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Article

Formation of Intermetallic Coatings on Titanium by Explosive Welding and Subsequent Heat Treatment of the Layered Metal Composite

by
Artem Igorevich Bogdanov
1,*,
Vitaliy Pavlovich Kulevich
1,
Roman Evgenevich Novikov
2 and
Victor Georgievich Shmorgun
1
1
Materials Science and Composite Materials Department, Volgograd State Technical University, 400005 Volgograd, Russia
2
Design and Technological Institute of Oil Refining and Petrochemical Equipment, 400078 Volgograd, Russia
*
Author to whom correspondence should be addressed.
J. Compos. Sci. 2025, 9(7), 379; https://doi.org/10.3390/jcs9070379
Submission received: 27 June 2025 / Revised: 14 July 2025 / Accepted: 18 July 2025 / Published: 21 July 2025
(This article belongs to the Special Issue Effect of Processing Techniques on the Characterization of Alloys Composites and Hybrids)
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Abstract

An approach for the formation of intermetallic coatings on the titanium surface based on titanium aluminides is proposed. The approach involves producing a layered steel-aluminum-titanium metal composite via explosive welding, followed by heat treatment to form a diffusion zone at the steel–aluminum interface with a thickness of more than 30 μm, sufficient for the spontaneous separation of the steel layer. As a result, an aluminum layer approximately 0.3 mm thick remains on the titanium surface. Subsequent heating at temperatures of 700–850 °C, below the allotropic transformation temperature of titanium, results in the transformation of the aluminum layer into titanium aluminides. The formation of the intermetallic coating structure occurs as a result of the upward transportation of TiAl3 fragments separated from the reaction zone by circulating melt flows. With increasing heat treatment time, these fragments become separated by the Al2O3 oxide phase.

1. Introduction

Titanium and its alloys have unique mechanical and physical properties and corrosion resistance, making them ideal for the aerospace, chemical, and energy industries [1]. However, titanium readily absorbs oxygen and nitrogen from the atmosphere, forming wide areas of solid solutions with them. The high solubility of these elements (up to 33 at. % of oxygen can dissolve in titanium) and their α-stabilizing effect result in the formation of an oxygen-enriched α-phase on the titanium surface, often called the alpha case. The presence of the alpha case embrittles the surface, significantly reducing ductility and, consequently, deteriorating the mechanical properties of the material. These alpha case-affected areas often serve as primary sites for crack initiation. Titanium alloys usually contain an insufficient amount of aluminum; as a result, instead of forming a passive Al2O3 oxide scale, a rapidly growing TiO2 scale forms on the surface that does not protect the alloy. It has been shown theoretically and experimentally that with an aluminum content of <50 at. %, predominantly non-protective oxide scales are formed on titanium alloys [2,3,4].
One of the ways to protect titanium from oxidation and alpha case formation is to create diffusion aluminide coatings with titanium aluminides on its surface [5]. Titanium aluminides combine relatively low density (3.9–4.2 g/cm3, depending on composition and constitution) with good high-temperature strength, and contain the necessary aluminum content (for example, 75 at. % in the TiAl3 compound) to form a continuous dense Al2O3 oxide scale on their surface, which provides effective protection of the substrate from high-temperature oxidation [6].
Various methods are used to obtain diffusion titanium aluminide coatings. Most methods (such as pack cementation [7,8,9], deposition techniques [10,11,12], surfacing [13,14,15], laser [16,17], or electron-beam [18] cladding) assume that the formation of the structure and composition of intermetallic coatings occurs directly via the process. Thus, Zarchi et al. [7] demonstrated that pack cementation (essentially an in situ chemical vapor deposition (CVD) process) techniques can be used to obtain diffusion titanium aluminide coatings, which are generally carried out by heating and aging in chemically active media (10%Al + 5%NH4Cl + 85%Al2O3) containing the applied substance. Szkliniarz et al. [8] used pack aluminizing to form the protective coating on the surface of Ti–45Al–8Nb–0.5(B, C) titanium alloy. The resulting coating consisted of TiAl2 and TiAl3 compounds. During oxidation tests, an Al2O3 oxide scale is formed, which improved the oxidation resistance of the alloy. In [11], a novel supersonic free-jet PVD method to produce high-density coatings based on titanium aluminides is proposed. To obtain the coating, evaporated titanium and aluminum nanoparticles were used, which were deposited on a titanium substrate heated to 800 K. The composition of the coating corresponded to the TiAl and TiAl3 phases. The above methods have many advantages, but in some cases, they require very complex equipment and are characterized by high temperatures and duration due to the low rates of boundary diffusion reactions because of the presence of an oxide diffusion barrier at the surfaces of the aluminum and titanium [12]. Long-term high-temperature exposure has a negative effect on the structure and properties of the protected titanium alloy. Work [13] discusses the formation of titanium aluminide coatings on titanium surface using a TIG welding. A titanium substrate was preliminarily coated with a powder mixture of titanium and aluminum in various ratios. It is shown that an increase in the aluminum content in the powder mixture resulted in the formation of a coating from single-phase (Ti3Al) to two-phase (Ti3Al + TiAl). The coatings increased the oxidation resistance of pure titanium several times. Mizuta et al. [14] developed a method of titanium aluminide (TiAl3, TiAl and Ti3Al) coating formation on titanium surface based on a TIG welding technique via reaction between aluminum liquid beads and the surface of titanium substrate. A layered coating structure consisting of TiAl, Ti3Al, and TiAl3 aluminides is obtained. Surfacing methods are characterized by simplicity, technological efficiency and availability of equipment. However, these methods are associated with significant overheating of the titanium substrate during the coating formation. The main disadvantage is the significant mixing of the surfacing material with the base metal. The use of laser and electron beams for heating allows partially solving this problem. Maliutina et al. [17] used a laser cladding technique to produce a protective TiAl-based coating from Ti48Al2Cr2Nb powder on TA6Zr4DE titanium alloy. Fully lamellar microstructure consisting of TiAl and Ti3Al phases is observed in the coating. In [18], Ti-45Al-8Cr and Ti-45Al-8Ta layers were obtained on titanium surface by a non-vacuum electron-beam cladding. During the cladding, there was partial mixing of the powder cladding layer and substrate material, which affected the composition of the resulting coating.
Alternative technological approaches for designing titanium aluminide diffusion coatings are based on a combination of several processes, including preliminary application of a pure aluminum (or mixture of aluminum and titanium elemental powders (foils) in the required ratio) to a titanium alloy substrate, followed by thermal impact to synthesize intermetallic phases via diffusion. In the case of powders, they can be applied to a titanium substrate using spraying technologies [19,20,21,22,23]. Also, the hot-dipping in aluminum [24,25,26,27,28,29] used to form a solid aluminum layer on the titanium surface. Subsequent thermal impact for the synthesis of intermetallics can be carried out by means of furnace heating, plasma, laser processing, etc.
Cizek et al. [19] deposited onto Ti-46Al-7Nb substrates four blends of Al powder containing different amounts of Ti using low-pressure cold spray. After cold spraying, the samples were heat treated at 500 °C to form TiAl3 aluminide. The coating significantly reduced the oxidation rate of the titanium alloy. Sienkiewicz et al. [22] used a warm spray process to form Ti-Al-Si coatings. Hot pressing was applied to reduce initial porosity and in order to obtain titanium aluminide intermetallic phases with Ti5(Si,Al)3 silicide precipitates. In [23], coating of aluminide on a TiAl-based alloy is carried out by thermal spraying pure aluminum and subsequent diffusion treatment at 1100 °C. The disadvantages of high-speed spraying methods include the fact that they are, in most cases, do not provide fully dense (non-porous) coatings capable of preventing the penetration of corrosive medium to the substrate, moreover, they are characterized by a low utilization rate of the sprayed material (up to 60%).
Patel et al. [26,27] deposited an aluminide coating on Ti6Al4V alloy by hot-dip aluminizing. After hot-dipping, the aluminum coated Ti6Al4V samples were subjected to a two-stage heat treatment, including solution annealing (900 °C, 1 h) and aging (500 °C, 6 h). The coating had a variable composition in different layers: (TiAl3 + TiAl2)/TiAl2/TiAl/Ti3Al (as it approached the titanium substrate) When using hot-dip aluminizing, the negative effect is the partial dissolution of the sample in the aluminum bath, which results in a change in the shape and size of the product, as well as the rate of diffusion processes as the gradients of the chemical potentials of titanium and aluminum change.
We have proposed a new approach for aluminizing using explosive welding (EXW) and heat treatment (HT). EXW, which is a bonding technique using explosive energy [30], was applied to the bonding of an aluminum plate to a titanium substrate. EXW allows forming a strong bonding of similar or dissimilar metals and obtaining layered composites of large area (up to 20 m2). This is facilitated by the appearance of a cumulative jet between the metals being joined during the EXW process, which removes oxides and impurities from their surface [31]. It is generally accepted that EXW refers to solid-state welding methods. The EXW process is quite fast, and the metals being joined do not have time to heat up. On the other hand, partial melting of metals may occur in the collision point of the metal plates. In this case, one can consider the formation of a metallurgical bond caused by melting and diffusion at high temperature near the interface in an explosively welded composite [32].
HT of the obtained composite leads to the formation of intermetallics at the Ti-Al interface due to reactive diffusion [33,34]. The main problem of this technology is the difficulty of directly applying onto the titanium surface an aluminum layer with the thickness about 0.1–0.3 mm, sufficient to form a coating through diffusion. Therefore, we propose obtaining a three-layer titanium-aluminum-steel composite by EXW at the first stage, where the outer steel layer serves as a protective layer for the thick aluminum layer. At the second stage, intermediate HT of the obtained three-layer composite is carried out to enable spontaneous separation of the steel layer [35]. As a result, an aluminum layer of a given thickness remains on the titanium surface. Then, the obtained Ti-Al composite is subjected to final HT to form an intermetallic structure of the coating. Using the proposed approach, we have previously obtained diffusion aluminide coatings on the surface of nickel alloy [36,37] and steel [38].
In this study, a titanium plate was coated with an aluminum and steel by EXW, and then initially heat treated to remove the protective steel layer. Next, aluminum-coated titanium specimens were subjected to HT at 700 °C or 850 °C. The interdiffusion phenomena occurring during EXW and heating were investigated.

2. Materials and Methods

A commercially produced pure VT1-0 titanium plate (VSMPO-AVISMA Corporation, Moscow, Russia) with a thickness of 3 mm was used as the base metal. As a cladding metal, an AD1 (1013) aluminum alloy sheet (RUSAL, Volgograd, Russia) with a thickness of 0.35 mm was prepared. To protect the aluminum cladding layer, a 1.5 mm thick 20880 low-carbon steel plate (VZPS, Vladimir, Russia) was used. The chemical compositions of the initial materials is presented in Table 1, Table 2 and Table 3.
The bonding surfaces were ground with 800-grit SiC paper and degreased in acetone prior to explosive welding. The welding scheme is shown in Figure 1. A mixture of ammonite 6GV with quartz sand (in a 50/50 ratio) was used as the explosive material. The detonation velocity of the explosive was about 2000 m/s. Calculated EXW modes are shown in Table 4. Details on the calculation of welding parameters (such as collision point velocity, Vc, impact velocity, Vi, stand-off distances, etc.) are presented in [31].
Explosively welded three-layer composites were initially heat treated at 640 °C for 1 h to remove the protective steel layer. These HT parameters accelerated the formation of an intermetallic layer at the steel–aluminum interface, with a thickness sufficient to cause spontaneous separation of the steel layer.
The aluminum-coated titanium was cut into square shapes with dimensions of 10 mm ×10 mm. Some specimens were heated to 700 or 850 °C and held for 20 h to form intermetallic coating at the Ti-Al interface via interdiffusion reactions. The lower temperature corresponds to the melting point of the aluminum alloy, while the higher temperature does not exceed the allotropic transformation temperature of titanium.
HT was performed in a SNOL-12/16 (OZ VNIIETO LLC, Moscow, Russia) electric furnace in air.
The cross-sectional microstructures of the samples were evaluated using scanning electron microscopy (SEM—Versa 3D, FEI, Morristown, NJ, USA). Elemental composition was determined using the Oxford 51N1286 AZtecLive Expert energy-dispersive X-ray spectroscopy (EDS) system equipped with an Ultim Max 65 detector (Oxford Instruments, Abingdon, UK). To enable microstructure observation and chemical analysis in SEM, the sample cross-sections were polished with abrasive papers and mirror-finished using a 0.5 μm diamond slurry.
Prior to this, specimens were mounted in conductive polyester resin using metallographic press POLYLAB S50L (KEMIKA, Moscow, Russia).
A Bruker D8 Advance Eco X-ray diffractometer (XRD—Bruker AXS GmbH, Karlsruhe, Germany) in the Bragg–Brentano geometry with Kβ filtered CuKα radiation (λ = 0.15406 nm) was used to identify the intermetallic phases.
The microhardness was measured on a PMT-3M device (JSC LOMO, Saint Petersburg, Russia) with an indenter load of 0.5–1 N.

3. Results and Discussion

The structure of 20880 steel + AD1 aluminum + VT1-0 titanium composite obtained after EXW is shown in Figure 2. Plastic deformation during EXW led to a change in the thickness of the constituent layers: 1.55 mm for steel, 0.32 mm for aluminum, and 2.9 mm for titanium.
Metallographic studies of the 20880 + AD1 interface structure after welding (Figure 2) revealed the presence of molten metal in the form of thin (~10 μm) localized areas near the beginning of the plate. Their hardness does not exceed ~3 GPa, and the area is on average ~0.003 mm2. At the end of the plate, molten metal of significantly greater thickness and extent is observed with an average area of 0.013 mm2, while its composition remains unchanged. The results of EDS analysis showed that the molten metal consists of a mechanical mixture of aluminum and the FeAl3 intermetallic compound (Figure 3).
The metallographic analysis of the VT1-0 + AD1 interface showed the formation of localized areas of molten metal at the interlayer boundary, with a thickness not exceeding 2–3 μm. According to the results of EDS analysis, the composition of the molten metal corresponds to the TiAl2 intermetallic compound (Figure 4).
From our previous studies [35], it is known that iron aluminides formed at the interface of explosively welded steel–aluminum composites, under conditions of both solid-phase and liquid-phase diffusion interaction, are prone to cracking upon reaching a certain thickness when the composite is cooled from the HT temperature, which leads to the destruction of the composite.
During experiments on HT of three-layer 20880 + AD1 + VT1-0 composites, it was established that spontaneous separation of the steel layer is guaranteed to occur during cooling of composites with a diffusion zone thickness of more than 30 μm. Destruction occurs due to thermal stresses at the steel–aluminum interlayer interface, caused by the difference in thermal expansion coefficients of the metals and the formation of a main crack in the intermetallic layer.
The three-layer composite was subjected to HT at 640 °C for 1 h, which ensured the formation of a diffusion zone of the required thickness (30–50 μm) (Figure 5a). The diffusion zone consists of two layers: an Fe2Al5 intermetallic compound, located on the steel side, and a thin layer of FeAl3 intermetallic on the aluminum side. XRD analysis (Figure 5b) confirmed the presence of Fe2Al5 and FeAl3 intermetallics, as well as FeAl2. The microhardness of the diffusion zone is ~12 GPa.
The destruction of the diffusion zone allowed the steel layer to separate from the composite and, thus, led to the formation of an aluminum coating on the titanium surface. At the same time, inclusions of fractured Fe-aluminides remained on the aluminum surface (Figure 6).
At the VT1-0 + AD1 interface, HT at 640 °C resulted in the formation of a thin intermetallic layer (<20 μm) (Figure 7a). Its microhardness ranges from 5.3 to 5.5 GPa. According to the EDS line scan results, the diffusion zone contains, on average, ~75 at. % Al and ~25 at. % Ti (Figure 7b), indicating that its composition corresponds to the TiAl3 intermetallic compound.
According to the Al-Ti phase diagram [39], due to the presence of a concentration gradient at the Al—TiAl3 interface, HT of the coating at a temperature above the melting point of aluminum should lead to a stable frontal increase in the thickness of TiAl3. It is known [33] that the formation of the intermetallic phase during HT in the presence of a liquid phase (Al) occurs in several stages. The process begins with the formation of intermetallic phase nuclei, the role of which is played by areas of molten metal. Then, the intermetallic nuclei intensively grow along the joint boundary with the formation of a continuous intermetallic layer. The TiAl3 layer formed during solid-phase interaction is in a complex stress state. As the thickness of the TiAl3 layer increases, the stress level in this layer also increases. When the critical stress level is reached, the continuous intermetallic layer fractures. This is due to the low ductility of the TiAl3 aluminide. TiAl3 fragments separated from the continuous layer expose a new surface, on which the chemical reaction resumes. The reaction of TiAl3 formation leads to the release of additional heat, which increases the melt temperature in the reaction zone. This causes the temperature gradient and convective melt flows. The circulating melt flows transport the separated TiAl3 fragments from the reaction zone and, together with the diffusion of titanium atoms, ensure the formation of the matrix structure. Increase in temperature reduces the viscosity of the melt and intensifies the heat flows transporting the separated new fragments of the intermetallic from the reaction surface into the melt. The fragmentation of the resulting aluminide is facilitated by the Rebinder effect, which consists of an adsorption decrease in the strength of solids, facilitating their deformation and destruction under the physicochemical influence of a liquid medium [40].
To identify the transformation patterns of the aluminum layer to intermetallic coatings, samples were heated at 700 and 850 °C with different holding times.
In the structure of the coating on titanium after HT at 700 °C for 1 h, two different layers can be distinguished (Figure 8): the outer layer and the layer adjacent to titanium. In the outer layer (Figure 8b), the eutectic structure of FeAl3 + (Al) is uniformly distributed in the aluminum matrix. The significant deviation in the Fe content in the aluminide in the eutectic composition can be explained by the small size of the analyzed inclusions (in some cases less than 200 nm), as neighboring areas of the aluminum matrix contribute to the region generating the characteristic radiation. In the layer adjacent to titanium (Figure 8c), the separated TiAl3 particles are located in the aluminum matrix.
The XRD pattern (Figure 9), obtained directly from the coating surface after HT at 700 °C for 1 h, contains peaks of the FeAl3 phase and aluminum, with additional peaks of TiAl3 titanium aluminide observed in the layer adjacent to titanium.
Increasing the heat treatment time at 700 °C to 4 h resulted in the formation of an aluminide coating based on the intermetallic compound TiAl3 (Figure 10), which is confirmed by the EDS (Figure 10e) and XRD results (Figure 11). The increase in time is accompanied by an increase in the thickness of the TiAl3 intermetallic layer and the particles separating from it and filling the volume of molten aluminum.
At the same time, when the TiAl3 particles reach the coating surface, oxidation processes begin. As a result, the outer coating layer undergoes a transformation: a frame-type structure is formed, in which the TiAl3 particles are separated from each other by an oxide phase (Figure 10b,e, point 3). In the XRD pattern obtained directly from the coating surface, in addition to the peaks of the TiAl3 phase, there are peaks of the TiAl2 aluminide and the low-temperature modification of κ-Al2O3 aluminum oxide, as well as peaks of “residual” (unreacted) aluminum. The formation of TiAl2 aluminide on the coating surface can be caused by the TiAl3→TiAl2 phase transformation occurring at the surface of the TiAl3 particles, caused by the consumption of Al for oxide formation.
In the middle part of the coating and in the layer adjacent to the titanium (Figure 10c,e), light inclusions are formed, whose formation is associated with the diffusion of Fe from intermetallic fragments remaining on the surface of the aluminum layer after steel separation. The chemical composition of the inclusions (Figure 10c and Figure 12) in the middle part is ~75 at. % Al, ~2 at. % Ti, and ~23 at. % Fe, which corresponds to the FeAl3 aluminide or a solid solution based on it. According to literature data, the FeAl3 phase can dissolve up to 6.5 at. % Ti; however, when cooled to room temperature, the solubility decreases to 2.5 at. % Ti [41].
The inclusions located closer to titanium contain ~73 at. % Al, ~19 at. % Ti, and ~8 at. % Fe. It is known that ~1.2 at. % Fe dissolves in the TiAl3 binary aluminide [41]. On the other hand, in the Al-Ti-Fe system, in addition to binary compounds, the formation of ternary phases τ1 (TiFe2Al), τ2 (TiFeAl2), and τ3 (Ti8Fe3Al22) is possible. The composition of the τ3-phase is closest to the composition of the detected inclusions. However, the diffraction pattern obtained from the middle part of the coating contains peaks only of FeAl3 and TiAl3 (Figure 11). Peaks from ternary compounds were not detected, which may be due to their small amount (below the detection limit) or may indicate the formation of a solid solution based on the aluminide—TiAl3(Fe).
Increasing the heat treatment time at 700 °C to 20 h (Figure 13) leads, on the one hand, to an increase in the thickness of the layer with the frame-type intermetallic–oxide structure, and on the other hand, to the formation of a diffusion zone between the coating and the titanium substrate. This diffusion zone is ~5–10 μm thick and consists of several continuous layers of TiAl2, TiAl, and Ti3Al aluminides (as they approach titanium). Its formation mechanism is attributed to a series of solid-phase reactions occurring due to the existing concentration gradient at the coating–titanium interface in the following sequence: TiAl3→TiAl2→TiAl→Ti3Al.
The structure and composition of Fe-containing inclusions in the middle part of the coating remained virtually unchanged, whereas the inclusions located closer to titanium became more finely dispersed, and their composition approached the composition of the solid solution of Fe in TiAl3 (Figure 13d,e, point 5).
In the XRD patterns (Figure 14) obtained from the coating surface after HT at 700 °C for 20 h, along with the κ-Al2O3, peaks of the stable modification of α-Al2O3 aluminum oxide are observed, which indicates the evolution of oxidation processes and the transformation of the low-temperature polymorph of Al2O3 into a higher-temperature form.
Increasing the HT temperature to 850 °C contributed to a more intensive formation of the TiAl3 intermetallic compound. Thus, after 1 h at 850 °C, the entire coating, 350 μm thick, had an intermetallic structure (Figure 15). The fundamental difference in the structure of the obtained coating, compared to the structure obtained after HT at 700 °C for 4 h, is the uniform distribution of Fe-aluminide inclusions throughout the coating volume, which is confirmed by the presence of FeAl3 peaks in the XRD pattern taken from the coating surface (Figure 16). A layered diffusion zone less than 2 μm thick is observed along the boundary with the substrate. According to EDS analysis, the layers correspond to intermetallic compounds: TiAl2, TiAl, and Ti3Al (Figure 15b,c).
Heat treatment at 850 °C for 20 h leads to the formation of a well-defined frame-type intermetallic–oxide (TiAl3 + TiAl2 + Al2O3) structure throughout the entire thickness of the coating (Figure 17). The thickness of the continuous diffusion zone at the boundary with titanium is ~20 μm.
According to the XRD results (Figure 18), the α-Al2O3 peaks become more pronounced, which may also indicate the formation of a continuous Al2O3 oxide layer on the coating surface. No other phases were detected (apart from the TiAl3 and TiAl2 aluminides) including those potentially present in the continuous diffusion zone. In addition, no peaks from titanium oxide (TiO2) were observed, likely due to the higher Gibbs energy of its formation compared to Al2O3.
The previously observed individual Fe-containing inclusions were no longer present in the coating structure. EDS analysis indicates that the maximum Fe concentration is in the transition zone between the intermetallic–oxide region of the coating and the continuous diffusion zone consisting of TiAl2, TiAl, and Ti3Al aluminide layers (Figure 19). According to point EDS analysis, this layer contains more than 5 at. % Fe and corresponds to the τ3 phase (Figure 17c,d, point 4).
Microhardness tests showed that, after HT at 700 °C, the microhardness of the coating in the upper part, where the frame-type intermetallic–oxide structure is formed, is ~5.0–5.5 GPa, increasing to 6.0 GPa near the interface with titanium, which corresponds to the hardness of monolithic TiAl3. An increase in the temperature to 850 °C leads to a decrease in the hardness of the coating with a pronounced frame-type structure. Moreover, the more the aluminide particles are separated, the lower the microhardness values. The minimum values are observed in the near-surface zone of the coating and are ~3.3 GPa. Upon transition to the interface with titanium, the coating hardness increases to 5.9 GPa. No cracks (chippings) were formed at the indentation sites in any of the test variants.
Thus, the obtained coating contains mostly TiAl3 aluminide, which, due to the high aluminum content, has good oxidation resistance. To confirm the possibility of using such coatings under high-temperature oxidation conditions, additional oxidation resistance tests must be carried out.

4. Conclusions

  • Explosive welding using a plane-parallel scheme at optimal process parameters ensures the fabrication of a three-layer titanium VT1-0—aluminum AD1—steel 20880 composite with a minimum level of chemical microheterogeneity (molten metal) at its interlayer boundaries. At the VT1-0—AD1 interlayer boundary the molten metal crystallized in the form of a continuous layer, consisting of a mechanical mixture of Al + TiAl3, and at the AD1- steel 20880 boundary—mainly in the form of separate small areas, consisting of a mechanical mixture of Al + FeAl3. The microhardness of the molten metal is within 1.5–3 GPa.
  • Heat treatment of explosively welded three-layer composite at 640 °C for 1 h leads to the formation of the brittle Fe2Al5 intermetallic layer in the diffusion zone at the aluminum-steel interface. Upon cooling, a main crack forms in this layer, leading to spontaneous separation of the protective steel layer from the aluminum.
  • Heat treatment of aluminum-coated titanium at temperatures of 700 and 850 °C leads to the formation of a diffusion layer on its surface based on TiAl3 titanium aluminide, which fills the entire volume of molten aluminum, due to a gradual increase in its thickness. The layer grows due to the upward transportation of TiAl3 fragments, which are separated from the diffusion zone by circulating melt flows. At the same time, a frame-type structure of the coating is formed, in which TiAl3 intermetallic particles are separated from each other by an oxide phase containing ~25 at. % oxygen. Between the coating and the titanium substrate there is a diffusion layer ~5–10 μm thick, consisting of continuous layers of TiAl2, TiAl, and Ti3Al (as they approach titanium). The mechanism of its formation is driven by solid-phase reactions occurring along the concentration gradient at the coating–titanium interface in the following sequence: TiAl3→TiAl2→TiAl→Ti3Al.
  • The microhardness of the coating with the TiAl3 + Al2O3 frame-type structure decreases with increasing heat treatment temperature from ~5.0–5.5 GPa to 3.3 GPa due to the increasing separation of individual TiAl3 intermetallic particles by an oxide phase. As the interface with titanium is approached, the microhardness increases to 6.0 GPa, which corresponds to the hardness of solid TiAl3.

Author Contributions

Conceptualization, V.G.S.; methodology, A.I.B. and V.P.K.; validation, V.P.K. and A.I.B.; investigation, A.I.B. and V.P.K.; writing—original draft preparation, A.I.B., V.P.K., and R.E.N.; writing—review and editing, V.G.S.; visualization, V.P.K. and R.E.N. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the Russian Science Foundation (project No. 25-29-20030, https://rscf.ru/en/project/25-29-20030/ (accessed on 1 July 2025)) and by the Volgograd Region Administration.

Data Availability Statement

The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author(s).

Acknowledgments

Part of this research (electron microscopy and energy dispersive X-ray spectroscopy) was carried out using the equipment of the Center for Collective Use of the Volgograd State Technical University.

Conflicts of Interest

Author Roman Evgenevich Novikov was employed by the company JSC, VNIKTIneftekhimoborudovanie, Volgograd, Russia. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interes.

References

  1. Gialanella, S.; Malandruccolo, A. Titanium and Titanium Alloys. In Aerospace Alloys; Topics in Mining, Metallurgy and Materials Engineering; Springer International Publishing: Cham, Switzerland, 2020; pp. 129–189. ISBN 978-3-030-24439-2. [Google Scholar]
  2. Dai, J.; Zhu, J.; Chen, C.; Weng, F. High Temperature Oxidation Behavior and Research Status of Modifications on Improving High Temperature Oxidation Resistance of Titanium Alloys and Titanium Aluminides: A Review. J. Alloys Compd. 2016, 685, 784–798. [Google Scholar] [CrossRef]
  3. Dong, E.; Yu, W.; Cai, Q.; Cheng, L.; Shi, J. High-Temperature Oxidation Kinetics and Behavior of Ti–6Al–4V Alloy. Oxid. Met. 2017, 88, 719–732. [Google Scholar] [CrossRef]
  4. Valenza, T.C.; Weber, P.K.; Marquis, E.A. Role of Nitrogen in the High-Temperature Oxidation of Titanium Alloys. Corros. Sci. 2024, 235, 112164. [Google Scholar] [CrossRef]
  5. Gurrappa, I.; Gogia, A.K. Development of Oxidation Resistant Coatings for Titanium Alloys. Mater. Sci. Technol. 2001, 17, 581–587. [Google Scholar] [CrossRef]
  6. Froes, F.H.; Suryanarayana, C.; Eliezer, D. Synthesis, Properties and Applications of Titanium Aluminides. J. Mater. Sci. 1992, 27, 5113–5140. [Google Scholar] [CrossRef]
  7. Zarchi, H.R.K.; Soltanieh, M.; Aboutalebi, M.R.; Guo, X. Thermodynamic Study on Pack Aluminizing Systems of Pure Titanium and Nickel. Trans. Nonferrous Met. Soc. China 2013, 23, 1838–1846. [Google Scholar] [CrossRef]
  8. Szkliniarz, W.; Moskal, G.; Szkliniarz, A.; Swadźba, R. The Influence of Aluminizing Process on the Surface Condition and Oxidation Resistance of Ti–45Al–8Nb–0.5(B, C) Alloy. Coatings 2018, 8, 113. [Google Scholar] [CrossRef]
  9. Du, H.; Tan, N.; Fan, L.; Zhuang, J.; Qiu, Z.; Lei, Y. Formation Mechanism of Aluminide Diffusion Coatings on Ti and Ti-6Al-4V Alloy at the Early Stages of Deposition by Pack Cementation. Materials 2019, 12, 3097. [Google Scholar] [CrossRef]
  10. Yumoto, A.; Hiroki, F.; Shiota, I.; Niwa, N. In Situ Synthesis of Titanium-Aluminides in Coating with Supersonic Free-Jet PVD Using Ti and Al Nanoparticles. Surf. Coat. Technol. 2003, 169–170, 499–503. [Google Scholar] [CrossRef]
  11. Pyachin, S.A.; Burkov, A.A.; Komarova, V.S. Formation and Study of Electrospark Coatings Based on Titanium Aluminides. J. Synch. Investig. 2013, 7, 515–522. [Google Scholar] [CrossRef]
  12. Baptista, A.; Silva, F.; Porteiro, J.; Míguez, J.; Pinto, G. Sputtering Physical Vapour Deposition (PVD) Coatings: A Critical Review on Process Improvement and Market Trend Demands. Coatings 2018, 8, 402. [Google Scholar] [CrossRef]
  13. Mridha, S.; Baker, T.N. Oxidation Protection Behaviour of Titanium Aluminide Coatings Developed by TIG Technique. Adv. Mater. Process. Technol. 2015, 1, 453–464. [Google Scholar] [CrossRef]
  14. Mizuta, N.; Matsuura, K.; Kirihara, S.; Miyamoto, Y. Titanium Aluminide Coating on Titanium Surface Using Three-Dimensional Microwelder. Mater. Sci. Eng. A 2008, 492, 199–204. [Google Scholar] [CrossRef]
  15. Henckell, P.; Ali, Y.; Metz, A.; Bergmann, J.P.; Reimann, J. In Situ Production of Titanium Aluminides during Wire Arc Additive Manufacturing with Hot-Wire Assisted GMAW Process. Metals 2019, 9, 578. [Google Scholar] [CrossRef]
  16. Hoosain, S.E.; Pityana, S.; Freemantle, C.S.; Tlotleng, M. Heat Treatment of In Situ Laser-Fabricated Titanium Aluminide. Metals 2018, 8, 655. [Google Scholar] [CrossRef]
  17. Maliutina, I.N.; Si-Mohand, H.; Sijobert, J.; Bertrand, P.; Lazurenko, D.V.; Bataev, I.A. Structure and Oxidation Behavior of γ-TiAl Coating Produced by Laser Cladding on Titanium Alloy. Surf. Coat. Technol. 2017, 319, 136–144. [Google Scholar] [CrossRef]
  18. Lazurenko, D.V.; Golkovsky, M.G.; Stark, A.; Pyczak, F.; Bataev, I.A.; Ruktuev, A.A.; Petrov, I.Y.; Laptev, I.S. Structure and Properties of Ti-Al-Ta and Ti-Al-Cr Cladding Layers Fabricated on Titanium. Metals 2021, 11, 1139. [Google Scholar] [CrossRef]
  19. Cizek, J.; Man, O.; Roupcova, P.; Loke, K.; Dlouhy, I. Oxidation Performance of Cold Spray Ti–Al Barrier Coated γ-TiAl Intermetallic Substrates. Surf. Coat. Technol. 2015, 268, 85–89. [Google Scholar] [CrossRef]
  20. Balcı, E.; Karakaş, A.; Bayram, B.; Kaba, M.; Muhaffel, F.; Tilki, P.K.; Tan, E.; Baydoğan, M. Formation of In Situ Al/TiAl3 Coatings on Electron Beam Melted (EBM) Ti-6Al-4V Alloy by Cold Spray and Induction Heating. J. Therm. Spray. Tech. 2025, 34, 1685–1699. [Google Scholar] [CrossRef]
  21. Ulianitsky, V.Y.; Dudina, D.V.; Shtertser, A.A.; Smurov, I. Computer-Controlled Detonation Spraying: Flexible Control of the Coating Chemistry and Microstructure. Metals 2019, 9, 1244. [Google Scholar] [CrossRef]
  22. Sienkiewicz, J.; Kuroda, S.; Murakami, H.; Araki, H.; Giżyński, M.; Kurzydłowski, K.J. Fabrication and Oxidation Resistance of TiAl Matrix Coatings Reinforced with Silicide Precipitates Produced by Heat Treatment of Warm Sprayed Coatings. J. Therm. Spray. Tech. 2018, 27, 1165–1176. [Google Scholar] [CrossRef]
  23. Sasaki, T.; Yagi, T.; Watanabe, T.; Yanagisawa, A. Aluminizing of TiAl-Based Alloy Using Thermal Spray Coating. Surf. Coat. Technol. 2011, 205, 3900–3904. [Google Scholar] [CrossRef]
  24. Bogdanov, A.I.; Kulevich, V.P.; Shmorgun, V.G.; Gurevich, L.M. Structure and Properties of Ti-Al Intermetallic Coatings Reinforced with an Aluminum Oxide Filler. Metals 2024, 14, 1336. [Google Scholar] [CrossRef]
  25. Deqing, W.; Ziyuan, S.; Yingli, T. Microstructure and Oxidation of Hot-Dip Aluminized Titanium at High Temperature. Appl. Surf. Sci. 2005, 250, 238–246. [Google Scholar] [CrossRef]
  26. Patel, P.; Jamnapara, N.I.; Zala, A.; Kahar, S.D. Investigation of Hot-Dip Aluminized Ti6Al4V Alloy Processed by Different Thermal Treatments in an Oxidizing Atmosphere. Surf. Coat. Technol. 2020, 385, 125323. [Google Scholar] [CrossRef]
  27. Patel, P.; Zala, A.; Parekh, T.; Kahar, S.D.; Jamnapara, N.I. High Temperature Oxidation Behavior of Thermal and Plasma Processed Aluminide Coated Ti6Al4V Alloys. Surf. Coat. Technol. 2022, 447, 128839. [Google Scholar] [CrossRef]
  28. Wang, X.; Li, C.; Li, M.; Cao, J. Enhancing High-Temperature Oxidation Resistance of Ti6Al4V Alloy by Simple Surface Aluminization. Corros. Sci. 2021, 192, 109810. [Google Scholar] [CrossRef]
  29. Zhang, Z.G.; Peng, Y.P.; Mao, Y.L.; Pang, C.J.; Lu, L.Y. Effect of Hot-Dip Aluminizing on the Oxidation Resistance of Ti–6Al–4V Alloy at High Temperatures. Corros. Sci. 2012, 55, 187–193. [Google Scholar] [CrossRef]
  30. Findik, F. Recent Developments in Explosive Welding. Mater. Des. 2011, 32, 1081–1093. [Google Scholar] [CrossRef]
  31. Shmorgun, V.; Bogdanov, A.; Kulevich, V.; Taube, A. Experimental Research of the Explosive Welding of Metal Plates with Different Initial Hardness. Mater. Manuf. Process. 2024, 39, 207–216. [Google Scholar] [CrossRef]
  32. Zhang, T.; Wang, W.; Yan, Z.; Zhang, J. Interfacial Morphology and Bonding Mechanism of Explosive Weld Joints. Chin. J. Mech. Eng. 2021, 34, 8. [Google Scholar] [CrossRef]
  33. Gurevich, L.M.; Shmorgun, V.G. Intermetallic Compound Formation During Reaction of Molten Aluminum with Titanium. Metallurgist 2016, 59, 1221–1227. [Google Scholar] [CrossRef]
  34. Shmorgun, V.G.; Bogdanov, A.I.; Kulevich, V.P. Structure and Phase Composition of the Al-Ti System Composites after Heat Treatment. Defect Diffus. Forum 2021, 410, 519–524. [Google Scholar] [CrossRef]
  35. Shmorgun, V.G.; Slautin, O.V.; Kulevich, V.P. Features of Diffusion Interaction in Steel-Aluminum Composite After Explosive Welding and Aluminizing by Melt Immersion. Metallurgist 2019, 63, 766–774. [Google Scholar] [CrossRef]
  36. Bogdanov, A.; Kulevich, V.; Shmorgun, V.; Taube, A. Formation of Thermally Grown Aluminum Oxide Scale on the Surface of Ni2Al3/Ni Layered Coating. Oxid. Met. 2022, 98, 199–216. [Google Scholar] [CrossRef]
  37. Shmorgun, V.G.; Bogdanov, A.I.; Taube, A.O.; Kulevich, V.P. Evaluation of Heat Resistance and Thermal Conductivity of Ni–Cr–Al System Layered Coatings. Metallurgist 2022, 66, 934–941. [Google Scholar] [CrossRef]
  38. Shmorgun, V.G.; Bogdanov, A.I.; Kulevich, V.P. The Effect of Aluminum Content in the Fe-Cr-Al System Alloys on the Oxide Films Phase Composition. Mater. Today: Proc. 2020, 30, 554–558. [Google Scholar] [CrossRef]
  39. Murray, J.L. (Ed.) Phase Diagrams of Binary Titanium Alloys; Monograph series on alloy phase diagrams; 2. print. ASM International: Metals Park, OH, USA, 1990; ISBN 978-0-87170-248-7. [Google Scholar]
  40. Rehbinder, P.A.; Shchukin, E.D. Surface Phenomena in Solids during Deformation and Fracture Processes. Prog. Surf. Sci. 1972, 3, 97–188. [Google Scholar] [CrossRef]
  41. Schuster, J.C.; Palm, M. Reassessment of the Binary Aluminum-Titanium Phase Diagram. J. Phase Equilibria Diffus. 2006, 27, 255–277. [Google Scholar] [CrossRef]
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Figure 1. EXW scheme. 1—chipboard; 2—titanium alloy; 3—aluminum alloy; 4—steel; 5—stand-off distance; 6—explosive; and 7—electric detonator.
Figure 1. EXW scheme. 1—chipboard; 2—titanium alloy; 3—aluminum alloy; 4—steel; 5—stand-off distance; 6—explosive; and 7—electric detonator.
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Figure 2. Structure of the three-layer 20880 + AD1 + VT1-0 composite after EXW.
Figure 2. Structure of the three-layer 20880 + AD1 + VT1-0 composite after EXW.
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Figure 3. Structure of the molten metal at the 20880 + AD1 interface after EXW (a), the distribution of chemical elements (b), and the results of point EDS analysis (c).
Figure 3. Structure of the molten metal at the 20880 + AD1 interface after EXW (a), the distribution of chemical elements (b), and the results of point EDS analysis (c).
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Figure 4. Structure of the molten metal at the VT1-0 + AD1 interface after EXW (a) and the results of point EDS analysis (b).
Figure 4. Structure of the molten metal at the VT1-0 + AD1 interface after EXW (a) and the results of point EDS analysis (b).
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Figure 5. Structure of the diffusion zone at the 20880 + AD1 interface after HT at 640 °C for 1 h (a) and XRD pattern (b).
Figure 5. Structure of the diffusion zone at the 20880 + AD1 interface after HT at 640 °C for 1 h (a) and XRD pattern (b).
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Figure 6. Structure of the aluminum-coated titanium after separation of the steel layer.
Figure 6. Structure of the aluminum-coated titanium after separation of the steel layer.
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Figure 7. Structure of the diffusion zone at the VT1-0 + AD1 interface after HT at 640 °C for 1 h (a) and the distribution of chemical elements (b).
Figure 7. Structure of the diffusion zone at the VT1-0 + AD1 interface after HT at 640 °C for 1 h (a) and the distribution of chemical elements (b).
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Figure 8. Structure of the coating after HT at 700 °C for 1 h (a–c) and the results of point EDS analysis (b). The horizontal lines (I, II) show the sections along the coating depth in which the XRD analysis was carried out.
Figure 8. Structure of the coating after HT at 700 °C for 1 h (a–c) and the results of point EDS analysis (b). The horizontal lines (I, II) show the sections along the coating depth in which the XRD analysis was carried out.
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Figure 9. XRD patterns of the coating after HT at 700 °C for 1 h (Figure 8a).
Figure 9. XRD patterns of the coating after HT at 700 °C for 1 h (Figure 8a).
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Figure 10. Structure of the coating after HT at 700 °C for 4 h (a–d) and the results of point EDS analysis (e). The horizontal lines (I, II) show the sections along the coating depth in which the XRD analysis was carried out.
Figure 10. Structure of the coating after HT at 700 °C for 4 h (a–d) and the results of point EDS analysis (e). The horizontal lines (I, II) show the sections along the coating depth in which the XRD analysis was carried out.
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Figure 11. XRD patterns of the coating after HT at 700 °C for 4 h (Figure 10a).
Figure 11. XRD patterns of the coating after HT at 700 °C for 4 h (Figure 10a).
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Figure 12. Element distribution maps in Fe-containing inclusions (Figure 10c).
Figure 12. Element distribution maps in Fe-containing inclusions (Figure 10c).
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Figure 13. Structure of the coating after HT at 700 °C for 20 h (a–d) and the results of point EDS analysis (e). The horizontal lines (I, II) show the sections along the coating depth in which the XRD analysis was carried out.
Figure 13. Structure of the coating after HT at 700 °C for 20 h (a–d) and the results of point EDS analysis (e). The horizontal lines (I, II) show the sections along the coating depth in which the XRD analysis was carried out.
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Figure 14. XRD patterns of the coating after HT at 700 °C for 20 h (Figure 13a).
Figure 14. XRD patterns of the coating after HT at 700 °C for 20 h (Figure 13a).
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Figure 15. Structure of the coating after HT at 850 °C for 1 h (a,b) and the results of point EDS analysis (c).
Figure 15. Structure of the coating after HT at 850 °C for 1 h (a,b) and the results of point EDS analysis (c).
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Figure 16. XRD patterns of the coating after HT at 850 °C for 1 h.
Figure 16. XRD patterns of the coating after HT at 850 °C for 1 h.
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Figure 17. Structure of the coating after HT at 850 °C for 20 h (a–c) and the results of point EDS analysis (d). The horizontal lines (I, II) show the sections along the coating depth in which the XRD analysis was carried out.
Figure 17. Structure of the coating after HT at 850 °C for 20 h (a–c) and the results of point EDS analysis (d). The horizontal lines (I, II) show the sections along the coating depth in which the XRD analysis was carried out.
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Figure 18. XRD patterns of the coating after HT at 850 °C for 20 h (Figure 17a).
Figure 18. XRD patterns of the coating after HT at 850 °C for 20 h (Figure 17a).
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Figure 19. Element distribution maps in continuous diffusion zone (Figure 17c).
Figure 19. Element distribution maps in continuous diffusion zone (Figure 17c).
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Table 1. Chemical composition of VT1-0 titanium (mass %).
Table 1. Chemical composition of VT1-0 titanium (mass %).
TiFeSiNOHCOthers
99.24–99.70≤0.25≤0.10≤0.04≤0.20≤0.01≤0.07<0.30
Table 2. Chemical composition of AD1 (1013) aluminum (mass %).
Table 2. Chemical composition of AD1 (1013) aluminum (mass %).
AlMgSiMnFeZnCuTi
>99.30≤0.05≤0.30≤0.025≤0.30≤0.10≤0.05≤0.15
Table 3. Chemical composition of 20880 steel (mass %).
Table 3. Chemical composition of 20880 steel (mass %).
CSiMnSPFe
≤0.035≤0.30≤0.30≤0.03≤0.02Bal.
Table 4. EXW modes.
Table 4. EXW modes.
MaterialLayer Thickness, mmHeight of the Explosive, mmStand-Off Distance, mmVc, m/sVi, m/s
208801.5800.52000530
AD10.35
VT1-03.02.0590
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MDPI and ACS Style

Bogdanov, A.I.; Kulevich, V.P.; Novikov, R.E.; Shmorgun, V.G. Formation of Intermetallic Coatings on Titanium by Explosive Welding and Subsequent Heat Treatment of the Layered Metal Composite. J. Compos. Sci. 2025, 9, 379. https://doi.org/10.3390/jcs9070379

AMA Style

Bogdanov AI, Kulevich VP, Novikov RE, Shmorgun VG. Formation of Intermetallic Coatings on Titanium by Explosive Welding and Subsequent Heat Treatment of the Layered Metal Composite. Journal of Composites Science. 2025; 9(7):379. https://doi.org/10.3390/jcs9070379

Chicago/Turabian Style

Bogdanov, Artem Igorevich, Vitaliy Pavlovich Kulevich, Roman Evgenevich Novikov, and Victor Georgievich Shmorgun. 2025. "Formation of Intermetallic Coatings on Titanium by Explosive Welding and Subsequent Heat Treatment of the Layered Metal Composite" Journal of Composites Science 9, no. 7: 379. https://doi.org/10.3390/jcs9070379

APA Style

Bogdanov, A. I., Kulevich, V. P., Novikov, R. E., & Shmorgun, V. G. (2025). Formation of Intermetallic Coatings on Titanium by Explosive Welding and Subsequent Heat Treatment of the Layered Metal Composite. Journal of Composites Science, 9(7), 379. https://doi.org/10.3390/jcs9070379

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