maximumoxidation resistance (8 times higher compared to titanium) was observed for the Ti-41Al-7Ta layer., Published by MDPI, Basel

Journal of alloys and compounds 875, 160004-160010 (2021). doi:10.1016/j.jallcom.2021.160004, In the last few decades, Ti-Al$_3$Ti composites have attracted great attention due to their outstanding mechanical characteristics, such as low density, high specific strength and stiffness, and ballistic properties. However, their application is still limited due to the low ductility and fracture toughness of the Al$_3$Ti phase. A promising way to improve the composite’s properties is to transform the Al$_3$Ti crystal structure from the tetragonal D0$_{22}$ type to the cubic L1$_2$ type. In this study, the stabilization of the L1$_2$ structure of titanium trialuminide during the fabrication of the Ti-Al3Ti composite is discussed. For this reason, the method of in situ synchrotron X-ray diffraction analysis was used to observe the reactions in the ternary Ti-Al-M systems (where M is Zn, Au, Ag, Ni, Pd, Pt, Mn, Fe, Co or Cr) during heating from room temperature to 830 °С. Zn and Ag were found to be the most efficient stabilizers of the L1$_2$ structure. In composites alloyed with Fe, Co, and Cr, the L1$_2$ structure of Al$_3$Ti was not stabilized. Formation of L1$_2$-structured titanium trialuminide in the remaining systems was accompanied by the formation of a large number of co-products. To select the elements stabilizing L1$_2$ structure in the composite with an excess amount of Ti, the following principle was formulated: the preferable stabilizers are the elements with FCC and HCP structures and a melting temperature below 1100 °С, and which do not form refractory Al-rich binary compounds with a melting point above 1000 °С., Published by Elsevier, Lausanne

Intermetallics 135, 107231 (2021). doi:10.1016/j.intermet.2021.107231, In recent decades, metal-intermetallic laminated (MIL) composites are of great interest to the scientific community. The intermetallic layers in such composites possess a strong crystallographic texture and can form various superstructures. However, these effects are rarely discussed in the literature. By application of synchrotron X-ray diffraction (SXRD) we show, that an intermetallic layer in explosively welded and annealed Ti-Al-based MIL composite consists of two modifications of titanium trialuminide: TiAl$_3$ with a D0$_{22}$ structure and its superstructure Ti$_8$Al$_{24}$. According to SXRD analysis, the volume fraction of the Ti$_8$Al$_{24}$ modification increases from Al/intermetallic interface towards Ti/intermetallic interface. This may be caused by the lack of Al for the formation of stoichiometric titanium trialuminide near the interface with Ti, which leads to the formation of a long-period structures having Ti$_{1+x}$Al$_{3-x}$ stoichiometry. Two types of fiber texture were formed in the titanium trialuminide layer: [001] near the Ti/intermetallic interface and near the Al/intermetallic interface, which is caused by peculiarities of Ti and Al atoms migration. To explain the features of the forming texture, hypothetical mechanisms of Al and Ti diffusion in the intermetallic layer are discussed in this study: a vacancy diffusion, an interstitial diffusion, and a six jump vacancy cycle (6JVC)., Published by Elsevier Science, Amsterdam [u.a.]

Sliding friction causes significant structural transformations in the subsurface layers of interacting materials. These changes are associated with complicated mechanochemical processes which include but not limited to plastic flow, refinement of structure, increase of dislocation density, oxidation, delamination and formation of wear debris. In this study we attempted to observe some of these processes using synchrotron X-ray diffraction using operando and ex situ approaches. For this reason a special friction tester was used, which allows probing the surface layer of the sample using X-ray microbeam. The research was carried out at Beamline ID13 of the European Synchrotron Radiation Facility. The as-quenched medium-carbon steel AISI-5135 was used in experiments. The effect of friction on X-ray line broadening, texturing and formation of iron oxides was analysed and discussed.

International audience; In this study, we describe an experimental setup and a new approach for operando investigation of structural evolution of materials during wear and friction. The setup is particularly suited for testing various friction pairs, including those in which both rubbing bodies are made of metals. The developed device allows circumventing the problems related to significant scattering of X-rays produced by metals and makes it possible using “real samples” in synchrotron beamlines operating in reflection mode. To demonstrate the capabilities of the device and the proposed new approach, an iron-based massive sample was subjected to thousands of friction cycles using a cemented carbide pin. The material was probed with synchrotron X-ray radiation within a few milliseconds after leaving the friction zone. The results of the microstructural and structural analysis, as well as results obtained from diverse mathematical models, allowed us to evaluate several features, including gradual accumulation of defects, microstructural refinement, dislocation density changes, surface layer oxidation, as well as several other phenomena caused by the dry sliding friction process. Mainly, it was possible to conclude that the process of wear occurred due to the cooperative action of oxidation and plastic deformation, which began during the first cycle of frictional interaction and was manifested in increasing the dislocation density, whose type was changed gradually during testing. The number of defects quickly reached a threshold value and subsequently fluctuated around it due to periodically repeated processes of defect accumulation and stress relaxation resulting from material wear. It was also observed that friction led to the quick formation of a mechanically mixed layer, consisting of the sample material and a mixture of two types of iron oxide – hematite and magnetite. The delamination of this layer was probably the primary wear mechanism.

Special features of the structure of surface layers formed on billets of commercial-purity titanium VT1-0 by cladding a powder aluminum-titanium mixture with an electron beam removed into air atmosphere are studied. X-ray phase analysis and transmission electron microscopy are used to show that the material remelted by the electron beam is Ti3Al titanium aluminide. The hardness of the deposited layer is 540 – 610 HV. The behavior of the material is studied under the conditions of sliding friction and friction against fixed abrasive particles. The results reflect decrease in the friction factor and increase in the wear resistance of the clad material as compared to commercially pure titanium.

The effect of additions of niobium in an amount of from 20 to 35 wt.% on the structure and properties of two-component Ti – Nb alloys is studied in cast condition and after a homogenizing annealing. The structure of the alloys is determined by optical and scanning electron microscopy, x-ray spectrum analysis and diffraction of synchrotron radiation. The lattice parameters of the formed phases and the mechanical properties of the alloys are assessed.

Bimetals produced by explosion welding of titanium alloy VT23 and steel 45KhNM through an intermediate layer of steel 08ps followed by a heat treatment consisting of quenching and tempering are studied. The three-layer composite is subjected to metallographic analysis prior to and after the heat treatment with the help of an optical microscope and a scanning electron microscope equipped with an energy dispersive analyzer. The chemical composition and the hardness of the welded materials and of various regions of the weld are determined, and the changes in these parameters after the quenching and tempering are assessed.

Al3Ti-based alloys attract exceptional attention due to their high specific mechanical properties. However, their application is still insufficient due to their low ductility and fracture toughness. Several approaches were previously proposed to address these problems. The first one is stabilization of the cubic modification of titanium trialuminide by alloying. Another approach consists in fabricating metal-intermetallic laminated composites (MIL). In this study, we combined both methods to synthesize the first MIL composite with cubic Al3Ti interlayers. Copper additions were used to stabilize the cubic modification of Al3Ti and produce a novel Ti-Al5CuTi2 MIL composite. First mechanical characterization by indentation tests showed that the binary Al3Ti intermetallic tended to crack at a load of 0.2 kg while the fracture was not observed in the Al5CuTi2 layers at least at a load of 1 kg. These results are an indirect evidence of a higher ductility and fracture toughness of the composite with cubic Al3Ti compared to tetragonal one. The sequence of the phase transformations in the Al-Ti-Cu system was studied using in situ synchrotron X-ray radiation diffraction. The formation of Al5CuTi2 occurred via several intermediate stages including eutectic melting of Al and Cu and the formation of binary AlCu and Al3Ti compounds. Keywords: Sintering, Titanium aluminide, Phase transformation, Synchrotron diffraction, Fracture toughness, Ternary compound

The paper presents results of the structural transformations in the surface of carbon steel specimens during the first tens of cycles of the friction loading with a hard-alloy indenter. The widespread type AISI 1020 carbon steel is used in the experiments which are carried out on the Microfocus Beamline ID13 of the European Synchrotron Radiation Facility. The experimental setup is designed to record the diffraction patterns during the friction. It is shown that at the initial stage of friction, the diffraction maxima significantly broaden due to the defect accumulation in the crystal lattice and, as a consequence, the growth in elastic micro-distortions and the size reduction of the coherent scattering areas. A serious increase is observed in the intensity of reflection from planes of {110} family due to the formation of the respective texture in the surface layers of steel specimens. A non-destructive method is used to detect the diffraction patterns both for non-moving and moving specimens.

Features of the structure of a layered material welded by explosion of high-strength titanium alloy and tool roller steel with an intermediate layer of the structural low-carbon steel have been studied. The structural transformations occurring in materials upon their dynamic interaction have been analyzed. Particular attention is paid to the structure of vortex zones formed at the interfaces of billets of various steels, as well as structural steel and titanium-based alloy. The structural analysis methods made it possible to fix stable and metastable joints appearing upon the explosive welding of various metals. To reveal features of structural transformations caused by prolonged heating, billets of titanium alloy and structural steel were also joined by diffusion welding. It has been shown that, in the course of the diffusion welding process, a continuous layer of stable brittle intermetallic compounds is formed along the entire interface of the welded materials. In the explosively welded materials, the intermetallic phases are distributed locally and, thus, they have a weaker embrittlement effect.

Explosively welded metal plates are characterized by the formation of local microvolumes at the interlayer boundaries within which there is mixing of interacting materials. These microvolumes can be arranged discretely along wavy boundaries or continuously in the form of thin interlayers along planar boundaries. Based on the results of many published works, it has been shown that the material is melted in these zones, and its subsequent solidification occurs at a high rate leading to the formation of metastable phases. In this paper, the formation of metastable phases in steel–steel, Ta–steel, Nb–Al, and Zr–Cu joints is analyzed. The cooling rates of these materials in the mixing zones is estimated. Calculations show that the cooling rate of the melts formed in the weld zones of the investigated composites is in the range 103–106 K/s. Cooling of mixing zones at such high rates results in the formation of metastable structures. In some cases, the crystallization of materials is suppressed and metallic glasses and quasicrystalline phases are formed in the melt zones.

In recent decades, spark plasma sintering (SPS) has become a widespread technique in the production of high-quality intermetallic-based materials. In this study, we used SPS to fabricate multilayer metal-intermetallic (MIL) composites from pure nickel and aluminum foils. The effect of sintering temperature and pressure on the structure and properties of the fabricated MIL composites is discussed. The sintering temperature was changed from 900 to 1100 °C, the pressure varied from 10 to 40 MPa. The structure of the materials was investigated using optical microscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray energy-dispersive spectroscopy (EDX), and X-ray diffraction (XRD). Depending on the sintering regimes the intermetallic layers in the composites consisted of Ni2Al3, Ni3Al, and NiAl of cubic and tetragonal modifications. Tetragonal NiAl appeared in the form of microtwinned lamellar martensite. A change in SPS temperature from 900 to 1100 °C led to an increase in the volume fraction of nickel-enriched intermetallic compounds, which was accompanied by improving composites strength. With an increase of the SPS pressure from 10 to 30 MPa, the number of pores and cracks in composites decreased. At the same time, their bending strength increased by 2 times (from 450 to 900 MPa). Fractographic studies showed that the fracture mechanism of the intermetallic layers depends on their elemental composition and varies from brittle transcrystalline to wavy “feathery”.

The precipitation behavior of ωo phase and creep properties of a Ti-45Al-9Nb-0.5B alloy at intermediate temperatures are investigated in this study. The prior βo phase located at lamellar colony boundaries in the as-cast microstructure is entirely replaced by the ωo phase after creep tests. The imposed stress evidently contributes to the nucleation and growth of the ωo phase. The precipitation of ωo phase inside α2 lamellae can be initiated in front of deformation twins located in adjacent γ lamellae, which are impeded at the lamellar interface. Higher applied stress is expected to further enhance the α2→γ phase transformation and to generate more deformation twins in the γ lamellae. A stress exponent of n = 4.2 is determined for the present creep tests. The microstructural degradation is predominantly induced by dynamic recrystallization (DRX). The decomposition of α2 lamellae via α2→ωo and α2→γ transformation reduces the creep resistance. The distribution and size of ωo precipitates have a pronounced impact on the cavity evolution at the tertiary creep stage. The ωo phase formation under the synergistic effects of the thermal exposure and applied stress accelerates creep failure.

In this study, the non-vacuum electron beam (EB) technology was used to clad commercially pure (CP-) Ti with Ta and Nb. The microstructure of the samples was characterized using optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD). The cladded layers were 1.7–2.7 mm thick and had a dense defect-free structure. Compositional inhomogeneity caused by dendritic liquation was observed in the cladded layers. High cooling rates during non-vacuum EB cladding led to the formation of the α’, α”, β, and ω metastable phases in the samples. The nanoscale ω phase was found in the regions with a high amount of Ta and Nb. Due to the increase in the Nb and Ta content, the microstructure of the samples was refined, and the microhardness increased from 330 HV to 400 HV. The impact toughness of the materials with cladded layers remained at a sufficiently high level (180–250 J/cm2). Corrosion tests carried out in hot nitric acid revealed that the addition of 15% Ta and 11.3% Nb to Ti decreased the corrosion rate from 0.104 mm/year to 0.004 mm/year, which was related to an increase in the fraction of Ta and Nb oxides in the oxide film. The produced materials can be recommended as a relatively cheap alternative for nuclear waste recycling when a hot solution of nitric acid is used.

The research was devoted to studying unlubricated tribological behaviors of γ-TiAl-based coatings in the temperature range 25–400 °C. These γ-TiAl-based intermetallic coatings alloyed with Fe or Mn were formed on CP-Ti workpieces using a non-vacuum electron beam deposition. The microstructure, phase and elemental analyses proved the formation of γ-TiAl and appearance of the ternary phases (Laves and G-phases). It was shown that friction coefficients obtained for three materials were barely different but their fluctuations were strongly dependent on surface oxidation and the phase composition. It was found that the Ti-45Al-8Mn (at.%) coatings consisting mainly of γ and α2 phases had lower wear resistance in comparison with the Ti-42Al-7Fe (at.%) and Ti-57Al-13Fe (at.%) coatings. Whereas the Ti-57Al-13Fe (at.%) coating contained γ and G phases possessed better wear resistance as compared to that of Ti-42Al-7Fe (at.%) coating with the structure represented by the γ matrix and a eutectic (α2 + Laves phases). The microprobe analysis, scanning electron and optical microscopy, and XPS measurements revealed the formation of highly oxidized mechanically mixed layers after the sliding tests. The Ti-45Al-8Mn (at.%) coating subsurface consisted of Al2O3, Al, TiO2, and Ti sub-oxides, whereas for both Ti-Al-Fe coatings the formation of an initial oxide film consisted of a titanium dioxide (rutile structure), alumina, and a low amount of iron oxide (hematite structure) was revealed. Thermal softening of the counter body provoked the iron oxide growth in the wear traces of the coatings alloyed with Fe. Tribooxidation behaviors of Ti-Al-Fe coatings may be interpreted as an example of adaptation the as-deposited structure and phases to high-temperature sliding condition and therefore these coatings can be recommended for protection of the titanium alloy components.

Titanium and titanium alloys are highly important structural materials for many industries where low density in combination with high mechanical strength and corrosion resistance are required. However, titanium is not applicable for tribological or high temperatures purposes due to its interaction with atmospheric gases and friction seizure during the contact with most metallic materials. To protect the surface of titanium and improve its wear resistance intermetallic coatings can be applied. In this study, the Ti-Al intermetallic layers were fabricated on Ti surface by electron beam melting of Al and Ti powders. By variation of Al/Ti ratio in the initial powders it was possible to control elemental and phase composition of the layers. The formation of TiAl, Al2Ti and Ti3Al phases was observed in the layers. Independently on Al content the layers had lamellar type of structure. Microhardness, wear resistance and oxidation resistance were measured to evaluate the quality of the layers. The microhardness and wear resistance were in good agreement with each other. The coating, consisted of pure Ti3Al phase, demonstrated the highest level of these properties. Oxidation resistance of the coatings increased proportionally to the aluminium content due to formation of alumina in oxide scale.

In this study, the effect of copper on the structure and properties of cast iron is discussed. The experimental samples, with copper content from 0.09 wt% to 14.2 wt%, were synthesized in an induction furnace. The structure of the samples was characterized using light microscopy (LM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The influence of copper on the volume fraction of graphite and pearlite, and its interlamellar spacing and the tendency of the composites to form a white iron structure are discussed. In particular, precipitation of e-copper was investigated. For a better understanding of the structural evolution, the isoplethal section of 3 wt% C in the Fe-Cu-C phase diagram was calculated. The hardness, tensile strength, friction coefficient and wear resistance of the composites were measured. The addition of copper leads to hardening and strengthening of the composites. However, at a high copper content, the strength of alloys decreases due to the formation of a brittle white iron structure. Copper has a positive effect on the friction coefficient and reduces wear resistance by promoting the formation of ledeburite.

The methods of three-dimensional printing widely used in the Russian Federation are discussed: FDM, SLA, SLS, and DMLS. Our own experience with three-dimensional modeling and prototyping of implants for reconstructive neurosurgical procedures is analyzed. An optimal method for three-dimensional printing of implants by direct laser metal sintering is developed and supported by evidence.

In this study, a laser cladding technique was used to produce a protective TiAl-based coating on TA6Zr4DE near-alpha titanium alloy. Ti48Al2Cr2Nb powder was used as a cladding material. The microstructure of samples was characterized using optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). Fully lamellar microstructure consisting of γ-TiAl (fcc) and α2-Ti3Al (hcp) phases was observed in the coating. Oxidation resistance of substrate and coating was evaluated by heating the samples in an air atmosphere at 700, 800 and 900 °С during 100 h. The oxidation process of TA6Zr4DE alloy surface led to a formation of multilayered oxide films as result of repeated growth and peeling. The coated samples showed better oxidation resistance in whole temperature range compared to that of the substrate. This behavior was explained by the composition of the cladded layer. Niobium and chromium contained in the cladded powder inhibited the intensive growth of TiO2 (rutile) and contributed to the formation of a protective layer composed mainly of alumina.

Heating of deformed metals always causes changes in their structure and properties. These changes are related to annihilation of the crystallographic defects and rearrangement of the dislocation structure. The currently existing knowledge on structural transformations occurring during the heating of deformed metals is mainly based on ex-situ metallographic observation of samples after they have been cooled to room temperature. In this study we attempted to observe defect annihilation and dislocations rearrangement in β-titanium alloy during heating by using in-situ synchrotron X-ray diffraction (SXRD). For this reason, a thorough peak profile analysis using modified Williamson-Hall (mWH) and modified Warren-Averbach (mWA) methods was applied to several hundreds of diffraction patterns obtained during continuous heating of cold rolled Ti45Nb alloy. Several stages of dislocation structure evolution were distinguished based on observation of changes in dislocation density, type of dislocation, energy of dislocations and crystallite size. Such analysis revealed several phenomena which haven't been reported in the literature so far. The results of synchrotron XRD analysis were in excellent agreement with measurements of mechanical properties.

Ti-Al-Nb based intermetallic layers of sufficient quality and thickness were obtained by non-vacuum electron beam cladding on the surfaces of Ti workpieces. Optical microscopy and X-ray tomography did not reveal any dramatical defects in the structure of cladded layers. X-ray diffraction as well as scanning and transmission electron microscopy were applied to thoroughly investigate the structure and phase composition of coatings. It was found that non-equilibrium cooling conditions of coatings provided by fast removal of heat to untreated Ti substrate after the electron beam cladding was terminated induced the proceeding of metastable phase transformations. For example, γ-phase formation was suppressed in these coatings. In coatings with 8 and 20 at.% Nb (46 and 43% Al respectively) along with ordered with α2, formation of disordered solution of the alloying elements in α-Ti took place. In high-Nb alloys β(B2) phase has undergone the diffusionless transformation to ω’, which is the intermediate phase in β → ω and the coating with the maximum Nb content characterized by appearance of γ1 as a main phase. ω-phase had negative influence to hardness and wear resistance of coatings, however, generally this paremeter increased in 1.3–1.75 times compared to cp-Ti. The high temperature creep and oxidation properties decreased proportionally with increasing Nb and decreasing Al content in the cladded layers.

A welding window is one of the key concepts used to select optimal regimes for high-velocity impact welding. In a number of recent studies, the method of smoothed particle hydrodynamics (SPH) was used to find the welding window. In this paper, an attempt is made to compare the results of SPH simulation and classical approaches to find the boundaries of a welding window. The experimental data on the welding of 6061-T6 alloy obtained by Wittman were used to verify the simulation results. Numerical simulation of high-velocity impact accompanied by deformation and heating was carried out by the SPH method in Ansys Autodyn software. To analyze the cooling process, the heat equation was solved using the finite difference method. Numerical simulation reproduced most of the explosion welding phenomena, in particular, the formation of waves, vortices, and jets. The left, right, and lower boundaries found using numerical simulations were in good agreement with those found using Wittman&rsquo, s and Deribas&rsquo, s approaches. At the same time, significant differences were found in the position of the upper limit. The results of this study improve understanding of the mechanism of joint formation during high-velocity impact welding.

Metastable alloys based on the Ti–Nb system are considered promising candidates to replace the biomaterials currently used in medicine. Several very promising alloys like TNTM, TNZT, etc., were recently developed by adding Zr, Ta, Mo, Fe, or other elements to the Ti–Nb system. However, only a few fundamental studies were devoted to the structural characterisation of Ti–Nb alloys in the as-cast state. In this study, we analyze the microstructure, the phase transformations, the lattice parameters, the interaction of different phases, and Young's modulus of a wide range of Ti–Nb alloys produced by suction casting. The structure of experimental samples was investigated using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and synchrotron X-ray diffraction (SXRD) analysis. The samples with a Nb content of less than 17.5 wt % consisted of α ′ phase. The pure α’’ phase was observed only in the alloy with 17.5 wt % Nb. The alloys with an intermediate content of Nb (20–30 wt %) contained a mixture of α’’, β and ω phases. The samples with 30–35 wt % Nb consisted of a mix of β and ω phases. The samples with 37.5 and 45 wt % Nb included two types of β phase. In addition to the regular β phase, a little detectable amount of bcc phase was observed with a larger lattice parameter named β minor . The mechanical properties strongly depended on the phase composition. We found that for α’’-dominated alloys, there is a correlation between Young's modulus and orthorhombicity and c/a ratio of α’’ phase. The lowest Young's modulus (47 GPa) was observed in the alloy with 17.5 wt % Nb, which has orthorhombicity close to unity and c/a ratio close to 1.58.

Non-vacuum electron beam cladding was applied to obtain CoCrCuFeNi cladding layers with thicknesses of 0.89 and 1.24 mm on a surface of mild steel. The cladding layers possessed the dendritic structure. Interdendritic space was filled with a Cu-rich phase. It was found by X-ray diffraction analysis that FCC solid solution phases were formed during crystallization. The lattice parameter of the dendritic phase was a=3.59 Å, while that of the interdendritic phase was equal to a=3.60 Å. The average microhardness values of the cladding layers were lower compared to the base material and equaled 156 HV and 190 HV.

In this study, forty-layered Ti-Al composites were fabricated in a single-shot explosive welding process. The structure of the composites was thoroughly investigated using scanning and transmission electron microscopy. Particular attention was paid to the structure of the mixing zones (vortexes) arising at the interfaces during explosive welding. The complicated process of mixing and rapid solidification of these zones led to formation of different stable and metastable structures. The vitrification of vortexes, formation of “disordered” Ti3Al and ordered solid solution of Al in hexagonal-Ti and Ti in FCC-Al were observed and discussed with respect to the conditions of solidification. Subsequent heat treatment was carried out at 640 °C under atmospheric and at 3 MPa pressure. For comparison, there were produced reference samples by reaction sintering at the same conditions as for the heat treatment. The heat treatment and reaction sintering promoted the formation of stable Al3Ti phase between Ti and Al. It was found that preliminary explosive welding accelerated the formation of Al3Ti layer and made heat treatment duration four times shorter. The application of pressure was found to play an important role at the final stage of heat treatment after explosion welding to avoid formation of defects between the plates. Keywords: Explosive welding, Multilayer, Titanium, Aluminum, Intermetallic, Composite

By using the method of non-vacuum electron beam cladding, copper-bearing surface layers have been obtained on mild steel substrates. These layers possessed enhanced wear resistance under sliding friction compared to the substrate material. Metallographic and TEM investigations revealed that copper in cladding layers was in the form of nanoscale inclusions distributed in the ferrite matrix as well as in the form of large precipitates in the interdendritic space. The latter is an undesirable effect that significantly reduces the reliability of the material. Technological experiments aimed at dilution of the cladding material with aluminium or carbon in order to reduce the amount of copper precipitate in the interdendritic space and, consequently, to improve the quality of the cladding layers have established that the latter approach is the most efficient. The addition of aluminium, which increases the solubility of copper in the iron, contributes to the formation of the embrittling intermetallic phase (AlFe) in the ferrite matrix. When applying cladding using a mixture containing copper, iron, and carbon, the structure of hypoeutectic cast iron with nanoscale precipitates of copper in ferrite and cement forms in the surface layer. The wear resistance of such layers is one order of magnitude higher than that of the base material.

This study considers the structure and properties of a high-temperature nickel-based alloy (ZhS6U) after different regimes of heat treatment. Cast samples were subjected to quenching and annealing at the temperatures of 900, 1000, 1100 and 1200°C during 1 hour. The structure was investigated by optical microscopy (OM) and scanning electron microscopy (SEM). Additionally, microhardness and compression strength were measured in this study. It was shown that a cast material consisted of crystallites with a length of 100 mm and had a dendritic cellular structure. The main phases observed in samples were: free-form carbides (MC-type), elongated carbides of M23C6 and M6C probable stoichiometry, γ′-phase and non-equilibrium eutectic with composition of (γ′ + γ). It was found that heat treatment had no influence on the microstructure of samples and the morphology of carbide particles. The minimum size of the γ′ reinforcing phase (below 0.3 µm) and its minimum volume fraction were obtained after quenching from 1200°C and holding for 1 hour. The maximum microhardness value reached 598 HV after quenching from 900°C. The minimum value (449 HV) corresponded to the samples quenched from 1200°C. Compression tests revealed that ultimate tensile strength (UTS) of all samples was almost at the same level (1900–2100 MPa). Plastic strain of materials heated up to 1200°C proceeded with formation of cracks.

In the present study the thin NiAl intermetallic foils formed on different types of substrates by magnetron sputtering technique were investigated. To provide the deposition of intermetallic NiAl compound in one step without additional heat treatment the composite targets assembled from parts of Al and Al plates were used. The structure of formed thin NiAl coatings was studied using scanning electron microscopy and X-ray diffraction analysis. Mechanical properties were assessed by nanohardness indentation and wear testing of deposited coatings. During sputtering the distance from the target to the substrates varied from 60 to 100 mm to estimate the effect of this parameter on structure and properties of the coatings. The results revealed that thin coatings sputtered at the closer distance from the target to the substrates had the higher hardness about 11 GPa and exhibited the high level of wear properties.

One of the ways to simultaneously increase the strength and the fracture and impact toughness of structural materials is by producing multilayered materials. In this paper we discuss the structure and properties of a seven-layer composite obtained by explosive welding of high-strength titanium alloys. The structure of the composite was characterized using light microscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). At the interfaces between plates, formation of waves and vortices was observed. The wave formation is discussed with respect to the kinetic energy loss. The vortices consisted of a mixture of two alloys and possessed a martensitic structure comprising &alpha, &prime, and &beta, phases of titanium. Localized plastic deformation occurred along the interfaces during explosive welding by formation of shear bands. The most intensive shear banding occurred in the vicinity of the upper interfaces. The local hardness at the interfaces increased due to the formation of the quenched structures. The interfaces between titanium alloys positively influenced the impact toughness of the composite, which increased in comparison with that of bulk titanium alloys by a factor of 3.5. The strength characteristics of the composite remained at the same level as that of the bulk material (1100&ndash, 1200 MPa).

In this study, the structure of explosively welded Ni–Al multilayer composites was investigated. In particular, the interface between Ni and Al plates was studied using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and transmission electron microscopy (TEM). Continuous interlayers of mixed Al and Ni were found at the interface. The Al and Ni in these zones were heated above their melting temperatures, non-uniformly mixed, and rapidly solidified. Several intermetallic phases, including the decagonal phase and metastable Al9Ni2, were observed in these zones using electron diffraction. A cellular dislocation structure formed in the Ni plates and a polygonized dislocation structure formed in the Al plates due to the extremely high strain rate deformation and heating. Subsequent heat treatment at 620 °C led to the rapid formation of stable intermetallic layers at the interfaces. The growth of the intermetallic layers was considerably faster in the explosively welded composite than in the reference sample. Keywords: Explosion welding, Composite, Intermeltallics, Quasicrystals

Structural investigations of the materials obtained by surface alloying with titanium-containing powder compositions using industrial electron acceleration were carried out. It was revealed that hardened particles of titanium carbides and borides were formed as a result of high-energy treatment. The highest value of materials studied microhardness was about 8.4 GPa. Friction testing against fixed abrasive particles showed that electron-beam cladding of the titanium and graphite mixture conduced to increasing material wear resistance by a factor of three.

Sintered compacts fabricated by spark plasma sintering (SPS) at 1050оС were investigated. Titanium and aluminum powders in a ratio of 25 % (at.) and 75 % (at.) respectively were chosen as starting materials. Powder mixture heating up to elevated temperatures led to a partial loss of an aluminum component and to the formation of a multiphase structure consisting of Al3Ti, Al2Ti, AlTi and AlTi3. The density of sintered powder mixtures was 3.7 g/cm3; an average microhardness value was about 470 HV.

Metal-intermetallic laminate composites are considered as promising materials for application in the aerospace industry. In this study, Ti-Al3Ti composites enclosed in titanium cases were produced by reactive spark plasma sintering. Sintering was carried out at 1103 K and 1323 K (830 °C and 1050 °C) for 10 minutes. In both cases, high-quality Ti-Al3Ti composites containing thin transition layers at the interfaces were obtained. Al2Ti, AlTi, and AlTi3 intermetallic phases and a solid solution of aluminum in titanium were observed in the transition layers by scanning and transmission electron microscopy. The material sintered at 1323 K (1050 °C) had higher strength in comparison with the composite obtained at 1103 K (830 °C). However, the hardness of the intermetallic component in the sample sintered at higher temperature decreased due to the grain growth. The impact toughness values of both materials were approximately identical.

In this study Ti-Ta-Zr coatings fabricated on VT1-0 titanium substrates by non-vacuum electron beam cladding in one, two and three passes were investigated. Coatings were characterized by a high quality; such defects as cracks and voids were not observed. The structure of coating was commonly dendritic. The acicular structure in the one-layered coating and in the first layer of multilayered coatings was revealed by using scanning electron microscopy (SEM). The results of the energy dispersive X-ray (EDX) analysis indicated the presence of tantalum and zirconium segregations in dendrite arms and in the space between them. It was found that dendritic branches contained the maximum of tantalum while an increased amount of zirconium was concentrated in the interdendritic space. The maximum concentration of alloying elements (56.87 wt. % Ta and 22.22 wt. % Zr) was obtained in the layer cladded in the third pass of an electron beam. The microhardness of Ti-Ta-Zr layers rose from 4.5 GPa to 6 GPa with an increase in .the percentage of alloying elements

Laminate composites with an intermetallic component are some of the most prospective constructional and functional materials. The basic formation method of such materials consists in heating a stack composed of metallic plates reacting at elevated temperatures to form intermetallic phases. The temperature of the process is usually approximately equal to a melting point of a more easily fusible component. In this study, an alternative technology of producing a titanium – titanium aluminide composite with a laminate structure is suggested. It consists in combining metallic (titanium and aluminum) powder mixtures pre-sintered at 400 оС with titanium plates, alternate stacking of these components and subsequent spark plasma sintering (SPS) of the fabricated workpieces. Applying this technology allowed for the fabrication of metal-intermetallic laminate (MIL) materials with an inhomogeneous structure of intermetallic interlayers. The phases revealed in the composite by X-Ray diffraction (XRD) were α-Ti, Al, Al3Ti and Al2Ti. Moreover, the results of the energy-dispersive analysis gave the evidence of the formation of Ti-enriched phases in powder layers after SPS. A small number of voids were observed between the structural components of the intermetallic layers. Voids were also detected at “metal-intermetallic” interfaces; however, the quality of connection between different layers in the composite was very high. The microhardness of an intermetallic layer formed in the composite was comparable to the microhardness of the Al3Ti compound. The microhardness of titanium was equal to 1600 MPa.

In this study the structure and properties of surface layers obtained on cp-titanium workpieces by non-vacuum electron beam cladding of titanium carbide powder were investigated. The structure of modified materials was examined by optical microscopy and scanning electron microscopy. It was shown that the cladded layer had a high quality and thickness of about 2.3 mm. The cladded layer microstructure consisted of high-strength titanium carbide crystals distributed in titanium matrix. Morphology of titanium carbide particles and their volume fraction changed in the direction from the surface layer to the heat affected zone. The average microhardness value of the cladded layer was ~500 HV. Surface alloyed layers were of higher wear resistance compared to cp-titanium.

Journal of alloys and compounds 807, 151649 - (2019). doi:10.1016/j.jallcom.2019.151649, The microstructure evolution and carbide precipitation in a Ti-46Al-8Nb-0.7C alloy as well as its creep properties at intermediate temperatures are investigated by high-energy X-ray diffraction and electron microscopy. The alloy with a nearly fully lamellar microstructure exhibits excellent creep resistance, which could be attributed to the good microstructural stability and strengthening effects from both P- and H-carbides. It is also found that the creep parameters have different effects on the precipitation of the carbides. The overall volume fraction of the carbides shows a positive correlation with the creep temperature and time. However, the thermal stability of P-carbides in the γ grain interior decreases at a higher creep temperature. The creep stress hardly affects the precipitation and morphology development of the P-carbides. On the contrary, a higher stress can promote the H-carbide formation at the γ/α2 interfaces via α2 lath decomposition in lamellar colonies., Published by ScienceDirect, Amsterdam [u.a.]

In this study, using a combination of several experimental and computational methods, an attempt to improve the understanding of some important phenomena accompanying the process of explosive welding is made. The high-speed shooting was used to observe the formation of a re-entrant jet. Various methods of the materials characterization were used to estimate the morphology of the interface, the distribution of the liquid phase and analyze the evolution of the structure in the process of high-velocity oblique collision. Simulating the process of high-velocity collision using the smoothed particles hydrodynamics (SPH) method allowed us to accurately reproduce formation of the wave boundary, vortex zones, as well as the formation of a jet moving ahead of the collision point. Based on the simulation results, several significant modifications of the Bahrani-Black-Crossland model of the waves formation were done, and a new explanation for the vortex zones formation was proposed. Numerical simulation of the cooling process showed that the solidification of the liquid phase occurs under conditions of the rapid solidification during melt spinning. Combining several numerical-based approaches, a welding window for the steel-steel system was built. The results obtained show a good agreement with currently existing concepts of welding during the high-velocity collisions. Keywords: Explosive welding, High-velocity impact welding, Wave formation, Jet formation, Welding window, SPH simulation

In this study, new multilayer TiAl-based composites were developed and characterized. The materials were produced by spark plasma sintering (SPS) of elemental Ti and Al foils and ceramic particles (TiB2 and TiC) at 1250 &deg, C. The matrix of the composites consisted of &alpha, 2-TiAl and &gamma, TiAl lamellas and reinforcing ceramic layers. Formation of the &alpha, 2 + &gamma, structure, which occurred via a number of solid&ndash, liquid and solid&ndash, solid reactions and intermediate phases, was characterized by in situ synchrotron X-ray diffraction analysis. The combination of X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and energy dispersive X-ray (EDX) analysis revealed that an interaction of TiC with Ti and Al led to the formation of a Ti2AlC Mn+1AXn (MAX) phase. No chemical reactions between TiB2 and the matrix elements were observed. The microhardness, compressive strength, and creep behavior of the composites were measured to estimate their mechanical properties. The orientation of the layers with respect to the direction of the load affected the compressive strength and creep behavior of TiC-reinforced composites. The compressive strength of samples loaded in the perpendicular direction to layers was higher, however, the creep resistance was better for composites loaded in the longitudinal direction. The microhardness of the composites correlated with the microhardness of reinforcing components.

International audience; During an explosion, the interfaces of welded materials experience fast heating due to high strain rate severe plastic deformation. This leads to the formation of local zones, where melting and mixing of welded materials is observed. These zones are frequently referred to as vortexes, eddies or swirls, due to the specific rotational movement of materials during mixing. This study is primarily devoted to the discussion of the structures that appear in these zones. Simple approaches to estimate the heating and cooling rates at the interfaces between explosively welded materials were proposed. It was concluded that the heating rate at the interfaces was of the order of 10(9) K/s, while the cooling rate achieved 10(7) K/s. Several combinations of explosively welded alloys (steel/steel, Ti alloy/steel, Zr/Cu, Zr/Ni, Ta/Cu, Al/ magnesium alloy and Cu/brass) were thoroughly analyzed using scanning electron microscopy, transmission electron microscopy and energy dispersive X-ray spectroscopy. In most of these combinations, metastable crystalline, quasicrystalline or glassy phases were observed. The formation of different types of metastable phases is discussed with respect to the compositions of the welded alloys. It was concluded that solidification conditions at the interfaces of explosively welded materials are similar to those during rapid solidification. Thus, the results of numerous experiments on rapid solidification of alloys could be applied to analyze the structures that appear in mixing zones. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.