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An metal–intermetallic material based on the combustion products of the layered system (Ti–Al–Mg)/Ti was first obtained using the self-propagating high-temperature synthesis (SHS) combined with pressing. Exothermic synthesis from elemental powders was carried out at a pressure of 10 MPa, and the hot product of synthesis was pressed at a pressure of 250 MPa. It was demonstrated that the SHS pressing process results in an inseparable bond between the "intermetallic/metal" layers. The main features of microstructure formation, phase composition, and strength properties of the transition zones at the interface between the reacting SHS compositions Ti–Al–Mg and the Ti substrate were investigated. The thickness of the transition zone between the layers was at least 15 μm. Energy-dispersive analysis (EDA) showed that Mg in the synthesized alloy is mainly located in intergranular layers, in the form of a small amount of Ti–Al–Mg compound, indicating incomplete reaction diffusion between the Ti–Al and Al–Mg layers. The microhardness of Ti–Al grains in the synthesized alloy is 5820 MPa on average, while that of the matrices based on Al–Mg is 3980 MPa. The hydrostatic density is 3.3 g/cm3, with a porosity of less than 13%. The porosity of the Ti–Al–Mg alloy obtained by the SHS pressing method was reduced by three times. [ABSTRACT FROM AUTHOR]

The morphology of microstructure and tensile properties of Ti-48Al-2Cr-2Nb (at％) alloy rods fabricated by the electron beam powder bed fusion (EB-PBF) process were investigated with a particular focus on the influence of scan speed of the electron beam. Homogeneous near lamellar structure composed of the α2 and γ phases can be obtained in the rod fabricated under the slowest scan speed. The fine lamellar spacing which contributes to the high strength of the alloy is derived from the fast-cooling rate of EB-PBF. On the contrary, a layered microstructure comprising a duplex-like region and an equiaxed γ grain layer (γ band) perpendicular to the building direction is obtained when increasing scan speeds. We observed for the first time that an increase in the scan speed results in a narrow width of the γ band. We also found that these microstructural changes have a significant influence on the mechanical properties of the rods. The near lamellar structure exhibits higher strength compared to the layered microstructure. Whereas, the rods with the layered microstructure show large ductility at room temperature. The elongation of each rod strongly depends on the width of the γ band owing to the preferential deformation of the γ band. [ABSTRACT FROM AUTHOR]

The influence of furnace annealing on the structure of cast metal in ingots of 200 mm diameter of the intermetallic Ti-28Al-7Nb-2Mo-2Cr titanium alloy produced by the method of electron beam melting and its welded joints produced by the method of electron beam welding was determined. It was determined that the EBM metal produced from the ingots of 200 mm diameter is satisfactorily welded under the conditions of applying such additional technological measures as preheating and local heat treatment. It is shown that annealing at the temperature of 1260 °C for 10 h led to the formation of a uniform microstructure in the base metal, HAZ and weld metal, decomposition of the duplex structure and absence of regions with a two-phase (γ+α2)-lamellar structure. The room temperature strength of welded joints after annealing is equal to 746 MPa or 98 % of the base metal strength. [ABSTRACT FROM AUTHOR]

This article evaluates the fabrication technologies of titanium aluminide (Ti-Al) and its practical applications by comparing it with the well-known Ti-Al binary phase diagram and US patents. Meanwhile, by analyzing and discussing the various patented Ti-Al fabrication technologies and applications, this article discusses the applications of Ti-Al-based alloys, mainly in the aircraft field. The improved fabrication processes and new application technologies are under patent protection. These technologies are classified into six categories: basic research on Ti-Al-based alloys, powder metallurgy of Ti-Al-based alloys, casting and melting of Ti-Al-based alloys, PM and AM manufacturing methods for aircraft applications, other fabrication technologies by Ti-Al-based alloys, and self-propagating high-temperature synthesis (SHS) of Ti-Al-based alloys. By comparing the principles and characteristics of the above techniques, the advantages, disadvantages, and application fields of each are analyzed and their developments are discussed. Based on the characteristics of Ti-Al, new fabrication and application technologies can be developed, which can overcome the existing disadvantages and be used to form new aircraft components. [ABSTRACT FROM AUTHOR]

The influence of furnace annealing on the structure of cast metal in 200 mm ingots from intermetallic titanium alloy Ti–28Al–7Nb–2Mo–2Cr produced by electron beam melting and of its welded joints produced by the method of electron beam welding was determined. It is established than the metal of 200 mm Ti–28Al–7Nb–2Cr–2Mo ingots based on titanium aluminide is readily welded under the conditions of application of such technological measures as preheating and local heat treatment. It is shown that annealing at the temperature of 1260 °C for 10 h led to formation of a uniform microstructure in the base metal, HAZ and weld metal, decomposition of the duplex structure and absence of regions with a two-phase (γ+α2)-lamel structure. Room temperature strength of welded joints after annealing is equal to 746 MPa or 98 % of base metal strength. [ABSTRACT FROM AUTHOR]

Works have been performed on optimization of the technological scheme of producing ingots for consumable electrodes with a stable chemical composition and properties. The paper presents the results of studying an ingot of 195 mm diameter from a titanium aluminide-based alloy of Ti-28Al-7Nb-2Mo system, made by double electron beam remelting. Further ingot remelting in the arc furnace was performed, which allowed producing a homogeneous and defect-free ingot of an optimal composition of Ti-28Al-7Nb-2Mo-0.3 (Y, Re, B). The influence of modifying on the structure and properties was studied. It was determined that addition of surfactants promotes refining of the structural components and improvement of the alloy mechanical properties. [ABSTRACT FROM AUTHOR]

Work has been performed on optimization of the technological scheme of producing ingots for consumable electrodes with a stable chemical composition and properties. The paper presents the results of studying an ingot of 195 mm diameter from a titanium aluminide-based alloy of Ti–28Al–7Nb–2Mo system, made by double electron beam remelting. Further ingot remelting in the arc furnace was performed, which allowed producing a homogeneous and defectfree ingot of an optimal composition of Ti–28Al–7Nb–2Mo–0.3 (Y, Re, B). The influence of modifying on the structure and properties was studied. It was determined that addition of surfactants promotes refining of the structural components and improvement of the alloy mechanical properties. [ABSTRACT FROM AUTHOR]

Al–3Ti–1B and Al–5Ti–1B master alloys represent the most popular modifiers for the majority of aluminum alloy groups. To date, several methods, requiring various conditions and resource costs, have been applied for producing these master alloys. The paper presents the results of a comparative analysis of methods for producing Al–3Ti–1B master alloy using both a Ti sponge and salts (K2TiF6 and KBF4) as the starting components. The degree of Ti and B recovery for three methods of the master alloy production was experimentally established. The phase and element compositions of slags were studied; the amount of fluorine gas, emitted during the master alloy production, was calculated. A method, using a titanium sponge and molten KBF4 + KCl mixture, was identified to ensure a recovery of Ti and B equal to 88.10 and 72.20%, respectively. The modifying ability of the produced master alloys was studied both according to the TP-1 method and using the laboratory and industrial unit of semi-continuous casting. [ABSTRACT FROM AUTHOR]

The effect of the linear energy input (EL), varied from 120 to 300 J/m due to a change in the electron beam current (I) from 4 to 20 mA and the scanning speed (v) from 2 to 8 m/s, on residual porosity, aluminum content and local distribution, and microstructure has been studied on as-built samples of a new six-component intermetallic beta-solidifying TiAl alloy Ti–44.5Al–2V–1Nb–2Cr–0.1Gd, at.% (Ti–31.0Al–2.5V–2.5Nb–2.5Cr–0.4Gd, wt.%) produced by selective electron beam melting (SEBM). It has been established that layer-by-layer processing at EL ≥ 250 J/m allows producing dense material with a residual porosity of less than 1 vol.%. It has been revealed that an increase in EL results in the average aluminum content reduction by ΔAl = 1.7 at.% at EL = 300 J/m and distribution inhomogeneity thereof in the vertical cross-section of the samples (building direction Z), with the formation of layered structure consisting of Al-enriched and Al-depleted alternating layers. It has been shown that a fine-grained equiaxed microstructure is formed after processing at EL < 200 J/m and I < 8 mA; an increase in EL and I results in the formation of columnar grains, predominantly located in Al-depleted layers, as well as an increase in their size and volume fraction. After all studied SEBM modes, both columnar and equiaxed grains exhibit lamellar intragranular ( γ + α 2 ) colonies with γ and β0/B2 phases at grain boundaries, which corresponds to the sequence of phase transformations predicted by thermodynamic simulation. [ABSTRACT FROM AUTHOR]

The dual microstructure concept for gamma titanium aluminides (γ-TiAl) processed via electron beam–powder bed fusion (PBF-EB) provides a huge potential for more efficient jet turbine engines. While the concept is feasible and the mechanical properties are promising, there are still some challenges. For an industrial application, the heat treatment window has to match the conditions in industrial furnaces. This study shows how the required heat treatment window can be achieved via advanced PBF-EB technology. Through using an electron beam with 150 kV acceleration voltage, the difference in aluminum between the designed aluminum-rich and aluminum-lean regions of the part is increased. Moreover, the aluminum content within each of these regions, respectively, is more homogenous compared to the 60 kV acceleration voltage. This combination provides a heat treatment window of 25 °C, enabling the industrial application of the dual microstructure concept for γ-TiAl. [ABSTRACT FROM AUTHOR]

The microstructures of intermetallic γ-titanium aluminide (TiAl) alloys are subjected to a certain degree of Al evaporation when processed by electron beam powder bed fusion (EB-PBF). The magnitude of the Al-loss is mainly correlated with the process parameters, and highly energetic parameters produce significant Al evaporation. The Al-loss leads to different microstructures, including the formation of inhomogeneous banded structures, thus negatively affecting its mechanical performance. For this reason, the current work deals with creating EB-PBFed TiAl capsules with the inner part produced using only the pre-heating step and melting parameters with low energetic parameters applying high beam speed from 5000 to 3000 mm/s. This approach is investigated to reduce the Al-loss and microstructure inhomogeneity after hot isostatic pressing (HIP). The results showed that the HIP treatment effectively densified the capsules obtaining a relative density of around 100%. After HIP, the capsules produced with the inner part melted at 3000 mm/s presented a lower area shrinkage (around 6.6%) compared to the capsules produced using only the pre-heating step in the core part (around 20.7%). The different magnitudes of shrinkage derived from different levels of residual porosity consolidated during the HIP process. The HIPed capsules exhibited the presence of previous particle boundaries (PPBs), covered by α2 phases. Notably, applying low energetic parameters to melt the core partially eliminates the particles' surface, thus reducing the PPBs formation. In this case, the capsules melted with low energetic parameters (3000 mm/s) exhibited α2 concentration of 3.5% and an average size of 13 µm compared to the capsules produced with the pre-heating step in the inner part with an α2 around 5.7% and an average size around 23 µm. Moreover, the Al-loss of the capsules was drastically limited, as determined by X-ray fluorescence (XRF) analysis. More in detail, the capsules produced with the pre-heating step reported an atomic percentage of Al of 48.75, while using low energetic melting parameters led to 48.36. This result was interesting, considering that the massive samples produced with standard parameters (so more energetic ones) revealed atomic Al percentage from 48.04 to 47.70. Finally, the recycled small particles showed a higher fraction of α2 phases with respect to the coarse particles, as determined by X-ray diffraction (XRD). [ABSTRACT FROM AUTHOR]

Titanium aluminide (TiAl) alloys have emerged as promising materials for high-temperature applications due to their unique combination of high-temperature strength, low density, and excellent oxidation resistance. However, the fabrication of TiAl alloys using conventional methods is challenging due to their high melting points and limited ductility. Selective laser melting (SLM), an additive manufacturing technique, offers a viable solution for producing TiAl alloys with intricate geometries and the potential for tailoring their microstructure. This study investigates the effect of in situ copper alloying and multiple laser scans on the microstructure and mechanical properties of TiAl-based alloys fabricated using SLM. The results demonstrate that copper alloying enhances the formation of the α2-Ti3Al phase, refines the microstructure, and improves the mechanical properties of TiAl alloys. Multiple laser scans allow for the creation of distinct microstructural regions within a single component, enabling the tailoring of properties that are suitable for specific operating conditions. The findings provide valuable insights into the fabrication and optimization of TiAl intermetallic alloys with diverse applications. [ABSTRACT FROM AUTHOR]

We have studied the technological properties, chemical composition, and structure of a metal powder composition (MPC, 40–100 μm) made from a new six-component intermetallic β-solidifying TiAl-alloy Ti–44.5Al–2V–1Nb–2Cr–0.1Gd, at. % (Ti–31.0Al–2.5V–2.5Nb–2.5Cr–0.4Gd, wt.%) by crucibleless induction melting inert gas atomization and intended for additive manufacturing of dense parts by selective electron beam melting (SEBM). It is shown that the main elements of the composition of the MPC are the same as in the electrode, and the phase composition of the MPC corresponds to a rapidly solidified metastable state (γ + α + β). High flowability and sphericity of the MPC were achieved. The Al content in the starting electrode reduces by 1.1–1.3 at.% (1.0–1.2 wt.%) after SEBM due to evaporation. The microstructure of the as-SEBM-built testpieces exhibited intragranular lamellar (γ + α2)-colonies and some γ- and β0/B2-phases at grain boundaries. It was found out that the cross-sectional distribution of Ti and Al along the building direction (Z) is nonuniform, resulting in nonuniform distribution of phases and grain sizes. No areas with duplex or coarse-grained γ-phase, which are characteristic for the 2nd-generation electron beam melted TiAl-alloy Ti-4822, were identified. [ABSTRACT FROM AUTHOR]

Herein, an innovative powder‐cored wire arc additive manufacturing (PC‐WAAM) process is proposed to fabricate γ‐TiAl thin‐walled intermetallic alloy. The metallography, phase composition, and mechanical properties at different thin‐wall locations are characterized. The results show that the alternatively distributed layer‐like microstructure composed of α2 (Ti3Al) and γ (TiAl) phases is obtained along the building direction. The content of α2 phase exhibits the tendency of decreasing from the bottom to top region. This unique microstructure characteristic is closely related to the typical thermal cycling history during deposition. Moreover, the tensile strength and microhardness of the top region are lower than the middle and bottom region. In general, the current PC‐WAAM technique shows promising capability of fabricating γ‐TiAl intermetallic alloy with low cost. This work becomes a valuable reference for understanding the evolution mechanism of microstructure and paves the way for the flexible and customized additive manufacturing of γ‐TiAl alloy. [ABSTRACT FROM AUTHOR]

The morphology of microstructure and tensile properties of Ti48Al2Cr2Nb (at%) alloy rods fabricated by the electron beam powder bed fusion (EB-PBF) process were investigated with a particular focus on the influence of scan speed of the electron beam. Homogeneous near lamellar structure composed of the ¡2 and £ phases can be obtained in the rod fabricated under the slowest scan speed. The fine lamellar spacing which contributes to the high strength of the alloy is derived from the fast-cooling rate of EB-PBF. On the contrary, a layered microstructure comprising a duplex-like region and an equiaxed £ grain layer (£ band) perpendicular to the building direction is obtained when increasing scan speeds. We observed for the first time that an increase in the scan speed results in a narrow width of the £ band. We also found that these microstructural changes have a significant influence on the mechanical properties of the rods. The near lamellar structure exhibits higher strength compared to the layered microstructure. Whereas, the rods with the layered microstructure show large ductility at room temperature. The elongation of each rod strongly depends on the width of the £ band owing to the preferential deformation of the £ band. [ABSTRACT FROM AUTHOR]

The products of the combustion synthesis in titanium, silicon, and aluminum powder mixtures under a wave combustion mode are studied using X-ray diffraction analysis and optical metallography. The synthesis products contain titanium silicide Ti5Si3 and titanium aluminide TiAl3, the ratio of which depends on the content of aluminum powder in the reaction mixtures. The combustion temperature of the mixtures decreases with an increase in the aluminum content owing to the substitution of titanium aluminide in the synthesis products for titanium silicide, which has a multiply less negative enthalpy of formation compared to that of the silicide. The effect of the combustion temperature on the dispersity of the structure of the synthesis products is considered using the concepts of the features of the growth of silicide and aluminide nuclei in a liquid metal solution. [ABSTRACT FROM AUTHOR]

In this work, an ultrafine-grained high-Nb–TiAl alloy with a nominal composition of Ti–45Al–8Nb–0.2W–0.2B (at%) was prepared by cryomilling and subsequent spark plasma sintering (SPS) technique. The chemical composition, particle size, morphology and crystallite size of cryomilled powder were studied. It is found that cryomilling can effectively reduce the particle size and enhance grain refinement. The ingots sintered at 900 and 1000 °C show an equiaxed near-γ microstructure with grain sizes < 700 nm, while the sample sintered at 1100 °C exhibits duplex microstructure. Especially, the one sintered at 1000 °C has excellent mechanical properties, whose compression yield strength, fracture strength, bending strength and plastic strain achieve 1310, 2174, 578 MPa and 16.8%, respectively. The reasons for the effect of cryomilling and the mechanical behavior of sintered ingots were discussed. It is suggested that cryomilling in combination with SPS is an effective way to synthesize high-Nb–TiAl alloy with ultrafine-grained structure. [ABSTRACT FROM AUTHOR]

Twin-wire plasma arc additive manufacturing (TW-PAAM) is an innovative process for titanium aluminide manufacture which is low in equipment cost and high in efficiency. However, as an in situ alloying process, the composition homogeneity is typically a source of concern. The present work investigates this subject by observing the element input mode at various welding wire positions with a high-speed camera system and particle tracking method. It is found that when the welding wires are in a high position, the droplet enters the molten pool from the tip of the titanium wire, and the alloy element input interval is long, resulting in the formation of bands with high aluminium content at the edge of the deposition layer. When the welding wires are close to the workpiece surface, the droplet transfer mode switches to a mixture of dual wire-bridge transfer and Ti wire-bridge transfer. The diameter and transfer interval of the droplets decrease, as well as the heterogeneity of the deposition layer. The conclusion establishes a correlation between droplet transfer mode and composition homogeneity, which is beneficial for optimizing the TW-PAAM titanium aluminide fabrication process. [ABSTRACT FROM AUTHOR]

In this article, an attempt was made to investigate the effect of the addition of silicon on the titanium aluminide compound formation from TiO2 and Al raw materials. Silicon has a eutectic with aluminum and can reduce its melting temperature, which can have effective impact on the formation of titanium aluminide compounds. On the other hand, due to the production of Ti5Si3 compound, it can be effective in increasing the oxidation resistance of compounds and composites containing titanium aluminide. With this aim in mind, the present paper has strove to determine the impact of this element on the formation of titanium aluminides and the type of titanium silicide phases by adding different amounts of silicon to TiO2 and Al raw materials. The key findings emerged, showed that when silicon is added to the system in small amounts (0.1), it not only does not have a positive effect on the reactions, it also prevents the formation of titanium aluminide compounds, but with an increase in its percentage (0.28), it also causes the formation of these titanium aluminide compounds and leads to the formation of Ti5Si3 phase. This phase changes from a discrete morphology to a continuous state as the percentage of silicon increases (0.6). With a further increase in the amount of silicon (1), the TiSi2 phase is formed, which is dispersed throughout the sample with a string-like structure. [ABSTRACT FROM AUTHOR]

Titanium aluminide (TiAl) alloy is attracting attention in the automobile and aviation industries as a promising lightweight heat-resistant alloy material. Parts used in high-temperature environments must have ductility and toughness at room temperature in addition to high strength at high temperatures, however, some alloys, such as TiAl alloys, are known to be difficult materials for casting and machining. Recently, manufacturing processes using additive manufacturing (AM) have been studied to solve these problems. In the present research, the effect of energy density during the AM process on surface roughness and on the strength of the built parts was studied by changing build parameters. As the energy density increased, the porosity and surface roughness decreased. Additionally, higher energy density tended to increase the fraction of lamellar structure. It was found, however, that an increase in lamellar structure does not necessarily lead to any improvement in tensile or creep strength at 750°C. We found that a constant energy density of 15 J/mm³ showed better tensile and creep properties than those of the standard parameter. Our results suggest that it is important to optimize the parameters according to the required properties of the parts. [ABSTRACT FROM AUTHOR]

Microstructure and tensile properties of Ti-8Al-2Cr-2Nb (at%) rods fabricated by electron beam powder bed fusion (EB-PBF) process were investigated by changing input energy density (ED) which is one of the important factors affecting formation of the melt pool. We found that unique layered micro structure consisting of an equiaxed γ grain layer (γ band) and a duplex region can be formed by EB-PBF with ED in the range of 13 to 31 J/mm³. It is interesting to note that the width of the γ band and the volume fraction of the γ phase in the duplex region decrease with increasing ED. On the other hand, the α2/γ lamellar grain in the duplex region increases with increasing ED. These morphological changes in the layered micro structure are attributed to variation of temperature distribution from melt pool caused by increasing ED. Moreover, we also found for the first time the strength of the alloys can be improved by decreasing width of the γ band and increasing of the α2/γ lamellar grain in the duplex region. Whereas, the width of the γ band and the fraction of the equiaxed γ grain in the duplex region should be increased to enhance ductility of the alloys. [ABSTRACT FROM AUTHOR]

The development of process parameters for electron beam powder bed fusion (PBF-EB) is usually made with simple geometries and uniform scan lengths. The transfer to complex parts with various scan lengths can be achieved by adapting beam parameters such as beam power and scan speed. Under ideal conditions, this adaption results in a constant energy input into the powder bed despite of the local scan length. However, numerous PBF-EB machines show deviations from the ideal situation because the beam diameter is subject to significant changes if the beam power is changed. This study aims to demonstrate typical scaling issues when applying process parameters to scan lengths up to 45 mm using a fourth generation γ-TiAl alloy. Line energy, area energy, return time, and lateral velocity are kept constant during the additive manufacturing process by adjusting beam power and beam velocity to various scan lengths. Samples produced in this way are examined by light microscopy regarding lateral melt pool extension, melt pool depth, porosity, and microstructure. The process-induced aluminum evaporation is measured by electron probe microanalysis. The experiments reveal undesired changes in melt pool geometry, gas porosity, and aluminum evaporation by increasing the beam power. In detail, beam widening is identified as the reason for the change in melt pool dimensions and microstructure. This finding is supported by numerical calculations from a semi-analytic heat conduction model. This study demonstrates that in-depth knowledge of the electron beam diameter is required to thoroughly control the PBF-EB process, especially when scaling process parameters from simply shaped geometries to complex parts with various scan lengths. [ABSTRACT FROM AUTHOR]

The effect of mechanical activation of tial powder on the structural and phase transformations in mechanochemical synthesis of the powder mixture of the composition 60.8fe + 39.2-i-1, intended to produce fe3al intermetallics, alloyed with titanium was studied. using a semi-empirical miedema's model, the changes of Gibbs energy for the binary ti-al, fe-ti and fe-al systems were calculated. the results showed that the driving force for the formation of intermetallic phases for all the binary systems is higher as compared to the formation of solid solutions and amorphous phases. a range of compositions was established, at which the formation of amorphous phases in the binary Ti-al and fe-al systems is possible. carrying out the mechanical activation of tial intermetallic powder in a high-energy planetary mill allowed reducing the size of a coherent scattering region from 280 to 9 nm with a partial amorphization. the formation of particles with a homogeneous microstructure consisting of intermetallic phase (Fe, Ti)3al and laves phases -- Fe2ti was revealed in the process of mechanochemical synthesis of a powder mixture 60.8fe + 39.2 Tial when using nanostructural tial powder. the change in the region of coherent scattering of powders of 60.8fe + 39.2Tial mixture, produced by the method of mechanochemical synthesis, was evaluated and it was established that interaction of a nanostructural powder tial with fe begins to occur when the size of a coherent scattering region becomes <70 nm. the resulting product has an amorphous-nanocrystalline structure with a size of the coherent scattering region of <15 nm. the use of the developed powder in thermal spraying technologies will allow producing coatings based on Fe3al intermetallics with a nanocrystalline structure, a higher modulus of elasticity and ductility. [ABSTRACT FROM AUTHOR]

The effect of mechanical activation of TiAl powder on the structural and phase transformations in mechanochemical synthesis of the powder mixture of the composition 60.8Fe + 39.2TiAl, intended to produce Fe3Al intermetallics, alloyed with titanium was studied. Using a semi-empirical Miedema’s model, the changes of Gibbs energy for the binary systems Ti-Al, Fe-Ti and Fe-Al were calculated. The results showed that the driving force for the formation of intermetallic phases for all the binary systems is higher as compared to the formation of solid solutions and amorphous phases. A range of compositions was established, in which the formation of amorphous phases in the binary systems Ti-Al and Fe-Al is possible. Carrying out the mechanical activation of TiAl intermetallic powder in a high-energy planetary mill allowed reducing the size of a coherent scattering from 280 to 9 nm with a partial amorphization. The formation of particles with a homogeneous microstructure consisting of intermetallic phase (Fe, Ti)3Al and Lavhes’s phases – Fe2 Ti was established in the process of mechanchemical synthesis of a powder mixture 60.8Fe+39.2 TiAl when using nanostructural TiAl powder. The change in the area of coherent scattering of powders of 60.8Fe+39.2TiAl mixture was evaluated, obtained by the method of mechanochemical synthesis, and it was established that interaction of a nanostructural powder TiAl with Fe begins to occur when the size of the coherent scattering area is <70 nm. The resulting product has an amorphous-nanocrystalline structure with the size of the coherent scattering area of <15 nm. The use of the developed powder in thermal spraying technologies will allow producing coatings based on Fe3Al intermetallics with a nanocrystalline structure, a higher modulus of elasticity and ductility. [ABSTRACT FROM AUTHOR]

In this work, titanium aluminide alloy have been fabricated via the laser deposition technique. The effect of some selected deposition parameters on the microstructure and mechanical properties of produced deposits were studied. The relationship between the laser power, and the microhardness of deposited samples on laser preheated substrate showed an incremental change in laser power from 200 to 600 W. This led to an overall decrease in microhardness of deposited samples from 426 to 373 HV. Sample deposited at 500 W gave the lowest Icorr of 1.8 x 10-8 and the highest Ecorr of -0.138 V. It is evident from the nanoindentation results that indentation modulus and stiffness of sample deposited at 600 W laser power had a lower value compared with 400 W laser power. However, the modulus of both samples fell within titanium alloy modulus range between 105-120 GPa. The microstructures of the deposits are mainly characterized with γ-TiAl and α2-Ti3Al phases and an improved hardness property almost two times higher than that of commercially pure titanium were achieved. It was concluded that changes in the laser power directly causes changes in the microstructure, hardness, stiffness, modulus of elasticity and corrosion resistance of the deposits. [ABSTRACT FROM AUTHOR]

Due to the inherent temperature brittleness and poor workability, the forming and fabrication of TiAl alloy is extremely difficult. Thus, in recent years, an innovative twin-wire-based plasma arc additive manufacturing (TW-PAAM) technique has been developed to fabricate the Ti-48Al alloy with low cost. In this research, the Ti-48Al alloys are fabricated by the TW-PAAM and the tungsten inert gas welding-based wire and arc additive manufacturing (TIG-WAAM). Afterward, the microstructure, residual stress and fatigue properties are characterized subsequently. The microstructure of the TiAl alloy was found to consist of a dendritic grain region and a fully lamellar colony region. The fully lamellar colonies composed of α2 and γ phases, and the size of the lamellar colonies tends to increase from the upper to the lower. The residual stress value in the TiAl alloy of lower part is higher than the upper part. Additionally, the mean residual stress value of TW-PAAM TiAl alloy (57.6 MPa) is lower than the TIG-WAAM TiAl alloy(68.4 MPa), decreasing by 15.7%. And the fatigue strength of TiAl alloy in the lower part shows poor fatigue properties compared to the upper part, which is mainly attribute to the effect of residual stress and the size of lamellar colonies. [ABSTRACT FROM AUTHOR]

In this work, titanium aluminide alloy have been fabricated via the laser deposition technique. The effect of some selected deposition parameters on the microstructure and mechanical properties of produced deposits were studied. The relationship between the laser power, and the microhardness of deposited samples on laser preheated substrate showed an incremental change in laser power from 200 to 600 W. This led to an overall decrease in microhardness of deposited samples from 426 to 373 HV. Sample deposited at 500 W gave the lowest Icorr of 1.8 x 10-8 and the highest Ecorr of -0.138 V. It is evident from the nanoindentation results that indentation modulus and stiffness of sample deposited at 600 W laser power had a lower value compared with 400 W laser power. However, the modulus of both samples fell within titanium alloy modulus range between 105-120 GPa. The microstructures of the deposits are mainly characterized with γ-TiAl and α2-Ti3Al phases and an improved hardness property almost two times higher than that of commercially pure titanium were achieved. It was concluded that changes in the laser power directly causes changes in the microstructure, hardness, stiffness, modulus of elasticity and corrosion resistance of the deposits. [ABSTRACT FROM AUTHOR]

The aim of this research was to study the tribological behaviour of Ti–48Al–2Nb–2Cr alloy under dry sliding reciprocating conditions. A reciprocating wear machine was employed to evaluate the typical abrasion resistance of the alloy. Infrastructure assessment of worn surfaces was performed by scanning electron microscopy (SEM) analysis equipped with Energy Dispersive X-Ray Spectroscopy (EDS). The average surface roughness of initial specimen was 32 nm. According to the SEM observations of worn surfaces and debris, the dominant wear mechanism under defined tribosystem was identified to be abrasive and delamination wear. The weight loss measurements showed that by increasing the applied load from 10 to 40 N, the weight loss was significantly increased from 5.4 to 18.5 µg after passing 1000 m slip distance. [ABSTRACT FROM AUTHOR]

A mathematical model was developed of the processes of alloying element evaporation at cold-hearth electron beam melting of ingots of alloys based on titanium aluminide of Ti–Al–Nb–Cr–Mo alloying system that establishes the dependence of alloying element concentration in the ingot on technological parameters of melting and chemical composition of the initial charge. It is shown that the developed mathematical model adequately describes the real evaporation process at electron beam melting of titanium aluminide alloy. The regularities of alloying element evaporation at electron beam melting of alloys based on titanium aluminide of Ti–Al–Nb–Cr–Mo system were established, which allow predicting the chemical composition of the ingots and optimizing the technological parameters of melting. Ref. 21, Tabl. 2, Fig. 5. [ABSTRACT FROM AUTHOR]

The paper presents the structure and phase composition of Ti−Al−Si powder composites produced in different conditions, which include vacuum sintering and self-propagating high-temperature synthesis (SHS). The certain ratios of reactive components are used in experiments for the formation of two-phase composites, matching the TiAl3 + Ti5Si3 and Ti3Al + Ti5Si3 compositions. The vacuum sintering of Ti−Al−Si powder composites provides mostly the formation of the two-phase structure, but the quantitative ratio of the appeared phases can considerably differ from the calculated compositions. The lattice parameters in these phases are rather distorted. The analysis of the synthesis in the wave mode combustion of Ti−Al−Si powder composites shows that the synthesis completes only in the TiAl3 + Ti5Si3 composite. This allows us to prepare the powder from the synthesized product. The paper analyzes the behavior of the synthesized powder based on the phase composition of the TiAl3 + Ti5Si3 composite after the vacuum sintering of the powder compacts. It is found that after the 1300°C vacuum sintering of the SHS products based on the TiAl3 + Ti5Si3 composite, its qualitative phase composition remains with a small change in the quantitative phase composition. The compaction of the SHS products is observed together with the reduction in the residual porosity. [ABSTRACT FROM AUTHOR]

Titanium Aluminide (TiAl) alloys are intermetallics that offer low density, high melting point, good oxidation and corrosion resistance compared to Ni-based superalloys. As a result, these alloys are used in aero-engine parts such as turbine blades, fuel injectors, radial diffusers, divergent flaps, and more. During operation, aero-engine components are subjected to high thermal loading in an oxidizing and corrosive environment, which results in wear and other material damage. Replacement of the entire component may not be desirable due to long lead time and expense. In such cases, repair and refurbishing may be the best option for the reclamation of TiAl parts. Unfortunately, approved repair technology is not currently available for TiAl based components. Additive Manufacturing (AM) based Directed Energy Deposition (DED) may serve as an option to help repair and restore expensive aero-engine parts. In this work, a review of efforts to utilize the DED technique to repair damaged TiAl-based aerospace parts locally is conducted. Replacing the entire TiAl part is not advisable as it is expensive. DED is a promising technique used to produce, repair, rework, and overhaul (MRO) damaged parts. Considering the high-quality standard of the aircraft industry, DED repaired TiAl parts to be certified for their future use in the aircraft is very important. However, there are no standards for the certification of TiAl repaired parts is reported. Case studies reveal that DED is under consideration for repair of TiAl parts. Hybrid technology comprising machining, repair and finishing capability in a single machine is an attractive implementation strategy to improve repair efficacies. The review shows that the investigations into development and applications of DED-based repairing techniques are limited, which suggests that further investigations are very much needed. [ABSTRACT FROM AUTHOR]

Boronising is a thermochemical treatment which enhances the resistivity of metals used as component in applications dominated by wear and corrosion. In this study, boronising was performed on a gamma-TiAl intermetallic alloy with the pack cementation method. The experiments took place at temperatures 1173–1323 K for 8–14 h and a compact hard boride layer was formed. Its thickness varied between 6 and 25 μm. An 80 μm wide boron diffusion zone with elevated hardness was detected via micro-hardness measurements. The measured thickness values were applied to a mathematical model based on Fick's second law of diffusion to extract the kinetic parameters of the process. Additionally, the presence of the ΤiΒ2 and the total absence of the TiB phase were confirmed via XRD measurements. The hardness of the coating and the substrate was evaluated using Vickers micro-hardness tester (above 1100 HV at the coating layer). [ABSTRACT FROM AUTHOR]

Hot deformation studies of a newly designed γ + α2 based TiAl alloy of composition Ti–42Al–6Nb–3Cr–0.1B at.% (nominal) realized through ingot metallurgy route using double vacuum arc remelting were carried out. Hot isothermal compression testing was performed in Gleeble™ 3500 at different temperatures ranging from 1123 to 1373 K at 50 K intervals and strain rates of 0.001–1 s−1. Processing maps were developed using an approach of dynamic material modeling of the flow curves to establish the safe hot working regime. Strain rate sensitivity and Zener–Holloman parameters were calculated and constitutive equation was derived. Microstructural investigation revealed dynamic recrystallization and activation of multiple twin systems as the main softening mechanisms operating at optimum hot working conditions. Safe hot working temperature and strain rate regime for the alloy was found to be in the temperature range of 1323–1373 K and strain rate range of 0.001–0.01 s−1. [ABSTRACT FROM AUTHOR]

This paper describes the effect of preliminary mechanical activation (MA) and Ti content on maximum temperature, maximum burning rate, composite particle size, mixture yield after MA, sample elongation during combustion, and the phase composition and morphology of combustion products in the Ni–Ti–Al system. The preliminary MA of a Ni + Al + Ti mixture expands the limit of titanium content at which samples can burn without preheating, from 17 to 59% (by weight). Mechanical activation is followed by a drop in the number of phases in the products and an increase in the burning rate, while the maximum synthesis temperature decreases. The augmentation of the Ti content in the Ni + Al + Ti mixture reduces the burning rate and maximum combustion temperature of both initial and mechanically activated mixtures. Moreover, as the titanium content increases, the average size of composite particles decreases and the yield of the activated mixture becomes larger. In the combustion of mechanically activated mixtures with a high (24–52%) titanium content, the Ti2Ni phase and the Ni2TiAl Heusler phase predominate in the products, while the traces of melting are visually observed. In the activated Ni + Al + Ti mixture, the Ti content at which the Heusler phase content in the combustion products becomes maximum is revealed. Most of the observed dependences are explained. [ABSTRACT FROM AUTHOR]

Mechanical alloying (MA) of Al60Ti40 (wt%) has been successfully done by using a planetary ball mill having mixed balls of 5 mm and 15 mm diameter to refine the crystallite size of the elemental powder and to get the new MAed phase of AlTi. The microstructural and morphological analysis of elemental as well as the processed powder was done with help of Scanning Electron Microscope and X-Ray diffraction technique. Mechanical alloying of elemental Al and Ti resulted in the formation of AlTi phases with the reflection of α-Ti3Al and TiAl3. The average particle size was reduced around 7 times after 60 h of milling. The mean crystallite size of MAed powder was also reduced up to 85 nm after 60 h of mechanical alloying under controlled conditions. [ABSTRACT FROM AUTHOR]

This study was conducted to reveal the relationship between the oriented microstructure and mechanical properties of Ti-48Al-2Cr-2Nb fabricated by electron beam melting (EBM). The microstructure observation in EBM sample showed that duplex structure/γ band layers fabricated by EBM process. Tensile and creep tests were conducted for two kinds of samples fabricated by EBM. One was a sample in which loading direction was parallel to the building direction (vertical sample) and another was sample in which the loading direction was normal (horizontal sample). The tensile test showed anisotropic tensile properties at room temperature, 650℃ and 750℃. The tensile strengths of the vertical samples were inferior to the horizontal samples due to the oriented duplex structure with γ band layers. The creep lives were 206 h tested at 650℃/450MPa and 298 h tested at 750℃/200 MPa in the vertical sample, whereas they were 332 h tested at 650℃/450 MPa and 326 h tested at 750℃/200 MPa in the horizontal sample; i.e., the creep test also showed the anisotropy of creep rupture life due to the oriented microstructure. [ABSTRACT FROM AUTHOR]

The results of experimental studies on the development of a method for obtaining titanium-containing bar ligature, the study of its structure and modifying ability are presented. The distinctive features of the new technology are the use of titanium sponge and/or titanium shavings as titanium raw materials, the primary alloying of aluminum with titanium, and then boron, the introduction of titanium in two stages: initially, 2/3 of the titanium metal raw materials are dissolved in the aluminum melt, and the remaining amount is introduced after the reduction of potassium tetrafluoroborate. Pre-impregnation of the titanium sponge with halide-containing flux and the use of a briquetted mixture of KBF4 + Al-powder are also provided. The experimental technology for the preparation of the Al–Ti–B melt is described, the extraction of titanium and boron into the ligature is calculated, its microstructure is investigated, and the chemical and molecular compositions of the resulting slags are determined. Deformation treatment for the production of bar ligature was carried out by the method of direct extrolling which made it possible to level the defects of the cast structure. It is established that the use of high-speed crystallization-deformation in the implementation of the combined direct extrolling process makes it possible to obtain alloying bars of a given diameter at minimal energy consumption with the required complex of mechanical and operational properties. A quantitative assessment of the modifying ability of the experimental cast-iron ligature and the deformed cast-iron rod obtained by the direct extrolling method was carried out in comparison with the mass-produced cast-iron ligature produced by KBM Affilips (the Netherlands/Belgium). Based on theoretical and experimental studies, the composition and technology for producing Al–Ti–B modifying ligature using titanium sponge and/or shavings and potassium tetrafluoroborate with a content of 3.0 ± 0.3% titanium and 1.0 ± 0.2% boron as alloying additives have been developed, which meets the requirements for the composition of aluminum ligatures. [ABSTRACT FROM AUTHOR]

The utilization of materials with high strength to density ratio enables efficiency improvements and is therefore demanded for many applications, particularly in the aerospace and other mobility sectors. However, the machining of these typically difficult-to-cut materials poses a challenge for conventional manufacturing technologies due to the high tool wear. Abrasive water jet (AWJ) machining is a promising alternative manufacturing technology for machining difficult-to-cut materials, since the tool wear is low and material independent. However, AWJ machining is limited regarding the producible geometries when conducting cuts through a material. This limitation can be resolved with AWJ milling operations which on the other hand are time-consuming. To approach this challenge, an enhanced AWJ milling operation is presented and investigated in this paper with the aim to expand the producible geometries. This operation consists of two kerfs, inserted from different sides of the workpiece, which intersect at their kerf ground. Consequently, a piece of material is separated without the cut material being entirely chipped. Thus, the operation possesses a high aggregated material removal rate. The investigations presented in this paper show and evaluate the effects that occur during the milling of kerfs with variable depths on titanium aluminide TNM-B1. Furthermore, a method to compensate these effects is introduced and thus the producible geometries for effective AWJ milling could be enhanced. [ABSTRACT FROM AUTHOR]

Synthesis is carried out in a Ti + Al mixture prepared by two methods, namely preliminary mechanical activation (MA) or preheating. Synthesis occurs in the cases of layer-by-layer combustion (SHS) and thermal explosion. The dependences of burning rates of activated Ti + Al mixtures on the MA duration are investigated. The relationships between the initial temperature and the rates and maximum combustion temperatures of initial mixtures along with the elongation of samples after combustion are determined. The phase composition of the initial mixtures after activation and of the synthesis products is described. The MA duration (12 min) at which the burning rate of the mixture is maximum is experimentally determined. For this mixture (12-min long MA), the dependence of the burning rates and maximum combustion temperatures along with the elongation of samples after combustion on the initial temperature is studied. Synthesis at which the content of the main phases (TiAl and Ti3Al) in the products is maximized is established. [ABSTRACT FROM AUTHOR]

The Al3Ti compound has potential application in the high temperature structure materials due to its low density, high strength and stiffness. The mechanical behaviors of the material under different loading rates were studied using compression tests. The results indicate that Al3Ti is a typical brittle material and its compressive strength is dependent on the strain rate. Therefore, a series of rate-dependent constitutive equations are needed to describe its mechanical behaviors accurately. However, it is still short of professional research on the material model for Al3Ti. In this study, the material model was developed on the basis of JH-2 constitutive equations using the experimental data. The model was then applied in simulating the impact process of Ti/Al3Ti metal-intermetallic laminate composites so as to validate the established model. Good agreement between simulation and experiment results shows the constitutive model predict the material responses under high rate and large deformation accurately. This work provides more support for the theoretical and numerical research on the intermetallic. [ABSTRACT FROM AUTHOR]

Gas turbine components are often operated in harsh conditions, which can lead to severe damage. As it is highly desirable from both an economical and an ecological point of view to restore these worn areas instead of manufacturing new components, repair technologies are of huge interest for companies supplying maintenance and overhaul of gas turbines. In this article, two thermal techniques are described that can be used for this application: cold gas spraying (CGS) and vacuum plasma spraying (VPS). The CGS process allows the deposition of metallic coatings with excellent mechanical properties; several examples including γ‐TiAl, Inconel (IN) 718, and IN 738 are given. Essential for the deposition of high‐performance coatings in CGS is to exceed the so‐called critical velocity. This is discussed also with experimental findings. As a final topic, experiments that use VPS for the repair of single‐crystal alloys are described. [ABSTRACT FROM AUTHOR]

The influence of preheating, burning mode, and mechanical activation on combustion of Ti–Al mixtures was studied. Process conditions that ensure a largest TiAl + Ti3Al content of combustion product have been outlined. [ABSTRACT FROM AUTHOR]

Casting technology of thin-wall TiAl alloy turbochargers was studied by investment casting and numerical simulation. Misruns and gas holes were the main defects observed in preliminary work due to the poor fluidity of alloy, and to gas entrapment. In order to eliminate these defects, cast parameters, such as centrifugal rotation rate and mould preheating temperature, were optimized by numerical simulation, meanwhile, the structure of the shell mould was optimized to improve the filling capacity of TiAl alloy. Pouring experiments were carried out by vacuum induction melting furnace equipped with a water-cooled copper crucible based on the above optimization. The quality of the TiAl alloy casting was analyzed by fluorescent penetrant inspection and X-ray detection. The results show that a centrifugal rotation rate of 200 rpm, mould preheating temperature of 600 °C, shell preparation through organic fiber addition can dramatically improve the mould filling capacity, and integrated turbochargers were finally prepared. [ABSTRACT FROM AUTHOR]

Ti-46Al-8Ta (at.%) intermetallic alloys exhibit acceptable strength at low and high temperatures with good oxidation resistance. Different alloying elements are usually added to TiAl-based alloys to develop required properties. In this work, effects of N addition up to 2 at.% on microstructural features and solidification behavior of the Ti-46Al-8Ta alloy is investigated. The achieved results showed that alloying with N causes dendrite refinement and reduction of the retained metastable B2 phase in the as-cast microstructure. The dendrite morphology is also changed from fourfold to fivefold and then sixfold symmetry by increasing N content. The effect of N on interlamellar spacing, amount of constituent phases, and lattice parameters was not uniform. Increasing N content resulted in an increase in both small punch maximum load and hardness up to 1.05 at.%, whereas further N alloying, despite increasing of hardness, led to a drop in the maximum load. [ABSTRACT FROM AUTHOR]

Elemental Ti and Al powders were milled and mixed as starting materials for the synthesis of titanium aluminide solid compacts by using the electric discharge sintering (EDS) technique. The polycrystalline compact with near full-density (> 99.6%) and the main phase of Ti3Al was produced in 170 μs by the EDS. In the early stage of electric discharging, the generated heat at the interface of metal and oxide film created an explosive force, inducing a dielectric breakdown of inherent oxide film. Once the oxide film was removed and the metals were melt, the formation of necks at the clean contact points occurred and the inter-diffusion between Ti and Al in liquid phase was initiated at the metallic contact areas with sequent alloying into an amorphous Ti3Al. During the full alloying and substantial neck growth, the heat dissipated through the mold, causing the crystallization of Ti3Al. During the EDS, pinch pressure (24–68 MPa) was also generated, which can densify the EDS compact. The fine microstructure, higher density, and greater hardness of EDS compact were results of the shorter exposure time to a high temperature and the generated pinch pressure, causing a higher densification and constrained grain growth, compared to conventional powder metallurgy methods. [ABSTRACT FROM AUTHOR]

TiAl-based composite materials have been produced by spin-casting self-propagating high-temperature synthesis metallurgy methods using thermite-type mixtures, general relationships in the formation of their composition and structure have been investigated, the synthesis conditions have been optimized, a method for obtaining large ingots has been proposed, and their composition and structure have been determined. We have obtained cast Nb- and Cr-doped TiAl-based composite materials using mixtures of Ti, Nb, Cr, and Ca oxides with a combined reducing agent (Al and Ca) under the effect of an overload above 200g. It has been shown that partial Ca substitution for Al in the starting mixture ensures complete reduction of the TiO2, and the resultant metallic phase contains calculated amounts of Ti and Al. Mixtures of optimized composition make it possible to produce a cast composite material similar in composition to alloy 4822. [ABSTRACT FROM AUTHOR]

An in situ synchrotron study of the specific features of the phase formation dynamics in mechanically activated 16 wt% Al + Ti powder composition is described, the high‐temperature synthesis being carried out under the condition of high volume inflammation by means of inductive heating. The kinetics of the phase formation were registered with an experimental complex, especially designed, constructed and adjusted for the method of dynamic diffraction analysis in synchrotron radiation beams. It has been experimentally in situ shown that increasing the time of mechanical activation of the initial powder mixture reduces the temperature at which components start to react and the time of realization of the high‐temperature synthesis. With the latter set at 1 min of mechanical activation, the temperature of the reaction in the mixture is T = 603°C; at 3 min of mechanical activation, T = 442°C; and at 7 min, T = 359°C. The maximum burning temperatures are: for 1 min of mechanical activation, Tmax = 1080°C; for 3 min, Tmax = 1003°C; and for 7 min, Tmax = 820°C. It was found that formation of both stable compounds Ti3Al, TiAl3, TiAl2, TiAl and metastable phases Ti9Al23, Ti5Al11, Ti2Al5, Ti3Al5 occurs at the stage of primary structure formation, before the system goes to thermal explosion. High‐temperature synthesis of a mixture of the studied composition takes place without formation of a liquid phase, in the solid‐phase combustion mode. It was found that the increase in the time of mechanical activation of the initial powder mixture contributes to the formation of a product with a dominant content of intermetallic compound Ti3Al. By synthesis of the powder mixture of composition 16 wt% Al + Ti, mechanically activated for 7 min, the content of Ti3Al in the final product was found to be 68%. The sequence of formation of metastable and basic phases in the process of self‐propagating high‐temperature synthesis of a mechano‐activated powder mixture of composition 3Ti + Al is established using in situ synchrotron studies. [ABSTRACT FROM AUTHOR]

In the current work, rotary friction welding of electron beam melted (EBM) γ-TiAl alloy Ti-48Al-2Cr-2Nb (at%) was investigated. Welding experiments were conducted using cylindrical bars of 12 mm diameter and 70 mm height in as-fabricated and heat treated (1275 °C/2 h/furnace cooling) conditions. No cracking problems were encountered during friction welding of as-fabricated EBM samples. However, in as-welded condition, the joints did not perform well in tensile tests and failures were observed to invariably occur at the weld interface. Friction welded joints produced in heat treated EBM samples were also found to suffer from the same problem. In both the cases, the weld region showed fine, fully lamellar γ + α2 microstructure and relatively high hardness. In order to overcome the problem, a post-weld heat treatment (PWHT) was carried out at 1275 °C/2 h/furnace cooling. After the PWHT, the weld region showed a more desirable duplex microstructure consisting of equiaxed primary γ and relatively coarser lamellar γ + α2. The PWHTed joints showed satisfactory tensile properties, and no failures were observed at the weld interface. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Many promising titanium aluminides and silicides could be synthesized in Ti-Si-Al system via mechanically activated self-propagating high-temperature synthesis (MASHS). The influence of mechanical activation and initial composition on phase formation, microstructure and synthesis behavior of mechanically activated Ti-rich mixtures in Ti-Si-Al system is investigated. Results indicate that Al can participate in the reaction and forms Ti3Al and TiAl3 phases beside Ti5Si3 phase by using mechanically activated reactants. Si and Al could be substituted each other in titanium aluminide and silicide to form solid solution of Ti3(Si,Al) and Ti5(Si,Al)3. In Ti-Si-Al system, combustion temperature is increased by increasing Si amount in the system while, ignition temperature is decreased profoundly from 1100 to 800 ∘C by applying mechanical activation prior to reaction and increasing Al in the system. In addition, Mechanical activation prior to synthesis gives rise to narrow grain size distribution and more uniform microstructure in comparison with SHS products. [ABSTRACT FROM AUTHOR]